Guidance for Industry 

Influenza: Developing Drugs 

for Treatment and/or 

Prophylaxis 

U.S. Department of Health and Human Services 

Food and Drug Administration 

Center for Drug Evaluation and Research (CDER) 

April 2011 

Clinical Antimicrobial
 
 

Guidance for Industry 

Influenza: Developing Drugs 

for Treatment and/or 

Prophylaxis 

Additional copies are available from: 

Office of Communications, Division of Drug Information
 

Center for Drug Evaluation and Research
 

Food and Drug Administration 

10903 New Hampshire Ave., Bldg. 51, rm. 2201
 

Silver Spring, MD 20993-0002
 

Tel: 301-796-3400; Fax: 301-847-8714; E-mail: druginfo@fda.hhs.gov 

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

U.S. Department of Health and Human Services 

Food and Drug Administration 

Center for Drug Evaluation and Research (CDER) 

April 2011 

Clinical Antimicrobial
 
TABLE OF CONTENTS 

I. INTRODUCTION............................................................................................................. 1
 

II. BACKGROUND ............................................................................................................... 2
 

III. DEVELOPMENT PROGRAM ....................................................................................... 4
 

A. General Considerations .................................................................................................................4
 

1. Nonclinical and Early Phase Clinical Development Considerations ..............................................4
 

a. Phase 2A: Challenge trials .......................................................................................................5
 

b. Phase 2 dose-ranging trials .......................................................................................................6
 

2. Drug Development Population.........................................................................................................7
 

3. Efficacy Considerations ...................................................................................................................7
 

4. Safety Considerations.......................................................................................................................9
 

B. Specific Efficacy Considerations for Phase 3 Trials..................................................................10
 

1. Trial Design....................................................................................................................................10
 

a. Treatment trials: Acute uncomplicated influenza...................................................................10
 

b. Treatment trials: Serious influenza in hospitalized patients...................................................10
 

c. Prophylaxis trials.....................................................................................................................11
 

2. Trial Population .............................................................................................................................12
 

3. Entry Criteria .................................................................................................................................13
 

4. Blinding ..........................................................................................................................................13
 

5. Dose Selection and Route of Administration..................................................................................14
 

6. Efficacy Endpoints..........................................................................................................................14
 

a. General considerations ............................................................................................................14
 

b. Treatment of acute uncomplicated illness...............................................................................15
 

c. Treatment of seriously ill hospitalized patients.......................................................................16
 

d. Prophylaxis .............................................................................................................................16
 

e. Reduction in complications.....................................................................................................17
 

7. Trial Procedures and Timing of Assessments ................................................................................17
 

8. Statistical Considerations for Phase 3 Trials.................................................................................19
 

a. Treatment trials .......................................................................................................................20
 

b. Prophylaxis trials ....................................................................................................................20
 

9. Accelerated Approval (Subpart H) Considerations........................................................................22
 

10. Risk-Benefit Considerations ......................................................................................................23
 

C. Other Considerations...................................................................................................................23
 

1. Relevant Nonclinical Safety Considerations ..................................................................................23
 

2. PK and PD Considerations ............................................................................................................23
 

a. PK measurement .....................................................................................................................23
 

b. PD measurement .....................................................................................................................24
 

c. Modeling considerations .........................................................................................................25
 

3. Labeling Considerations ................................................................................................................25
 

4. Animal Rule (Subpart I) and Animal Model Considerations .........................................................25
 

5. Emergency Access Considerations.................................................................................................26
 

a. IND use ...................................................................................................................................26
 

b. Emergency use authorization ..................................................................................................26
 

6. Stockpiled Drug Products ..............................................................................................................27
 

7. CMC Considerations......................................................................................................................28
 

REFERENCES............................................................................................................................ 29 
 

 

 

Contains Nonbinding Recommendations 

Guidance for Industry1
 

Influenza: Developing Drugs for 

Treatment and/or Prophylaxis 

This guidance represents the Food and Drug Administration’s (FDA’s) current thinking on this topic. It 

does not create or confer any rights for or on any person and does not operate to bind FDA or the public. 

You can use an alternative approach if the approach satisfies the requirements of the applicable statutes 

and regulations. If you want to discuss an alternative approach, contact the FDA staff responsible for 

implementing this guidance. If you cannot identify the appropriate FDA staff, call the appropriate 

number listed on the title page of this guidance. 

I. INTRODUCTION 

The purpose of this guidance is to assist sponsors in the development of drugs for the treatment 

and/or prophylaxis of illness caused by influenza viruses A and B, including both seasonal and 

pandemic varieties.2 Specifically, this guidance addresses the Food and Drug Administration’s 

(FDA’s) current thinking regarding the overall development program and designs of clinical 

trials and nonclinical studies to support the development of influenza drug products.3 This 

guidance includes discussions on the following topics: 

•	 Nonclinical development 

•	 Early phases of clinical development 

•	 Phase 3 protocol designs and endpoints for the treatment of both uncomplicated and 

serious influenza 

1

 This guidance has been prepared by the Division of Antiviral Products in the Center for Drug Evaluation and 

Research (CDER) at the Food and Drug Administration. 

2

 Influenza viruses are designated by type (i.e., A, B, or C), subtype (specifically for influenza A: H and N numbers 

based on 16 hemagglutinin and 9 neuraminidase antigens), and by strain within types or subtypes. During a typical 

annual influenza epidemic, influenza B and two principal subtypes of influenza A (i.e., H3N2 and H1N1) circulate 

in varying proportions. New strains arise by ongoing antigenic drift within each of these types or subtypes. Many 

other influenza A subtypes occur in other host species, principally birds, and may cause occasional sporadic human 

infections. Influenza C has been reported as a cause of only sporadic mild disease and has not been a focus of either 

drug or vaccine development to date. 

3

 For the purposes of this guidance, all references to drugs include both human drugs and therapeutic biological 

products unless otherwise specified. 

1 
 

 

 

 

Contains Nonbinding Recommendations 

•	 Protocol designs for prevention of symptomatic influenza 

•	 The role of animal data in an influenza drug development program 

•	 Considerations relating to the potential for emergency use of influenza drugs, including 

advance development of protocols for further exploration and verification of drug effects 

under epidemic and pandemic conditions 

Sponsors considering development of antiviral drugs for the treatment or prophylaxis of disease 

with novel influenza strains, or in a pandemic influenza setting, are encouraged to consult this 

guidance and to communicate with the FDA through the pre-investigational new drug application 

(pre-IND) consultation program and frequently throughout drug development. Proposals for fast 

track designation can be considered at any time during drug development, depending on 

appropriate fulfillment of the designated criteria. 

This guidance does not address drug development for the treatment and/or prophylaxis of 

influenza C. This guidance also does not address development of influenza vaccines or vaccine 

adjuvants. Inquiries regarding vaccines should be addressed to the Center for Biologics 

Evaluation and Research (CBER). 

This guidance does not contain discussion of the general issues of clinical trial design or 

statistical analysis. 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.

4 

FDA’s guidance documents, including this guidance, do not establish legally enforceable 

responsibilities. Instead, guidances describe the Agency’s 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 

Effective vaccines are the central element in influenza control, but antiviral drugs are used for 

treatment of established influenza illness, and for postexposure or pre-exposure prophylaxis in 

selected situations. Antiviral drugs have been approved for treatment or prophylaxis of influenza 

A, influenza A and B, and influenza (not otherwise specified) based on trials in illness caused by 

circulating influenza virus strains. Approved antiviral drugs for influenza fall into two classes, 

neuraminidase inhibitors and the adamantanes. 

Influenza infections can produce a wide spectrum of clinical illness ranging from a self-limited 

febrile illness with respiratory symptoms to severe disease with complications sometimes 

4 We update guidances periodically. To make sure you have the most recent version of a guidance, check the FDA 

guidance Web page at 

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

2 
 

Contains Nonbinding Recommendations 

resulting in hospitalization and death. The severity of influenza depends on the virus strain and 

host, and is not always predictable at an individual level. To date, antiviral drugs have shown the 

ability to modestly reduce symptoms in uncomplicated or otherwise self-limited illness. 

