Human Immunodeficiency 

Virus-1 Infection: 

Developing Antiretroviral 

Drugs for Treatment 

Guidance for Industry 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
U.S. Department of Health and Human Services 

Food and Drug Administration 

Center for Drug Evaluation and Research (CDER)
  
 
November 2015 

Clinical/Antimicrobial 
 
Revision 1 

   
Human Immunodeficiency 

Virus-1 Infection: 

Developing Antiretroviral 

Drugs for Treatment 

Guidance for Industry 

 
 
 
Additional copies are available from: 

 
Office of Communications, Division  of Drug Information 

Center for Drug Evaluation  and Research 

Food and  Drug Administration 
 
10001 New Hampshire Ave., Hillandale Bldg., 4th Floor  
 
Silver Spring, MD  20993-0002  

Tel: 855-543-3784 or 301-796-3400;  Fax: 301-431-6353; Email:  druginfo@fda.hhs.gov  

http://www.fda.gov/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/default.htm 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
U.S. Department of Health and Human Services 

Food and Drug Administration 

Center for Drug Evaluation and Research (CDER)
  
 
November 2015 

Clinical/Antimicrobial 
 
Revision 1 

 
   
TABLE OF CONTENTS 
 
 
I.   INTRODUCTION............................................................................................................. 1
  
II.   BACKGROUND ............................................................................................................... 2
  
III.   DEVELOPMENT PROGRAM ....................................................................................... 6
  
A.   General Considerations ................................................................................................................. 6
  
1.  Pharmacology/Toxicology Development Considerations ................................................................ 6
  
2.  Nonclinical Virology Development Considerations ........................................................................ 7 
 
a.   Mechanism of action ................................................................................................................. 8
  
b.   Antiviral activity in cell culture ................................................................................................ 8
  
c.   Cytotoxicity  and mitochondrial toxicity  ................................................................................... 8 
 
d.   Combination antiviral activity .................................................................................................. 9
  
e.   Activity in animal models ......................................................................................................... 9
  
f.   Resistance and cross-resistance ................................................................................................. 9
  
3.  Drug Development Population ...................................................................................................... 10 
 
4.  Early Phase Clinical Development Considerations ....................................................................... 11 
 
a.   First-in-human trials ................................................................................................................ 11 
 
b.   Phase 1b (proof-of-concept) trials........................................................................................... 11 
 
c.   Phase 2 trials and dose finding................................................................................................ 12 
 
5.  Efficacy Considerations................................................................................................................. 12 
 
6.  Safety Considerations .................................................................................................................... 13 
 
B.   Specific Efficacy Trial Design Considerations .......................................................................... 14 
 
1.  Trial Design and Trial Population ................................................................................................ 14 
 
2.  Randomization, Stratification, and Blinding .................................................................................. 19 
 
3.  Choice of Controls ......................................................................................................................... 20 
 
4.  Efficacy Endpoints  ......................................................................................................................... 21 
 
5.  Trial Procedures and Timing of Assessments ................................................................................ 21 
 
6.  Statistical Considerations .............................................................................................................. 22 
 
a.   Analysis populations ............................................................................................................... 22 
 
b.   Efficacy analyses .................................................................................................................... 22 
 
c.   Noninferiority margin ............................................................................................................. 23 
 
d.   Missing data............................................................................................................................ 23 
 
e.   Interim analyses and data monitoring committees .................................................................. 24 
 
f.   Other analyses of interest and secondary  endpoints ................................................................ 24 
 
g.   Statistical analysis plan ........................................................................................................... 24 
 
h.   Submission of data and programs ........................................................................................... 25 
 
7.  Accelerated Approval (Subpart H) Considerations ....................................................................... 25 
 
C.   Other Considerations ................................................................................................................... 26 
 
1.  Clinical Virology Considerations  .................................................................................................. 26 
 
2.  Pharmacokinetic/Pharmacodynamic Considerations .................................................................... 27 
 
3.  Pediatric Populations .................................................................................................................... 28 
 
4.  Early Access/Treatment INDs........................................................................................................ 29 
 
REFERENCES............................................................................................................................ 31 
 
APPENDIX A:  RECOMMENDED APPROACH FOR EVALUATING VIROLOGIC 

RESPONSE IN CLINICAL TRIALS SUPPORTING ANTIRETROVIRAL APPROVALS.  33 
 
i   
APPENDIX B:  NONINFERIORITY MARGIN RECOMMENDATIONS AND 

JUSTIFICATIONS ..................................................................................................................... 39 
 
 
ii 
  Contains Nonbinding Recommendations 
Human Immunodeficiency Virus-1 Infection:  Developing 

Antiretroviral Drugs for Treatment 

1
 
Guidance for Industry  
 
 
 
 
This guidance represents the current thinking of the Food and Drug Administration (FDA or Agency) on 
this topic. It does not create any rights for any person and is not binding on FDA or the public.  You can 
use an alternative approach if it satisfies the requirements of the applicable statutes and regulations.  To 
discuss an alternative approach, contact the FDA staff responsible for this guidance as listed on the title 
page. 
 
 
 
 
I.  INTRODUCTION  
 
This guidance provides recommendations for the development of antiretroviral drugs regulated 
within the Center for Drug Evaluation and Research at the Food and Drug Administration (FDA) 
for the treatment of human immunodeficiency virus-1 (HIV-1 or HIV) infection.2  Specifically, 
this guidance addresses the FDAs current thinking regarding the overall development program  
and clinical trial designs for antiretroviral drugs to support an indication for the treatment of 
HIV-1 infection. The organization of the guidance parallels the development plan for a 
particular drug or biologic. 
 
This guidance does not address the use of antiretroviral drugs for preventing transmission of 
HIV-1 infection. Also, this guidance does not address the development of therapeutics without 
antiviral mechanisms, intended to mitigate or reverse clinical or pathophysiological outcomes of 
immunologic suppression caused by HIV-1 infection.  
 
Additionally, this guidance does not contain discussion of the general issues of statistical 
analysis or clinical trial design.  Those topics are addressed in the ICH guidances for industry E9 
Statistical Principles for Clinical Trials and E10 Choice of Control Group and Related Issues in 
Clinical Trials, respectively.3  This guidance also does not contain details regarding nonclinical 
                                                 
1 This  guidance has been  prepared by the Division of  Antiviral Products in the Center for Drug Evaluation and  
Research at the Food and Drug  Administration.  
 
2 For the purposes of this guidance, all references to drugs  include both human  drugs and therapeutic biological 
products  unless otherwise specified.  
 
3  We  update  guidances periodically.  To make sure you  have the most recent version of a guidance, check the FDA  
Drugs guidance Web page  at  
http://www.fda.gov/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/default.htm.  
1 
 Contains Nonbinding Recommendations 
safety and toxicology studies that should be conducted in standard animal models as described in 
the guidance for industry Nonclinical Safety Evaluation of Drug or Biologic Combinations.   
 
In general, FDAs guidance documents do not establish legally enforceable responsibilities.  
Instead, guidances describe the Agencys current thinking on a topic and should be viewed only 
as recommendations, unless specific regulatory or statutory requirements are cited.  The use of 
the word should in Agency guidances means that something is suggested or recommended, but 
not required. 
 
 
II.  BACKGROUND 
 
Brief summaries of HIV infection, HIV treatment, and the regulatory history of antiretroviral 
drug development are included below to support the rationale for this drug development 
guidance. 
 
HIV Infection and Treatment 
 
HIV infection is a chronic viral infection that, when untreated, causes a progressive destruction 
of the immune system resulting in acquired immunodeficiency syndrome (AIDS).  The key 
component of the immune deficiency associated with untreated HIV replication is a marked 
reduction in cluster of differentiation 4 (CD4) positive T-cells, but derangements in other 
immunologic parameters also play a role in the immune deficiency syndrome.  AIDS is defined 
as the presence of HIV infection with a CD4+ cell count fewer than 200 cells/millimeter (mm)3  
and/or the presence of an AIDS-defining clinical condition, which includes any number of 
opportunistic infections, malignancies, or other clinical syndromes as defined by the Centers for 
Disease Control and Prevention (CDC 2014). 
 
Current treatment of HIV consists of a combination of antiretroviral drugs, typically three drugs 
from two or more classes.  Sometimes more than three drugs are used in patients who have been 
treated previously and are known or presumed to harbor viral strains with reduced susceptibility.  
In addition, some combination antiretroviral therapy (cART) regimens include a drug that 
increases or prolongs exposures of one or more drugs in the regimen because of an intentional 
drug interaction. 
 
The goal of antiretroviral treatment is to indefinitely maintain suppression of plasma HIV- 
ribonucleic acid (RNA) levels (also called viral load) below the level of detection of sensitive 
HIV-RNA assays (less than the lower limit of quantification, target not detected).  The 
Department of Health and Human Services (HHS) Guidelines for the use of antiretroviral agents 
in HIV-1-infected adults and adolescents provides recommended regimens for initiating first-line 
therapy in treatment-naive patients.4  If a recommended regimen fails, there are numerous other 
drugs that can be used in a variety of possible combinations.  Continued suppression of HIV
                                                 
4 Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents, Department of Health 
and Human Services Panel on Antiretroviral Guidelines for Adults  and  Adolescents  A Working Group of  the 
Office of AIDS Research  Advisory Council (http://aidsinfo.nih.gov/contentfiles/AdultandAdolescentGL.pdf). 
2 
 Contains Nonbinding Recommendations 
RNA can be maintained indefinitely in the majority of individuals who adhere to appropriate 
cART regimens. 
 
Regulatory History of Antiretroviral Drug Development and Approval 
 
Most antiretroviral drugs initially entered the market via accelerated approval based on changes 
in surrogate endpoints, primarily plasma HIV-RNA levels but also CD4+ cell counts, before 
routine monitoring with HIV-RNA.  Before 1997, traditional approvals were based on clinical 
endpoint trials assessing the effects of a drug on mortality and/or progression of HIV disease.  
With the success of combination therapy, subsequent decline of HIV-related illnesses (Palella et 
al. 1998; Hogg et al. 1999), and the routine use of HIV-RNA monitoring to assess response to 
treatment, it became clear that a requirement for clinical endpoint trials for every traditional 
approval was no longer feasible.  In July 1997, we convened an advisory committee meeting to 
consider the use of changes in HIV-RNA levels as endpoints in clinical trials supporting 
traditional approval of antiretrovirals.5    
 
In 1996 and 1997, a collaborative group of pharmaceutical, academic, and government scientists 
investigated relationships between treatment-induced changes in HIV-RNA levels and clinical 
endpoints collected from ongoing and completed antiretroviral trials (Murray et al. 1999; Hill et 
al. 1999).  Several analyses of more than 5,000 patients in multiple trials identified a relationship 
between initial decreases in plasma HIV-RNA levels and reduction in the risk of clinical 
progression and death. This relationship was observed across a range of patient characteristics 
including pretreatment CD4+ cell counts and HIV-RNA levels, prior drug experience, and 
treatment regimen (Marschner et al. 1998).  
 
Based on these data, the Antiviral Drug Advisory Committee concluded that treatment-induced 
decreases in HIV-RNA levels were highly predictive of meaningful clinical benefit and that 
HIV-RNA measurements could serve as endpoints in trials designed to support both accelerated 
and traditional approvals.  Specifically, the committee stated that accelerated approvals could be 
based on studies that show a drugs contribution toward shorter term reductions in HIV-RNA 
(e.g., 24 weeks), a surrogate endpoint reasonably likely to produce clinical benefits, while 
traditional approvals could be based on trials that show a drugs contribution toward durability of  
HIV-RNA suppression (e.g., for at least 48 weeks), a surrogate endpoint more convincingly 
related to long-term benefit in the setting of life long therapy.  The committee also recommended 
that changes in CD4+ cell counts be consistent with observed HIV-RNA changes when 
considering approval of an antiretroviral drug. 
 
                                                 
5 See http://www.fda.gov/ohrms/dockets/ac/97/transcpt/3303t1.pdf. 
3 
 Contains Nonbinding Recommendations 
Subsequently, additional data further supported the utility of an endpoint of viral load  
suppression for predicting a clinical benefit in HIV progression.  Such data include: 
 
 	  Analysis of 12 clinical endpoint trials (originally submitted to the FDA in support of 
approval) that showed that a difference of a 0.5 logarithm (log) HIV-RNA reduction from  
baseline between treatment arms was also associated with a reduction in clinical disease 
progression  
 
	   Results from the Strategies for Management of Antiretroviral Therapy (SMART) trial 
that showed a strategy of continuous viral suppression provided a lower risk of disease 
progression than a strategy of drug conservation that allowed for treatment holidays until 
CD4+ cell counts declined to a specified amount (SMART Study Group 2006)  
 
	   Epidemiologic reports (Hogg et al. 1999) that showed the current treatment strategy of 
maximal viral suppression with combination antiretroviral treatment has dramatically 
reduced AIDS morbidity and mortality  
 
	   Data from numerous trials that showed incomplete viral suppression results in emergence 
of viral resistance, viral rebound, and loss of efficacy of individual drugs and sometimes 
entire drug classes  
 
All drugs that received accelerated approval, either before 1997 or since that time, have 
subsequently received traditional approval.  Since 1997, 13 antiretroviral drugs entered the 
market via an accelerated approval based on 24-week changes in HIV-1 RNA.  All of these 
drugs were confirmed to have durable virologic suppression at 48 weeks and beyond.  Although 
a percentage of people on cART develop virologic failure over time, in no case did longer term  
data reveal that a drug lost the efficacy initially seen at time of accelerated approval.  However, 
longer term data have shown more subtle differences between treatment arms comparing 
different drugs or dosing regimens and have been useful for choosing optimal doses or preferred 
regimens in treatment guidelines. 
 
