Chronic Hepatitis C Virus 
Infection:  Developing 
Direct-Acting Antiviral 
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 2017 
Clinical/Antimicrobial 
 
   
Chronic Hepatitis C Virus 
Infection:  Developing 
Direct-Acting Antiviral 
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  
Phone: 855-543-3784 or 301-796-3400; Fax: 301-431-6353; Email: druginfo@fda.hhs.gov 
https://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 2017 
Clinical/Antimicrobial 
   
TABLE OF CONTENTS 
 
I.  INTRODUCTION............................................................................................................. 1 
II.  BACKGROUND ............................................................................................................... 2 
III.  DEVELOPMENT PROGRAM ....................................................................................... 3 
A.  General Drug Development Considerations ................................................................................ 3 
1. Nonclinical Virology Development Considerations ........................................................................ 3 
a.  Mechanism of action ................................................................................................................. 3 
b.  Antiviral activity in cell culture ................................................................................................ 3 
c.  Cytotoxicity and mitochondrial toxicity ................................................................................... 4 
d.  Antiviral activity in animal models ........................................................................................... 4 
e.  Combination antiviral activity ................................................................................................... 5 
f.  Resistance and cross-resistance ................................................................................................. 5 
2. General Considerations for Phase 1 and Phase 2 Development ..................................................... 5 
a.  Phase 1a/first-in-human trials.................................................................................................... 7 
b.  Phase 1b (proof-of-concept) trials............................................................................................. 7 
c.  Phase 2 trials with combination DAA regimens ....................................................................... 8 
3. Drug Development Population ........................................................................................................ 9 
4. Efficacy Considerations ................................................................................................................. 10 
5. Safety Considerations .................................................................................................................... 11 
B.  Phase 3 Efficacy Trial Considerations ....................................................................................... 11 
1. Trial Design ................................................................................................................................... 11 
a.  Treatment-naive and non-DAA treatment-experienced populations ...................................... 12 
b.  DAA treatment-experienced population ................................................................................. 12 
2. Trial Population ............................................................................................................................. 13 
3. Entry Criteria ................................................................................................................................. 13 
a.  Assessment of cirrhosis ........................................................................................................... 13 
b.  HCV genotype considerations ................................................................................................ 13 
c.  DAA treatment experience ...................................................................................................... 14 
4. Randomization, Stratification, and Blinding.................................................................................. 14 
5. Specific Populations....................................................................................................................... 14 
a.  HIV-1/HCV coinfected patients .............................................................................................. 14 
b.  Patients with decompensated cirrhosis and pre- or post-transplant ........................................ 15 
c.  Pediatric populations ............................................................................................................... 16 
d.  Patients with advanced chronic kidney disease ...................................................................... 18 
6. Dose Selection ................................................................................................................................ 18 
7. Efficacy Endpoints ......................................................................................................................... 19 
8. Trial Procedures and Timing of Assessments ................................................................................ 20 
9. Statistical Considerations .............................................................................................................. 20 
a.  Analysis populations ............................................................................................................... 21 
b.  Efficacy analyses .................................................................................................................... 21 
c.  Noninferiority comparison ...................................................................................................... 22 
d.  Handling of missing data ........................................................................................................ 22 
10.  Accelerated Approval (Subpart H) Considerations .................................................................. 22 
C.  Other Considerations................................................................................................................... 23 
1. Relevant Nonclinical Safety Considerations .................................................................................. 23 
2. Pharmacokinetic Considerations ................................................................................................... 25 
i 
   
a.  Pharmacokinetic assessments .................................................................................................. 25 
b.  Specific pharmacokinetic evaluation ...................................................................................... 25 
3. Clinical Virology Considerations .................................................................................................. 26 
a.  HCV RNA assessments and data reporting ............................................................................. 26 
b.  HCV genotype or subtype determination ................................................................................ 26 
c.  Resistance analyses ................................................................................................................. 27 
4. Expanded Access Considerations .................................................................................................. 28 
GLOSSARY OF ACRONYMS ................................................................................................. 30 
REFERENCES ............................................................................................................................ 31 
APPENDIX:  STUDY POPULATION TERMS AND TREATMENT RESPONSE 
DEFINITIONS ............................................................................................................................ 35 
ii 
  Contains Nonbinding Recommendations 
Chronic Hepatitis C Virus Infection:   
Developing Direct-Acting Antiviral Drugs for Treatment 
Guidance for Industry1 
 
 
 
 
This guidance represents the current thinking of the Food and Drug Administration (FDA or Agency) on 
this topic.  It does not establish 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 office responsible for this guidance as listed on the 
title page.   
 
 
 
 
I.  INTRODUCTION  
 
The purpose of this guidance is to assist sponsors in the clinical development of direct-acting 
antiviral (DAA) drugs for the treatment of chronic hepatitis C (CHC) from the pre-
investigational new drug application (pre-IND) stage through the new drug application (NDA) 
and postmarketing stages.2  For the purposes of this guidance, the Food and Drug Administration 
(FDA) defines direct-acting hepatitis C virus (HCV) antivirals as drugs that interfere with 
specific steps in the HCV replication cycle through direct interaction with the HCV genome, 
polyprotein, or polyprotein cleavage products.  Specifically, this guidance addresses the FDAs 
current thinking regarding the overall development program and clinical trial designs to support 
DAA drugs.  The organization of this guidance parallels the drug development plan. 
 
This guidance does not address the development of drugs that target host functions necessary for 
viral replication or of immune-based drugs for the treatment of HCV infection such as new 
interferon (IFN) drugs.  This guidance also does not address treatment of acute hepatitis C or the 
use of therapeutics without antiviral mechanisms intended to mitigate or reverse clinical or 
pathophysiological outcomes of CHC, such as prevention of hepatocellular carcinoma (HCC) or 
reversal of fibrosis.  The main focus of this guidance is on development of DAAs as part of IFN-
free regimens.  Because safe and highly effective FDA-approved IFN-free treatment options are 
available, the Division of Antiviral Products (DAVP) recommends against studying an IFN-
containing regimen in a DAA treatment-naive population. 
 
                                                 
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 regulated in CDER unless otherwise specified. 
1  Contains Nonbinding Recommendations 
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 safety 
and toxicology studies unless specific to HCV drug development.  Such studies for direct-acting 
HCV antivirals generally should be conducted in standard animal models as described in the 
guidance for industry Nonclinical Safety Evaluation of Drug or Biologic Combinations.  
 
We encourage sponsors considering development of antiviral drugs for the treatment of CHC to 
communicate with the FDA through the pre-IND consultation program.4  Pre-IND consultation 
with the FDA is optional although it may be particularly helpful for sponsors with limited 
experience in the IND process or with unusual drugs or treatment approaches.    
 
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 
 
HCV is a small positive-strand ribonucleic acid (RNA) virus in the Flaviviridae family.  There 
are at least seven HCV genotypes, numbered 1 to 7; most genotypes have been divided into 
multiple subtypes (e.g., genotype 1 subtypes 1a and 1b) (Smith, Bukh, et al. 2014).  Because 
reported HCV genotype 7 is extremely rare, this guidance will only focus on HCV genotypes 1-
6.  In the United States, genotype 1 is the most common (70 to 80 percent of HCV infections), 
followed by genotypes 2 and 3.  The remaining genotypes occur less commonly in the United 
States but may predominate in other parts of the world (Gower, Estes, et al. 2014). 
 
In the United States, about 3 million people have CHC (Armstrong, Wasley, et al. 2006; 
Klevens, Dale, et al. 2012).  CHC causes cirrhosis and HCC and is the most common reason for 
liver transplantation in the United States.  By 2007, there were more annual deaths in the United 
States related to HCV than human immunodeficiency virus (HIV) (Ly, Xing, et al. 2012).  
 
The ultimate goal of CHC treatment is to reduce the occurrence of end-stage liver disease and its 
complications including decompensated cirrhosis, liver transplantation, and HCC.  Clinicians use 
sustained virologic response (SVR)  defined as no detectable HCV RNA  in blood several 
months after completing a course of treatment  to determine if treatment is a success and is 
                                                 
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 
https://www.fda.gov/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/default.htm. 
 
4 See the FDA Pre-IND Consultation Program web page at 
https://www.fda.gov/Drugs/DevelopmentApprovalProcess/HowDrugsareDevelopedandApproved/ApprovalApplicat
ions/InvestigationalNewDrugINDApplication/Overview/default.htm.  
2  Contains Nonbinding Recommendations 
considered a virologic cure (Shiratori, Ito, et al. 2005; Singal, Volk, et al. 2010).  Achieving a 
virologic cure is associated with a substantial decrease, but not elimination, in the risk of HCC. 
 
Total duration of treatment and choice of regimen may depend on HCV genotype or subtype and 
disease factors such as the HCV RNA level or the presence or absence of cirrhosis.  The ability 
to achieve SVR rates greater than 90 percent using only DAAs (with and without ribavirin 
(RBV)) in many populations of HCV-infected patients has been well established.  Throughout 
this guidance, antiviral treatment efficacy refers to SVR assessed 12 weeks following cessation 
of treatment (SVR12). 
 
 
III.  DEVELOPMENT PROGRAM 
 
A.  General Drug Development Considerations 
 
In addition to nonclinical development and early phase drug development, an overall drug 
development approach with respect to target population, efficacy, and safety is addressed in the 
following sections.  
 
1.  Nonclinical Virology Development Considerations 
 
Information about pre-investigational new drug testing and appropriate nonclinical assays is 
available on the FDA website.5  Sponsors with virology development for HCV DAAs should 
consider the guidance for industry Antiviral Product Development  Conducting and Submitting 
Virology Studies to the Agency.  Additional recommendations for nonclinical and clinical 
virology specific to the development of HCV DAAs are summarized throughout this guidance.  
 
a.  Mechanism of action 
 
A sponsor should investigate the mechanism by which a DAA exhibits anti-HCV activity 
through evaluations 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-HCV activity, which may include assessments of activity against unintended 
HCV target proteins, related host proteins, or other viruses. 
 
b.  Antiviral activity in cell culture 
 
A sponsor should characterize in cell culture the antiviral activity of an investigational drug to 
demonstrate its activity and identify a preliminary target concentration for evaluation in HCV-
infected patients.  Sponsors should use HCV replicon systems to assess antiviral activity of 
investigational drugs targeting nonstructural components, and 50 and 90 percent effective 
                                                 
5 See the FDA Getting Started With the Division of Antiviral Products Pre-IND Process web page at 
https://www.fda.gov/Drugs/DevelopmentApprovalProcess/HowDrugsareDevelopedandApproved/ApprovalApplicat
ions/InvestigationalNewDrugINDApplication/Overview/ucm077546.htm.  
 