Currently, no antiviral drug has been shown to definitively reduce serious complications, 

hospitalization, or mortality in a randomized clinical trial. Although this guidance addresses 

approaches to studying both self-limited and serious influenza, most regulatory experience 

involves trials in the treatment of uncomplicated illness (i.e., self-limited illness treated at home 

without secondary complications) and prophylaxis. 

Concerns about the possibility of pandemic spread of novel influenza strains have led to 

increased interest in influenza drug development;5 however, seasonal influenza remains a major 

public health concern. Because of their close relationship, seasonal and pandemic influenza are 

considered together in the discussions of regulatory approaches. 

Although terms such as avian influenza, epidemic influenza, and pandemic influenza have been 

used interchangeably in some scientific and media publications, they have important differences, 

as noted below: 

•	 Avian influenza refers to any of a number of subtypes and strains that might be 

transmitted from birds to humans causing sporadic cases and clusters, and that might 

subsequently acquire capacity for rapid and widespread human-to-human transmission. 

•	 Epidemic influenza refers to a greater number of cases of influenza illness occurring in a 

community or region during a given period of time. 

•	 Pandemic influenza refers to a strain of predominantly avian, mammalian, or reassortant 

origin that has acquired capacity for transmission among humans and has emerged as a 

novel cause of widespread disease, dominating or replacing previously circulating 

subtypes (seasonal influenza) in human populations. Although sporadic cases of novel 

strains raise concerns regarding a potential pandemic, it is difficult to predict which strain 

might emerge as a source for a pandemic. In addition, substantial additional genetic 

change is likely as a novel strain progresses from sporadic to pandemic. The difficulty in 

predicting the emergence of pandemic strains is illustrated by the recent antigenically 

novel reassortant strain of a previously circulating subtype (previously referred to as 

swine-origin influenza virus), which caused the first influenza pandemic of the 21st 

century.6 

5

 See documents and information at http://www.pandemicflu.gov. 

6

 The 2009 pandemic strain of the H1N1 subtype differs antigenically from the H1N1 that has circulated in humans 

for decades; is reported to be most closely related but not identical to H1N1 strains that have circulated in swine, 

containing genes of swine, avian, and human origin; and has not been detected in nonhuman hosts before the 

emergence of human outbreaks in 2009. The new strain also illustrates the lack of predictable correspondence 

between subtype and antiviral susceptibility, having emerged with a pattern of resistance mutations more similar to 

the seasonally circulating H3N2 than to the then most recent circulating H1N1 strains in human populations. 

3 
 

 

Contains Nonbinding Recommendations 

III. DEVELOPMENT PROGRAM 

A. General Considerations 

Influenza drug efficacy is evaluated in clinical trials conducted in the setting of circulating, 

naturally occurring influenza illness. However, a drug effective in the treatment of seasonal 

influenza may not be effective or as effective in pandemic influenza or in sporadic cases caused 

by other novel strains. In addition, changes in seasonal strains, including emergence of 

resistance, can decrease drug effectiveness over time. Thus, information on potential differences 

in drug responsiveness among strains or subtypes, including novel strains isolated from human 

infections, should be explored by generating and assessing additional data from cell culture and 

animal studies, and by collecting and analyzing clinical data when feasible. 

Because of the public health implications of both epidemic and pandemic influenza, the variable 

nature of the disease, and limited therapeutic options and challenges in studying new options, 

novel approaches to the influenza drug development are of great interest. Development 

pathways can be designed to provide information supporting access to investigational drugs if 

public health emergency arises during the development process. Another important 

consideration is advance development of protocols for further exploration and verification of 

drug effects under changing epidemic and pandemic conditions. 

1. Nonclinical and Early Phase Clinical Development Considerations 

Before initiating clinical trials, sponsors should investigate the mechanism of action and antiviral 

activity of the candidate drug using multiple types, subtypes, and strains of influenza virus 

derived from human clinical infections and from animals that can serve as sources for new 

clinical strains. For a candidate drug with a mechanism other than direct antiviral effect, 

sponsors should conduct cell culture, biochemical, and genetic studies to support their animal 

toxicity studies (e.g., mouse knockout of the proposed target, receptor binding studies, and amino 

acid sequence homology analyses). Different proposed mechanisms of action may affect the 

types of trials warranted to explore risk-benefit balance (e.g., potential effects of 

immunomodulators on disease processes in patients with pre-existing immunologic 

abnormalities). 

Candidate drugs should be assessed for antiviral activity in cell culture assays and, on the basis 

of those assay results, for in vivo activity in appropriate animal models of influenza infection.7 

Sponsors may need to assess the potential of their candidate drugs to enhance replication of other 

pathogens that mimic or complicate influenza, including other respiratory viruses and bacteria 

associated with similar illnesses or complications. 

Although not a regulatory requirement or replacement for clinical trials, cell culture and animal 

studies can: (1) make valuable contributions to clinical trial designs, including dosing 

7

 The National Institutes of Health (National Institute of Allergy and Infectious Diseases, Division of Microbiology 

and Infectious Diseases, Virology Branch) has an antiviral drug screening program designed to help identify 

potentially active antiviral drugs, including those to treat influenza. Information about this program and related 

activities can be accessed at http://www.niaid.nih.gov/topics/viral/Pages/Default.aspx. 

4 
Contains Nonbinding Recommendations 

considerations and resistance monitoring plans; (2) assist in exploring the generalizability of 

clinical trial results; and (3) be used to: 

•	 Explore a candidate drug’s activity against various strains of influenza including novel 

strains 

•	 Explore the effects of viral inoculum size of influenza exposure 

•	 Compare dosing regimens and routes of administration 

•	 Determine concentrations of the candidate drug at appropriate anatomic sites 

•	 Explore exposure-response relationships 

•	 Explore activity in immunocompromised hosts 

•	 Characterize viral resistance and transmissibility 

•	 Characterize treatment timing relative to the onset of clinically evident illness 

Proposals for animal studies should include supporting information on the selection, justification, 

and characterization of the animal model, and details of the natural history of disease in the 

model, as well as the proposed study design. When designing animal studies, sponsors should 

consider factors such as the relevance of the viral strain and need for adaptation to the host, the 

natural history of disease in the animal model, viral inoculum effects, dose and timing effects, 

and available information linking animal data to human exposure-response and outcomes. 

Virologic assessment and resistance monitoring are integral to the antiviral drug development for 

influenza. Sponsors should address virologic proposals together with their proposals for 

nonclinical studies and clinical trials throughout the development process, beginning with preIND interactions with the FDA. 

a. Phase 2A: Challenge trials 

After initial antiviral activity assessments and phase 1 human pharmacokinetic (PK) and 

tolerability trials, several sponsors have conducted challenge trials. In challenge trials, healthy 

volunteers are administered an investigational antiviral drug either before (prophylaxis trials) or 

after (treatment trials) inoculation with the established challenge strain of influenza virus. 

Challenge strains are influenza viruses that produce a milder set of symptoms compared to 

naturally occurring influenza. Pharmacodynamic (PD) endpoints in challenge trials include 

clinical respiratory symptoms, nasal discharge weight, and quantitative measurements of viral 

shedding in nasal washes. Sponsors are encouraged to include assessments of resistance in their 

challenge trials. 