Given that HIV-RNA is a validated surrogate for predicting efficacy of antiretrovirals, a 
paradigm of accelerated approval (based on viral load changes at 24 weeks) followed by 
traditional approval (based on viral load changes at 48 weeks) is no longer needed for the 
development of antiretrovirals.  Instead traditional approval can be the initial approval for all 
antiretroviral drugs, with the duration of viral load assessments dependent on the population 
studied, as will be described in this guidance.  Table 1 summarizes recommended treatment 
durations to support approvals of indications for the listed groups.  The general groups of patient 
types included in Table 1 take into account both viral susceptibility and treatment history.  
Because patients in Group 2 and Group 3 have characteristics that may overlap, decisions 
regarding which group best describes a particular individual will be a matter of clinical judgment 
to some extent.  Because community drug resistance profiles and the availability of new drugs 
change over time, sponsors may develop protocol inclusion criteria for Group 2 patients that best 
describe a multidrug resistant population for which their particular investigational drug would be 
suitable at the time of enrollment in a protocol.  
 
4 
 Contains Nonbinding Recommendations 
Table 1: Recommendations for Efficacy and Safety Determination Time Points According 
to HIV Patient Population6  
Patient Population   Efficacy Determination   Safety Determination 
Time Point  Time Point 
Group 1:  Virologic response at 48  Safety outcomes through 48 
Fully susceptible to all  weeks  weeks 
approved drugs, treatment
naive, or previous treatment 
with a well-documented 
treatment history 
demonstrating no virologic 
failure.  
Group 2:  Virologic response at 2  Safety outcomes through 24 
Drug resistance to multiple  weeks (or less) plus  weeks 
drugs and multiple drug  virologic follow-up at 24 
classes. Not able to  weeks  
construct a treatment 
regimen that can suppress 
HIV-RNA to levels below 
assay quantification limits. 
Group 3:  Virologic response at 24-48  Safety outcomes through 
Drug resistance present and  weeks*  24-48 weeks 
able to construct a treatment 
regimen that can suppress 
HIV-RNA to levels below 
assay quantification limits. 
* Twenty-four weeks of data is appropriate for drugs that  have some benefit over existing options (e.g., better 
efficacy, tolerability, ease of administration), while 48  weeks is recommended for drugs with comparable 
characteristics to existing  options. 
 
 
                                                 
6 The terminology Group 1 patients, treatment-naive patients, and patients who received previous treatment with a 
well-documented treatment history demonstrating no virologic failure are used interchangeably throughout the 
guidance.   Similarly,  treatment-experienced (with virologic failure)  refers to either  Group 2 or  Group 3 and the 
terms are used interchangeably throughout the guidance.   
5 
 Contains Nonbinding Recommendations 
III.  DEVELOPMENT PROGRAM 
 
A.  General Considerations 
 
1.  Pharmacology/Toxicology Development Considerations  
 
Pharmacology/toxicology development for HIV-1 antivirals should follow existing guidances for 
drug development (see, for example, section III.C.3., Pediatric Populations).7    
 
The above-referenced guidances suggest that nonclinical combination studies generally should 
be conducted to support clinical trials for combination drugs involving two or more entities in 
early stages of development.  In the ICH guidance for industry M3(R2) Nonclinical Safety 
Studies for the Conduct of Human Clinical Trials and Marketing Authorization for 
Pharmaceuticals, section I.C., Scope of the Guidance, states, Pharmaceuticals under 
development for indications in life-threatening or serious diseases (e.g., advanced cancer, 
resistant HIV infection, and congenital enzyme deficiency diseases) without current effective 
therapy also warrant a case-by-case approach to both the toxicological evaluation and clinical 
development in order to optimize and expedite drug development.   
 
For new HIV drug combinations of two or more early stage entities that are not expected to offer 
benefits over currently effective therapy, combination toxicology studies usually should precede 
phase 2 and phase 3 clinical trials evaluating the investigational combination as referenced in 
ICH M3(R2) cited above.  Usually no more than two drugs should be tested simultaneously in a 
particular arm of a toxicology study. However, the evaluation of more than two drugs and the 
inclusion of a combination arm in a general toxicology study can also be considered.  The design 
of such studies should be discussed with the Division of Antiviral Products (DAVP).  For 
combinations that are expected to offer benefits over currently effective therapy, such as treating 
drug-resistant HIV in patients with few remaining options or substantially improving treatment 
response in other patient groups, the FDA may conclude the benefits of these combinations 
outweigh the potential risks of foregoing the combination toxicology studies when all of the 
following apply: 
 
 	  Mechanisms of action or in vitro data of potential off-target effects do not suggest a 
potential for additive or synergistic toxicity of significant clinical concern.8  
 
 	  Studies in animals or humans of absorption, distribution, metabolism, and excretion of 
the individual drugs show no potential for an unmanageable interaction (one that cannot 
be addressed with dose adjustments) or serious toxicity for the combination. 
 
                                                 
7 See the ICH guidances for industry M3(R2) Nonclinical Safety Studies for the Conduct of Human Clinical Trials  
and Marketing Authorization for Pharmaceuticals and S6 Preclinical Safety Evaluation of Biotechnology-Derived  
Pharmaceuticals. 
 
8 If in  vitro signals are investigated and  found not to  be  relevant in  vivo, this point can  be  disregarded.  
6 
 Contains Nonbinding Recommendations 
 	  Toxicology studies (of at least 3 months duration) of the individual drugs show an 
appropriate safety margin9 for the intended clinical dose(s) or exposures for toxicities that 
are potentially serious and/or unable to be adequately monitored clinically. 
 
 	  Phase 1 clinical data in healthy volunteers or HIV-infected patients receiving the 
individual drugs show no substantial or unmanageable safety concerns.  Phase 1 data 
should include single- and multiple-dose pharmacokinetic (PK) and safety trials, at a 
minimum.  Additional safety data from phase 1 and phase 2 trials with the individual 
drugs are encouraged when possible and may be warranted if one or more of the drugs 
demonstrate a potential serious safety risk.  
 
 	  There are no concerning overlapping toxicities for the individual drugs based on animal 
toxicology studies and phase 1 or phase 2 clinical data (if available). 
 
 	  Clinically significant PK drug-drug interactions are considered unlikely or can be reliably 
managed with dose adjustments such that safety margins based on individual drug 
exposures are not exceeded. 
 
After considering the above points, sponsors should discuss with the DAVP the design, rationale, 
and/or potential requirement for conducting combination toxicology studies.  Generally, 
combination trials in healthy volunteers should not be the first-in-human trials for the individual 
drugs unless the drugs cannot be administered separately and unless combination toxicology 
studies have been completed according to ICH guidance. 
 
Nonclinical combination toxicology/safety studies of an early stage antiretroviral drug plus an 
approved or late-stage antiretroviral drug generally are not warranted and are not feasible 
because individual antiretrovirals are often combined with multiple other antiretrovirals in 
multiple different regimens over a lifetime of treatment.  Therefore, unless data from nonclinical 
studies of an early stage investigational antiretroviral suggest a potential for serious synergistic 
toxicity with an approved therapeutic drug combination, we do not anticipate nonclinical 
combination toxicology studies. 
 
Applicants can choose to submit carcinogenicity studies with an initial new drug application 
(NDA) or as required postmarketing studies.   
 
2.  Nonclinical Virology Development Considerations 
 
Antiretrovirals for the treatment of HIV-1 should be tested in cell culture for antiviral activity 
before submission of an initial investigational new drug application (IND).  Information about 
                                                 
9 The margin will depend on the nature of the  toxicologic/pathologic findings.  Margins much greater than 10 may  
be  needed  for life-threatening  toxicities, while margins less than  10 may be appropriate for less serious toxicities. 
 
7 
 Contains Nonbinding Recommendations 
pre-INDs and information regarding appropriate nonclinical assays is available from the FDA.10   
Additional recommendations for general antiviral drug development can be found in the 
guidance for industry Antiviral Product Development  Conducting and Submitting Virology 
Studies to the Agency. 
 
a.  Mechanism of action  
 
The mechanism by which an antiretroviral drug specifically inhibits HIV replication or a virus-
specific function should be investigated in studies that include evaluation of the effect of the 
drug on relevant stages of the virus life cycle.  Mechanism of action investigations should 
include appropriate controls for assessing the specificity of anti-HIV activity, which may include 
assessments of activity against HIV proteins that are not targeted by the investigational drug, 
relevant host proteins, and other viruses. 
 
b.  Antiviral activity in cell culture  
 
The antiviral activity of a new drug should be characterized in cell culture to demonstrate anti-
HIV activity and identify a target plasma concentration for evaluation in HIV-infected patients.  
Anti-HIV activity studies should include assessments against a broad range of clinical and 
laboratory viral isolates including different groups and subtypes (or clades).  The effective 
concentration (EC) at which virus replication is inhibited by 50 and 90 percent (e.g., EC  and 
50
EC  for cell-based assays; inhibitory concentration (IC ) and IC  for biochemical or 
90 50 90
subcellular assays) should be determined using a quantitative assay. 
 
Sequestration of the drug by serum proteins also should be assessed and a serum-adjusted EC  
50 
value determined.  We recommend evaluation of the drugs antiviral activity at different 
concentrations of human serum and extrapolation to a 100 percent human serum EC  value.  
50
 
c.  Cytotoxicity and mitochondrial toxicity 
 
The cytotoxic effects of the drug should be quantified directly in the cells used for assessing anti-
HIV activity, and a 50 percent cytotoxic concentration (CC ) and a therapeutic index should be 
50
calculated. Cytotoxicity should be assessed using various human cell lines and primary cells 
cultured under proliferating and nonproliferating conditions.  Some investigational drugs (e.g., 
active triphosphate of nucleoside analog inhibitors) should be evaluated in biochemical assays 
for activity against host deoxyribonucleic acid (DNA) polymerases and mitochondrial DNA and 
RNA polymerases (Arnold et al. 2012). 
 
Additionally, it is important to examine the effects of investigational drugs on mitochondrial 
toxicity (e.g., lactic acid production, mitochondrial DNA content, mitochondrial morphology, 
glucose utilization) early in development before dosing humans.  When mitochondrial toxicity is 
evaluated, experimental conditions should be justified based on current best practices (e.g., 
                                                 
10 See the FDA Web site at 
http://www.fda.gov/Drugs/DevelopmentApprovalProcess/HowDrugsareDevelopedandApproved/ApprovalApplicati 
ons/InvestigationalNewDrugINDApplication/Overview/ucm077546.htm.  
8 
 Contains Nonbinding Recommendations 
examining mitochondrial toxicity in both glucose-containing medium and galactose-containing 
medium (Marroquin et al. 2007; Hynes et al. 2013)).  Cytotoxicity and mitochondrial toxicity 
assessments under proliferating conditions should be evaluated with drug exposures for several 
cell divisions. These biochemical and cell-based assessments for potential cellular and  
mitochondrial toxicity should be performed as a complement to in vivo toxicology assessments 
and not in lieu of in vivo studies. Results from these studies should be interpreted in the context 
of the in vivo toxicology, nonclinical, and clinical PK data to help assess clinical risk. 
 
d.  Combination antiviral activity  
 
We anticipate that most, if not all, antiretrovirals will be used to treat HIV-1 in combination with 
other approved drugs. Early in development, cell culture combination antiviral activity  
relationships of the new drug with two representatives of each antiretroviral drug class should be 
evaluated to determine whether the combination antiviral activity is antagonistic.  If antagonism  
is seen with either member of a class, all members of the class should be evaluated.  Additional 
combination antiviral activity studies with other investigational antiretroviral drugs should be 
conducted if future combination therapy with other drugs is anticipated.  For all combination 
antiviral activity assessments, sponsors should provide antagonism, additivity, or synergy values 
(e.g., combination index values) when the two drugs are combined at or near their individual 
EC  values, and studies should include controls for cytotoxicity.  Combination antiviral activity 
50
relationships for HIV and hepatitis C virus (HCV) or hepatitis B virus (HBV) drugs with similar 
mechanisms of action (e.g., nucleo(t)side analogue polymerase/reverse transcriptase inhibitors, 
protease inhibitors) also should be assessed before testing combinations of the drugs in 
HIV/HCV- or HIV/HBV-coinfected patients.  
 
e.  Activity in animal models 
 
Demonstration of anti-HIV activity in an animal model is not required.   
 
f.  Resistance and cross-resistance 
 
The ability of HIV to develop resistance to an antiretroviral when subjected to drug pressure 
should be examined in appropriate cell culture models.  Amino acid substitutions associated with  
the development of resistance to the investigational drug should be determined and validated by 
introducing the mutations into the HIV genome, and determining the conferred fold-shift in 
susceptibility using appropriate cell culture and/or biochemical assays.  Results from these 
studies should be used to: 
 
 	  Identify resistance pathways  
 
 	  Assess whether the genetic barrier for resistance development is relatively high or low 
(e.g., whether one mutation or multiple mutations confer drug resistance and whether few 
or many passages with the drug are required for resistance to occur)  
 
 	  Predict whether the genetic barrier for resistance may vary as a function of in vivo 
concentration of the new drug 
9 
 Contains Nonbinding Recommendations 
 
   Assess the potential for cross-resistance with other anti-HIV drugs  
 
   Support the drugs hypothesized mechanism of action 
 
Resistance studies should include evaluation of the potential for cross-resistance, both to 
approved drugs and also to drugs in development when possible, particularly focusing on those 
in the same drug class and other classes targeting the same protein or protein complex.  The 
antiviral activity of the investigational drug should be assessed against mutant viruses that are 
resistant to drugs within the same drug class as the investigational drug as well as a 
representative sample of viruses resistant to other approved antiretroviral drugs.   
 