3  Contains Nonbinding Recommendations 
concentrations (EC  and EC ) should be determined.  We recommend evaluating the drugs 
50 90
antiviral activity at different concentrations of human serum and extrapolating a 100 percent 
human serum-adjusted EC  value.  Sponsors can evaluate the antiviral activity of drugs that 
50
target HCV entry functions using HCV pseudoparticle systems.  For any anti-HCV drug, we 
recommend assessments of antiviral activity against HCV grown in cell culture, when 
appropriate.   
 
Cell culture studies should include assessments of antiviral activity against those HCV genotypes 
and subtypes most common in the United States and those types for which an indication will be 
sought.  We also recommend assessments of antiviral activity against replication models using 
HCV components derived from multiple clinical isolates because antiviral activity can vary for 
strains within each subtype.  If sponsors observe differences in susceptibility for different clinical 
isolates within the same viral genotype or subtype, sponsors should conduct additional genotypic 
and phenotypic characterizations to identify genetic polymorphisms that may affect HCV 
susceptibility to the drug. 
 
c.  Cytotoxicity and mitochondrial toxicity 
 
Sponsors should quantify directly the cytotoxic effects of the drug in the cells used for assessing 
anti-HCV activity and should calculate a 50 percent cytotoxic concentration (CC ) and 
50
therapeutic index (CC /EC ).  Sponsors should assess cytotoxicity using various cell lines and 
50 50
primary cells cultured under proliferating and nonproliferating conditions.  Sponsors should also 
assess, with appropriate controls, nucleos(t)ide analog polymerase inhibitors for bone marrow 
precursor cell toxicity.   
 
Sponsors should assess mitochondrial toxicity for all investigational nucleos(t)ide analogs and 
other drug classes as appropriate based on mechanism of action or any signals of mitochondrial 
toxicity in nonclinical studies or clinical trials.  Mitochondrial toxicity assessments should 
include evaluation of cytotoxicity in glucose- versus galactose-containing medium (Crabtree 
effect) (Marroquin, Hynes, et al. 2007).  Sponsors should also evaluate the inhibition of 
mitochondrial RNA polymerase for nucleos(t)ide analogs (Arnold, Sharma, et al. 2012).  Positive 
controls for mitochondrial toxicity studies should be included in the nonclinical studies and 
should be relevant to the class of the investigational drug, whenever possible. 
 
d.  Antiviral activity in animal models 
 
In general, studies of anti-HCV activity in an animal model are not needed.  However, if 
sponsors conduct such studies to support an anti-HCV therapy program, the sponsors should 
provide a detailed description of the animal model.  Reported data from animal model studies 
should include the HCV genotype or subtype used, time course plots of viral load data for each 
animal, and an assessment of resistance development that includes monitoring the persistence of 
resistant virus in the absence of anti-HCV treatment.   
 
4  Contains Nonbinding Recommendations 
e.  Combination antiviral activity 
 
Most, if not all, HCV DAAs will be used to treat CHC in combination with other anti-HCV 
drugs.  Early in development, sponsors should characterize cell culture combination antiviral 
activity relationships of the investigational drug and other drugs anticipated to be used in 
combination to determine whether the combination antiviral activity is antagonistic.  For all 
combination antiviral activity assessments, sponsors should provide combination index values 
when the two drugs are combined at or near their individual EC  values, and studies should 
50
include controls for cytotoxicity and antagonism (Coelmont, Paeshuyse, et al. 2006).  
Combination antiviral activity relationships for HIV and HCV drugs with similar mechanisms of 
action (e.g., HIV nucleos(t)ide analogue reverse-transcriptase inhibitors, HCV nucleos(t)ide 
analogue NS5B polymerase inhibitors) should be assessed before testing combinations of the 
drugs in HIV-1/HCV co-infected patients.  
 
f.  Resistance and cross-resistance 
 
Sponsors should examine in cell culture models the ability of HCV to develop resistance to a 
DAA when the virus is subjected to drug selection.  Sponsors should determine the amino acid or 
nucleotide substitutions associated with the development of resistance to the investigational drug 
and validate the substitutions by introducing the changes into the HCV genome and determining 
the conferred fold shift in susceptibility (based on EC  and EC  values) using cell culture or 
50 90
biochemical assays.  Sponsors should use the results from these studies to:  (1) characterize the 
genetic barrier for resistance; (2) predict whether a clinically achievable concentration of the 
investigational drug can reduce the enrichment of drug-resistant viral populations; (3) identify 
potential resistance pathways; and (4) support the drugs hypothesized mechanism of action.  
The resistance barrier for an HCV DAA refers to the capacity of the drug to retain its antiviral 
activity when the virus acquires genetic changes in the drug target (Kwong, Najera, et al. 2011).6    
 
Resistance studies should include evaluation of the potential for cross-resistance with approved 
drugs, particularly focusing on those in the same drug class and other classes with the same viral 
target.  If a sponsor intends to develop a drug to be used in patients previously treated with drugs 
in the same class, the sponsor should evaluate the activity of the investigational drug against 
HCV variants that emerge in patients treated with other drugs in the class.  In addition, sponsors 
should evaluate the activity of other representative approved drugs in the class against HCV 
variants associated with resistance to the investigational drug.   
 
2.  General Considerations for Phase 1 and Phase 2 Development 
 
In addition to assessing safety and pharmacokinetics, phase 1 trials should provide an initial 
assessment of antiviral activity of the DAA.  Phase 2 trials should characterize the effects of dose 
and treatment duration of the DAA or DAAs as part of combination regimens with regard to both 
antiviral activity and safety. 
                                                 
6 For the purposes of this guidance, a drug is generally defined as having a low resistance barrier when one or two 
specific nucleotide changes from the wild-type virus consensus sequence are adequate to confer HCV resistance to a 
clinically relevant concentration of the drug. 
5  Contains Nonbinding Recommendations 
 
Based on HCV replication dynamics in infected patients (Rong, Dahari, et al. 2010), the error-
prone nature of HCV genome replication, and the fact that the activity of a DAA is often reduced 
by a single amino acid substitution in the drug target, multiple anti-HCV drugs with 
nonoverlapping resistance pathways generally are needed to suppress preexisting and emerging 
drug-resistant variants for most patients to achieve SVR.  Sponsors can develop a DAA for 
dosing in combination with other DAAs and/or in regimens that include RBV.  The overall 
design of a phase 2 clinical development program should attempt to demonstrate the contribution 
of individual drugs in the regimen (as described in section III.A.4., Efficacy Considerations). 
 
We recommend that sponsors have the following information before conducting phase 2 trials of 
combinations of DAAs: 
 
  Mechanism of action for each drug in the combination 
 
  Resistance and cross-resistance patterns for each drug in the combination 
 
  Combination antiviral activity data from cell culture studies  
 
  Anti-HCV activity data from clinical trials (e.g., short-term monotherapy trials, dose-
finding trials in combination with other antiviral drugs)  
 
  Phase 1 human safety data on each drug  
 
  Dose selection rationale that considers potential for overlapping toxicities with the 
individual components 
 
  Drug-drug interaction data if the metabolism profiles suggest an interaction potential 
between drugs in the investigational combination regimen and comedications potentially 
administered by HCV-infected patients enrolled in the trial or trials 
 
A primary objective of a phase 2 program should be demonstration of proof of concept of 
efficacy (i.e., SVR) with appropriate safety and tolerability for DAA-containing regimens that 
are planned for study in phase 3.  Early on-treatment virologic responses and end-of-treatment 
responses often are not predictive of SVR12 for DAA-containing regimens.  Therefore, post-
treatment response data, such as SVR4 and SVR12, should be available before progression to 
phase 3.  Specifically, for an end-of-phase 2 meeting, SVR4 data from all enrolled patients in 
key supporting phase 2 trials and all available SVR12 (or longer) data from phase 2 trials should 
be submitted to support progression to phase 3.  All available SVR data from all regimens under 
study in the drug development program should be used to select appropriate drug regimens and 
patient populations for study in phase 3. 
 
Phase 2 trials should include a representative population of patients with chronic HCV infection.  
These populations can include, but are not limited to, relevant racial and ethnic subgroups (e.g., 
blacks/African Americans, Hispanics/Latinos), patients with prior pegylated- (peg-) IFN/RBV 
treatment failures, patients with prior DAA treatment failures, and patients with compensated 
6  Contains Nonbinding Recommendations 
cirrhosis.  Inclusion of these groups in phase 2 will assist in sample size calculations and 
estimations of expected SVR rates in phase 3. 
 
We have provided the following recommendations and examples for potential phase 1 and phase 
2 trial designs for HCV DAAs based on the current state of the field.  
 
a.  Phase 1a/first-in-human trials 
 
In general, we recommend single- and/or multiple-ascending-dose trials in healthy adult subjects 
to assess safety and pharmacokinetics for the first-in-human trials.  Sponsors also can conduct 
single-dose and short-duration multiple-dose pharmacokinetic (PK) trials in HCV-infected 
patients. 
 
b.  Phase 1b (proof-of-concept) trials 
 
The first proof-of-concept antiviral activity trial in HCV-infected patients should be a repeat-
dose, randomized, dose-ranging, monotherapy trial with collection of intensive PK, safety, and 
HCV RNA data.  Doses selected for phase 1b should be predicted to provide plasma and/or liver 
tissue drug exposures that exceed by severalfold the protein binding-adjusted, cell culture EC  
50
value of the drug for the relevant HCV genotype or subtype.  The doses evaluated also should 
take into account any safety margins previously identified in animal toxicology studies and in 
any trials conducted in healthy subjects.  We generally recommend that sponsors conduct initial 
antiviral activity phase 1b trials in patients with CHC who are naive to previous anti-CHC 
therapy (including the investigational drug) and who have minimal fibrosis and no significant 
comorbidities.  Following demonstration of safety and antiviral activity in treatment-naive 
patients, sponsors can plan additional trials in treatment-experienced patients, as appropriate. 
 