Challenge trials can provide useful exposure-response and safety information, as well as an 

opportunity to demonstrate pharmacological antiviral activity in humans under controlled 

conditions outside the influenza season. Data from challenge trials can contribute to dose 

selection for phase 2B and phase 3 trials, and provide the opportunity to explore the effects of 

different times of drug initiation relative to virus exposure. However, challenge trials should not 

be considered efficacy trials that can be used to support marketing approval, because challenge 

strains typically produce a milder set of symptoms compared to naturally occurring influenza, 

and inoculation in challenge trials may differ from acquisition in naturally occurring infections 

(e.g., amount of inoculum in challenge trials could be larger or smaller at various mucosal sites 

5 
Contains Nonbinding Recommendations 

compared to naturally occurring infections). In addition, challenge trial results may not predict 

treatment outcomes for novel circulating influenza strains and pandemic strains because tissue 

distribution, viral replication, and host responses to novel strains can vary from those recognized 

in well-characterized challenge strains. 

Whether challenge trials are feasible is dependent on the availability of adequately safety-tested 

challenge strains and ethics considerations. Proposals for challenge trials should include 

documentation of the safety testing and biologics investigational new drug application (IND) 

status (in CBER) of the influenza challenge strains. It is important for a sponsor wishing to use 

any new challenge strains to coordinate and consult with CBER staff reviewing the IND. The 

use of novel strains of high or unknown pathogenicity is not an option for reasons of ethics, 

safety, and containment. 

Sponsors should provide dosing rationale for challenge trials on the basis of animal and human 

PK and tolerability data, cell culture EC50 values (adjusted for protein binding), animal model 

PK/PD data, and any other relevant information. 

b. Phase 2 dose-ranging trials 

The design of phase 2 dose-ranging trials depends on the type of population for phase 3 trials, as 

well as the phase 1 safety profile of the investigational drug. We recommend that sponsors 

conduct phase 2 trials before designing phase 3 trials. Proceeding directly to phase 3 from phase 

1 or phase 2A trials may fail to produce useful phase 3 data, especially if selection of doses and 

regimens are not scientifically justified. Phase 2 dose-ranging trials usually are designed with 

adequate statistical power to detect differences in viral shedding (e.g., duration, quantitative 

differences from baseline), as well as differences in clinical symptoms that are included as 

secondary endpoints. Differences in virologic endpoints, together with numerical trends in 

clinical symptoms, are used to choose doses for further study in phase 3. 

It should be noted that clinical dose-response trials are one type of adequate and well-controlled 

trial that, if appropriate clinical endpoints in appropriate populations are measured, can 

contribute to substantial evidence of effectiveness (21 CFR 314.126). In addition, exposureresponse trials and their analyses can provide support for approval of different doses, dosing 

regimens, or dosage forms. Depending on the trial endpoints, exposure-response information 

can: 

• Help to connect cell culture antiviral activity (EC50) and exposure 

• Help to link animal and human findings 

• Provide guidance for designing clinical endpoint trials that use a rational dose range 

• Characterize activity against different influenza types and subtypes 

• Allow a risk-benefit analysis at different doses 

At present, it is not clear what PK exposure parameters or PD response parameters best predict 

anti-influenza efficacy outcomes. However, duration of viral shedding in nasal washes is often 

measured, together with clinical symptoms such as nasal congestion, feverishness, sore throat, 

cough, aches, fatigue, headaches, and chills/sweats. Typical influenza disease is restricted 

6 
 

 

 

 

Contains Nonbinding Recommendations 

mostly to the respiratory tract and does not generally cause systemic viremia; however, there are 

occasional reports of isolation of viral RNA (e.g., A/H5N1) from other organ systems. 

Therefore, choice of virologic parameters for exposure-response analyses may depend on the 

influenza strain being studied. Sponsors are encouraged to discuss their choice of PD parameters 

with the FDA in a clinical development meeting during phase 1 or phase 2. 

For detailed information on trial design, see the guidance for industry Exposure-Response 

Relationships — Study Design, Data Analysis, and Regulatory Applications and Population 

Pharmacokinetics, and the ICH guidance for industry E4 Dose-Response Information to Support 

Drug Registration. 

2. Drug Development Population 

Although influenza affects the entire population, phase 3 development plans can initially focus 

on treatment or prophylaxis of acute uncomplicated influenza in otherwise healthy individuals. 

However, we recommend that sponsors conduct trials in: (1) persons at high risk of influenza 

complications, such as the elderly; (2) persons with underlying respiratory or cardiac disease; 

and (3) immunocompromised persons who may not experience the same benefit or safety profile 

as otherwise healthy adults. Such trials should be conducted as soon as appropriate data permit 

initiation of trials in these populations. 

Influenza occurs worldwide with differing seasonality but often with similar viral strains causing 

outbreaks across continents. Because the timing and magnitude of outbreaks in a given location 

may be difficult to predict, influenza drug development programs can involve diverse geographic 

locations. Protocols with a range of both northern and southern hemisphere sites increase 

efficiency of drug development by allowing collection of data through different influenza 

seasons. 

When sponsors rely on foreign clinical trial data — whether as part of multinational trials 

including the United States or as part of trials conducted entirely outside the United States — to 

support the marketing approval of their candidate drugs, they should supplement the foreign data 

with information about circulating influenza strains, patterns of clinical illness, trial population 

demographics, standards of medical care, and the use of other medical interventions in the 

countries where the trials were conducted. Sponsors should evaluate the relevance of foreign 

data under applicable FDA regulations, with considerations of trial conduct standards, trial 

population demographics, availability of sites for regulatory inspection, and applicability of 

disease manifestations and the standard medical care compared to that in the United States. 

Sponsors also can consult the guidance for industry Acceptance of Foreign Clinical Studies and 

the final rule “Human Subject Protection; Foreign Clinical Studies Not Conducted Under an 

Investigational New Drug Application.”8 

3. Efficacy Considerations 

Efficacy trials for influenza treatment generally focus on symptom improvement in otherwise 

healthy persons with acute uncomplicated influenza. However, large trials in otherwise healthy 

8 See 73 FR 22800, April 28, 2008 (revising 21 CFR 312.120). 

7 
 

 

 

Contains Nonbinding Recommendations 

populations may not be appropriate for some drugs if major limiting safety concerns have been 

identified in earlier development. 

In general, treatment and prophylaxis indications for influenza are different indications, and each 

indication should be supported by two adequate and well-controlled trials. However, sometimes 

a single persuasive trial may be sufficient for each indication, depending on other supportive 

evidence.9

 Two trials that differ in design parameters and populations usually are more useful 

than two identically designed trials or a single large trial. For example, one treatment trial in 

adults and one treatment trial in children may be considered sufficient to support a treatment 

indication in adults and children. Additional trials in special populations can be used to extend 

and/or further define indications. Data from trials for different influenza-related indications 

(e.g., treatment of acute uncomplicated illness, treatment of severe illness requiring 

hospitalization, postexposure prophylaxis, and seasonal prophylaxis) can provide supportive 

safety and efficacy information to the extent appropriate based on dosing, duration of treatment, 

and populations studied. 

With regard to indications for pandemic or avian influenza (as contrasted with seasonal 

influenza) or for a specific influenza subtype, molecular targets of antiviral drugs in general have 

not been shown to be subtype-specific. However, resistant strains can emerge in different 

subtypes and within the same subtype. It may not be possible to predict antiviral drug efficacy 

against novel strains with little or no population immunity or strains with virulence factors that 

differ from the strains studied in clinical trials. However, some drug effect is likely if the 

molecular target remains sufficiently similar.10 Information about strains circulating during a 

clinical trial is useful and should be collected and correlated with clinical outcomes where 

possible. 

Influenza development plans may be eligible for consideration under 21 CFR part 312, subpart E 

(Drugs Intended to Treat Life-Threatening and Severely-Debilitating Illnesses), fast track, or 

priority review if the specifics of the development plan justify such an approach. However, 

accelerated approval using surrogate endpoints under 21 CFR part 314, subpart H,11 is not 

applicable to influenza drug development because clinical benefits are assessed over a short time 

period and no surrogate marker has been reliably identified as reasonably likely to predict 

important clinical outcomes. For example, measurements of viral burden or shedding are not 

well standardized or characterized in relation to clinical outcomes, and clinical status generally 

can be measured at least as frequently and as rapidly as virologic status. In addition, most 

9

 See the guidance for industry Providing Clinical Evidence of Effectiveness for Human Drug and Biological 

Products for characteristics of a single adequate and well-controlled clinical trial that can contribute to a conclusion 

that such trial would be adequate to support an effectiveness claim. 