3.  Drug Development Population  
 
We encourage the evaluation of antiretroviral drugs in a wide range of patients including 
treatment-naive and treatment-experienced patients (Groups 1 to 3), as appropriate.  However, 
the drug development population depends to a large extent on specific characteristics of the drug, 
such as resistance profile, tolerability, pharmacologic profile, and route of administration.  A 
drug with a daily subcutaneous or intravenous route of administration may be appropriate for a 
highly treatment-experienced patient with few remaining options, but generally is not appropriate 
for a treatment-naive individual.  A drug with a favorable resistance profile that retains activity 
to viral strains resistant to approved drugs is likely to fill an unmet medical need in treatment-
experienced patients. However, such a drug need not be restricted to treatment-experienced 
patients if it is well tolerated and favorable in other aspects (e.g., convenient dosing schedule).  
Investigational drugs intended for treatment-naive patients should be at least as efficacious, well 
tolerated, and convenient to administer as approved drugs for use in treatment-naive patients and 
ideally should have some favorable characteristic (e.g., tolerability, improved drug interaction 
profile) for at least a subgroup of naive patients if deficient in another aspect. 
 
We encourage the study of antiretrovirals in patients having the greatest need for new drugs, 
such as patients who cannot tolerate other antiretrovirals or have developed resistance to multiple  
antiretrovirals.  We realize that trials in heavily treatment-experienced patients may need to be 
supported by preliminary data from trials in healthy volunteers and in HIV-infected populations 
with little or no prior antiretroviral therapy to define preliminary activity, safety, and 
pharmacokinetics.  
 
HIV is a disease that is present worldwide and clinical trials typically are conducted 
internationally. However, trials should include adequate U.S. patient representation and patients 
infected with Clade B virus to ensure applicability of trial results to the U.S. population.  An 
adequate representation of males and females, races, ages, and weights are recommended during 
all stages of drug development, especially in phase 3 trials.  Inclusion of a diverse patient 
population early in drug development may help to identify potential efficacy or safety issues and 
can help to inform phase 3 trial designs.  At an end-of-phase 2 meeting, sponsors are encouraged 
to discuss with the DAVP the anticipated number of women and the racial representation in 
clinical trials. Extending trial site enrollment caps to allow for enrollment of underrepresented 
populations has also helped to increase trial diversity. 
10 
  Contains Nonbinding Recommendations 
 
4.  Early Phase Clinical Development Considerations  
 
a.  First-in-human trials  
 
For first-in-human trials, we recommend single- and multiple-ascending-dose trials in healthy 
adult subjects to assess safety and pharmacokinetics and to avoid development of resistance that 
could occur from subtherapeutic exposure in HIV-infected individuals.   
 
b.  Phase 1b (proof-of-concept) trials 
 
The first proof-of-concept trial in HIV-infected patients should be a multiple-dose study that 
allows for short-term (e.g., several days to 2 weeks depending on the drug class, resistance 
profile in cell culture, potency, and pharmacokinetics) evaluation of a drugs effect on reducing 
HIV-RNA levels from baseline and also provides for evaluation of safety for a short duration.  
Duration of monotherapy should be minimized to reduce the risk of resistance while still being 
able to assess activity. Mean changes in HIV-RNA from baseline should be the primary 
endpoint.  Examples of proof-of-concept trials include: 
 
 	  A randomized placebo-controlled trial comparing the investigational drug as 
monotherapy, at several dose levels, to placebo in HIV-infected patients who are 
described in Group 1.11  The trial duration depends on the anticipated resistance barrier of  
the drug based on cell culture studies. Some drugs with an anticipated low genetic barrier 
to resistance would not be appropriate candidates for study in a monotherapy trial of any 
duration. For drugs with a presumed low barrier to resistance, sponsors should discuss 
proof-of-concept trials with the DAVP.  Drugs with a presumed high barrier to resistance 
emergence generally can be studied for up to 2 weeks.   
 
 	  A randomized placebo-controlled trial comparing the investigational drug, at several dose 
levels as functional monotherapy to placebo in Group 2 or Group 3 HIV-infected patients 
who are failing their current regimen.   
 
Adding one new drug to a regimen not producing complete viral suppression is 
sometimes referred to as functional monotherapy.  Functional monotherapy is not 
recommended for long durations.  The primary assessment of activity should occur at 
2 weeks (or perhaps sooner for some drugs).  After the initial placebo-controlled 
comparison of efficacy, patients can be followed on open-label treatment for longer 
periods for safety, durability of response, and emergence of resistance.  However, we 
recommend that trials contain provisions for changing the background regimen after 
2 weeks (or earlier) in an attempt to maximize the likelihood of a fully suppressive 
regimen.  Also, patients randomized to placebo can be allowed to receive the 
investigational drug after 2 weeks (or earlier) in addition to an optimized background 
                                                 
11 Group 1 patients are recommended because they have many treatment options in the event of emergence of  drug  
resistance to the investigational drug and because they are less likely to  have  partial resistance at baseline that could  
affect the determination of drug activity. 
11 
  Contains Nonbinding Recommendations 
regimen, provided that there are supporting pharmacology/toxicology data for longer 
term administration.   
 
c.  Phase 2 trials and dose finding 
 
The goal of early phase 2 trials is to characterize an active, tolerable, and safe dose(s) of an 
antiretroviral drug as part of a combination regimen for further study in phase 3 trials.  Sponsors 
should conduct mechanistic modeling of the drug concentration-viral kinetics and the 
concentration-safety profile from short-term  monotherapy trials to choose doses for early phase 2 
trials. As a general rule, doses selected for phase 2 should provide exposures expected to 
exceed, by several-fold, the protein binding-adjusted, cell culture EC  value of the drug for the 
50
relevant HIV genotype/subtype. However, for some drug classes, specifically nucleo(t)side 
reverse transcriptase inhibitors (NRTIs), intracellular triphosphate concentrations rather than 
plasma concentrations are more related to pharmacodynamic effect.  Sponsors should avoid 
selecting doses that provide exposures that are expected to be subtherapeutic to reduce the risk of 
selecting for resistant virus. 
 
Phase 2 dose-ranging trials can have the same  designs as recommended for phase 3 (see section 
III.B., Specific Efficacy Trial Design Considerations), but generally should evaluate a wider 
range of doses and should be smaller in scope such that preliminary safety and efficacy of the 
doses can be assessed before larger trials. A 24- to 48-week trial duration generally should be 
sufficient for phase 2 dose ranging trials. Phase 2 dose-ranging studies that have demonstrated a 
significant dose response can provide supportive data for an approval of an antiretroviral drug.  
Generally, dose-ranging studies should include a sufficient range of doses to demonstrate a dose- 
or exposure-response relationship. 
 
5.  Efficacy Considerations  
 
In general, NDAs should include at least two adequate and well-controlled trials conducted in the 
proposed population(s) intended for labeling. Applicants can submit an NDA in a single 
population, either treatment-naive or treatment-experienced patients.  Alternatively, applicants 
can choose to pursue an indication for both treatment-naive and -experienced patients.  In this 
circumstance, the NDA should contain at least one adequate and well-controlled phase 3 trial in 
each patient population, with adequate supporting data from phase 2 trials.  A trial in either 
Group 2- or Group 3-type patients could support an indication for treatment-experienced patients 
in general; the exact wording and extent of the claim would depend on the trial design and 
population supporting the indication.  For example, labeling claims for efficacy against drug-
resistant strains of the same class should be supported by a trial that investigates the new drug in 
patients who have failed one drug in the same class (or more than one drug depending on the 
cross-resistance profile of the approved drugs in the class).  
 
12 
  Contains Nonbinding Recommendations 
Sponsors should consult existing guidance regarding circumstances in which one phase 3 clinical 
trial may be supportive of approval.12  
 
Applicants should consult 21 CFR 300.50 for specific regulatory considerations regarding fixed-
dose combinations.  In brief, two or more drugs can be combined in a single dosage form when 
each component makes a contribution to the claimed effects of the drug, and the dosage of each 
component is such that the combination is safe and effective for a significant patient population 
requiring such concurrent therapy as defined in the labeling for the drug.  Clinical factorial 
designs are not needed if there are other data that support the use of the combination.  Examples 
include, but are not limited to: 
 
 	  Cell culture data showing that the combination can delay the development of resistance 
compared to single drugs with relatively loss resistance barriers  
 
 	  PK data showing that one component can increase exposures of the other active drug 
(e.g., the effect of ritonavir or cobicistat on HIV protease inhibitors) 
 
 	  Clinical data of similar combinations showing the contribution of different drug classes in 
combination HIV regimens  
 
HIV treatment development plans may be eligible for consideration under 21 CFR part 312, 
subpart E, Drugs Intended to Treat Life-Threatening and Severely-Debilitating Illnesses, and 
may be eligible to receive fast track or breakthrough therapy designation.13,14   
 
6.  Safety Considerations   
 
The majority of past antiretroviral approvals were based on databases including approximately 
500 patients receiving the approved dose for at least 24 to 48 weeks depending on the 
population. For initial approvals (Groups 1 to 3), depending on the intended labeling indication 
claim and the particular drugs safety profile, safety data on 300 to 500 patients receiving the 
intended dose for 24 to 48 weeks should be sufficient (see Table 1).  Efficacy supplements for 
expanding the indication after initial approval can rely on the safety experience of all populations 
studied (previous and new); therefore, the number of patients needed to support the new 
indication generally depends on that needed to demonstrate efficacy.  Applicants are encouraged 
to discuss their proposed safety database with the DAVP before submitting an NDA.  On 
occasion, specific findings in nonclinical or phase 1 and phase 2 development may indicate the 
need for a database that is larger or longer in duration to adequately evaluate potential drug 
toxicity.  
                                                 
12 See the guidance for industry Providing Clinical Evidence of Effectiveness for Human  Drug and Biological 
Products.  
 
13 See section 506  of the Federal Food, Drug, and Cosmetic Act (21 U.S.C.  356) as amended by section 902 of the 
Food and Drug Administration Safety and Innovation Act of  2012.  
 
14 See the FDA Web site Fact Sheet:  Breakthrough Therapies at 
http://www.fda.gov/regulatoryinformation/legislation/significantamendmentstothefdcact/fdasia/ucm329491.htm.  
13 
  Contains Nonbinding Recommendations 
 
Most of the safety database should be from controlled trials.  Safety data from uncontrolled trials 
or treatment access trials may be useful, but often lack the degree of detailed reporting obtained 
in controlled clinical trials.  In addition, the assessment of causal relationships between a drug 
and an adverse event is more difficult to assess from uncontrolled safety data.  Trials assessing 
dose response can be useful for evaluating drug-related adverse reactions. 
 
To support specific labeling claims, see the guidance for industry Adverse Reactions Section of 
Labeling for Human Prescription Drug and Biological Products  Content and Format.   
Sponsors should predefine specific clinical adverse events or clinically meaningful laboratory 
changes to evaluate in a phase 3 protocol.  Phase 2 data may help to define which adverse 
reactions or laboratory evaluations to target.  Replicated findings from adequately designed trials 
demonstrating substantial, clinically meaningful advantages over other therapy can be used to 
support specific safety claims.   
 
B.  Specific Efficacy Trial Design Considerations  
 
1.  Trial Design and Trial Population 
 
The appropriate trial design depends on the population being studied.  Refer to the three patient 
groups outlined in section II., Background. 
 
It is important to emphasize that treatment-naive patients have several approved treatment 
options that are highly effective, well-tolerated, and convenient to use (e.g., 1 tablet or capsule 
once daily for an entire regimen).  Although an active and tolerable antiretroviral regimen can be 
identified in 24 weeks or less, modest differences in virologic efficacy, emergence of resistance, 
and loss of tolerability are sometimes detected when treatment-naive patients are followed 
through 48 weeks and beyond. Given that the initial regimen generally should be the best 
available and that loss of response to an initial regimen often can affect the choice of subsequent 
drugs because of resistance, regimens for treatment-naive patients are evaluated stringently and 
are compared to known, high-performing, control regimens.   
 
Lower efficacy or less tolerability of a new drug/regimen compared to known controls in 
treatment-naive patients is an important issue that can affect approval for this use or lead to 
precautionary language in labeling.  Standard regimens for treatment-experienced patients are 
less well defined than regimens for treatment-naive patients; it is sometimes appropriate to 
evaluate the effectiveness of potentially promising drugs in combination with an optimized 
background of antiretroviral drugs for treatment-experienced patients at time points earlier than 
48 weeks. 
 
Group 1 Patients (fully susceptible to all approved drugs, treatment-naive or previous 
treatment with a well-documented treatment history demonstrating no virologic failure) 
 
The most feasible trial design for this group is a randomized active-controlled noninferiority trial 
(see Appendix B for a discussion of noninferiority margins).  In this design, patients should be 
randomized to a standard three-drug regimen or to the same standard regimen with the 
14 
  Contains Nonbinding Recommendations 
investigational drug substituting for one of the components of the regimen and followed for at 
least 48 weeks.  As discussed in Appendix B, the efficacy contribution of the substituted 
component should be known based on previous trial data. 
 
Multiple doses of the investigational drug can be studied in active-controlled noninferiority 
studies to better define an optimal dose (but a dose known to be less effective could not be 
ethically chosen).  An observed dose response would strongly support efficacy. 
 
Add-on superiority trials (e.g., three approved drugs plus the investigational drug compared to 
three approved drugs) are interpretable if the results demonstrate superiority but are considered 
less feasible because the response rate in treatment-naive patients is high (greater than 80 
percent); and when lack of response occurs, it is often for reasons other than lack of virologic 
response, such as poor adherence or early drop out for adverse events.  Consequently, four active 
drugs have not often shown improved efficacy over three drugs in this population.  Similarly, 
showing superiority to current commonly used control regimens in an active-controlled 
substitution trial is difficult for the same reasons. 
 