The maximum recommended duration of DAA monotherapy for an initial phase 1b trial depends 
on several factors, such as the drugs mechanism of action, pharmacokinetics, expected 
resistance barrier, trial population, and availability of other drugs within and outside of the drug 
class.  For example, for an NS3/4A protease inhibitor or NS5A inhibitor with a low resistance 
barrier and overlapping resistance pathways with other drugs in the class, the recommended 
maximum duration of monotherapy is about 3 days.  In this example, we do not recommend that 
monotherapy exceeds 3 days because 3 days is usually sufficient to demonstrate proof-of-
concept antiviral activity and to identify drug doses for evaluation in phase 2 trials, and previous 
data with these DAA classes indicate resistant virus is rapidly selected during monotherapy.  
Prolonged selection of resistance may reduce the efficacy of other treatments and limit future 
treatment options for trial patients.   
 
On the other hand, a dosing duration of 3 to 7 days may be justified for a DAA that represents a 
novel DAA class, has a relatively higher predicted resistance barrier, or requires several days of 
dosing before achieving steady state plasma concentrations.  Additionally, multiple weeks of 
monotherapy could be appropriate for a drug that does not specifically target intracellular HCV 
replication, for which demonstration of an HCV RNA decline would require clearance of 
infected cells.  All DAA monotherapy trial protocols should include justification for the 
7  Contains Nonbinding Recommendations 
proposed duration of treatment.  Additionally, monotherapy trials of a drug with an unusually 
long half-life that could lead to resistance should include plans to minimize risk to patients. 
 
c.  Phase 2 trials with combination DAA regimens 
 
Specific phase 2 trial designs for all oral, combination DAA regimens can vary greatly 
depending on the drug class or classes, intended patient population, HCV genotype, available 
treatment options, and emerging data from other HCV DAA development programs.  In general, 
phase 2 trial designs should be randomized comparisons of several different DAA combinations 
(all investigational drugs or approved drugs plus investigational drugs) at various doses and 
treatment durations.  The number of DAAs in a regimen depends on individual drug potency and 
estimated resistance barriers as determined in earlier stages of drug development.  RBV can be 
included in some or all of the treatment arms depending on the DAAs, the HCV genotype or 
subtype, and the patient population being evaluated.  We recommend SVR12 as the primary 
endpoint.  Patients should be followed through week 24 following treatment cessation to further 
confirm the reliability of SVR12 as a marker of virologic success.  Sponsors should stratify trial 
randomization according to genotype or subtype or other key baseline characteristics predicted to 
have a significant effect on treatment outcome.  
 
Initial trials should include frequent HCV RNA monitoring and both patient- and treatment arm-
specific stopping rules for poor virologic outcomes (e.g., virologic breakthrough or relapse).  
When feasible, protocols should include opportunities for patients with virologic failure to 
receive appropriate alternative therapeutic regimens that could consist of investigational and/or 
approved drugs.  Final SVR12 and SVR24 efficacy outcome data from patients who received 
protocol-specified retreatment (approved and/or investigational) should be collected and 
included in final reports or other relevant regulatory submissions because these data could be 
informative for future clinical trial design and for clinical practice. 
 
We anticipate that the number of single- and multiple-class DAA treatment-experienced patients 
will increase as more HCV DAAs are used in practice.  We encourage sponsors to develop and 
evaluate new treatment regimens to address the treatment challenges for this population.  Patients 
who did not achieve SVR with a full therapeutic duration of a DAA combination regimen may 
be particularly difficult to treat.  Many of the host and viral factors that contributed to treatment 
failure with the prior DAA combination regimen or regimens will remain, such as cirrhosis, 
advanced liver disease, poor immune clearance of HCV replication complexes and infected cells, 
high baseline HCV RNA levels, suboptimal exposures, poor adherence, poor tolerability, or drug 
resistance (i.e., enrichment of HCV viral populations with reduced susceptibility to one or 
multiple HCV DAA classes).   
 
Multiple rounds of DAA treatment failure may severely limit treatment options for patients; 
therefore, initial trials in DAA-experienced patients should include regimens and treatment 
durations that are predicted to provide patients with the best chance of achieving SVR.  For 
example, exploration of relatively short treatment durations should be considered only after 
preliminary evidence of SVR has been demonstrated for longer treatment durations.  Also, 
because of the number of promising DAA classes approved or in development that would be 
8  Contains Nonbinding Recommendations 
appropriate to test in DAA-experienced populations, we strongly encourage cross-company 
collaboration when needed to construct a scientifically justified regimen.    
 
Because retreatment regimens may need to be individualized based on many factors such as prior 
DAA treatment history and drug resistance characteristics, we are not able to provide detailed 
guidance on appropriate trial designs for all possible circumstances.  The need for drug 
resistance screening depends on the specific drug classes in the regimen, emerging data from 
other trials in DAA-experienced populations, and the characteristics of the patient population. 
 
Patients who were exposed to short, nontherapeutic treatment durations of one or more DAAs, 
such as in short-course monotherapy trials, but otherwise never failed treatment with a regimen 
intended to result in SVR or patients who were responding virologically but discontinued prior 
treatment early for reasons unrelated to efficacy, may be eligible for later phase 2 trials (or phase 
3 trials) of regimens that have demonstrated preliminary evidence of SVR in DAA-naive 
patients.  
 
3.  Drug Development Population 
 
Drug development programs should include as broad a population as appropriate for the 
characteristics of the antiviral drug.  However, a DAA may have differential activity against 
different HCV genotypes or subtypes; therefore, sponsors can target drug development to a 
specific genotype) or to regimens that are optimized for specific subtypes.  We recommend 
including patients diagnosed with compensated cirrhosis in phase 2 and phase 3 trials.  Also, we 
encourage phase 3 studies of combinations of HCV DAA antivirals in patients with the greatest 
need for new drugs, such as patients with bleeding disorders, transplant patients, patients with 
advanced chronic kidney disease (CKD), patients with decompensated cirrhosis, and patients 
who previously failed DAA-based treatment.   
 
Similarly, patients on opioid maintenance therapy should be studied after the potential for drug-
drug interactions between the investigational drug and medications used for opioid maintenance 
therapy is understood.  To choose an appropriate dose and rule out or manage important drug-
drug interactions, sponsors can study DAAs in combination with other DAAs, with or without 
RBV in HIV-1/HCV coinfected patients, as soon as appropriate, based on the availability of data 
(see section III.B.5.a., HIV-1/HCV coinfected patients).  Supportive data such as hepatic and 
renal impairment trials and drug-drug interaction trials (e.g., antiretrovirals for HIV, 
immunosuppressants for transplant) may be needed before sponsors can conduct trials in the 
above-mentioned subgroups.  
 
CHC is a global disease and clinical trials are typically conducted internationally.  However, we 
recommend that trials include adequate U.S. patient representation to ensure applicability of trial 
results to the U.S. population.  An adequate representation of sexes, races, ages, and weights is 
recommended during drug development, especially in phase 3 trials.  Because race (e.g., black, 
Asian) and ethnicity (e.g., Latino) may affect response rates to anti-HCV treatment, including 
sufficient representation of such groups in clinical trial demographics is important for conducting 
meaningful analyses (Hepburn, Hepburn, et al. 2004).  In addition, we encourage sponsors to 
include hepatitis B virus (HBV)/HCV coinfected patients and CHC patients with active illicit 
9  Contains Nonbinding Recommendations 
injection drug use so that the clinical trial data can reflect the spectrum of patients who will use 
CHC treatments after approval.  Sponsors should share with the FDA their pretrial initiation 
work to ensure the sites selected have sufficient numbers of patients from these populations (e.g., 
women, blacks/African Americans, Hispanics/Latinos, patients with cirrhosis, patients with 
bleeding disorders, patients with HBV/HCV coinfection, patients using injection drugs) to enroll 
in phase 2 and phase 3 clinical trials. 
 
4.  Efficacy Considerations 
 
Sponsors should perform phase 2 trials to select an optimal dose or doses and treatment duration 
or durations for further evaluation in phase 3 trials.  See section III.B.6., Dose Selection, for 
additional considerations.  For more detailed guidance on phase 3 trial design issues, see section 
III.B.1., Trial Design.  
 
Sponsors should establish efficacy in key subpopulations including patients:  
 
  Who have and do not have cirrhosis 
  Who have HCV genotypes (e.g., 1, 2, 3, 4, 5, or 6, depending on susceptibility) 
  Who are DAA naive and DAA experienced 
 
Sponsors can submit an NDA to gain approval for a drug in a single population.  Such an 
application should include at least two adequate and well-controlled trials conducted in the 
proposed population intended for labeling.  Alternatively, sponsors can choose to pursue an 
indication for different populations.  In this case, the NDA should contain at least one adequate 
and well-controlled phase 3 trial in each patient population, with adequate supporting data from 
well-controlled phase 2 trials (see section III.B., Phase 3 Efficacy Trial Considerations). 
 
Trial designs for combinations of investigational DAAs with or without RBV should include 
provisions for demonstrating that each component of the combination therapy contributes to the 
desired effect.  It is generally recognized that monotherapy with a DAA does not have sufficient 
antiviral durability to result in a high rate of SVR12.  Therefore, if a novel combination regimen 
consisting of two DAAs with nonoverlapping resistance pathways demonstrates favorable 
efficacy, both drugs likely contribute to treatment efficacy.  Establishing the contribution of each 
additional drug in a combination regimen can be accomplished using modified factorial trial 
designs.   
 
When a factorial design is not used, additional data may be used as supportive evidence of a 
DAAs contribution to efficacy of a multiple DAA combination regimen.  Examples of data 
supporting contribution of efficacy include but are not limited to the following: 
 
  Cell culture data showing that DAA combinations slow or prevent the emergence of 
resistance compared to single drugs 
 
  Early phase 2 clinical trial data showing that the addition of a drug to a DAA 
combination improves SVR or reduces the emergence of viral variants with resistance-
associated substitutions 
10  Contains Nonbinding Recommendations 
 
  Data demonstrating strong evidence of efficacy of a combination regimen relative to 
historical results with one or more components of the combination regimen    
 
Sponsors should consult 21 CFR 300.50 regarding combining drug products in a single dosage 
form.  Additional recommendations for codevelopment of two investigational drugs can be found 
in the guidance for industry Codevelopment of Two or More New Investigational Drugs for Use 
in Combination. 
 
HCV 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.  HCV 
treatment drugs also may be eligible for fast track, breakthrough,7 and priority review 
designation if the specifics of the relevant criteria are met.8,9 
 
5.  Safety Considerations 
 
In general, we recommend that initial marketing applications for drugs intended to treat CHC in 
patients without decompensated cirrhosis contain a safety database of about 1,000 to 1,500 
patients exposed to the proposed dose and duration of treatment.  However, if significant safety 
signals emerge during drug development, the sponsor may need to increase the safety database or 
conduct specific safety studies.   
 