10 Some proposals for drug development may be based on strains predicted to interact with a specifically designed 

molecule such as antisense oligonucleotides, small interfering RNAs, and monoclonal antibodies. Given the 

propensity of known strains to antigenic drift, it is difficult to ensure that a planned intervention can be designed to 

bind only to a single specific portion of a predicted future pandemic strain protein or RNA. Usually, development is 

directed toward a conserved component of both circulating and hypothesized future pandemic strains, and it may be 

prudent to use mixtures of different antibodies or RNA segments to minimize escape mutations. 

11 See also 21 CFR part 601, subpart E, for the accelerated approval provisions for therapeutic biologics for serious 

or life-threatening illnesses. 

8 
 

 

Contains Nonbinding Recommendations 

patients clear virus with or without treatment, and the magnitude and timing of treatment-related 

changes in viral shedding has not been clearly associated with clinically meaningful changes in 

disease resolution. Exploratory analyses of viral burden measurements at relevant sites and their 

relationship to adequately monitored and measured clinical outcomes may contribute to future 

understanding of the relationships between viral levels in clinical specimens and clinical 

outcome. 

Although using two or more antiviral drugs in combination might provide greater therapeutic 

benefit than using each drug alone in certain settings, such added value of combination therapy 

has yet to be established for influenza. Combination therapy, particularly with drugs from 

different classes, can potentially result in synergistic or additive antiviral activity, or prevent or 

delay emergence of resistance. Combining drugs also can be useful in cases where circulating 

viruses of different types or subtypes are known to harbor resistance-associated substitutions, 

and there are no readily available point-of-care tests capable of distinguishing between virus 

types or viruses with substitutions. In this situation, the objective of the combination is to 

provide initial treatment for each of the major diagnostic possibilities, rather than to enhance 

treatment effect against a specific virus. 

However, combination treatment can result in increased toxicity and impractical dosing 

regimens. In addition, hypothesized antiviral synergy might not be clinically meaningful. 

Therefore, trial designs should demonstrate the activity of each component of combination 

therapy (i.e., contribution of each component to the combination).12 Establishing the 

contribution of each component, generally using factorial designs, is important whether the 

proposed combination contains two or more antiviral drugs (e.g., a co-packaged combination, or 

a fixed-dose combination) or a drug and a therapeutic biological product. Sponsors should 

consult 21 CFR 300.50 for specific regulatory considerations regarding fixed-dose combinations. 

4. Safety Considerations 

It is important to develop a robust safety database from adequate and well-controlled human 

trials in appropriate populations because a wide variety of affected populations with a range of 

comorbidities could interact with both disease and treatment. An application for initial approval 

of a new influenza drug for the treatment of uncomplicated influenza should include safety data 

from at least 1,500 patients at the dose and duration proposed for marketing. A safety database 

larger than 1,500 patients may be needed if early safety signals have been identified in 

development. Drugs that are intended to affect host cells or host responses, rather than directly 

affecting the virus, may need additional safety assessments (including special laboratory 

evaluations as appropriate for the agent) on more patients for unintended consequences of the 

host alterations. For new drugs showing important clinical benefit in serious influenza in 

hospitalized patients, an initial safety database of approximately 500 patients at the dose and 

duration proposed for treatment use may be sufficient for filing a marketing application for the 

treatment of serious influenza. 

12 See the draft guidance for industry Codevelopment of Two or More Unmarketed Investigational Drugs for Use in 

Combination. When final, this guidance will represent the FDA’s current thinking on this topic. For the most recent 

version of a guidance, check the FDA guidance Web page at 

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

9 
 

Contains Nonbinding Recommendations 

Sponsors should provide a toxicity grading scheme for clinical trials. For trials of influenza 

prophylaxis or treatment of uncomplicated influenza, we recommend toxicity scales appropriate 

for use in healthy volunteers.13 For treatment of serious influenza or treatment of influenza in 

patients with underlying medical conditions, other toxicity grading scales can be used (e.g., those 

adopted by the AIDS Clinical Trials Group, National Cancer Institute, or the World Health 

Organization). 

B. Specific Efficacy Considerations for Phase 3 Trials 

1. Trial Design 

a. Treatment trials: Acute uncomplicated influenza 

Placebo-controlled trials are appropriate in settings and populations where the expected serious 

risk of nontreatment is small.14 For trials evaluating treatment of uncomplicated mild to 

moderate influenza, placebo-controlled rather than noninferiority designs should be used because 

the risks of receiving placebo are low, and the efficacy of available treatment is modest (1-day 

difference in time-to-symptom improvement), variable, and cannot be predicted well enough to 

support an adequate noninferiority margin. The variable clinical course of influenza in any given 

season, as well as the potential for differences in pathogenicity and host immunity as new 

influenza strains emerge and change over time, also makes uncontrolled data or historical 

controls difficult to interpret and inadequate to support efficacy of investigational drugs. 

In addition to placebo-controlled trials, the following designs should be considered for acute 

uncomplicated influenza treatment trials: (1) superiority trials with approved antivirals and/or 

symptomatic treatment as active controls in otherwise healthy adults or children; and (2) doseresponse (or concentration-response) trials where higher doses show significantly greater 

responses than lower doses. 

It is possible that future influenza drugs may be approved with large enough effect sizes relative 

to placebo that they may in turn be used as active controls in noninferiority treatment trials. 

b. Treatment trials: Serious influenza in hospitalized patients 

From a public health perspective, it is important to have treatments available for serious 

influenza in hospitalized patients. However, there are few trials of antiviral drugs in this setting. 

In addition, because no trial has definitively demonstrated substantial clinical efficacy of an 

13 See the guidance for industry Toxicity Grading Scale for Healthy Adult and Adolescent Volunteers Enrolled in 

Preventive Vaccine Clinical Trials. 

14 Some public health authorities may not recommend routine treatment of influenza with currently approved 

antivirals because of concerns about risk-benefit, including the risk of resistance emergence. 

10 
 

 

 

 

Contains Nonbinding Recommendations 

antiviral drug in serious influenza or in hospitalized patients,15 determination of a noninferiority 

margin is not possible. As a result, an active-controlled noninferiority trial is not possible.16 

Despite the lack of definitive randomized trials showing a specific magnitude of benefit of 

antivirals in the treatment of serious influenza, we acknowledge investigator concerns about 

randomizing hospitalized patients with serious influenza to placebo alone. Consequently, 

sponsors can consider the following reasonable trial design alternatives in serious influenza: (1) 

a randomized and blinded dose-response (or duration-response) trial, in which a significant dose 

response is demonstrated; and (2) a superiority add-on trial, in which the combination of an 

investigational drug plus a standard of care is shown to be superior to a standard of care (such as 

a drug approved for uncomplicated influenza used off-label for the treatment of serious 

hospitalized influenza). Showing efficacy differences in dose-response trials and superiority 

trials is challenging if all treatment arms are believed to have similar benefit. Adequate 

frequency and intensity of patient assessments are important to maximize the likelihood of 

detecting potential, clinically relevant differences. 