Switch trials enroll patients fully suppressed on an initial regimen and randomize them to either  
continue their current regimen or to change one (or occasionally two) of the drugs in their 
existing regimen to a new drug(s).  In clinical practice, patients sometimes switch one or more 
components of a regimen to improve tolerability or to have a more convenient regimen; 
therefore, data on comparability of regimens following a treatment switch is useful.  However, 
switch trials are discouraged for supporting initial approval of an indication for initiation of HIV 
treatment because they do not allow an evaluation of the ability of a drug/regimen to induce a 
treatment suppression and only allow examination of maintenance of suppression.  Switch trials 
can be conducted in addition to other phase 3 trials outlined in this guidance or conducted 
postmarketing to support additional labeling statements or display of data in the Description of 
Clinical Trials section of the package insert.  The FDAs recommended primary endpoint and 
analysis of switch trials differs from that for Group 1 patients initiating treatment (see sections 
III.B.4., Efficacy Endpoints, and III.B.6., Statistical Considerations, respectively).  We also 
recommend that patients in Switch trials remain on randomized regimens for a minimum of 48 
weeks to allow a stringent assessment of loss of viral suppression in patients who were otherwise 
suppressed on a regimen at trial enrollment.  
 
Group 2 Patients (drug resistance to multiple drugs and multiple drug classes and unable 
to construct a regimen that suppresses HIV-RNA to below assay quantification limits)  
 
This population is also referred to as heavily treatment-experienced.  Noninferiority trials 
generally are not feasible in this population because there usually is no appropriate active control 
with a sufficiently well-described effect that can be used to define a noninferiority margin.  
 
If two investigational drugs with activity against multidrug resistant virus are available for study 
simultaneously, a factorial design as described for Group 3 is a reasonable option.   
 
15 
  Contains Nonbinding Recommendations 
When only one new drug is available for study in a clinical trial, a randomized placebo-
controlled superiority trial should be conducted where the primary endpoint is assessed at an 
early time point (see Figure 1).  Longer term placebo-controlled comparisons have fallen out of 
favor because continued use of the unmodified old (failed) regimen increases the risk of 
emergence of resistance to the investigational drug or the background drugs.  In our 
recommended design, patients experiencing ongoing viral replication on their current regimen 
and who need a new drug to construct a new viable regimen are continued on their current 
regimen, and randomized to add either placebo or the investigational drug (randomization to the 
investigational drug could be for one or more dose levels).  The primary efficacy evaluation of 
investigational drug versus placebo occurs over a short duration (7 days to 2 weeks), before 
development of a significant risk for resistance to the new drug or additional resistance to the 
background drugs. After the placebo comparison, all patients can receive the investigational 
drug (at one or various dose levels) added to a new background of approved drugs that are 
optimized by use of resistance testing.  In this proposal, a second assessment occurs at 24 weeks 
to assess for: 
 
   A dose response (if multiple doses are included)  
   Response by baseline susceptibility or resistance profile  
   Safety 
   Durability of initial response  
   Emergence of resistance to the investigational drug and to other drugs in the regimen  
 
The primary efficacy analysis is the short duration (e.g., up to 2 weeks) comparison to placebo.  
At 24 weeks, the comparison is no longer controlled unless a dose response is being evaluated.  
Given that doses chosen for study in HIV trials usually are on the plateau portion of a dose-
response curve, demonstration of a dose response is considered unlikely.  This design is similar 
to one of the recommended phase 1b trial designs discussed above, except that this phase 3 trial 
is larger and allows for a more thorough evaluation of baseline characteristics and response at 24 
weeks. In addition, this trial should be conducted only after smaller initial proof-of-concept 
trials identify reasonably active doses to reduce the likelihood of administering suboptimal doses 
to this vulnerable population. Evaluation for both safety and efficacy beyond 24 weeks is 
recommended and could be accomplished during the postmarketing period. 
 
16 
  Contains Nonbinding Recommendations 
Figure 1: Schematic of Possible Trial Design in Heavily  
Treatment-Experienced Patients  
Old Regimen 
+  New Drug 
New Regimen (Optimized) 
  +  New Drug 
Old Regi men  Randomize 
(Failing) 
Old Regimen 
 
+ Placebo 
24 weeks 
Secondary Endpoints 
Safety  
Dose Response (if multiple  
Up to  2 wks. 
doses studied)  
Primary Efficacy  Endpoint  Resistance Emergence 
Safety  Baseline Resistance/Response 
 
 
This type of trial design, which includes a primary efficacy analysis at 2 weeks (or less) and a 
safety analysis at 24 weeks, may be appropriate for a population of heavily treatment-
experienced patients when the investigational drug is expected to offer antiviral activity in the 
setting of multiple-drug resistance.  First drugs of a new class or second generation drugs of an 
existing class that can treat drug-resistant strains are candidates for this type of design.  Trials 
conducted in this population would support only a limited treatment indication for use in patients 
who cannot construct a viable regimen without a new antiretroviral drug. 
 
Criticisms of this approach primarily relate to the uncontrolled design of the trial beyond the 
primary (2-week or less) comparison and the concern that it does not allow for an adequate 
assessment of the durability of the virologic effect and of longer term safety.  However, the 
unmet medical need in this population and the potential to decrease further development of 
resistance to the background regimen in the trial patients outweigh the modest loss of certainty in 
the interpretation of results from this type of trial design.   
 
After decades of antiretroviral drug development, many experts agree that active antiretroviral 
drugs can be identified within days to weeks of HIV-RNA monitoring based on early viral load 
kinetics. Durability of response is related to the ability to use a drug with an active supportive 
regimen.  In fact, even drugs with low barriers of resistance have become  preferred when 
combined with other active drugs in treatment-naive patients.  In a heavily treatment-experienced 
population, multiple types of regimens are likely to be used with a new drug, so there is no well-
defined benchmark to compare noninferiority.  The assessments that the above trial design 
provides  with respect to comparative short-term activity, longer term observations for 
virologic rebound or virologic durability, and safety and potential dose-response  are adequate 
17 
  Contains Nonbinding Recommendations 
to support approval of a limited indication for a population at high risk of suffering substantial 
HIV-related complications. 
 
Modifications to the trial design shown in Figure 1 could include:  (1) unequal randomization 
with more patients randomized to the short-term functional monotherapy (old regimen plus new 
drug) arm; and (2) adding functional monotherapy to both arms but deferring it in Arm 2 for the 
time period of the functional monotherapy assessment.  For example, Arm 1 would receive the 
investigational drug as functional monotherapy for Days 1 to 14 and Arm 2 would receive the 
new drug as functional monotherapy for Days 15 to 28 (after continuing their old regimen for 
Days 1 to 14). An advantage of increasing the number of subjects receiving functional 
monotherapy (in both arms) may be an ability to conduct more meaningful resistance analyses, 
particularly when there are multiple drug-resistant patterns for the drug class. 
 
Group 3 Patients (drug resistance present and able to construct a regimen that suppresses 
HIV-RNA below assay quantification limits) 
 
An active-controlled noninferiority comparison (as described for Group 1) with or without 
comparisons of multiple doses of the investigational drug is an appropriate trial design.  For this 
population, patients should be followed for at least 24 to 48 weeks.  NDA submissions can be 
made after an analysis at 24 weeks, if the drug demonstrates superiority over approved drugs.  
Choice of the active control is less straightforward than treatment-naive trials because second-
line regimens are not well defined in treatment guidelines and generally are left up to clinical 
judgment depending on the situation.  However, we recommend using controls that were 
previously studied in large randomized trials to justify the choice of a noninferiority margin (see 
Appendix B). 
 
An add-on superiority trial, where patients are randomized to a new regimen consisting of 
approved drugs versus a new regimen of approved drugs plus the investigational drug, is another 
possible trial design. The approved drugs in the regimen usually are selected after taking into 
account patient history and resistance testing.  It is desirable for patients in both arms to have a 
sufficient number of drugs to construct a fully suppressive regimen.  However, if too many 
patients in the enrolled population have many remaining treatment options, particularly drugs 
with a high level of potency, it is likely that adding another drug to the regimen would not 
demonstrate superiority. 
 
If two investigational drugs are available for study at the same time, a randomized controlled 
superiority trial with a factorial-type design can be used.  This design may be useful when 
studying patients who are unable to construct a viable antiretroviral regimen from approved 
drugs. In this type of trial design, where both A and B are investigational drugs, patients could 
be randomized to one of the following trial arms: 
 
   Arm 1:  Approved drugs + A+ B 
   Arm 2:  Approved drugs + A 
   Arm 3:  Approved drugs + B 
 
18 
  Contains Nonbinding Recommendations 
To demonstrate efficacy for drug A, Arm 1 would need to be superior to Arm 3, and to 
demonstrate efficacy for drug B, Arm 1 would need to be superior to Arm 2.  
 
2.  Randomization, Stratification, and Blinding 
 
We encourage sponsors to conduct double-blind trials whenever feasible.  For add-on superiority 
trials of a new antiretroviral plus background therapy compared to background therapy alone, 
patients randomized to the latter should receive a matching placebo.  In open-label protocols, 
patients may be more likely to drop out of the trial if they know they are not receiving the new 
treatment.   
 
There are situations in which blinding drugs or regimens may not be feasible, but in most cases 
the difficulties associated with blinding a trial are not insurmountable.  For example, blinding 
may be difficult when drugs require dose adjustments based on drug interactions with other 
drugs in the regimen; however, this could be accomplished by similarly dose adjusting the 
placebo. In most cases, blinding only one component of a regimen is needed in trials adding 
investigational drugs to a common background drug.  Background therapy does not need to be 
blinded. 
 
Sponsors designing trials in which blinding may be difficult or infeasible should discuss the 
proposal with the DAVP in advance to review potential modifications that might facilitate 
blinding and to discuss the potential effect of open-label therapy on interpretation of results.  
When blinding is impossible, open-label protocols should have detailed procedures for treatment 
switches and toxicity management because differential implementation of protocol procedures 
among treatment arms in open-label trials may impair interpretability of results.  For example, 
the validity of the results of open-label trials may be questioned if there are large differences 
among treatment arms with respect to nonprotocol-specified treatment discontinuations and, on a 
case-by-case basis, could affect the extent of labeling claims.  In such instances, we anticipate 
additional sensitivity analyses using different methods of handling treatment discontinuations or  
missing data.  
 
Sponsors should consider stratification of patients by important baseline factors such as, but not 
limited to, viral load (below 100,000 copies/milliliter (mL) versus equal to or above 100,000 
copies/mL15), CD4+ cell count (fewer than 200 versus greater than or equal to 200), and 
geographic area. Baseline resistance scores (phenotypic, genotypic, or overall susceptibility) can 
be used as a stratification factor in treatment-experienced trials.  The resistance scoring method 
and application should be discussed with the DAVP (e.g., use of partial scores, discordance 
between genotypic and phenotypic assay results).  
 
                                                 
15 Other viral load cut-offs could be used, but  baseline values above 100,000 copies/mL has been  predictive of  
reduced response rates in  previous programs.  Also a cut-off of  100,000 often  divides a naive population  roughly in 
half allowing  for sizable subgroups. 
19 
  Contains Nonbinding Recommendations 
3.  Choice of Controls 
 
Sponsors should include treatment regimens consistent with standards of clinical practice while 
the trial is being conducted.  Because of the evolving nature of accepted standards of HIV 
treatment, appropriate comparison regimens are expected to change over time.  In general, 
current HIV treatment guidelines emphasize the importance of using at least three potentially 
active drugs (if possible) when constructing a regimen.  However, some of the newer approved 
drugs have a genetic barrier that could possibly support study of two-drug combinations.  From a 
patient management perspective, use of control regimens that have been determined to be 
suboptimal, based on clinical studies or consensus of expert panels reviewing pertinent data, 
would jeopardize the viability of a trial and possibly future treatment options for patients, and 
therefore should not be used. Protocol proposals with control arms that deviate from current 
standards of care should be discussed with the DAVP before implementation and sponsors 
should consider ethics consultation. 
 
Cross-class comparisons may be appropriate for Group 1 (treatment-naive) trials.  An 
investigational drug with the potency of a nonnucleoside reverse transcriptase inhibitor 
(NNRTI), integrase strand transfer inhibitor (INSTI), or protease inhibitor/metabolism inhibitor 
(PI/MI) combination can be compared to efavirenz (EFV), an INSTI, or one of the HHS 
Antiretroviral Treatment Guidelines-recommended PIs/MIs.  If two treatment-naive trials are 
being conducted, an in-class comparison in one trial and a cross-class comparison in the other 
trial can provide useful comparative information for a prescriber.  EFV and PIs (including a PI 
plus low-dose ritonavir) have been used as comparators in many active-controlled trials in 
treatment-naive patients, and choice of noninferiority margins for Group 1 trials are based, in 
part, on what is known about their contribution toward efficacy as part of a treatment regimen 
(see Appendix B). An INSTI is also considered to be an adequate comparator because all 
INSTIs have been demonstrated to be at least as efficacious as EFV with a tolerability profile 
that facilitates blinding.  
 
For treatment-naive trials, a drug with the potency of an NRTI can be compared to one of the 
other two NRTIs in the regimen.  Comparing a drug from another class to an NRTI may be 
considered on a case-by-case basis. When studying an NRTI in noninferiority trials, the third 
drug in at least one of the trials should be EFV or another similar NNRTI or an INSTI with a low 
barrier to resistance, but not a PI/MI.  The relative contributions of NRTIs to an EFV-based 
regimen can be reasonably inferred from previous data.  This is not the case for regimens that 
include a PI/MI. See Appendix B for the recommended noninferiority margin for a 
noninferiority trial that uses EFV as the active control. 
 