We recommend using data from randomized, controlled trials with an active comparator or a 
comparison of immediate versus delayed treatment to obtain comparative safety data (see section 
III.B., Phase 3 Efficacy Trial Considerations).  
 
B.  Phase 3 Efficacy Trial Considerations 
 
1.  Trial Design 
 
The benefit-risk profile of the investigational drug and the available approved treatment options 
for the indicated population are important factors for determining an appropriate trial design.  
We recommend that at least one of the pivotal efficacy trials be designed as a randomized trial 
with an active-control arm.  The active comparator in a phase 3, controlled trial should be an 
antiviral drug that is approved and recommended for treatment of chronic HCV infection by 
                                                 
7 See the FDA fact sheet for breakthrough therapies at 
https://www.fda.gov/regulatoryinformation/lawsenforcedbyfda/significantamendmentstothefdcact/fdasia/ucm32949
1.htm.  
 
8 See the guidance for industry Expedited Programs for Serious Conditions  Drugs and Biologics for information 
regarding fast track, breakthrough, and priority review designation. 
 
9 Accelerated approval, which can rely on a surrogate endpoint or an intermediate clinical endpoint that is 
reasonably likely to predict clinical benefit, does not apply to drug development for hepatitis C because the FDA 
considers the endpoint used in clinical trials for full approval to be a validated surrogate endpoint (SVR12) that is 
known to predict clinical benefit. 
11  Contains Nonbinding Recommendations 
authoritative scientific bodies based on clinical evidence that also reflects current practice at the 
time of trial initiation. 10  A randomized, active-controlled design allows for a direct comparison 
of the safety and efficacy of the study regimen to an FDA-approved, recommended treatment 
option.  We recommend sponsors discuss with the FDA their choice of an active control and 
choice of study population before trial initiation.  Although randomized, controlled, comparative 
trials are preferable, in some situations single-arm trials using a historical control may be 
acceptable.  However, historical controls have limitations including the difficulty to establish 
patient comparability at baseline for many potential prognostic factors.  We discuss trial design 
considerations by type of regimen and intended population in more detail below. 
 
a.  Treatment-naive and non-DAA treatment-experienced populations 
 
We prefer a randomized, active-controlled noninferiority (NI) or superiority trial design over a 
single-arm design, and at least one of the pivotal trials should be designed as such.  Sponsors 
considering an NI trial design should discuss in advance their justification for the proposed NI 
margin based on historical control effect, trial designs, and the data analysis plans.  
 
In addition to a randomized, active-controlled trial or in situations where a randomized, active-
controlled trial is not feasible, and a single-arm trial is under consideration, we recommend an 
immediate versus deferred design in patients who are not considered to need immediate 
treatment.  In this design, patients should be randomized to the DAA-based regimen or placebo 
for the intended treatment duration.  At the end of treatment, patients randomized to the placebo 
arm can receive the DAA-based regimen.  The purpose of the deferred treatment design is to 
collect comparative safety data.  The primary efficacy comparison (either superiority or 
noninferiority depending on regimen studied) should be to a historical reference of a 
recommended HCV treatment regimen rather than a comparison to those receiving placebo (in 
the deferred treatment arm) because it is expected that no patient will respond virologically while 
receiving placebo.  Sponsors should include sufficient information in the protocol to support the 
historical control used.  Sponsors should also make adequate provisions in the trial to maintain 
the trial blind and should minimize the potential for patients in the placebo arm to drop out.  
 
As an alternative to an immediate versus deferred treatment design, a dose or treatment duration 
comparison trial could also be used.  Consistent with the immediate versus delayed treatment 
design, the primary efficacy comparison should be between each of the trial arms and a historical 
reference of a recommended HCV treatment regimen at the time of trial initiation.  
 
b.  DAA treatment-experienced population 
 
Patients failing DAA-containing regimens constitute an emerging population in need of effective 
HCV therapies.  Trial designs and the number of patients needed to support an indication in 
patients who have failed treatment with DAA-containing regimens depend on the specific 
characteristics of the patient population and the availability of other treatment regimens.  
                                                 
10 See the HCV treatment guidelines provided by the AASLD for the current HCV treatment recommendations 
available at https://www.hcvguidelines.org.   
12  Contains Nonbinding Recommendations 
Sponsors should engage in early discussions with the DAVP regarding development plans in 
DAA treatment-experienced patients. 
 
2.  Trial Population 
 
Sponsors should ensure that patients enrolled in a trial have CHC as confirmed by at least one of 
the following: 
 
  They are positive for anti-HCV antibody, HCV RNA, or an HCV genotype at least 6 
months before screening and positive for anti-HCV antibody and HCV RNA at the time 
of screening  
 
  They are positive for anti-HCV antibody and HCV RNA at the time of screening with 
clinical or laboratory evidence of CHC disease, such as the presence of fibrosis by biopsy 
or noninvasive tests 
 
3.  Entry Criteria  
 
a.  Assessment of cirrhosis 
 
Even in the era of highly effective DAA combination therapy, cirrhosis has been demonstrated to 
be a significant factor affecting treatment outcomes (Afdhal, Reddy, et al. 2014).  Determining 
trial patients baseline cirrhosis statuses remains critical for making correlations between the 
presence of cirrhosis and efficacy, safety, and pharmacokinetics.  Sponsors should evaluate a 
sufficient number of trial patients with documented cirrhosis throughout the course of drug 
development to explore safety and efficacy correlations between cirrhosis and outcomes.   
 
To define presence or absence of cirrhosis, the use of a noninvasive modality in a protocol 
should be supported by references that summarize performance characteristics and sensitivity 
and specificity of the modality for identifying patients with cirrhosis.  
  
b.  HCV genotype considerations 
 
Certain DAAs demonstrate antiviral activity against multiple HCV genotypes, and sponsors may 
want to seek an indication for HCV treatment in several genotypes.  Sponsors should establish 
efficacy for each HCV genotype independently, and as seen with HCV genotype 1, some DAA 
regimens may provide different efficacy for different subtypes.  Enrollment of enough patients 
with genotypes 4, 5, or 6 into trials to fully characterize efficacy may not be feasible for trials 
conducted only in the United States because of the low prevalence of these genotypes in the 
United States.  Clinical trial data should be sufficient to inform differences in response between 
each of the most common subtypes and identify whether any subtypes have decreased efficacy to 
the proposed regimens.  The total population size for each genotype or subtype should be 
discussed with the DAVP before phase 3 trial initiation.  The nonclinical virology data should 
characterize the anti-HCV activity and resistance barrier of the individual DAA or DAAs for 
HCV replicons (or other appropriate cell culture system) derived from patient isolates from the 
major subtypes represented in the United States.  See also section III.C.3., Clinical Virology 
13  Contains Nonbinding Recommendations 
Considerations, for recommendations regarding HCV genotype or subtype determination in 
clinical trials.   
 
c.  DAA treatment experience 
 
All clinical trial protocols should describe entry criteria related to prior DAA treatment 
experience.  If DAA treatment-experienced patients are eligible, the protocol should indicate the 
specific DAA drug or class experience that is eligible or exclusionary.  To support a broad 
indication for DAA treatment-experienced patients, efficacy should be demonstrated in study 
populations previously exposed to a variety of DAA classes, including those that are shared with 
the investigational DAA or DAAs.  In such cases, efficacy should be specifically demonstrated 
in patients with drug resistance-associated substitutions that emerged from prior therapy with the 
same DAA class or classes as the investigational DAA or DAAs; sponsors should consider 
conducting resistance analyses at screening to enrich for these patients.   
 
4.  Randomization, Stratification, and Blinding 
 
We encourage sponsors to conduct double-blinded trials whenever feasible to minimize any 
potential biases.  The primary endpoint (SVR12) is an objective endpoint; however, other aspects 
of the trial can be influenced by knowledge of treatment assignment.  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, or investigators could provide patients different levels of encouragement to continue 
in the trial.  
 
Sponsors can consider stratification of patients by important baseline factors that are predictive 
of SVR.  Stratification factors depend on the regimen and population studied but could include 
one or more of the following:  HCV genotype or subtype, key baseline viral polymorphisms or 
resistance-associated substitutions, prior treatment history, baseline HCV RNA, or presence or 
absence of cirrhosis.  In international trials, patients should be stratified by geographic area 
(inside versus outside the United States).  
 
5.  Specific Populations 
 
Patients with hepatic impairment, pre- or post-transplant patients, patients with advanced CKD, 
and patients with decompensated cirrhosis are populations with unmet medical needs.  Early in 
drug development, we strongly encourage sponsors to discuss the process to determine 
appropriate timing for initiating trials in these populations.  This section also includes 
information on HIV-1/HCV coinfected patients although we no longer consider this population 
as having an unmet medical need.  
 
a.  HIV-1/HCV coinfected patients  
 
About 30 percent of patients infected with HIV-1 are coinfected with HCV (Sulkowski 2008).  
Patients with HIV-1/HCV coinfection are at higher risk of more rapid progression of liver 
disease and higher rates of liver-related morbidity and mortality compared to HCV mono-
infected patients.  The SVR rates in HIV-1/HCV coinfected patients receiving all oral antiviral 
14  Contains Nonbinding Recommendations 
drugs are similar to HCV mono-infected patients; therefore, both HIV-1/HCV coinfected patients 
and HCV mono-infected patients can enroll into the same clinical trial.  Sponsors can also study 
HIV-1/HCV coinfected patients in a separate trial to obtain efficacy and safety data at the 
proposed dose or doses and treatment duration.  The number of patients needed may depend on 
the effect of drug interactions on exposures of the DAA.  More patients may be needed if an 
increase or decrease in DAA is expected because of drug interactions.  We strongly encourage 
sponsors to have data on HIV-1/HCV coinfected patients at the time of submission of an original 
NDA.  See section III.B., Phase 3 Efficacy Trial Considerations. 
 
The NDA should also include the following data: 
 
  As needed, based on the investigational drugs potential for drug interactions, drug 
interaction data with the most commonly used HIV drugs.  The drug interaction data 
should be available before trial initiation in HIV-1/HCV coinfected patients taking 
antiretrovirals that are expected to have interactions with an investigational DAA or 
DAAs.  
 
  Safety data including HIV RNA data to assess loss of HIV efficacy (rebound in HIV 
RNA viral load) and changes in CD4 cell counts. 
 
b.  Patients with decompensated cirrhosis and pre- or post-transplant 
 
As compared to compensated disease, decompensated disease may require treatment with more 
drugs and/or longer durations to achieve viral suppression.    
 