Because outbreaks of influenza are unpredictable and enrollment of serious or hospitalized 

patients probably will be more difficult than enrollment of uncomplicated cases, sponsors should 

consider collaborating with clinical trial networks with a wide range of sites. Trial design 

proposals should delineate how the proposed design (including sample size and power) will be 

able to detect an effect of the investigational drug on improving the patients’ clinical status. 

c. Prophylaxis trials 

Prophylaxis trial designs include interventions in communities after documentation of circulating 

influenza, and household or institutional settings with documented exposure to a definite or 

clinically presumed case. Both sample size and risk-benefit assessments of such trials may be 

affected by the assumed intensity of exposure. For example, household or nursing home contacts 

may be at greater risk of disease than randomly recruited community dwellers. In settings in 

which there are definite recommendations from public health entities for drug prophylaxis (e.g., 

after onset of an outbreak within a nursing home), placebo controls will not be possible. 

In populations in which prophylaxis is not considered necessary, standard-of-care, placebocontrolled trials can be considered. In prophylaxis trials, the rates of symptomatic infection in 

placebo groups vary greatly depending on the season and population, and the number of illness 

outcomes in any treatment group may be small. Vaccination status and changes in circulating 

viral strains also may effect the number of symptomatic cases observed. The small number of 

15 A limited number of observational and case-control studies have reported various types of clinical benefit of 

antivirals for serious influenza; however, the margin of benefit was modest (both clinically and statistically). There 

were also questions about the reliability of the data because of potential biases when comparing treated and 

untreated groups. Observational comparisons between presumed active treatments, or between different times of 

treatment initiation, also have major risks of bias, compromising the ability to derive reliable estimates of effect size 

from such comparisons. 

16 See the draft guidance for industry Non-Inferiority Clinical Trials. When final, this guidance will represent the 

FDA’s current thinking on this topic. For the most recent version of a guidance, check the FDA guidance Web page 

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

11 
 

 

Contains Nonbinding Recommendations 

outcomes and resulting large confidence intervals in a noninferiority comparison can make it 

difficult to establish the effect of a new drug. For example, if two active drugs are compared and 

few or no cases of influenza illness are observed, this result can indicate similar effects of the 

two drugs, or lack of a true influenza outbreak, which would make it difficult to conclude the 

two drugs have similar effects. 

We consider the most straightforward household influenza prophylaxis trial design to be when: 

(1) all symptomatic infected index cases receive the same care (i.e., none is treated with any 

active drug, or all are treated with the same candidate drug, or all are treated with a specified 

alternative intervention); and (2) households are then randomized to the investigational drug or 

control (e.g., placebo), such that all members of the same household receive the same drug or 

control. This design does not provide information regarding whether treatment of the index case 

can itself decrease secondary transmission, or the potential interactions between the two 

interventions (e.g., reduction of prophylactic effect because of selection and shedding of resistant 

virus in the index case). To answer questions regarding influenza transmission, a four-arm 

factorial-design trial can be used in which index cases and household contacts are both 

randomized to treatment or placebo. Alternatively, sponsors can consider two or more separate 

trials with differing designs depending on the importance of each of these questions in the 

context of the specific candidate drug. 

2. Trial Population 

As mentioned previously, although influenza affects the entire population, phase 3 trials can 

initially focus on acute uncomplicated influenza in otherwise healthy individuals. However, 

sponsors also should conduct trials enrolling persons at high risk of influenza complications, 

such as the elderly, individuals with underlying conditions such as respiratory or cardiac disease, 

and immunocompromised persons (e.g., HIV-infected patients, organ transplant recipients, or 

patients receiving cancer chemotherapy). These patients may not experience the same benefit or 

safety profile from the candidate drug when compared with other patient populations. It can be a 

challenge to design trials for patients at risk. Possible trial design alternatives to placebocontrolled designs include but are not limited to dose-response trials, active-controlled 

superiority trials, combination versus single therapy trials, and single-arm or active-controlled 

safety trials. 

In addition, trials in populations with little immunity to influenza and high or prolonged viral 

replication (e.g., young children and immunocompromised patients) may provide useful 

information about potential patterns of resistance emergence and relationships between the 

treatment dose or duration and clinical outcomes. In trials of serious influenza, we encourage 

enrollment of patients with influenza-related complications, such as those needing intensive care 

support or mechanical ventilation. 

To fulfill the Pediatric Research Equity Act requirements and extend treatment and/or 

prophylaxis indications to pediatric age groups, sponsors need to conduct adequate and wellcontrolled trials with clinical efficacy endpoints and complete safety evaluations.17 PK and 

safety trials will not be considered adequate to extend the indications to children, particularly 

17 See the Pediatric Research Equity Act. 

12 
Contains Nonbinding Recommendations 

those younger than 12 years of age. Antiviral drug efficacy in children cannot be extrapolated 

from data generated from trials in adults because: (1) prior exposure and immunity typically 

present in adults may affect influenza illness and response to treatment differently than in 

children; and (2) viral shedding may differ in pediatric and adult age groups. 

Sponsors can include adolescents in adult trials as appropriate, depending on an individual 

candidate drug’s pharmacologic characteristics. 

3. Entry Criteria 

For treatment trials, entry criteria should include documented influenza in the community and 

occurrence of influenza-like symptoms. Laboratory confirmation generally is not available at the 

time treatment is initiated. 

Incorporation of a rapid test into the entry criteria might lead to a more reliably influenzainfected population for analysis (as later confirmed by polymerase chain reaction (PCR), culture, 

or serologic titres). However, all of the currently available rapid tests have limitations, and the 

positive and negative predictive values of some rapid tests may not be much better than those of 

clinical screening criteria during a seasonal epidemic. Novel influenza strains may have 

different test performance and/or different optimal sampling sites that may not be predictable 

from trials with previously circulating strains. We recommend enrollment based upon clinical 

symptoms followed by confirmation with a sensitive and specific RT-PCR diagnostic assay at a 

central laboratory. 

Vaccination status can be an entry criteria or a stratification factor, and is likely to affect efficacy 

outcomes. The likelihood of detecting treatment benefit in a highly vaccinated population may 

be decreased because the incidence and severity of illness may be reduced. However, such 

likelihood may be increased if pre-existing immunity and drug treatment are additive or 

synergistic, as some trials suggest. Antiviral drugs might theoretically have deleterious effects 

on response to a live-virus influenza vaccine if they are administered in the same time period as 

the vaccine and inhibit replication of the vaccine virus. Therefore, individuals who have recently 

received a live-virus influenza vaccine generally should be excluded from participation. Drug 

effects in response to inactivated vaccine are less likely. Documentation of vaccination status 

and performance of appropriate statistical interaction analyses are important parts of trial design, 

conduct, and interpretation. 

For prophylaxis trials, entry criteria generally should be broad and reflect the population 

intended for use. Most trials will be conducted in otherwise healthy adults. Trials can be 

designed to look at families, college students, or perhaps individuals with underlying health 

conditions in institutionalized settings (e.g., nursing homes). 

4. Blinding 

Double-blinding of treatments is important, given the subjectivity of endpoints and the potential 

for confusion between the natural variability of influenza and the drug effects (either beneficial 

or adverse). 

13 
 

 

Contains Nonbinding Recommendations 

5. Dose Selection and Route of Administration 

Animal studies, challenge trials, and dose-ranging trials in naturally occurring influenza disease 

can all contribute to dose selection for pivotal clinical trials. Exposure-response relationships 

can be assessed in all of these settings. PD parameters, such as those relating to viral clearance, 

also can be explored. As previously noted, we strongly recommend that sponsors conduct 

adequate phase 2 trials before designing the phase 3 trials. 

For some drugs, more than one route of administration can be considered, which may result in 

different dosing, safety, and efficacy issues. For example, an oral form may be desirable for 

uncomplicated influenza, whereas an intravenous formulation may be more desirable for 

seriously ill patients who may not be able to take oral formulations. For inhalational routes, it 

can be challenging to determine appropriate dosing for clinical trials based on nonclinical data. 

In addition, if a novel strain is associated with viral replication in a broader range of organ 

systems than the usual seasonal influenza, an inhalational route may be insufficient to have an 

antiviral effect in organs other than the lungs and respiratory tract. The safety of drugs delivered 

by inhalational routes should be evaluated in subjects with pre-existing pulmonary disease, with 

appropriate safety precautions and monitoring, because individuals with pulmonary disease may 

be at highest risk for both influenza complications and adverse reactions caused by inhalational 

drugs. 