For treatment-experienced patients (Group 2 and Group 3), there are no standard regimens.  
Active controls depend on the exact patient population studied with respect to baseline resistance 
and also depend on a sufficiently robust demonstration of efficacy of active controls in  
previously conducted trials. Noninferiority margins can be based on a rationale similar to that 
described in Appendix B. Noninferiority trial proposals should be discussed with the DAVP in 
advance. 
 
20 
  Contains Nonbinding Recommendations 
4.  Efficacy Endpoints  
 
We recommend the following primary efficacy endpoints for phase 2 and phase 3 trials: 
 
	   For Group 1 trials:  the proportion of patients with HIV-RNA levels less than the lower 
limit of quantification at 48 weeks using a sensitive, FDA-licensed test.  If more sensitive 
tests are approved, sponsors are encouraged to base the primary endpoint on an approved 
test with the lowest lower limit of quantification.  The method for calculating these 
proportions is described in Appendix A. 
 
	   For Group 2 trials:  the proportion of patients with HIV-RNA decreases from baseline 
exceeding 0.5 log  at an early time point (up to 2 weeks).  Other increments can also be 
10
used, such as 1 log  decline from baseline.  
10
 
	   For Group 3 trials:  the proportion of patients with HIV-RNA levels less than the lower 
limit of quantification at 48 weeks using a sensitive, FDA-licensed test.  A 24-week time 
point can be used for superiority comparisons when a drug is expected to offer an 
advantage over currently available options.  
 
	   For Switch trials:  the proportion of patients with HIV-RNA greater than  or equal to 
the lower limit of quantification at 48 weeks using a sensitive, FDA-licensed test.  This 
differs from the endpoints in Group 1 to 3 trials in that the endpoint focuses on and is 
powered for virologic failure and not success.  This is because in Switch trials patients 
are starting with HIV-RNA levels that are already suppressed below the assay limit of 
quantification. In other words, the endpoint of interest is the proportion of people with 
suppressed HIV-RNA at baseline who lose virologic control after switching to a new 
drug or regimen.16    
 
Secondary endpoints should include: 
 
   Mean changes in viral load from baseline for treatment-experienced patients 
 
   Changes in CD4+cell counts from baseline 

 
5.  Trial Procedures and Timing of Assessments 
 
Recommended critical time points for measuring viral RNA depend on the patient population 
studied. Early time points (1 to 4 weeks) are critical assessments for Group 2.  Beyond the first 
month, HIV-RNA, CD4+ cell counts, and safety assessments are typically collected at Weeks 8, 
12, 16, 24, 36, and 48 and every 3 to 6 months beyond 48 weeks.  Longer term follow-up out to 
                                                 
16  Previous Switch  trials have used  the proportion of patients with HIV-RNA below 50  copies/mL as the primary  
endpoint.  However, most of the patients who were not counted as treatment successes did not experience actual 
virologic failure but were not considered  successes for other reasons, such as stopping the drug  because of adverse 
reactions, lost to follow-up, or withdrawing consent, among others.  Because most Switch trials are not blinded and 
enroll patients who may have  some interest in switching to  the new treatment, it appeared that treatment failures for 
reasons other than true virologic failure were introducing bias into a treatment success analysis.  
21 
  Contains Nonbinding Recommendations 
96 weeks and beyond is recommended, particularly for treatment-naive patients.  Longer term  
follow-up can be completed as a postmarketing commitment or a postmarketing requirement if 
there is a safety concern identified in the 48-week dataset that needs further evaluation.  
 
Protocols should include procedures for clinical management based on changes in HIV-RNA.  
To facilitate interpretation of study results, it is critical that management decisions be made in a 
uniform manner.  This is particularly important for open-label studies.  Protocol procedures that 
allow treatment switches for patients who never achieve HIV-RNA levels below an assay limit 
should be applied consistently across treatment arms.  For example, some protocols allow 
treatment-naive patients who have not achieved an HIV-RNA reduction of 1 log  by 8 weeks to 
10
switch their antiviral regimen.  These criteria may vary depending on the population studied and 
the response that is expected or desired. 
 
6.  Statistical Considerations 
 
Sponsors should designate the hypotheses to be tested before trial initiation.  These hypotheses 
should be stated in the protocol or the statistical analysis plan (SAP).  If sponsors choose to test 
multiple hypotheses, they should address issues related to the potential inflation of false positive 
results (overall type I error rate) caused by multiple comparisons.  These issues should be 
discussed with the DAVP in advance of trial enrollment, and should be incorporated into SAPs 
as appropriate. 
 
a.  Analysis populations  
 
The Full Analysis Set, as defined in ICH E9,  should be used for the primary efficacy and safety 
analyses. Patients who discontinued from the trial before receiving any trial drugs generally can 
be excluded if balanced across treatment arms and relatively few in number (approximately less 
than 1 percent). 
 
b.  Efficacy analyses  
 
For trial Group 1- and Group 3-type patients, the primary efficacy endpoint should be the 
proportion of patients with HIV-RNA less than the lower limit of quantification at 48 weeks (or 
24 weeks for drugs with a likely treatment advantage over available options for treatment-
experienced patients) using a sensitive, FDA-approved viral load assay.  For Switch trials, the 
endpoint is the proportion of patients with HIV-RNA greater than or equal to the limit of 
quantification at 48 weeks. The method for calculating the proportions for all trials is described 
in Appendix A.  For Group 2 patients, the primary efficacy endpoint should be the proportion of 
patients with HIV-RNA decreases from baseline exceeding 0.5 log  or greater at an early time 
10
point (up to 2 weeks). 
 
The primary efficacy analysis should be adjusted for at least one or two of the most important  
covariates (e.g., baseline HIV-RNA).  The covariates that will be included in the primary 
analysis should be prespecified in the protocol.  Cochran-Mantel-Haenszel analyses and 
Breslow-Day statistics can be used to examine the homogeneity of treatment effects.  The 
22 
  Contains Nonbinding Recommendations 
calculation of the difference between two proportions and its confidence interval can be based on 
stratum-adjusted Mantel-Haenszel proportions.    
 
For subgroup analyses, the analysis of the primary efficacy endpoint should be performed within 
important demographic and baseline characteristics such as sex, race, age group, region, baseline 
HIV-RNA viral load, baseline CD4+ cell count, clade, and baseline resistance score (when 
appropriate). The purpose of subgroup analyses is to evaluate the consistency of the primary 
efficacy endpoint result across a range of baseline factors.  However, simply by chance, a drug 
that has a homogeneous overall effect in a trial population will often show different effects in 
some subgroups, sometimes even showing significant heterogeneity.  Therefore, subgroup results 
should be interpreted with caution. 
 
We encourage sponsors to collect data regarding drug-adherence and change of treatment 
including switching treatment and adding additional therapy.  These data are important to 
determine reasons for discontinuation so that patients who discontinue assigned therapy early can 
be appropriately classified in the analysis. 
 
c.  Noninferiority margin 
 
In noninferiority trials, the choice of noninferiority margins for statistical hypotheses should be 
discussed with the DAVP before trial initiation because one margin is not appropriate for all trial 
designs. The sponsor should attempt to define a margin (M ) based on prior knowledge of the 
1
quantitative contribution of the active control (i.e., the substituted part of the drug regimen) to 
the regimen as a whole.  This contribution should be determined in a similar population with a 
similar length of follow-up of the proposed trial (see Appendix B).   
 
In addition, the noninferiority margin (M ) used in the study may need to be smaller than M  (the 
2 1
whole effect of the active control) to preserve a clinically important fraction of the active control.  
For noninferiority testing, sponsors should employ two-sided 95 percent confidence intervals 
adjusted for multiple comparisons or other appropriate testing procedures. If noninferiority is 
shown, then superiority can be assessed. For additional information regarding noninferiority 
trials in general, see Appendix B, ICH E10, and the draft guidance for industry Non-Inferiority 
Clinical Trials.17  
 
d.  Missing data 
 
There is no single optimal way to deal with missing data from clinical trials.  Sponsors should 
make every attempt to limit loss of patients from the trial, and when the loss is unavoidable, 
collect information that can help explain the cause  of the loss and the final status of the patient.  
Analyses excluding patients with missing data or other post-treatment outcomes are potentially 
biased because patients who do not complete the trial may differ substantially in both measured 
and unmeasured ways from patients who remain in the trial.  The method of how missing data 
will be handled should be specified in the protocol or the SAP.  A patient retention and follow-up 
                                                 
17  When final, this guidance will represent the FDAs current  thinking on this topic.   
23 
  Contains Nonbinding Recommendations 
plan should be included in the protocol providing details on how to minimize missing data and 
collect follow-up information.  
 
e.  Interim analyses and data monitoring committees  
 
If interim (or futility) analyses are performed, these analyses should be prespecified in the 
protocol and the SAP. The purpose of the interim analysis should be stated in the analysis plan.  
If an adaptive design such as withdrawal of a treatment arm or sample size re-estimation based 
on an interim analysis is applied, then the adaptive design procedures should be prospectively 
prespecified.18  It is important that the interim analysis does not affect trial conduct and thereby 
compromise trial results.    
 
Use of a data monitoring committee (DMC) may be appropriate depending on the design of the 
proposed phase 3 trial.  If a DMC is used, a detailed charter with the composition of the 
committee members and the operational procedures should be provided for review.19  
 
f.  Other analyses of interest and secondary endpoints 
 
Sponsors can present secondary analyses on other endpoints of interest.  An analysis of change in 
CD4+ cell count from baseline at Week 24 or 48 among the treatment groups is a recommended 
secondary endpoint. In the event that a CD4 cell count at Week 48 time window is missing, we 
suggest that there be a planned analytic approach to impute missing data.  Examples include, but 
are not limited to, last observation carried forward, baseline observation carried forward, and 
mixed-effect models.  It may be useful to compare results with other approaches to examine 
sensitivity of outcome to the method chosen.  
 
Secondary endpoints will not be sufficient to support efficacy in the absence of an effect for the 
primary endpoint.  The protocol should propose a multiple testing strategy for secondary 
endpoints that adjust for multiplicity to be applied after the result for the primary endpoint is 
significant. 
 
g.  Statistical analysis plan  
 
Before unblinding any phase 2b or phase 3 trial, sponsors should have in place a detailed 
finalized SAP.  Although sponsors can update or modify an SAP as long as the trial remains 
blinded, sponsors should recognize that a detailed discussion may be needed concerning data 
access and appropriate firewalls for maintaining the integrity of the blind.  If any major 
modification occurs, sponsors should discuss the modifications with the DAVP.  Ideally, the 
SAP should be prepared at the time the protocol is made final, but we recognize that changes are 
sometimes made later, but before unblinding.  The SAP should be considered as part of the 
                                                 
18 See ICH E9 and the draft  guidance for industry  Adaptive Design Clinical Trials for Drugs and Biologics (when 
final, this guidance will represent the FDAs current thinking on this topic). 
 
19 See the guidance for clinical trial sponsors Establishment and Operation  of Clinical Trial Data  Monitoring  
Committees. 
24 
  Contains Nonbinding Recommendations 
protocol, and it can be either a section within the protocol (encouraged) or a separate document.  
The SAP should include: 
 
   Details on endpoint ordering 

   Analysis populations 

   Structure of statistical hypotheses to be tested  

   Statistical methods including the mathematical formulations  

   Level of significance or alpha-level  

   Alpha adjustments for multiple comparisons or interim analyses if applied 
  
   Definition of visit window 

   Handling of missing data  

   Sensitivity analyses   

 
It is important that the SAP prospectively identify any covariates that are to be used in the 
analysis. It is also important to choose covariates that are expected to strongly influence 
outcome.  
 
h.  Submission of data and programs 
 
Applicants should provide the following in the NDA:  
 
 	  The standard operating procedure for randomization code generation.  
 
	   The screening dataset including the information on all patients screened.  
 
	   The raw datasets consisting of variables that come directly from case report forms 
(CRFs) or other original source documents.  
 
	   The analysis datasets including variables for key efficacy and safety analyses.     
 
	   Algorithms and programs used to create analysis datasets directly from the raw datasets 
and programs for the primary and key secondary statistical analyses.  If the analysis 
datasets were created from intermediate datasets other than original raw datasets from  
CRFs, applicants should provide the intermediate datasets and programs to cover both 
steps. 
 
For additional information on regulatory submissions, see the guidance for industry Providing 
Regulatory Submissions in Electronic Format  Certain Human Pharmaceutical Product 
Applications and Related Submissions Using the eCTD Specifications. 
 
7.  Accelerated Approval (Subpart H) Considerations  
 
Full approval based on an endpoint of HIV-RNA suppression at the time points specified in 
section III.B.4., Efficacy Endpoints, is the anticipated pathway for marketing approval.  
Suppression of HIV-RNA is a fully validated surrogate for HIV clinical disease progression.  In 
25 
  Contains Nonbinding Recommendations 
addition, shorter term HIV-RNA changes are predictive of longer term HIV-RNA suppression in 
the setting of active antiretroviral drug regimens.   
 
C.  Other Considerations 
 
1.  Clinical Virology Considerations20  
 
Clinical resistance analyses should examine all patients that experience viral rebound, have no 
antiviral response or an incomplete antiviral response, or discontinue before suppression.  As 
such, the number of virologic failures in this analysis may be different from the number of 
virologic failures in the snapshot approach analysis (see Appendix A).  The examination of 
virologic failures in the clinical resistance analysis is designed to be more conservative to detect 
all possible signals and markers of resistance.  
 
Proof-of-concept and efficacy trials should assess the development of HIV genotypic resistance 
to the investigational drug. Phenotypic and genotypic resistance testing should be performed on 
baseline and on-treatment failure samples (preferably the rebound confirmation sample) for 
patients who demonstrate virologic rebound (defined as a 1 log  increase in HIV-RNA from  
10
nadir value or a confirmed HIV-RNA above 400 copies/mL after confirmed suppression to 
below 50 copies/mL or who meet other resistance criteria).  Any changes, including mixtures, in 
the amino acid coding sequence of the targeted genome region present in on-treatment or follow-
up samples, but not in the baseline sample, should be reported as having emerged during therapy.  
 