We encourage active-controlled trials when possible; however, safety and efficacy data can be 
derived from dose or treatment duration comparisons or single-arm trials with a historical 
reference.  Sponsors should discuss in advance with the DAVP the number of decompensated 
patients needed to support labeling claims.  The demonstrated safety profile of the regimen in 
phase 2 and phase 3 clinical trials in patients with compensated liver disease would determine 
the minimum acceptable safety database for the decompensated patient population.   
 
As needed, and based on a particular investigational drugs metabolic profile, sponsors should 
conduct drug interaction trials with the most commonly used immunosuppressive drugs to 
support concomitant dosing of a DAA regimen and immunosuprressive drugs in post-transplant 
patients..  These data should be available before sponsors begin trials in post-transplant patients.  
 
We strongly recommend that an original NDA submission for the treatment of HCV with a 
combination of DAAs contain some clinical data from patients with decompensated cirrhosis, as 
well as pre- and post-transplant patients.  Such data should include the following:  
 
  As relevant, based on the investigational drugs potential for drug interactions, drug 
interaction data with the most commonly used immunosuppressive drugs 
 
  Safety data from a cohort or cohorts of patients with decompensated cirrhosis and pre- or 
post-transplant patients who received the drug for the recommended treatment duration 
15  Contains Nonbinding Recommendations 
 
The safety evaluation of populations with advanced liver disease may need to incorporate 
additional safety analyses to assess the safety of the investigational drug in this unique 
population.  Specific hepatic safety monitoring and treatment discontinuation criteria should be 
discussed with the DAVP during the protocol development phase to incorporate case selection 
criteria and laboratory cutoff values specific to the population. 
 
Evaluation by an independent adjudication committee is encouraged to review all serious hepatic 
events, deaths, liver transplantations, and changes in prespecified alanine transaminase, aspartate 
transaminase, and bilirubin parameters in this cohort of patients with decompensated liver 
disease and/or those patients listed for liver transplantation.   
 
The NDA should include assessments based on the Model for End Stage Liver Disease and Child 
Pugh Turcotte scores at 12 weeks following cessation of treatment (SVR12 time point) compared 
to the patients baseline values.  We recommend long-term follow-up to characterize clinical 
outcomes such as progression or regression of liver disease, liver-related mortality, occurrence of 
hepatocellular carcinoma, or liver failure requiring liver transplantation. 
 
Plans for expanded access trials or safety trials also should be considered for this population 
early in development.  See section III.C.4., Expanded Access Considerations. 
 
c.  Pediatric populations 
 
The rapid evolution of HCV drug development and treatment affects pediatric development 
programs.  Therefore, we encourage sponsors to begin discussions about their pediatric 
formulations and clinical development plans early in development because pediatric assessments 
are required under the Pediatric Research Equity Act (PREA) as part of the overall drug 
development program for a new active ingredient, new indication, new dosage form, new 
dosing regimen, or new route of administration,11 unless the FDA waives or defers those 
assessments.12  A sponsor is required to submit a pediatric study plan  which includes an 
outline of the pediatric assessments that the sponsor plans to conduct or a request for a waiver or 
deferral of the requirement to submit those assessments  no later than 60 days after an end-of-
phase 2 meeting or such other time as may be agreed upon by the FDA and the sponsor.13  In the 
absence of a serious safety signal in adults, we recommend sponsors enroll adolescents 
                                                 
11 See section 505B(a)(1)(A) of the Federal Food, Drug, and Cosmetic Act (FD&C Act); 21 U.S.C. 355c(a)(1)(A).  
Section 505B(a)(1)(B) of the FD&C Act also requires that an original (drug or biological product) application for a 
new active ingredient with an adult oncology indication that is (i) intended for the treatment of an adult cancer; 
and (ii) directed at a molecular target that the Secretary determines to be substantially relevant to the growth or 
progression of a pediatric cancer must submit with the application reports on the investigation described in 
(section 505B(a)(3) of the FD&C Act). 
 
12 See section 505B(a)(4) and (a)(5) of the FD&C Act. 
 
13 See section 505B(e)(2)(A)(ii) of the FD&C Act; see also the draft guidance for industry Pediatric Study Plans:  
Content of and Process for Submitting Initial Pediatric Study Plans and Amended Initial Pediatric Study Plans.  
When final, this guidance will represent the FDAs current thinking on this topic. 
16  Contains Nonbinding Recommendations 
concurrently with adults in phase 3 trials and make every effort to submit confirmatory PK and 
safety data from a small cohort in this age group at the time of the original NDA.  Note that, 
because young children with HCV infection rarely have progressive liver disease requiring 
treatment, evaluation of patients younger than 3 years of age may not be required.14 
 
In addition to requiring pediatric assessments of certain drugs, PREA also requires that when 
conducting those assessments sponsors use a formulation of the drug that is appropriate for each 
age group being studied.15  Formulation development is expected to be the most challenging 
aspect of pediatric DAA development because many drug products will contain two or more 
drugs in a fixed-dose combination.  Adult formulations generally will be considered to be 
appropriate for adolescent patients (about 12 to 18 years of age) (Momper, Mulugeta, et al. 
2013), but younger children, some of whom may not be able to swallow pills, may require 
different formulations.  Therefore, pediatric formulation development should begin as early as 
possible to enable the creation of appropriate pediatric formulations of HCV drugs.   
 
In general, pediatric clinical studies can be initiated after phase 2 adult data characterizing the 
safety profile and preliminary evidence of efficacy (SVR) are available.  Initial pediatric PK data 
and results of available modeling and simulation should be discussed with the DAVP before dose 
selection for pediatric treatment studies.  Pediatric extrapolation of efficacy is acceptable for 
HCV DAA drugs because the course of HCV infection and the effects of DAAs are sufficiently 
similar between adult and pediatric populations.  Therefore, after critical PK parameters for a 
drug are identified from adult data, pediatric development programs can rely on matching the 
relevant pediatric and adult exposure parameters to demonstrate effectiveness in pediatric 
populations.  Additional data should be submitted to support safety in pediatric populations and 
to assess whether SVR rates are comparable to those observed in adult trials (although not 
statistically powered for efficacy comparisons).   
 
Because the number of pediatric patients available for enrolling in HCV clinical trials may be 
limited, we recommend that sponsors focus pediatric development on their best available 
regimen that is expected to be highly effective based on adult data.  We encourage sponsors to 
work collaboratively to identify such regimens.  In general, pediatric studies should provide 
confirmatory PK data and a safety database of about 100 patients receiving the proposed dose for 
the proposed duration of treatment, which would adequately be distributed across the age range 
groups for which studies are required and would not be waived or deferred.  If clinical trials in 
adults have demonstrated differences in safety profile or treatment regimen based on fibrosis 
stage, pediatric patients should be assessed for presence or absence of cirrhosis using the most 
appropriate modality for each study location.  If clinically indicated biopsies are performed, 
sponsors should provide biopsy data at the time of the NDA submission.  
                                                 
14 Pediatric assessments will be waived in cases where the FDA finds that necessary studies are impossible or 
highly impracticable (because, for example, the number of patients is so small or the patients are geographically 
dispersed) (section 505B(a)(5)(i) and section 505B(a)(5)(i) of the FD&C Act).  For drugs that trigger the 
requirements of PREA, if the FDA finds that there are so few patients with progressive liver disease in the birth to 3 
years of age range that studies are impossible or highly impracticable, any required assessments in children 
younger than 3 will be waived. 
 
15 See section 505B(a)(2)A) of the FD&C Act. 
17  Contains Nonbinding Recommendations 
 
d.  Patients with advanced chronic kidney disease 
 
HCV infection is a common comorbidity in hemodialysis patients.  The prevalence rate of HCV 
among patients undergoing hemodialysis within a U.S. hemodialysis network was reported as 7.8 
percent (range:  5.5 to 9.8 percent) (Finelli, Miller, et al. 2005), and it is estimated that more than 
60,000 HCV-infected patients will require hemodialysis by 2020 (Butt, Wang, et al. 2011).  A 
significant relationship has been observed between HCV infection and increased mortality 
among patients on long-term dialysis (Fabrizi, Dixit, et al. 2012).    
 
HCV infection can also negatively affect renal transplantation.  Compared to non-HCV-infected 
CKD Stage 4/5 patients, HCV-infected CKD Stage 4/5 patients have poor graft survival and 
higher overall mortality outcomes following renal transplantation (Fabrizi, Martin, et al. 2005; 
Terrault and Adey 2007).  
 
Peg-IFN-based regimens have been evaluated in advanced CKD patients, and dosing 
recommendations are available for patients receiving dialysis.  However, SVR rates are poor (56 
percent), and tolerability is low (Fabrizi, Martin, et al. 2011).  Therefore, the achievement of 
optimal SVR rates in this population will likely require treatment with IFN- and RBV-free 
combination DAA regimens. 
 
We encourage active-controlled trials when feasible; however, at a minimum a delayed-
treatment, placebo-controlled group should be employed in clinical trials in this population.  This 
will facilitate interpretation of the safety data given the anticipated increased rate of adverse 
events in the CKD population compared to those without CKD.  
 
The minimum acceptable safety database for this population will be determined by the 
demonstrated safety profile of the regimen in other populations.  We encourage sponsors to study 
patients in each of the important CKD subgroups (e.g., CKD Stage 4/5, hemodialysis, peritoneal 
dialysis).  Trials should be stratified based on the degree of CKD severity (and dialysis status) 
because these factors may affect drug clearance.  We encourage sponsors who are considering 
trials in this population to engage in early discussions with the DAVP. 
 
6.  Dose Selection 
 
Sponsors can use results from proof-of-concept antiviral activity monotherapy trials to guide 
dose selection for subsequent phase 2 trials in which DAAs are studied for longer durations as 
part of a combination regimen.  We recommend that sponsors develop models of the 
concentration-viral kinetics and concentration safety using all available drug exposure, viral 
kinetic, and safety data from studies to predict the most active and tolerable doses to be 
evaluated in phase 2 trials.  Mechanistic concentration-viral kinetic models, if developed, should 
include an appropriate targeted drug effect, components to describe virologic breakthrough, 
relapse, and long-term viral response (i.e., SVR), and relevant covariates for describing 
differences in response between HCV genotypes and subtypes or viral populations with or 
without drug resistance-associated polymorphisms or substitutions.  Sponsors should analyze 
independently results from patients infected with different HCV genotypes and subtypes, as 
18  Contains Nonbinding Recommendations 
sample sizes permit, to begin to evaluate dose-response relationships for relevant subpopulations.  
When applicable, these mechanistic modeling approaches can use viral kinetic model structures 
and the corresponding disease progression parameter values from the literature.  
 