The use of an antiviral drug with an inhalational device for delivery is subject to the FDA 

regulations at 21 CFR part 3, which provide procedures for determining which FDA center has 

primary jurisdiction for a combination product with components potentially subject to review in 

different centers. Generally, combination products are regulated through the Center for Drug 

Evaluation and Research (CDER) because the drug component represents the primary 

mechanism of action of the product. Drug review can involve consultation and collaboration 

across divisions or centers depending on the specific attributes of each component. The sponsor 

of a proposed combination product should ensure that adequate information is provided to the 

FDA about the device as well as the drug in such a combination, including any proprietary 

information that may be needed for review. If there are questions about which center has 

primary jurisdiction, a determination can be requested at the time of initiating interactions with 

the FDA.18 

6. Efficacy Endpoints 

a. General considerations 

Efficacy endpoints can involve combinations of objective measurements, evaluations by health 

care professionals, and patient-reported symptoms. Efficacy endpoints have not been 

definitively standardized for all types of influenza trials; however, duration of defined influenza 

symptoms has been used in registrational trials of acute uncomplicated influenza. There have 

been recent advances in endpoint assessment using patient-reported components of outcome 

18 For more information, contact the Office of Combination Products 

(http://www.fda.gov/CombinationProducts/default.htm). 

14 
 

 

Contains Nonbinding Recommendations 

measurements.19 Because of the variability of influenza illness and drug effects in previous 

trials, most clinical trials warrant examination of multiple secondary endpoints to show 

consistency of effect with the primary endpoint. Rationale for both primary and secondary 

endpoints should be included in protocol submissions and discussed prospectively with the FDA. 

For treatment trials, virologic measurements are important secondary endpoints and can be used 

as components of entry criteria or evaluability. Currently, we do not consider virologic 

endpoints to be appropriate primary endpoints in phase 3 treatment trials because: (1) there is no 

established predictive relationship between magnitude and timing of viral reductions and extent 

of clinical benefit of how a patient “feels, functions, or survives”; (2) optimal sampling site, 

methods including collection procedures, and assays for clinically relevant virologic 

measurements have not been established; and (3) available data suggest substantial variability in 

results and conclusions using different methods for collecting and analyzing virologic data. 

In addition, unlike trials in HIV and hepatitis C virus, influenza clinical outcomes occur in the 

same time frame as virologic changes. Therefore, using virologic endpoints does not shorten 

trial duration. Previous influenza trials do not suggest that virologic endpoints would provide a 

quicker or easier way to distinguish between therapies than direct measurements of clinical 

outcome. Thus, even if more evidence can be collected regarding the predictive value of 

virologic measurements, such measurements would not necessarily reduce the trial size or 

duration, although they could further contribute to secondary analyses. 

Viral assays also contribute to the laboratory confirmation of endpoints in prophylaxis trials. 

Identification of specific viral subtypes and strains also can be valuable for secondary analyses. 

Sponsors should explore the development of methodology for quantitative cultures and 

quantitative RT-PCR at relevant sites, and for assessment of relationships between viral burden 

(including asymptomatic shedding) and secondary transmission. Sponsors should also provide 

assay performance data with currently circulating strains to support the use of the proposed 

assays in their trials. 

In trials of acute uncomplicated influenza, concomitant use of symptomatic relief medications 

may make the endpoint evaluation more difficult. Confounding caused by concomitant 

medicines may be mitigated if protocols are standardized to measure their administration. 

Alternatively, a standardized regimen of symptom relief medication (e.g., acetaminophen) may 

be used as an active comparator to an influenza antiviral drug in a superiority design trial. 

If sponsors propose claims of reduction in complications, objective criteria should be delineated 

and justified prospectively. Information on the specifics of diagnosis and management should be 

collected in the protocol. 

b. Treatment of acute uncomplicated illness 

The primary endpoint in treatment trials in adults for acute uncomplicated influenza should be 

the time to a pre-defined level of symptom improvement. Components of the primary endpoint 

19 See the guidance for industry Patient-Reported Outcome Measures: Use in Medical Product Development to 

Support Labeling Claims. 

15 
Contains Nonbinding Recommendations 

should include fever with a constellation of symptoms (e.g., cough, coryza, headache, body 

aches, sore throat). This clinical symptom endpoint is not considered a surrogate endpoint 

because it measures clinically relevant symptoms associated with influenza. For treatment of 

acute illness in otherwise healthy individuals, demonstrating reductions in secondary 

complications or mortality is not necessary for an antiviral to be considered clinically useful. 

Secondary clinical endpoints should be time to return to normal activity, and time to resolution 

of fever, and/or other individual symptoms included in the primary endpoint. The emergence of 

drug resistance is an important tertiary endpoint in all influenza trials. 

Sponsors should provide justification for a standardized and/or well-accepted instrument for 

symptom measurement. We discourage adding scores for different symptom types into an 

aggregate score or area under the curve of symptoms. We consider these analyses exploratory 

because it is difficult to equate the units of severity of different symptoms. 

The population for both the primary analysis and additional analyses should include all subjects 

with confirmed influenza (i.e., intent-to-treat (ITT) infected population). Exploratory analyses of 

on-treatment or per-protocol populations may be used to identify problems with dosing 

approaches or instructions. 

c. Treatment of seriously ill hospitalized patients 

For seriously ill influenza patients requiring hospitalization, a primary endpoint should include 

clinical signs and symptoms, duration of hospitalization, time to normalization of vital signs and 

oxygenation, requirements for supplemental oxygen or assisted ventilation, and mortality. 

Choice of endpoint may depend on the clinical setting and/or viral strains. A single best 

endpoint has not been identified in seriously ill hospitalized patients, and clinical trial proposals 

should be provided for advance discussion. Sponsors are encouraged to provide evidence for the 

ability of their proposed endpoint to directly measure how a patient feels, functions, or survives, 

taking into account all relevant documentation from literature sources and clinical trials. Such 

endpoint is intended to demonstrate whether the candidate drug produces a more rapid and/or 

more complete improvement in the condition of the patient compared to the control. Further 

developmental work to evaluate the most relevant clinical endpoint for assessing benefit in trials 

of serious influenza treatment is needed and strongly encouraged. 

d. Prophylaxis 

The primary endpoint for prophylaxis trials should be the occurrence of symptomatic, 

laboratory-confirmed influenza. Symptom diaries, along with serology and targeted cultures or 

nucleic acid amplification tests (NAATs), have been used to identify laboratory-confirmed cases 

of symptomatic influenza. Additional analysis of all subjects with influenza-like symptoms 

(with or without laboratory confirmation) can be a useful secondary endpoint. However, such 

approach may include noninfluenza illnesses with symptoms similar to influenza that are not 

susceptible to anti-influenza drugs, and would presumably reduce the effect size. 

We recommend a secondary analysis that compares the prophylactic effect of all subjects (both 

symptomatic and asymptomatic) with laboratory evidence of influenza infection. However, the 

16 
Contains Nonbinding Recommendations 

clinical benefit of preventing asymptomatic infection is unclear, because the goal of influenza 

prophylaxis is to prevent symptomatic illness, and not just asymptomatic laboratory-identified 

seroconversion. On the one hand, it may be preferable to avoid infection altogether because 

asymptomatically infected persons might shed and transmit virus despite the presence of the 

prophylactic drug. On the other hand, asymptomatic infection may offer protection against 

illness if a new exposure occurs after subjects have stopped taking a prophylactic drug. 