We recommend performing genotypic resistance analyses on the baseline samples from all 
subjects in trials in Group 1, Group 2, or Group 3 populations. Firstly, baseline resistance 
information helps to construct an effective background regimen in treatment-experienced 
patients and treatment-naive patients because of transmission of drug-resistant virus.  Secondly, 
baseline genotypic and/or phenotypic resistance data are important in evaluating the effect of 
transmitted or drug-selected baseline resistance-associated substitutions on antiviral response, 
especially in the case of new drugs in an established class.  In addition, baseline samples can be 
analyzed to identify HIV genetic polymorphisms that are associated with differential antiviral 
activity with the new drug. 
 
Virologic response by baseline genotype and phenotype analyses should be performed on a 
censored population to assess the effect of baseline resistance on outcome without confounding 
factors such as early discontinuation for adverse events.  Therefore, patients who discontinue 
study treatment while suppressed or who discontinue study treatment before confirmed 
suppression for adverse event, noncompliance, protocol violation, pregnancy, or withdrawal of 
consent should be censored from the analysis. In general, patients who discontinue while 
suppressed (HIV-RNA below 50 copies/mL) or discontinue before Week 4 should be censored 
from baseline resistance and response analyses.  Sponsors can discuss with the DAVP cases 
where analyzing a subset of patients with baseline resistance data may be appropriate. 
                                                 
20 See the  Attachment to  Guidance on Antiviral Product Development  Conducting and  Submitting Virology  
Studies to the Agency:  Guidance for Submitting HIV Resistance Data and the guidance for industry  Role of HIV  
Resistance Testing in Antiretroviral Drug Development. 
26 
  Contains Nonbinding Recommendations 
 
Viral resistance-associated polymorphisms or substitutions observed in clinical trials but not 
identified and characterized in nonclinical virology experiments should be evaluated 
phenotypically by introducing the amino acid changes into the HIV genome, and determining the 
conferred fold-shift in susceptibility to the drug using appropriate cell culture and/or biochemical 
assays. Phenotypic data can confirm the resistance association of an infrequently occurring 
genotypic treatment-emergent substitution.  However, treatment-emergent substitutions that 
occur frequently should be considered potentially genotypically resistance-associated even if 
they do not show a shift in phenotypic susceptibility.  Phenotypic analyses of baseline and on-
treatment failure clinical isolates should be analyzed and compared using patients representative 
of the HIV genetic diversity and virologic responses observed in clinical trials.  For baseline 
resistance and response analyses, phenotypic testing of a large subset of baseline samples may be 
needed when an adequate genotypic resistance algorithm cannot be established.   
 
Sponsors should consider genotyping regions outside the direct HIV genome target depending on 
the characteristics of the antiviral drug and interactions of the target with other viral proteins.  In 
cases when resistance is suspected based on viral RNA kinetics (rebounding viral load while the 
patient maintained adherence to study drugs), but genotypic evidence of resistance is not 
detected, sponsors also should consider performing additional genotypic analyses using a method 
sufficiently sensitive to detect minority variants.  
 
2.  Pharmacokinetic/Pharmacodynamic Considerations 
 
Trials conducted in HIV-infected patients should assess pharmacokinetics and the relationship 
between exposure and virologic suppression and toxicity in all patients.  
 
Sponsors can use a combination of intensive and sparse sampling throughout development to 
characterize the pharmacokinetics of the investigational drug and sometimes other HIV drugs in 
the regimen as appropriate.  For example, an intensive sampling schedule should be implemented 
in monotherapy trials.  In longer term trials, however, an intensive sampling schedule might not 
be feasible, or may be feasible only in a subset of patients or over a limited period of time (i.e., a 
single assessment at steady state).  Sparse PK samples should be obtained from as many patients 
in longer duration trials as possible, and the PK samples from these trials can be combined with 
intensive PK data from earlier trials for analysis.  Sparse PK samples should be obtained at the 
time of virologic assessments, such as at Weeks 4, 8, 12, 24, 36, or 48 or as otherwise specified 
in a protocol. 
 
Sponsors can use the following two broad approaches to characterize the relationship between 
drug exposure and viral kinetics or virologic suppression of the investigational drug, depending 
on the development stage and purpose of the analysis.  Both approaches allow for exploration of 
relevant covariates. 
 
1. 	  To aid the design of phase 2b or phase 3 trials, with respect to selection of dosage 
regimen, a mechanistic approach relating drug concentrations and viral kinetics is most 
appropriate. A mechanistic modeling approach should also account for the development 
of resistance to the investigational drug. 
27 
  Contains Nonbinding Recommendations 
 
2. 	  A simplified analysis relating proportion of patients with virologic suppression or 
virologic failure and appropriate exposure variable (e.g., minimum concentration or area 
under the plasma drug concentration versus time curve) can be used to support evidence 
of effectiveness and justify dose selection.21    
 
Additional analyses of the exposure-safety relationship(s) using similar approaches as described 
in # 2 also should be performed to assist in evaluating the balance between effectiveness and 
toxicity of different dosage regimens. 
 
3.  Pediatric Populations 
 
Under the Pediatric Research Equity Act (PREA), sponsors must study a drug in all relevant 
pediatric populations when submitting an application under section 505 of the Federal Food, 
Drug, and Cosmetic Act (FD&C Act) (21 U.S.C. 355) or section 351 of the Public Health 
Service Act (42 U.S.C. 282) for a new active ingredient, new indication, new dosage form, new 
dosing regimen, or new route of administration.  However, PREA requirements may be waived 
or deferred in certain circumstances.   
 
Although a detailed discussion of addressing PREA requirements is beyond the scope of this 
guidance, several points relevant to drugs for HIV treatment are addressed below.  In addition, 
under the Best Pharmaceuticals for Children Act, drugs are eligible for 6 months of additional 
exclusivity if sponsors conduct pediatric clinical trials specified in a Written Request.  New 
drugs for treatment of HIV may be issued a Written Request if the FDA determines that 
information relating to the use of the drug may produce health benefits in relevant pediatric 
populations. 
 
Only adult patients should be enrolled in early trials of novel antiretrovirals, reserving drug 
administration to pediatric patients until the pharmacokinetics, pharmacodynamics, and safety of 
the drug are reasonably well defined.22  Sponsors are encouraged to begin discussions of their 
pediatric formulation and clinical development plan early in development, but pediatric clinical 
trials should be initiated after phase 2 adult data characterizing the safety profile and initial 
antiviral efficacy are available.  Under PREA, sponsors must submit an initial pediatric study 
plan to the FDA no later than 60 days after the end-of-phase 2 meeting.23  If clinical trials in 
adults have demonstrated no significant safety concern that would preclude study in children, 
evaluation of adolescents using the adult dose and formulation is encouraged (Momper et al. 
                                                 
21 See the guidance for industry Exposure-Response Relationships  Study  Design, Data  Analysis, and Regulatory  
Applications. 
 
22 See the guidance for industry E11 Clinical  Investigation of Medicinal Products in the Pediatric Population. 
 
23 See section 505B(e)  of the FD&C  Act, as amended by  section 506 of the  Food and Drug Administration Safety  
and Innovation Act  of 2012, and the draft  guidance for industry  Pediatric Study Plans:  Content  of and  Process for 
Submitting  Initial Pediatric Study Plans and Amended Pediatric Study Plans. When final,  this guidance will 
represent the  FDAs current thinking  on this topic. 
28 
  Contains Nonbinding Recommendations 
2013). Ideally, dose confirmation and safety data in this older pediatric age group (i.e., 12 to 17 
years of age) should be available at the time of NDA submission.   
 
The overall pediatric development program should include: 
 
 	  Juvenile nonclinical studies (if necessary).  
 
 	  Development of age-appropriate formulation(s).  Clinical pharmacology trials to assess 
single- or multiple-dose pharmacokinetics (as appropriate for the drug) across the 
pediatric age range (4 weeks to younger than 18 years of age).  Of note, there may be 
circumstances in which evaluating drugs in children younger than 4 weeks of age is 
appropriate and should be discussed with the DAVP.  Dose selection for the clinical 
pharmacology assessment and subsequent trials assessing efficacy and safety should be 
discussed with the DAVP. 
 
	   A sufficient number of patients in the pediatric safety database who have received the 
drug at the to-be-marketed dose or higher for at least 6 months to reasonably characterize 
the safety profile of the drug in pediatric patients.  Generally, a safety database that 
includes at least 100 pediatric patients (with adequate representation across the age range 
of 4 weeks to 17 years of age) treated for at least 6 months should be sufficient, but this 
number may vary based on drug-specific issues. In addition to collection of safety data, 
HIV-RNA should be collected to assess activity along with resistance data in patients 
with virologic failure.  
 
 	  A plan for long-term follow-up to assess growth and development, other potential safety 
concerns relevant to the investigational drug, and durability of virologic suppression.   
Follow-up over a period of at least 3 years of treatment is anticipated, but a 
postmarketing requirement provided after initial pediatric labeling also may be 
appropriate. 
 
The course of HIV infection and the effects of antiretroviral drugs are considered sufficiently 
similar in pediatric and adult patients to allow extrapolation of efficacy.  Information about 
pediatric extrapolation can be found in other guidance.24  Although pediatric efficacy of 
antiretroviral drugs is generally extrapolated from adult trials based on bridging 
pharmacokinetics, HIV-RNA should be collected in the pediatric trials to assess activity along 
with resistance data in patients with virologic failure.  
 
4.  Early Access/Treatment INDs 
 
Treatment INDs or other access protocols for antiretroviral drugs may be appropriate when 
sufficient clinical trial data have been generated to characterize a reasonably safe and active dose 
of an investigational drug.  Ideally, the initiation of a treatment IND would occur after phase 3 
trials are fully enrolled or well underway so as not to interfere with phase 3 drug development.  
                                                 
24 See the draft guidance for industry General Clinical Pharmacology Considerations for Pediatric Studies for 
Drugs and Biological Products.  When final, this guidance will represent the FDAs current thinking on this topic. 
29 
  Contains Nonbinding Recommendations 
Treatment INDs can provide early access while phase 3 trials are being completed, analyzed, 
submitted, and reviewed by the FDA.  Individual patient INDs and treatment access protocols for 
intermediate size populations can occur earlier in drug development.  
 
Historically, early access programs for the treatment of HIV infection allowed many patients to 
gain access to lifesaving drugs. However, for some individuals, early access to a drug resulted in 
sequential monotherapy and led to the emergence of multidrug resistance.  Because treatment of 
HIV requires multiple drugs to achieve and maintain viral suppression below detection and to 
reduce the emergence of drug resistance to single drugs or drug classes, treatment INDs that 
include two or more investigational drugs or that allow co-enrollment in several treatment IND 
programs simultaneously are desirable.  Treatment use of multiple investigational drugs should 
be supported by: 
 
 	  Data and rationale that characterize the potential for PK-based drug interactions and 
potential for overlapping toxicity. Data to support dose modifications (if needed) when 
substantial drug interactions are present.  
 
 	  Information suggesting the lack of antagonistic antiviral activity and minimal or no 
overlapping resistance profiles. 
 
30 
  Contains Nonbinding Recommendations 
REFERENCES 
 
 
Arnold, JJ, SD Sharma, JY Feng et al., 2012, Sensitivity of Mitochondrial Transcription and 
Resistance of RNA Polymerase II Dependent Nuclear Transcription to Antiviral 
Ribonucleosides, PLoS Pathog, 8(11):e1003030. 
 
Bartlett, JA, J Johnson, G Herrera et al., 2006, Long-Term Results of Initial Therapy with 
Abacavir and Lamivudine Combined with Efavirenz, Amprenavir/Ritonavir, or 
Stavudine, J Acquir Immune Defic Syndr, 43:284-92. 
 
Centers for Disease Control and Prevention, 2014, Revised Surveillance Case Definition for HIV 
Infection  United States 2014, MMWR, April 11, 63(RR03);1-10. 
 
Chuang-Stein, C and R Demasi, 1998, Surrogate Endpoints in AIDS Drug Development:  
Current Status, Drug Information Journal, 32:439-448.  
 
Hill, AM, R DeMasi, and D Dawson, 1999, Meta-Analysis of Antiretroviral Effects on HIV-1 
RNA, CD4 Cell Count and Progression to AIDS or Death, Antiviral Therapy, 3:139-145. 
 
Hogg, RS, B Yip, and C Kully, 1999, Improved Survival Among HIV-Infected Patients After 
Initiation of Triple-Drug Antiretroviral Regimens, CMAJ, 160:659-65. 
 
Hynes, J, S Nadanaciva, R Swiss, et al., 2013, A High-Throughput Dual Parameter Assay for 
Assessing Drug-Induced Mitochondrial Dysfunction Provides Additional Predictivity 
Over Two Established Mitochondrial Toxicity Assays, Toxicology In Vitro, 27:560-569. 
 
Marroquin, LD, J Hynes, JA Dykens et al., 2007, Circumventing the Crabtree Effect:  Replacing 
Media Glucose with Galactose Increases Susceptibility of HepG2 Cells to Mitochondrial 
Toxicants, Toxicol Sci, 97:539-47. 
 
Marschner, IC, AC Collier, RW  Coombs et al., 1998, Use of Changes in Plasma Levels of 
Human Immunodeficiency Virus Type 1 RNA to Assess the Clinical Benefit of 
Antiretroviral Therapy, J Infect Dis, 177:40-7. 
 