Sponsors should use the model to identify the appropriate population for treatment and to reduce 
the risk of selecting for resistant virus caused by subtherapeutic exposure.  Optimal doses 
identified based on single-drug results may not be optimal for combination treatments, and we 
recommend that the sponsor evaluate a range of doses in subsequent trials.   
 
To optimize the regimen with respect to dose and treatment duration in phase 3 trials, sponsors 
can combine drug efficacy data from phase 1 and phase 2 trials in a single model to predict SVR 
in the planned trials.  Sponsors should evaluate such a model against on-treatment data of the 
regimen and refine drug efficacy parameter estimates as necessary.   
 
7.  Efficacy Endpoints 
 
As mentioned, the recommended primary endpoint for approval in trials evaluating CHC 
treatments is SVR12.  Sponsors should measure viral RNA clearance (SVR12) using an FDA-
approved sensitive and specific quantitative HCV RNA assay.  Use of unapproved assays should 
be discussed in advance with the FDA. 
 
Evaluating clinical outcomes in prospective, randomized controlled clinical trials of CHC is 
challenging because of the difficulty of maintaining patients on a randomized arm without 
intervening therapy for a sufficient duration (many years) to identify late-occurring clinical 
events such as HCC or need for liver transplantation.  However, multiple observational cohorts 
show correlations between SVR24 and improvements in clinical outcomes such as development 
of HCC, hepatic events, fibrosis, and all-cause mortality.16  These observational data support the 
use of SVR as a validated surrogate of HCV disease progression.  
 
In a previous version of this guidance, SVR24 was the recommended endpoint for CHC clinical 
trials.  However, the FDA examined whether assessing SVR12 could be used as a primary 
efficacy endpoint by examining the correlation between SVR12 and SVR24 in more than 13,000 
patients pooled from multiple clinical trials of peg-IFN-based regimens (Chen, Florian, et al. 
2013).  In brief, there was a high rate of concordance between SVR12 and SVR24.  Sensitivity 
and specificity for SVR12 was 99 percent and 98 percent, respectively; in subsequent analyses of 
trials of IFN-free regimens, similar concordance between SVR12 and SVR24 was shown.  
Therefore, the FDA considers SVR12 a suitable primary endpoint for registrational trials for both 
IFN-based and IFN-free regimens to support approval. 
 
Although SVR12 has been shown to predict SVR24, the concordance of SVR12 and SVR24 
results should continue to be assessed in clinical trials, particularly for new DAA classes and 
                                                 
16 Yoshida, Shiratori, et al. 1999; Yoshida, Arakawa, et al. 2002; Shiratori, Ito, et al. 2005; Okanoue, Itoh, et al. 
1999; Imai, Kawata, et al. 1998; Arase, Ikeda, et al. 2007; Veldt, Heathcote, et al. 2007; Braks, Ganne-Carrie, et al. 
2007; Bruno, Stroffolini, et al. 2007; Manos, Zhao, et al. 2009; Singal, Volk, et al. 2010; Backus, Boothroyd, et al. 
2011, Simmons, Saleem, et al. 2015 
19  Contains Nonbinding Recommendations 
combination drug regimens.  Additional post-treatment follow-up (e.g., 1 year or longer) may be 
necessary if one or more drugs in the regimen has a long plasma or intracellular half-life or 
prolonged antiviral activity.  At the time of NDA submission, sponsors should have analyzed all 
available SVR12 and SVR24 data (and longer term follow-up data as applicable) from phase 2 
and phase 3 trials to assess concordance of these results and the results of the analyses included 
in the application package.  If the drug or drugs are approved, the FDA will generally request 
any additional follow-up data from phase 3 registrational trials as a postmarketing commitment.  
 
Secondary endpoints should include the following:  
 
  Virologic failure rate (relapse after end of treatment and virologic breakthrough on 
treatment) to aid in the optimization of a dosage regimen and treatment duration 
 
  SVR24 rates 
 
  Percentage of virologic failure patients with treatment-emergent, resistance-associated 
changes in their HCV population   
 
8.  Trial Procedures and Timing of Assessments 
 
Recommended key time points for measuring HCV RNA depend on the drug regimen and 
patient population.  Key on-treatment measurements can include weeks 1, 2, 4, 8, 12, and 24 or 
at the end of therapy.  For all regimens, additional visits for HCV RNA monitoring should be 
included, as appropriate, to ensure timely detection of a virologic breakthrough or other 
treatment futility.   
 
Sponsors can use measurements of viral RNA at earlier time points in protocol decision-making 
for determining appropriate futility rules for stopping treatment depending on an individuals 
response. 
 
After completion of treatment, viral RNA should be measured at weeks 4, 12, and 24 of follow-
up.  
 
9.  Statistical Considerations 
 
In general, the sponsor should submit a detailed statistical analysis plan stating the trial 
hypotheses and analysis methods before trial initiation. For information on statistical analysis 
topics and issues, see the FDA guidances for industry Providing Clinical Evidence of 
Effectiveness for Human Drug and Biological Products and Non-Inferiority Clinical Trials to 
Establish Effectiveness and the journal article Statistical Considerations on Subgroup Analysis in 
Clinical Trials (Alosh, Fritsch, et al. 2015).   
 
20  Contains Nonbinding Recommendations 
a.  Analysis populations 
 
In general, all randomized patients should be included in the primary efficacy analysis.  
However, if a substantial proportion of randomized patients do not receive treatment in either or 
both arms, then additional sensitivity analyses are likely needed.  
 
b.  Efficacy analyses 
 
The primary efficacy analysis should compare the proportion of patients who achieve SVR12 
across treatment arms.  This analysis determines whether effectiveness has been demonstrated.17  
 
For subgroup analyses, sponsors should analyze SVR12 for patients with important demographic 
and baseline characteristics (e.g., geographic region, sex, race, age group, HCV 
genotype/subtype, HCV drug resistance-associated polymorphisms or substitutions, screening 
serum HCV RNA, baseline weight, baseline body mass index, baseline alanine aminotransferase, 
baseline fibrosis/cirrhosis, and, if applicable, prior response to DAA-based regimens).18  The 
purpose of these analyses is to evaluate the consistency of the SVR12 endpoint result across 
these subgroups.   
 
Single-arm trial designs where the SVR12 is compared to historical rates (superiority or 
noninferiority depending on regimens studied) should prespecify the historical rate in the 
protocol for efficacy comparisons.  The historical rate should be based on the intended regimen 
and patient population.   
 
Effects on secondary endpoints are not sufficient to support efficacy in the absence of 
demonstrating an effect on the prespecified primary endpoint.  The protocol should propose a 
multiple testing strategy for important secondary endpoints that adjust for multiplicity 
conditional on demonstrating the primary endpoint.   
 
Patients who experience virologic relapse or who stop treatment because their HCV RNA was 
not adequately suppressed should be regarded as virologic failures in all analyses.  For other 
patients who discontinue treatment early, investigators should determine if these patients 
switched treatments or added additional therapy.  Sponsors should note this information in the 
protocol case report forms and capture the information in the electronic dataset.  This 
information can be used to understand reasons for patients discontinuation and how patients will 
be included in the analysis.  
 
                                                 
17 Patients who discontinue therapy, for whatever reasons, before the protocol-defined treatment duration can still be 
considered responders if they have confirmed absence of HCV RNA 12 weeks after the originally planned treatment 
duration. 
 
18 Subgroup analyses by age, race, and sex are required as well as an analysis of whether modifications of dose or 
dosage intervals are needed for these subgroups (21 CFR 314.50(d)(5)(v) and (vi)(a)). 
21  Contains Nonbinding Recommendations 
c.  Noninferiority comparison 
 
Before initiating NI trials, sponsors should discuss with the DAVP the choice of an NI margin 
for statistical hypotheses.  The sponsor should justify the NI margin based on prior evidence of 
the quantitative contribution of the active control (substituted part of the drug regimen) to the 
regimen as a whole (M ).  This contribution should be determined in a similar population with a 
1
similar length of follow-up to the proposed trial.  In addition, the NI margin (M ) generally 
2
should be smaller than M  to preserve a clinically important effect compared to an active control.  
1
If approved drugs have response rates that are 95 percent or higher, a clinically acceptable NI 
margin (M ) is 5 percent or less; otherwise, if the SVR rates for approved drugs are all less than 
2
95 percent, sponsors should discuss with the DAVP the size of the NI margin and provide 
adequate justification.  For NI testing, sponsors should employ two-sided 95 percent confidence 
intervals, and the overall type I error rate should be controlled using adjustments for multiple 
comparisons or other appropriate testing procedures.   
 
Sponsors can assess both NI and superiority in an NI trial provided that the NI comparison is 
conducted first, and superiority is conducted only after testing for NI.  For additional information 
regarding NI trials in general, see ICH E10 and the guidance for industry Non-Inferiority 
Clinical Trials to Establish Effectiveness. 
 
d.  Handling of missing data  
 
There is no single optimal way to deal with missing data in clinical trials.  Sponsors should make 
every attempt to limit loss of patients from the trial to make the findings interpretable.  When a 
loss is unavoidable, sponsors should explain the causes of missing data and attempt to determine 
the final status of a patient who does not complete the protocol.  Analyses excluding patients 
with missing data or other post-treatment outcomes can be 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. 
 
For the primary analysis, sponsors can consider a patient as having achieved SVR12 if the 
patients week 12 follow-up HCV RNA measurement is missing, but the patient achieved 
SVR24.  Sponsors should consider a patient as not having achieved SVR12 if he or she 
discontinues from a trial before having an HCV RNA measurement at 12 weeks of follow-up or 
if the patient has missing HCV RNA values at the end of the scheduled 12- and 24-week follow-
up periods.  
 
Appropriate sensitivity analyses may be needed to demonstrate that the primary analysis is 
robust to the assumptions regarding missing data. 
 
10.  Accelerated Approval (Subpart H) Considerations 
 
Accelerated approval, which can rely on a surrogate endpoint or an intermediate clinical 
endpoint that is reasonably likely to predict clinical benefit,19 does not apply to drug 
                                                 
19 See section 506(c) of the FD&C Act; 21 CFR part 314, subpart H.  
22  Contains Nonbinding Recommendations 
development for hepatitis C because the endpoint used in clinical trials for full approval is 
considered a validated surrogate endpoint (SVR12) that is known to predict clinical benefit. 
 