In addition to the primary objective of preventing symptomatic influenza illness, there is interest 

in ascertaining whether disease is milder in persons who develop it while receiving prophylaxis 

compared to persons not receiving prophylaxis. This outcome may be difficult to assess in most 

prophylaxis trials because of the relatively low numbers of breakthrough cases among 

individuals receiving active antiviral drugs. However, if appropriate collection of symptom 

information is prospectively included during protocol planning, such severity-of-illness 

comparison can be a useful analysis for potentially supporting additional statements in product 

labeling. 

e. Reduction in complications 

Findings and symptoms that are part of influenza illness should not be considered separate 

complications if they are part of a multicomponent principal endpoint. Bacterial infection 

complications should meet pre-defined criteria according to appropriate expert guidelines. For 

example, a clinical diagnosis of bronchitis may be part of the clinical spectrum of influenza 

itself, and may not meet the criteria for a secondary bacterial infection. We encourage sponsors 

to propose prospectively definitions of potential serious outcomes for secondary analysis, 

including those outcomes expected to occur with low frequency and therefore not likely to have 

sufficient event numbers for primary analysis. Methods of diagnosis and confirmation of 

secondary infections should be described in detail in the protocol and be consistent across all 

trial sites. Diagnoses of secondary complications should be confirmed by objective clinical, 

laboratory, and medical imaging findings as appropriate. In the absence of such objective 

confirmation, labeling statements regarding efficacy claims for the prevention of secondary 

complications are unlikely. 

7. Trial Procedures and Timing of Assessments 

Intensive clinical assessment is important in the period shortly after treatment initiation in 

treatment trials and presumed exposure in prophylaxis trials. The typical self-limited disease 

course may limit the ability to detect treatment effects at later time points. Prophylaxis and 

treatment trials should include sufficiently long follow-up to detect symptom recurrence after 

temporary improvement, late adverse events, or emergence of resistant virus. Protocols should 

include frequent self-assessments (e.g., use of diary cards), along with observer assessments at 

less frequent intervals or as triggered by self-assessment results. Self-assessments should 

continue until resolution of all clinical signs and symptoms. For trials in hospitalized patients, 

some aspects of clinical assessment may be suitable for frequent measurement, and/or may be 

routinely recorded in hospital medical records and available for analysis, especially during the 

initial period of acute illness. Self-reporting of symptoms may become more important in 

patients who are improving but still symptomatic. 

17 
 

 

 

 

Contains Nonbinding Recommendations 

Available in vitro diagnostic tests for influenza, ranging from research laboratory procedures to 

marketed test kits, use multiple methods, and require anywhere from minutes to days to 

complete. Marketed test kits for influenza are regulated by the Center for Devices and 

Radiological Health (CDRH), and include several rapid tests designed to detect viral antigens or 

enzyme activity within 30 minutes.20 The ability to obtain specific types of diagnostic 

specimens, and to achieve the desired test sensitivity and specificity in the setting of infection, 

may vary with factors such as severity of disease, patient age, treatment timing, collection 

technique, and characteristics of novel viral strains, such as principal anatomic distribution and 

sites of viral replication. Currently, FDA-cleared rapid tests for influenza can be labeled as 

detecting influenza A, detecting influenza A and B without distinguishing between the two types, 

or detecting and distinguishing between influenza A and B. One subtype-specific NAAT for 

H5N1 has been recently cleared. Tests labeled for influenza A (or A and B) may detect a 

number of subtypes in analytic testing. However, clinical experience is limited to the subtypes 

and strains circulating at the time when trials supporting the FDA clearance of the tests were 

conducted. 

Although results would likely not be available at trial entry, we recommend inclusion of a 

sensitive and specific assay (e.g., real-time RT-PCR assay) for laboratory confirmation of 

influenza infection to assist in defining the infected population for trial analyses in influenza 

treatment trials. 

We consider diagnostic and monitoring assays that are used in a clinical trial but have not been 

cleared by the FDA to be investigational. Drug sponsors should provide sufficient information 

on the methodology and performance of such assays to allow the FDA to evaluate the 

appropriateness of the assays for their intended use. Use of an investigational assay in a clinical 

trial does not constitute FDA clearance or endorsement of the assay. If a diagnostic assay 

proposed for use in a clinical trial has not been previously cleared by the FDA but eventually 

may be developed for commercial distribution, the sponsor should consider early discussions 

with CDRH as well as CDER to facilitate collaborative or consultative review and comment as 

appropriate. 

In trials designed to evaluate the efficacy of an anti-influenza drug for treatment, viral influenza 

cultures (i.e., nose and/or throat swabs or nasal wash) should be performed at baseline (before 

dosing) and at appropriate intervals during and after drug treatment. Duration of viral shedding 

is a valuable secondary endpoint but may be difficult to determine if cultures are performed 

infrequently. Measurement of anti-influenza antibodies should be performed at baseline and 

20 CDRH regulates in vitro diagnostic tests for influenza and has published the following guidances for industry and 

FDA staff on its Web site at http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/default.htm: In 

Vitro Diagnostic Devices to Detect Influenza A Viruses: Labeling and Regulatory Path and Establishing the 

Performance Characteristics of In Vitro Diagnostic Devices for the Detection or Detection and Differentiation of 

Influenza Viruses on development of influenza diagnostics (when final, this guidance will represent the FDA’s 

current thinking on this topic), and a Laboratory Safety Tip, Cautions in Using Rapid Tests for Detecting Influenza 

A Viruses 

(http://www.fda.gov/MedicalDevices/Safety/AlertsandNotices/TipsandArticlesonDeviceSafety/ucm109356.htm), 

that discusses cautions in the use of rapid influenza tests that can detect influenza virus antigens or viral enzyme 

activity within 30 minutes. 

18 
 

 

Contains Nonbinding Recommendations 

during follow-up, preferably about 4 weeks after diagnosis. Serology should use standardized 

methodology, and supporting information for the assay should be provided in advance. 

Seroconversion response to influenza antigens is assessed as an increase by a factor of 4 or 

greater to assist in confirming influenza diagnosis in treatment trials, and as part of the outcome 

definition of laboratory-confirmed symptomatic influenza in prophylaxis trials. Therefore, it is 

important to assess whether an antiviral drug interferes with antibody response once infection is 

established in treatment trials and to evaluate the extent of effects on seroconversion in 

prophylaxis trials. 

Subtyping and genotyping may be important for exploration of relationships between viral type 

and treatment, and for identification of sources of viral transmission in trials of prophylaxis. 

Baseline susceptibility and emergence of resistance to the trial drug should be examined in 

clinical trials, regardless of trial designs. If standardized and generally accepted susceptibility 

testing methods are not available, samples should be retained for future testing until the trial has 

been completed and data have been analyzed. In some instances, more than one approach to 

susceptibility testing may be warranted. For example, enzyme inhibition assays may be useful in 

screening samples but may generate different results from virus yield assays; yet both may be 

important for the assessment of drug resistance. Recent trials have shown higher rates of 

resistance to influenza drugs when a clonal analysis is employed. We recommend that resistance 

be evaluated early in development to better inform phase 3 protocol design. Sponsors should 

consult existing guidance on virology studies and submission of resistance data for aspects 

relevant to influenza.21 

Interactions between vaccines and antiviral drugs may warrant consideration in some trial 

designs. Timing of serum sample collections to assess seroconversion should be considered to 

distinguish between antibody responses to vaccine and infection-related seroconversion as a 

diagnostic confirmation. 

Sponsors should provide detailed viral resistance monitoring plans that describe proposed 

analyses, sample collection timing, assay characteristics with different influenza types and 

subtypes, and assay methodologies. Such plans should be provided to the FDA for review early 

in development, and updates to the plans should be discussed at appropriate intervals during 

development. The issue of relative fitness of resistant viruses should be approached with great 

caution, given the complexity of potential determinants of infectivity and virulence, and the 

potential for multiple mutations with diverse and sometimes compensatory consequences. 

8. Statistical Considerations for Phase 3 Trials 

Sponsors should provide a protocol with a statistical analysis plan for review for FDA 

concurrence before subject enrollment. 