Momper, JD, Y Mulugeta, DJ Green, A Karesh, KM Krudys, HC Sachs, LP Yao, and GJ 
Burckart, 2013, Adolescent Dosing and Labeling Since the Food and Drug 
Administration Amendments Act of 2007, JAMA Pediatr, Oct, 167(10):926-32. 
 
Murray, JS, MR Elashoff, LC Iacono-Connors et al., 1999, The Use of Plasma HIV RNA as a 
Study Endpoint in Efficacy Trials of Antiretroviral Drugs, AIDS, 13:797-804. 
 
Palella, FJ, KM Delaney, AC Moorman et al., 1998, Declining Morbidity and Mortality Among 
Patients with Advanced Human Immunodeficiency Virus Infection, N. Engl. J. Med., 
338:853-60. 
 
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Saag, MS, P Cahn, F Raffi et al., 2004, Efficacy and Safety of Emtricitabine vs. Stavudine in 
Combination Therapy in Antiretroviral-Naive Patients:  A Randomized Trial, JAMA 
292:180-9. 
 
Strategies for Management of Antiretroviral Therapy (SMART) Study Group, WM El-Sadr, JD 
Lundgren, JD Neaton, F Gordin, D Abrams, RC Arduino, A Babiker, W Burman, 
N Clumeck, CJ Cohen, D Cohn, D Cooper, J Darbyshire, S Emery, G Fatkenheuer, 
B Gazzard, B Grund, J Hoy, K Klingman, M Losso, N Markowitz, J Neuhaus, A Phillips, 
and C Rappoport, 2006, CD4+ CountGuided Interruption of Antiretroviral Treatment, 
N Engl J Med, 355:228396. 
 
Van Leth, F, P Phanuphak, and K Ruxrungtham, 2004, Comparison of First-Line Antiretroviral 
Therapy with Regimens Including Nevirapine, Efavirenz, or Both Drugs, Plus Stavudine 
and Lamivudine:  A Randomized Open-Label  Trial, the 2NN Study, Lancet, 363:1253-63. 
32 
  Contains Nonbinding Recommendations 
APPENDIX A:   

RECOMMENDED APPROACH FOR EVALUATING VIROLOGIC RESPONSE IN 

CLINICAL TRIALS SUPPORTING ANTIRETROVIRAL APPROVALS 
 
 
The time to loss of virologic response (TLOVR) method previously used in labeling by the 
DAVP for determining virologic successes at critical time points has often led to multiple queries 
between the DAVP and the applicant. Briefly, to be called a virologic success (HIV-RNA below 
50 copies) by TLOVR,25 a patient needed to have an HIV-RNA level below a detection limit on 
two time points and should not have experienced confirmed rebound (two time points) above the 
limit.  This algorithm was, at times, cumbersome when patients were less than perfectly adherent 
or when patients needed to stop treatment for brief periods.   
 
DAVP statistical and clinical reviewers recently completed a project titled Handling 
Uncertainty in Endpoint Selection and Other Endpoint Issues.  The goal of the project was to 
determine if simplified endpoints could be used for approval at Week 48.  The team evaluated 18 
trials from 7 NDAs with 8,046 patients.  Results obtained using the TLOVR algorithm, which 
used data from every visit to consider the pattern of HIV responses, were compared to a less 
complicated  snapshot approach that only used HIV-RNA data at the visit (window period) of 
interest. A high concordance between the TLOVR algorithm and snapshot results was observed.  
Using the TLOVR algorithm, 61 percent of the 8,046 patients remained in the study for 48 weeks 
and were virologic responders compared to 61 percent of the patients using the snapshot  
approach; 18 percent were virologic nonresponders using the TLOVR algorithm compared to 17 
percent using the snapshot approach and approximately 20 percent discontinued before Week 48 
using both approaches. Differences between the two methodologies are minimal.  
 
Based on the findings from the project and the ease of the snapshot method, pending 
supplemental NDAs and future NDAs should include virologic outcome results based on the 
snapshot approach in product labeling. 
 
Snapshot Approach 
 
For analysis of virologic outcome at a given time point, a window period for possible virologic 
assessments can be used as follows: 
 
   Window size is one-half the duration of time between study visits. 
 
   Windows can be smaller at earlier time points than later time points. 
 
                                                 
25 Previously, labels used the term  virologic success or  virologic failure to  describe patients who had HIV-RNA 
levels below or equal to or above 50 copies, respectively.   However, we now prefer  not to use the terms success or 
failure, but rather just state whether the viral load was below or above 50 copies.  Transient  blips of HIV-RNA  
above 50 copies occur for a variety of reasons and this  does not always  signify true virologic failure to the regimen.  
True virologic failure may only be determined after assessment of  drug adherence, repeat  HIV-RNA testing with  
continued treatment, and/or resistance testing.  Snapshot time windows allow time for clinical assessment and 
retesting to  reduce the number of patients counted as having  HIV-RNA levels above 50  copies/mL because of  
transient blips. 
  33
  Contains Nonbinding Recommendations 
 	  If trial-defined windows differ from the proposed windows in Table A, alternatives 
should be discussed with the DAVP.  In most cases the protocol-defined windows for 
completed trials are appropriate; however, for future trials we encourage standardization 
and recommend the windows in Table A. 
 
Table A: Proposed Windows  
Visit  Window (Through End-of-Study  Window (Days) 
Week) 
(Express in Days for Nonoverlap) 
24  18-30  127-210 
48  42-54  295-378 
96  90-102  631-714 
 
Table B is an example of efficacy presentation in labeling.  
 
Table B:  Virologic Outcome at 48-Week Window (295 to 378 Days) 
  Drug A  Drug B  
HIV-RNA < 50 copies/mL   60%  50% 
HIV-RNA  50 copies/mL#   20%  30% 
No Virologic Data at Week 48 Window     
   Reasons     
Discontinued study/study drug due to AE  10%  8% 
or Death*     
 Discontinued study/study drug for Other  6%  6% 
Reasons**     
   On study but missing data in window  4%  6% 
 Assays  with  other lower limits (below 50 copies/mL) also can be used.  
# Includes patients who changed any component of  background therapy to a new  drug class, changed background  
components that were not permitted per protocol, or changed any background drug in the regimen because of lack of 
efficacy (perceived or documented) before Week 48; patients who discontinued study drug or study before Week 48 
for lack or loss of efficacy and patients who are equal to or above 50 copies/mL in the 48-week window. 
* Includes patients who discontinued because of adverse event (AE)  or death at any time point  from Day 1 through
  
the time window if this resulted in no  virologic data during the specified  window. 

** Other Reasons includes:   withdrew consent, loss to  follow-up, moved, among others. 
 
 
Principles of snapshot analysis 
 
Some general concepts of the snapshot approach include the following: 
 
 	  The primary efficacy endpoint should be primarily a virologic endpoint and not a clinical 
endpoint. This method follows a Virology First hierarchy. 
 
	   Because this is primarily a virologic endpoint, the hierarchy for assessing row and 
column percentages is HIV-RNA below 50 copies/mL or HIV-RNA equal to or above 50 
copies mL, first, for any given time window followed by reasons for No Virologic Data 
in the 48-Week Window. 
 
  34
  Contains Nonbinding Recommendations 
 	  Percentages not included in the HIV-RNA below or equal to or above 50 copies/mL rows 
should describe reasons for no data at a specified analysis time window.  These 
percentages should not represent comprehensive safety or clinical efficacy analyses. 
 
Procedures for calculating virologic outcome 
 
The following examples use a detection limit of 50 copies/mL, but approved sensitive assays 
with other detection limits also can be used. 
 
 	  Data in the window  
 
Virologic outcome should be determined by the last available measurement while the 
patient is on treatment and continued on trial within the time window (see Table A).   
 
	   Examples:  HIV-RNA = 580 copies/mL at Day 336, HIV-RNA below 50 copies/mL 
on Day 350. This should be categorized as HIV-RNA below 50 copies/mL, even if 
an aliquot from the same sample was retested.  
 
	   In the rare example that someone would have HIV-RNA below 50 copies/mL at Day 
336 and then equal to or above 50 copies/mL at Day 350, the result would be counted 
as above 50 copies/mL (we believe this will be rare, because undetectable patients 
would not likely have a second lab result in a window). 
 
 	  No data in the window 
 
	   If there are no data in a time window, then percentages for each category of missing 
data should be tallied. 
 
	   There are three main reasons for no data in the window: 
 
1. 	  Discontinued study due to Adverse Event or Death.  Any patient who 
discontinues because of an AE or death before the window should be classified as 
Discontinued due to AE or Death (as appropriate), regardless of the HIV-RNA 
result, even if the HIV-RNA is below 50 copies/mL at the time of 
discontinuation.26  However, if a patient has an HIV-RNA value in the time 
window and also discontinues after the viral load was tested in the time window, 
the viral load data should be used to classify the patients response.  This is the 
Virology First hierarchy. Example:  HIV-RNA below 50 copies/mL at Day 336 
and discontinues because of AE or even dies on Day 360  this person is 
categorized as having HIV-RNA below 50 copies/mL.  Likewise if HIV-RNA is 
552 copies/mL on Day 336 and the patient discontinues on Day 360, the patient is 
categorized as having HIV-RNA equal to or above 50 copies/mL.  
 
                                                 
26 There should not  be a separate category for  Death.   We  believe a separate category for Death is misleading, 
because it does not account for all deaths in the trial.  Instead, text describing percentages of deaths can be included 
in the CLINICAL STUDIES section  of product labeling.  
  35
  Contains Nonbinding Recommendations 
2. 	  Discontinued study for Other Reasons.  The examples above also apply to this 
category.  If a patient discontinues the study before the window because of  lack of 
efficacy then the patient should be included in the HIV-RNA equal to or above 50 
row and not in the Discontinued for Other Reasons row. To further clarify, for 
patients who Discontinued for Other Reasons, it is important to realize that in the 
Virology First hierarchy only patients who have achieved virologic suppression 
can be counted as Discontinued for Other Reasons.  If a patient discontinues 
because the subject withdrew consent and his or her HIV-1-RNA result at the time 
of discontinuation was equal to or above 50 copies/mL, then he or she should be 
categorized as HIV-RNA equal to or above 50 and NOT as Discontinued for 
Other Reasons.  However, if a patient discontinued because of  Lost to Follow-Up  
and the last HIV-RNA result was 49 copies/mL, then the patient can be 
categorized as Discontinued for Other Reasons.  
 
Likewise, if patients changed background treatment  not permitted by protocol  
 they should be considered an efficacy failure and captured in the HIV-RNA 
equal to or above 50 copies/mL row. 
 
3. 	  On study but missing data in window.  Only data in the window can be used for 
patients remaining on study. For example, if there are no data during Days 295 to 
378, but there is an HIV-RNA below 50 copies/mL on Day 380, this patient 
should be considered On Study but Missing Data in Window. This patient can 
count as below 50 copies at subsequent analysis points (e.g., 96 weeks), if he or 
she remains undetectable at the subsequent analysis window (e.g., 96 weeks).  
Conversely, if there are no data during Days 295 to 378, but there is an HIV-RNA 
equal to or above 50 copies/mL on Day 280, this patient also should be classified 
as On Study but Missing Data in Window. 
 
Optimized Background Therapy Substitutions After Randomization  
 
Typically trials have permitted one in-class substitution of an optimized background therapy 
(OBT) drug for documented toxicity reasons.  As more drugs became available, cross-class 
substitutions were permitted in some trials; however, drug substitutions potentially can affect 
long-term durability of a regimen particularly if the OBT change occurred later in the trial.  OBT 
substitutions (in-class or cross-class) permitted per protocol for documented toxicity reasons can 
be permitted on or before the first trial visit without penalty.  If OBT substitutions for toxicity 
reasons occur after the first trial visit, then patients should be categorized as having HIV-RNA 
equal to or above 50 copies/mL if they have HIV-RNA above 50 copies/mL at the time of 
switch. 
 
Applicants have asked to amend the algorithm such that only cross-class switches are classified 
as primary endpoint failures because not allowing in-class OBT substitutions may create 
disincentives. Specifically, investigators may not have incentive to ensure follow-up after an 
OBT switch because those patients are deemed as analysis failures, or investigators may 
unnecessarily increase early switches to avoid classifying patients as failures in the primary 
efficacy analysis.  
 
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We decided not to amend the algorithm for the following reasons: 
 
	   All in-class switches are not the same.  With the expanded number of drugs in each class 
and the approval of second generation drugs within the same class, switching therapy 
after knowledge of viral load changes may confound the results.  One would then have to 
decide which switches are appropriate for the population being studied. 
 
	   We attempted to make the snapshot as concise and stringent as  possible to reduce the 
amount of end-of-NDA-review negotiations over single cases.  Having to decide which 
in-class switches are appropriate for specific populations (e.g., naive, experienced) would 
complicate the algorithm.  Example:  In what population is a switch from atazanavir to 
darunavir considered acceptable?    
 
 	  We believe that the unwanted scenarios mentioned above can be minimized.  Both types 
of analyses can be performed, perhaps allowing cross-class switches in sensitivity 
analyses. However, for FDA labeling purposes, the snapshot should be used.  Therefore, 
investigators could be informed that not all analyses may result in their particular patient 
counting as a failure if he or she switches background drugs and that follow-up should be 
maintained. 
 
 	  We do not believe that there is one correct analysis.  All analyses only approximate truth.  
The snapshot approach strives for efficiency and consistency across multiple 
applications. This should not prohibit academic investigators from presenting a variety 
of analyses at scientific meetings.  Differences can be described. 
 