C.  Other Considerations 
 
1.  Relevant Nonclinical Safety Considerations 
 
Pharmacology/toxicology development for single HCV DAAs should follow existing guidances 
for drug development.20   
 
The ICH guidance for industry M3(R2) Nonclinical Safety Studies for the Conduct of Human 
Clinical Trials and Marketing Authorization for Pharmaceuticals recommends nonclinical 
combination studies to support clinical trials of combination drugs for entities in early stages of 
development.  Section I.C., Scope of the Guidance, states, Pharmaceuticals under development 
for indications in life-threatening or serious diseases (e.g., advanced cancer, resistant human 
immunodeficiency virus (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 HCV drug combinations (consisting of two or more investigational drugs) that are not 
expected to represent an advantage (in terms of efficacy, tolerability, safety, use in specific 
populations, ease of administration) over approved combination therapies, sponsors should 
usually submit combination toxicology studies as part of an IND to conduct combination clinical 
trials.  However, usually no more than two drugs should be tested simultaneously in a particular 
arm of a toxicology study.  Sponsors should discuss with the DAVP the design of such a study.  
For DAA combinations that are expected to treat patients who have limited or no treatment 
options or to improve response rates in patients who are at risk of serious morbidity or for DAA 
combinations that are expected to have a substantial improvement over approved therapies, the 
FDA may conclude that 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 of the individual 
drugs do not suggest a potential for additive or synergistic toxicity of a serious nature. 
 
  Animal and human studies on 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. 
 
  Toxicology studies (of at least 3-month durations) of the individual drugs show 
substantial safety margins for the intended clinical dose or doses or exposures. 
 
                                                 
20 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(R1) Preclinical Safety Evaluation of Biotechnology-
Derived Pharmaceuticals.  
23  Contains Nonbinding Recommendations 
  Phase 1 clinical data in healthy subjects or HCV-infected patients receiving the individual 
drugs show no substantial safety concerns.  Phase 1 data should include single- and 
multiple-dose PK and safety trials, at minimum.  We encourage sponsors to have 
additional safety data from phase 1 and phase 2 trials that may be needed if one or more 
of the drugs demonstrate a potential serious safety risk.  
 
  No overlapping toxicities of concern exist for the individual drugs based on animal 
toxicology study findings and phase 1 or phase 2 clinical data. 
 
  Sponsors consider clinically significant PK-based drug interactions unlikely or reliably 
managed with dose adjustments such that safety margins based on individual drug 
exposures are not exceeded. 
 
After considering the above points, sponsors can first evaluate (in phase 1 and phase 2 trials) 
drug combinations in HCV-infected patients who are treatment naive or have remaining 
treatment options.  After initial trials in treatment-naive patients (or in patients who have 
remaining approved treatment options) help to define the most active doses, sponsors can study 
patients with few or no remaining treatment options.  This approach helps to ensure that patients 
with no remaining treatment options are not exposed to suboptimal doses or combinations that 
could severely jeopardize their chances for achieving SVR.   
 
Combination trials in healthy subjects or patients with early stage CHC should not be the first-in-
human trials unless the drugs cannot be administered separately and unless combination 
toxicology studies were completed.  We recommend referring to relevant guidances for industry 
when designing such trials.21 
 
In general, nonclinical combination studies of an investigational DAA plus an approved DAA, 
IFN, or RBV are not needed.  Therefore, unless data from nonclinical studies of an 
investigational DAA suggest a potential for serious synergistic toxicity with an approved 
therapeutic drug, combination toxicology studies are not anticipated. 
 
Sponsors should submit carcinogenicity studies for HCV products that are expected to be used 
chronically.  The DAVP allows the sponsor of products for serious and life-threatening 
indications (such as HCV) to begin carcinogenicity studies (with written agreement) before 
submitting an NDA and to submit the studies during the postmarketing period under section 
505(o)(3) of the Federal Food, Drug, and Cosmetic Act.22  Because of the likelihood of 
retreatment for patients who fail therapy (an intermittent chronic, recurrent dosing paradigm23), 
generally sponsors that have clinical indications for HCV DAAs with treatment durations of 24 
or more weeks should conduct carcinogenicity studies. 
                                                 
21 See guidances for industry ICH M3(R2) and Nonclinical Safety Evaluation of Drug or Biologic Combinations. 
 
22 See also the guidance for industry Postmarketing Studies and Clinical Trials  Implementation of Section 
505(o)(3) of the Federal Food, Drug, and Cosmetic Act. 
 
23 See the ICH guidance for industry S1A The Need for Carcinogenicity Studies of Pharmaceuticals. 
24  Contains Nonbinding Recommendations 
 
2.  Pharmacokinetic Considerations 
 
a.  Pharmacokinetic assessments 
 
Trials conducted in HCV-infected patients should include an assessment of pharmacokinetics 
and the relationship between drug exposure (e.g., minimum or maximum plasma concentration 
(C  or C ), area under curve) and virologic success and toxicity in all patients.  
min max
 
Sponsors can use a combination of intensive and sparse sampling throughout development to 
characterize the pharmacokinetics of investigational drugs.  For example, sponsors should 
implement an intensive sampling schedule in early phase 1 monotherapy trials.  In longer term 
trials, however, an intensive sampling schedule might not be feasible.  Alternatively, sponsors 
can combine sparse sampling from these trials with intensive PK data from earlier trials for 
analysis.  Sponsors should obtain sparse PK samples at the time of key virologic assessments.  
These data can then be subjected to appropriate population PK analysis.  Documenting dosing 
times and plasma sampling times is important. 
 
Sponsors can use the following two broad approaches to characterize the relationship between 
exposure and viral kinetics or virologic success of the investigational drug, depending on the 
development stage and purpose of the analysis.  Both approaches should account for differences 
in response between relevant viral subtypes and allow for exploration of relevant covariates.  For 
these analyses, sponsors should consider virologic relapse and the development of resistance to 
the investigational drug when assessing differences between treatment regimens.  When 
applicable, sponsors should use the developed exposure-response relationships to support 
proposed dosing and treatment duration for subsequent trials. 
 
  To aid the design of phase 2b and phase 3 trials, with respect to dose, duration, regimen 
choice, and population, a mechanistic approach relating drug concentrations and viral 
kinetics is most appropriate   
 
  When sufficient SVR12 data are available, a simplified analysis relating the proportion of 
patients with virologic success and the appropriate exposure variable (e.g., C , area 
min
under curve) can be used to support evidence of effectiveness and justify dose selection   
 
In exposure-response safety analyses, sponsors should consider the toxicities that are related to 
the investigational drug, and infrequent but severe safety events in order to inform dose selection 
and dose adjustments.  The appropriate exposure parameter and modeling approach depends on 
the investigational drug and toxicity. 
 
b.  Specific pharmacokinetic evaluation  
 
We strongly encourage PK evaluation in patients with renal impairment and hepatic impairment, 
to inform the need for dose modifications, early in drug development, so these patients can be 
enrolled into phase 2 and phase 3 trials as appropriate.  In general, we recommend that sponsors 
conduct these trials with the final regimen rather than the individual components separately.  
25  Contains Nonbinding Recommendations 
Sponsors can find specific recommendations related to trial design and data analysis in the 
relevant FDA clinical pharmacology guidances.  
 
3.  Clinical Virology Considerations  
 
a.  HCV RNA assessments and data reporting 
 
For antiviral activity and efficacy trials, sponsors should measure HCV RNA levels using a 
sensitive and specific quantitative assay.  Clinical trial protocols should describe the HCV RNA 
assay or assays to be used, including a brief description of assay performance characteristics.  
Protocols or final reports should include the names and addresses of the laboratories conducting 
HCV RNA assessments (e.g., central laboratory, assay vendor).   
 
In clinical trial protocols, final reports, and HCV RNA datasets, sponsors should use clear and 
consistent language to describe low-level HCV RNA results following guidelines for reporting 
HCV RNA levels as described in FDA-approved assay package inserts.  Specifically, HCV RNA 
detected but less than the lower limit of quantification (LLOQ) should be reported as < {LLOQ 
value in IU/mL} Detected, and HCV RNA not detected should be reported as Target Not 
Detected or HCV RNA Not Detected.  We do not recommend using terms such as 
undetectable or greater than the limit of detection or less than the limit of detection (LOD) (> 
LOD or < LOD, respectively), even if the validated assay LOD and LLOQ are equal, because 
HCV RNA levels can still be detected at a certain rate depending on the actual HCV RNA 
concentration.  
 
A detected or not detected HCV RNA cutoff can be problematic for trial endpoints or treatment 
decision-making because it is inherently less reproducible compared to an HCV RNA cutoff that 
is within the validated quantitative range of the assay.  Therefore, we encourage sponsors to use 
the assay LLOQ (or other quantitative HCV RNA threshold as appropriate) as the HCV RNA 
cutoff for treatment futility rules and trial endpoints including SVR, virologic relapse, and 
virologic breakthrough.  See also Appendix: Study Population Terms and Treatment Response 
Definitions for recommended terms and definitions related to virologic response and treatment 
history. 
 
b.  HCV genotype or subtype determination 
 
A validated assay with accuracy that is comparable to HCV genotyping or subtyping reference 
methods (Smith, Bukh, et al. 2014) should be used for HCV genotype or subtype screening and 
randomization of patients; we also recommend using an FDA-approved assay.  Clinical trial 
protocols should describe the HCV genotype or subtype assay or assays to be used, and include a 
brief description of assay performance characteristics.  Genotyping or subtyping assays (or 
historical data) based only on nucleotide sequence analysis of the 5-noncoding region of the 
HCV genome should be avoided because of poor performance in distinguishing between certain 
HCV genotypes and subtypes 1a and 1b (Chevaliez, Bouvier-Alias, et al. 2009).  Clinical assays 
used for HCV genotype or subtype determination may not resolve HCV subtypes other than 1a 
and 1b.  Therefore, in patients with nongenotype 1 HCV infections, sponsors should perform 
26  Contains Nonbinding Recommendations 
retrospective analyses to identify HCV subtypes based on reference methods (Smith, Bukh, et al. 
2014) or phylogenetic analyses of the drug target sequence or sequences.  
 
c.  Resistance analyses 
 
For efficacy trials, sponsors should perform treatment-emergent resistance testing for patients 
who do not achieve SVR.  Treatment-emergent genotypic and phenotypic resistance analyses 
should focus on samples collected while patients are on the investigational drug; if on-treatment 
HCV RNA levels are not adequate for analysis, then sponsors should analyze the first available 
follow-up sample with adequate HCV RNA.  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 developed during therapy.  Enrichment 
of substitutions from mixtures at baseline should also be reported; how these data are considered 
in treatment-emergent resistance analyses may depend on clinical trial design and nucleotide 
sequencing methods.  Sponsors should conduct similar treatment-emergent resistance analyses 
for all patients in early-phase monotherapy trials. 
 