Datasets for Snapshot Approach 
 
For a submission with multiple trials, each trial should have its own dataset for the snapshot 
analysis. The datasets should contain, at minimum, the following information:   
 
 	  Study identification (ID) 
 
 	  Patient study ID 
 
 	  Study day and date of last double-blind treatment 
 
 	  Virologic outcome based on the snapshot approach (i.e., HIV-RNA below 50 copies/mL, 
HIV-RNA equal to or above 50 copies/mL, discontinued due to AE or death, 
discontinued for other reasons, on study but missing data during window) 
 
 	  The HIV-RNA measurement and the corresponding study day and date used to determine 
the above virologic outcome if the measurement was not missing 
 
 	  Study day and date when the patient switched to open-label treatment because of lack or 
loss of virologic suppression, if applicable 
 
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 	  Discontinuation study day and date, reason for discontinuation, and last on double-blind, 
treatment measurement before discontinuation for the patients who discontinued drug  
 
The treatment phase in the dataset should be defined and only include three categories as 
follows:  screening (or baseline), treatment, and follow-up.  
 
 
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APPENDIX B: 

NONINFERIORITY MARGIN RECOMMENDATIONS AND JUSTIFICATIONS 

 
1.0 	 Justification for a Noninferiority Margin Using EFV as a Control Arm in 
Treatment-Naive Studies on a Background of Dual Nucleoside Therapy 
 
The noninferiority margin for comparing the potent anchor drug or third drug in regimens for 
Group 1 HIV treatment-naive patients is 10 to 12 percent.  This margin is an M  delta, based on 
2
the treatment effect we clinically wish to preserve compared to active controls.  We have known 
for years, based on well-controlled superiority trials, that an M  for assessing comparability to a 
1
PI or NNRTI as a third drug added to a dual nucleo(t)side background is large (approximately 45 
percent  using lower confidence bounds for the endpoint of HIV-RNA below 50 or 400 
copies/mL at 48 weeks).  The rationale is as follows. 
 
1.1 EFVs treatment effect is highly reproducible and dual nucleosides alone are known to be 
largely ineffective for durable virologic suppression  
 
Few individuals (approximately 2 percent or less) receiving only two nucleoside analogues 
achieve viral load suppression below 400 copies/mL.  Even fewer suppress HIV-RNA below 50 
copies/mL.  The few that suppress below the detection limit are those individuals with low 
baseline viral loads below 5,000 copies and high CD4+ cell counts. These people are known as 
long-term nonprogressors but few enroll in registration trials.  Beginning in 1995, suppressing 
viral load below assay detection limits was a new phenomenon, recognized when PIs and 
NNRTIs became available and were added to a dual nucleo(t)side backbone.  Before PIs and 
NNRTIs, long-term suppression (less than 24 to 48 weeks) of viral load was rare.  The addition 
of a PI or an NNRTI to two nucleosides basically converted a negligible viral load response (less 
than 2 percent) to a response rate of 60 to 90 percent, owing to the potency of PIs and NNRTIs, 
marked antiretroviral synergy of an antiviral regimen, and a formidable resistance barrier that 
three drugs confer compared to two drugs. 
 
Several drug labels contain examples of response rates observed with dual nucleoside therapy.  
All of these studies show that dual nucleoside therapy is associated with a negligible response 
rate (defined as suppressing viral load below an assay limit). The genetic barrier for two 
nucleo(t)side analogue drugs is known to be insufficient to durably suppress viral load in most 
individuals based on calculations of reservoirs, replication rates, and potential for pre-existence 
of antiretroviral mutations.  Examples of dual nucleoside response rates are listed in Table C.  
 
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Table C:  Virologic Response Rates for Dual Nucleoside Studies  
(Approximately 48 Weeks) 
Drug Label  Nucleoside  Nucleoside  Triple Response 
Study  Backbone  Response Rate < 400  Rate 
at 48 Weeks 
Nelfinavir   ZDV/3TC  3%  58% 
-Study 511 
Indinavir  ZDV/3TC  2%  45% 
-ACTG* Trial 320 
Indinavir  ZDV/3TC  0%  80% 
Merck Trial-035 
*  ACTG = AIDS Clinical Trial Group 
 
EFV has been extensively studied in triple regimens in clinical studies of 48 weeks duration in 
treatment-naive patients and was part of the control regimen in many of these studies.  In Table 
D, response rates for proportion below 400 copies/mL for triple regimens that included EFV 
ranged from 64 percent to 84 percent, and for proportion below 50 copies/mL ranged from 37 
percent to 80 percent. (Note that the 37 percent response rate is an outlier and samples were 
believed to be mishandled in that study; excluding results from this trial, the range is 59 to 80 
percent.) In contrast, dual nucleo(t)side treatment consistently showed a response rate of less 
than 5 percent. Therefore, the treatment effect for EFV is reliably around 60 to 80 percent and 
with the use of fixed-dose combinations has been closer to 80 percent. 
 
Table D: Virologic Response Rates for EFV-Based Regimens 
Drug Label (or  Regimens  Percentage of Patients 
Reference)  With HIV-RNA < 400 (50) 
Trial  Copies/mL* 
(Bartlett et al. 2006)  ABC/3TC/EFV  81% (72%) 
CLASS Trial   ABC/3TC + AMP/ritonavir    75% (59%) 
ABC/3TC + d4T   80% (60%) 
Atazanavir   ZDV/3TC + ATV   70% (32%) 
Study AI 424-034  ZDV/3TC + EFV   64% (37%) 
Efavirenz    ZDV/3TC + EFV   70% (64%) 
Study 006  ZDV/3TC + IDV   48% (43%) 
(Van Leth et al. 2004)  D4T + 3TC + NVP  (70%) 
2NN Trial  d4T + 3TC + NVP  (65%) 
  d4T + 3TC + EFV  (70%) 
d4T + 3TC + EFV + NVP 
Abacavir  ZDV/3TC + EFV   71% (69%) 
CNA 30024     ABC/3TC + EFV   74% (70%) 
(Saag et al. 2004)  FTC +ddI + EFV  81% (78%) 
Study 301A  D4T + ddI + EFV  68% (59%) 
Tenofovir  TDF + 3TC + EFV  80% (76%) 
Study 903  D4T + 3TC + EFV  84% (80%) 
continued 
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Table D, continued 
Drug Label (or  Regimens  Percentage of Patients 
Reference)  With HIV-RNA < 400 (50) 
Trial  Copies/mL* 
Tenofovir  TDF + FTC + EFV  81% (77%) 
Study 934  ZDV + 3TC + EFV  70% (68%) 
Lamivudine  ZDV+ 3TC (bid) + EFV   65% (63%) 
EPV20001  ZDV + 3TC (qd) + EFV  67% (61%) 
Abacavir  ABC (bid)+ 3TC + EFV  (68%) 
CNA 30021 Study   ABC (qd) + 3TC + EFV  (66%) 
* Response rate estimates include analyses based on missing-equals-failure analyses and time to loss of virologic 
response analyses.  However, because analysis types rarely vary by more than a few percentage points, analysis type 
was not specified for the purpose of this summary. 
 
One should note that by 48 weeks the proportion below 50 copies/mL and proportion below 400 
copies/mL are fairly similar for most EFV regimens, within 10 percent and usually within 
5 percent, except for one outlier mentioned above. 
 
In the trials above, the dual nucleo(t)sides ABC+3TC, d4T+3TC, TDF+3TC (or FTC), and 
ZDV+3TC with added EFV, performed similarly.  TDF+FTC has on occasion performed slightly 
better, but in some cases treatment effect may be driven by better tolerability rather than  
virologic response. 
 
1.2 EFV has been shown to be superior to two older PIs that are well known to be active controls 
responsible for the sharp decline in AIDS mortality in the last decades  
 
In previous studies two nucleosides plus indinavir (IDV) has been shown to be superior to two 
nucleosides alone at approximately 48 weeks (proportion below 400 copies/mL).  In ACTG 320, 
ZDV+3TC+IDV was superior to ZDV+3TC by approximately 40 percent.  In the Merck Trial
035, ZDV+3TC+IDV was superior to ZDV+3TC by 80 percent (+/- 18 percent);27 therefore, the 
lower confidence bound is 62 percent. In Study 006, EFV was superior to the known active 
control IDV by 21 percent (+/- 11.5 percent) for proportion of patients achieving below 50 
copies/mL.  In this trial the 95 percent lower confidence bound for EFV compared to a highly 
active control was 9.5 percent. Therefore, the contribution of EFV is probably at least 10 percent 
more than the treatment effect of IDV. 
 
We are recommending a noninferiority margin (M ) of 10 to 12 percent, which is much less than 
2
the lower bound of the treatment effect of either EFV or IDV based on historical studies.  An M  
2 
of 10 to 12 percent is clinically reasonable because it preserves a large portion of the treatment 
effect. In addition, in the setting of ongoing monitoring of viral load, failing therapy may be 
detected sufficiently early to allow individuals to change their regimen and avoid clinical 
consequences of disease progression. 
 
                                                 
27 1.96 times the standard error of the risk difference  
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Other support for EFV comes from studies in which EFV was superior to nelfinavir (NFV) in 
both a treatment-naive (ACTG 384) and treatment-experienced study.  NFV is known to be 
superior to ZDV+3TC by a margin of 55 percent (+/- 2 percent); lower bound 53 percent. 
 
2.0 	 Justification for a Noninferiority Margin Using an NRTI as a Control Arm in 
Group 1 Treatment-Naive Studies 
 
As stated in section III.B.3., Choice of Controls, investigational NRTIs should be compared only 
to control NRTIs in the context of an NNRTI or INSTI-based regimen.  Because PIs/MIs have a 
high genetic barrier to resistance and a substantial proportion of patients may achieve 
undetectable HIV-RNA levels with a PI/MI alone, the quantitative contribution of an NRTI to a 
PI/MI-based regimen is unknown.  First generation NNRTIs, however, are known to have a low 
genetic barrier to resistance and when used as monotherapy, nearly 100 percent of individuals 
will develop resistance in a matter of days to weeks.  This has been documented for nevirapine, 
and based on a similar resistance profile is believed to be the same for EFV.  First generation 
INSTIs also have a low barrier to genetic resistance.  Therefore, because of synergy, nearly all of 
the response rate in an NNRTI-based regimen also can be attributed to the two nucleo(t)side 
components of the regimen.   
 
Based on early studies with NNRTIs such as nevirapine and delavirdine, one NRTI in 
combination with an NNRTI was not sufficient to achieve and maintain undetectable HIV-RNA 
levels. Conservatively one could attribute half of the treatment effect to each NRTI.  In two 
recent trials in treatment-naive patients, the lower bound for the treatment effect for an 
EFV/tenofovir/emtricitabine regimen was 77 percent (pooled data from two trials).  Therefore, 
half of the treatment effect (38 percent) could be attributed to each NRTI.  If one wanted to 
preserve an additional 50 percent of the effect, the margin is 19 percent.  However, clinically we 
do not want to lose more than 10 to 12 percent of the treatment effect (M  margin).  Similarly, 
2
for the reasons stated, an M  of 10 to 12 percent is an acceptable margin for an endpoint of HIV
2
RNA below 50 copies/mL at 48 weeks. 
 
3.0 	 Justification for Noninferiority Margin in Switch Trials 
 
Based on the noninferiority margin justifications above, we know that the contribution for an 
anchor drug or other drug in a treatment regimen in Group 1-type patients is sufficiently large 
(M ) such that margin choice is driven by the amount of virologic failure that is clinically 
1
tolerable (M ). In previous Switch trials the rate of virologic failure (proportion of patients equal 
2
to or above 50 copies/mL) was typically in the range of 1 to 3 percent.  If one assumes 2 percent 
will have HIV-RNA equal to or above 50 copies/mL at 48 weeks in both treatment arms, then a 
stringent noninferiority margin of 4 percent allows trial sizes that are comparable to those for 
Group 1 trials using 10 to 12 percent as a noninferiority margin using an endpoint of treatment 
success (HIV-RNA below 50 copies/mL).  A margin of 4 percent for virologic failure in Switch 
trials is clinically tolerable; therefore, a margin in this general range is recommended and 
considered feasible from a drug development standpoint. 
 
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4.0  Justification for Noninferiority Margin in Group 2, Treatment-Experienced, Trials 
 
The justification of a valid noninferiority margin in treatment-experienced trials is based on past 
performance of the active control and comparison of prior trial conditions to the current trial.  
The noninferiority margin determination for HIV treatment-experienced trials is complicated by 
variations in response rates across trials, use of different background drugs, and differences in 
baseline patient characteristics.  The noninferiority margin should take these variables into 
account and a new protocol should attempt to replicate the original superiority trial for the 
active-controlled drug with respect to patient characteristics and protocol procedures.  One issue 
encountered in establishing a noninferiority margin includes the change in virologic response 
rates for optimized background regimens over time. As presented in Table E, the proportion of 
patients with HIV-RNA below 50 copies/mL from  the optimized treatment regimen (control) in 
three recent trials to support approval of new drugs increased from 2004 to 2008.  As expected, 
the patient characteristics, namely the phenotypic susceptible score (PSS) at baseline,28  
influenced the response rates. 
 
Table E: Virologic Response (HIV-RNA Below 50 Copies/mL) for OBT (Control) Over 
Trials/Time  
Drug/Trial/Time  PSS=0  PSS=1  PSS=2   PSS > 3  
Maraviroc  3%  5%  7%  42% 
Motivate Trials  
2004-2006 
Raltegravir   2%  29%  39%  61% 
Benchmark 
Trials 
2006-2007 
Etravirine  6%  32%  62%  75% 
DUET Trials 
2005-2008 
 
Sponsors are encouraged to provide detailed supporting documentation for noninferiority 
treatment-experienced trials early in the protocol development stage.  The proposed 
noninferiority margin should be discussed with the FDA at the time of submission of the 
protocol for FDA comments. 
 
                                                 
28 A PSS is the number of drugs to which a patients virus is susceptible according to phenotypic laboratory  
resistance tests.   A score of zero means that the patient  has no remaining drugs to  which his or her virus has full  
susceptibility. 
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