Sponsors should analyze pretreatment samples from clinical trial patients to identify HCV 
genetic polymorphisms in DAA target genes, and sponsors should also evaluate the effect of 
HCV polymorphisms on treatment response.  These analyses should consider both the 
investigational DAA or DAAs and any background DAA or DAAs evaluated in combination.  
Sponsors should determine the prevalence of HCV populations carrying detectable resistance-
associated polymorphisms, both in the full trial population and in the U.S. trial patient population 
specifically.    
 
Sponsors should follow patients who have detectable resistance-associated substitutions at 
treatment cessation or follow-up for an extended period (at least 1 year after treatment cessation 
or until the initiation of alternative HCV therapies) to assess the persistence of resistance-
associated substitutions.  The potential persistence of resistance-associated substitutions should 
be characterized for patients enrolled in phase 1 and phase 2 clinical trials so that preliminary 
long-term follow-up data are obtained by the time of completion of phase 3 trials.  Genotyping 
methodology should be capable of assessing the quantity of resistant viruses during the 
outgrowth of a wild-type virus.   
 
Clinical trials of DAA regimens for patients previously exposed to a DAA or DAAs of the same 
class or classes or other classes with the same viral target should include plans to explore the 
efficacy effect of prior DAA exposure, considering the duration of prior DAA exposure, time 
since prior DAA exposure, and the detection of DAA resistance-associated substitutions.  For 
initial proof-of-concept studies in these patient populations, we encourage sponsors to use 
sensitive and quantitative genotypic resistance assays to characterize the relative and absolute 
quantity of DAA-resistant variants at baseline and to relate these findings to treatment outcome.  
Sponsors should use results from these analyses to guide the design of subsequent trials (e.g., 
whether to include patients based on the detection of DAA-resistant viral populations). 
 
Drug resistance-associated polymorphisms or substitutions observed in clinical trials should be 
evaluated phenotypically by introducing the changes into the HCV genome and determining the 
27  Contains Nonbinding Recommendations 
conferred fold shift in susceptibility to the drug using appropriate cell culture or biochemical 
assays.  Sponsors should perform phenotypic analyses of HCV replicons or viruses derived from 
treated patients if resistance is suspected but treatment-emergent genotypic resistance patterns 
are unclear.  Sponsors should report fold changes in antiviral activity based on EC  and EC  (or 
50 90
EC ) values.  Because resistance pathways can be complex and a variety of factors can affect 
95
drug resistance in treated patients, the lack of an observed phenotypic reduction in HCV 
susceptibility conferred by a specific amino acid substitution does not necessarily preclude a role 
for the substitution in HCV drug resistance. 
 
Because nucleotide sequencing technologies and data standards are evolving, sponsors should 
consult with the DAVP for current recommendations regarding the organization and submission 
of drug resistance datasets. 
 
4.  Expanded Access Considerations  
 
Some HCV-infected patients who are unable to take or who have not responded to approved 
treatments and who are at substantial risk of liver disease progression may be able to seek 
treatment with an investigational drug or drugs, before the drug or drugs are approved, through 
expanded access under 21 CFR 312.310, 312.315, or 312.320.  Treatment INDs or treatment 
protocols for DAAs may be appropriate when sufficient clinical trial data have been generated to 
develop a treatment protocol (including planned dosing) that meets the requirements of 21 CFR 
312.320.  Ideally, submission of a treatment IND or protocol should occur after sponsors fully 
enroll patients in phase 3 trials or have the trials well underway so as to avoid interference with 
phase 3 drug development.  A treatment IND or protocol can provide access to an investigational 
drug while phase 3 trials are being completed, analyzed, and submitted by the sponsor and 
reviewed by the FDA.  Alternatively, individual patient and intermediate-size patient population 
expanded access may be possible.  In contrast to treatment INDs or protocols for larger 
populations during or after phase 3 trials, expanded access for individual patient and 
intermediate-size patient populations can occur earlier in drug development.  
 
Historically, expanded access programs for the treatment of HIV infection allowed many patients 
to gain access to lifesaving drugs.  However, for some individuals, expanded access to an 
investigational drug resulted in what amounted to sequential monotherapy and the emergence of 
multidrug resistance.  Because treatment of CHC requires multiple drugs to achieve SVR and to 
reduce the emergence of drug resistance to single drugs or drug classes, expanded access 
programs that include two or more investigational drugs or that allow co-enrollment in several 
expanded access programs simultaneously are desirable, particularly for difficult-to-treat 
populations.  However, treatment use through expanded access of multiple investigational drugs 
should be supported by the following: 
 
  Data and rationale that characterize the potential for PK-based drug interactions and 
potential for overlapping toxicity; data to support dose modifications, if needed 
 
  Information suggesting the potential for additive or synergistic activity and no or minimal 
overlapping resistance profiles 
 
28  Contains Nonbinding Recommendations 
See section III.A.2., General Considerations for Phase 1 and Phase 2 Development, for the data 
needed to support treatment use through expanded access of multiple investigational drugs in a 
treatment regimen. 
 
29  Contains Nonbinding Recommendations 
GLOSSARY OF ACRONYMS 
 
CC    cytotoxic concentration  
CHC    chronic hepatitis C 
CKD    chronic kidney disease 
DAA    direct-acting antiviral 
EC    effective concentration 
HBV    hepatitis B virus 
HCC    hepatocellular carcinoma 
HCV    hepatitis C virus 
HCV RNA  hepatitis C virus ribonucleic acid 
HIV    human immunodeficiency virus 
IFN    interferon 
IU    international unit 
LLOQ   lower limit of quantification 
LOD    limit of detection 
mL    milliliter 
NI    noninferiority 
peg    pegylated 
PK    pharmacokinetic 
RBV    ribavirin 
RNA    ribonucleic acid 
SAP    statistical analysis plan 
SVR    sustained virologic response 
SVR4    sustained virologic response 4 weeks after stopping treatment 
SVR12   sustained virologic response 12 weeks after stopping treatment 
SVR24   sustained virologic response 24 weeks after stopping treatment 
 
30  Contains Nonbinding Recommendations 
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Y Shiratori, and M Omata, 2002, Interferon Therapy Prolonged Life Expectancy Among Chronic 
Hepatitis C Patients, Gastroenterology, 123(2):48391.  
 
Yoshida, H, Y Shiratori, M Moriyama et al., 1999, Interferon Therapy Reduces the Risk for 
Hepatocellular Carcinoma:  National Surveillance Program of Cirrhotic and Noncirrhotic 
Patients With Chronic Hepatitis C in Japan, IHIT Study Group, Inhibition of 
Hepatocarcinogenesis by Interferon Therapy, Ann Intern Med, 131(3):17481.  
 
Zeuzem, S, V Soriano, T Asselah, JP Bronowicki, AW Lohse, B Mullhaupt, M Schuchmann, 
M Bourliere, M Buti, S Roberts, E Gane, JO Stern, G Kukolj, L Dai, WO Bocher, and FJ Mensa, 
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Ribavirin, in Treatment-Naive Patients With Chronic Genotype-1 HCV Infection:  Interim 
Results of SOUND-C2, EASL International Liver Congress, Abstract 101.  
 
34  Contains Nonbinding Recommendations 
APPENDIX:  
STUDY POPULATION TERMS AND TREATMENT RESPONSE DEFINITIONS 
 
Table A includes recommended terms and definitions for documentation of prior hepatitis C 
virus (HCV) treatment history and responses (i.e., for trial inclusion criteria).  
 
  Some flexibility in the definitions may be appropriate, particularly when the level of 
detail indicated in the table is not typically available. 
 
  Peg-IFN refers to a pegylated interferon product. 
 
  For prior treatment history, multiple terms can be considered as appropriate to document 
responses to multiple rounds of treatment.  If only one term is used per patient, the most 
recent direct-acting antiviral (DAA) based treatment should take precedence. 
 
  Specific details regarding all prior drug or class experience should be noted as part of 
collecting protocol-specified data.   
 
Table A:  Recommended Terms and Definitions for HCV Treatment History 
TREATMENT-NAIVE  Naive to all anti-HCV treatment. 
P/R-ONLY  Did not achieve sustained virologic response (SVR) with 
EXPERIENCED*  previous P/R treatment, and never received an HCV DAA.   
Previously treated with an HCV DAA in any context (e.g., IFN-
free or IFN-containing treatment).  Patients can be further 
DAA-EXPERIENCED  subcategorized according to specific DAA or DAA class 
experience or by type of prior response (e.g., virologic 
breakthrough or relapse). 
* P/R = peg-IFN/RBV (ribavirin) 
 
 
35  Contains Nonbinding Recommendations 
Table B includes recommendations for protocol definitions of response or nonresponse to 
investigational regimens for HCV. 
 
Table B:  Recommended Protocol Definitions for Response or Nonresponse 
HCV RNA < LLOQ* at X weeks following cessation of 
SVR(X) 
treatment. 
HCV RNA  LLOQ at the end of treatment.  For example, can 
On-Treatment Virologic  include patients who experienced virologic breakthrough 
Failure  (confirmed or unconfirmed) or met an on-treatment virologic 
futility rule. 
Subcategory of On-Treatment Virologic Failure.  Confirmed  1 
log  IU/mL HCV RNA on-treatment increase from nadir, or 
10
Virologic Breakthrough  
confirmed increase in HCV RNA  LLOQ if HCV RNA 
previously declined to < LLOQ (detected or not detected). 
HCV RNA < LLOQ at end of treatment, but HCV RNA 
quantifiable ( LLOQ) during follow-up; can include patients 
Virologic Relapse 
who experienced late virologic relapse who also achieved 
primary SVR endpoint. 
Did not achieve SVR and did not meet any virologic failure 
Nonvirologic Failure 
criteria (e.g., adverse event, lost to follow-up).  
* RNA = ribonucleic acid; LLOQ = lower limit of quantification 
36