21 See the guidance for industry Antiviral Product Development — Conducting and Submitting Virology Studies to 

the Agency and its attachment Guidance for Submitting Influenza Resistance Data. 

19 
Contains Nonbinding Recommendations 

a. Treatment trials 

The primary efficacy analyses should focus on the population with laboratory-confirmed 

influenza, a baseline characteristic even if it is not defined until after baseline data are collected. 

The primary endpoint in treatment trials in adults for acute uncomplicated influenza illness 

should be the time to a pre-defined level of symptom improvement. Analyses of safety data 

should be based on all randomized subjects given the likelihood that treatment decisions in 

clinical practice would be made before confirmation of diagnosis. 

The unit of randomization and analysis in such trials is the individual trial subject. We 

recommend stratification by time since onset of symptoms when there is a sufficiently wide 

window for enrollment to make this stratification meaningful. Consideration of other possible 

stratification variables also can be useful when a trial is to be conducted in a heterogeneous 

population in which specific characteristics such as viral strain, smoking status, location, or the 

use of nonprescription symptom relief medication or other concomitant treatments might affect 

the natural history of illness and/or the magnitude of treatment effect. 

Sponsors should avoid censoring subjects in the ITT infected population in these short-term 

trials. There should be an explicit and adequate plan to address issues relating to missing data. 

b. Prophylaxis trials 

In prophylaxis trials, the primary endpoint should be the occurrence of symptomatic, laboratoryconfirmed influenza. 

Examples of populations that can be enrolled in prophylaxis trials, each with its own design and 

analysis considerations, include households, communities of healthy adults, and nursing homes. 

•	 Households. Households with multiple members in the appropriate age categories 

should be identified and screened in advance. When an index case is reported in a 

screened household, that household should be randomized to one treatment arm. There 

are three possible designs, as follows: 

1.	 Index cases are untreated and all contacts in a household are randomized to the same 

treatment, either placebo or candidate drug 

2.	 Index cases are treated and all contacts in a household are randomized to different 

treatments, which could be placebo or candidate drug 

3.	 Factorial trials with four arms are conducted that include all four combinations of 

index cases (treated or untreated) and contact cases (treated or untreated): 

− Index treated and contacts given prophylaxis (with candidate drug) 

− Index treated and contacts given placebo 

− Index untreated and contacts given prophylaxis (with candidate drug) 

− Index untreated and contacts given placebo 

20 
Contains Nonbinding Recommendations 

The second design is a less powerful test of prophylaxis than the first design if treating 

the index case reduces the risk of influenza infection to the contact cases. The third 

design is recommended if one wishes to assess the benefit of: (1) index case treatment on 

contact case risk; and (2) contact case prophylaxis. 

In household trials, the entire household is both the randomized unit and the unit of 

analysis. The primary efficacy analysis should compare the treatment groups for the 

percentage of households in which at least one randomized contact case developed 

symptomatic, laboratory-confirmed influenza. In other words, if one contact case in the 

household becomes symptomatically infected, the household is counted as infected. If 

none of the contact cases becomes infected, the household is considered not infected. 

Secondary analyses also can compare the percentage of contact cases that had 

symptomatic, laboratory-confirmed influenza in the active and placebo treatment groups. 

Designs in which different contact cases in the same household receive different 

regimens raise concerns of drug sharing and intrahousehold correlation. Analysis using 

individual contact cases as the unit of analysis also may cause similar problems. 

Stratification on the size of household can be used, but is not expected to produce any 

consequential increase in power. 

•	 Communities of healthy adults. For community trials with healthy adults (e.g., trials 

conducted in college campuses), subjects should be screened at the beginning of the flu 

season and randomized to control or test prophylaxis arms when there is occurrence of a 

predefined epidemiological signal that an influenza epidemic is underway in the target 

community, or in a larger community (e.g., the county where the college campus is 

located). 

•	 Nursing homes. For trials in nursing homes, screening, randomization, and analysis 

should be similar to those for trials in communities of healthy adults. Nursing home trials 

should involve more careful definition and monitoring of clinical endpoints because 

subjects may lack mental acuity for self-assessment and staff need to monitor many 

aspects of all subjects’ health. These concerns should be considered in treatment trials in 

nursing homes as well. 

In prophylaxis trials in nursing homes and other community dwellings, the individual 

trial subject is both the unit of randomization and the unit of analysis. 

Statistical power in prophylaxis trials depends on the number of protocol-defined endpoint 

outcomes (i.e., symptomatic, laboratory-confirmed infection) and the effect size of the 

intervention, rather than the number of subjects enrolled. Therefore, the sample size of 

prophylaxis trials should be based on the number of such outcomes expected and a conservative 

estimate of effect size. Because incidence of influenza varies unpredictably from year to year, 

the number of subjects in a community prophylaxis trial during one flu season may yield fewer 

than the expected number of influenza illnesses. We recommend monitoring total number of 

influenza cases to determine whether it is lower than expected. It is appropriate to continue the 

21 
Contains Nonbinding Recommendations 

trial into a second flu season if influenza attack rates are low, even if such continuation was not 

initially specified in the protocol. There should be no unblinding of results at the end of the first 

season if the total number of influenza illnesses is still inadequate at that point. 

For prophylaxis trials, principal analyses and power calculations can be based on the odds ratio 

or relative risk comparing the prophylaxis failures (i.e., symptomatic, laboratory-confirmed 

influenza) between the treatment arms. Because failures tend to be few in the active prophylaxis 

arms, exact statistical procedures should be used instead of normal approximations for 

inferences. 

Minimizing missing data is important in prophylaxis trials that have a small number of treatment 

outcomes. Investigators should be diligent in obtaining the final status of subjects either on or 

off the assigned treatment, regardless of whether they are in the trial or have been terminated 

from the trial. If a subject does not come back for evaluation after the sponsor has exhausted all 

reasonable means to persuade the subject to do so, the following information should be collected 

and documented: the subject’s status (e.g., whether alive or not), a description by the subject and 

his or her contacts of the subject’s flu symptoms and adverse events, and the general well-being. 

Subjects with diary cards that are missing data for several days (i.e., less than 1 week) and 

subjects with negative laboratory confirmation who miss their follow-up serology assessment 

should be considered to have missing data. Subjects with missing data in community and 

nursing home trials are counted as not having symptomatic, laboratory-confirmed influenza in 

the primary analysis. A household with no confirmed cases of influenza that has at least one 

contact case withdrawn from the trial should be defined as a household with missing data. 

Households with missing data and no identified influenza cases are counted as not having 

symptomatic, laboratory-confirmed influenza in the primary analysis. 

Because prophylaxis failures are defined based on flu symptoms and laboratory confirmation 

with viral assays, the source of these symptoms and the performance of these assays will have an 

effect on the observed failures and, therefore, on the trial power and analysis. The assay 

specificity (i.e., the assay’s ability to classify a sample as negative when it is truly negative) is 

likely to have the most influence. The use of a highly specific and sensitive assay or assays 

(such as RT-PCR) is of great importance in increasing trial power. Sponsors should provide a 

detailed description of the assay’s methodology and supporting sensitivity and specificity data 

with isolates representing the diversity of influenza viruses. 

Sponsors must ensure that pertinent investigational records such as diary cards and copies of the 

original laboratory sheets are retained so that they are available at the time of any FDA 

inspection (21 CFR 312.62(c)). 

9. Accelerated Approval (Subpart H) Considerations 

The criteria described in regulations in 21 CFR part 314, subpart H (accelerated approval based 

on a surrogate endpoint considered reasonably likely to predict clinical benefit in patients with a 

22 
 

Contains Nonbinding Recommendations 

serious or life-threatening disease)22 have not been used for approval of influenza antivirals, and 

are unlikely to be appropriate in most instances, because typical influenza clinical trials involve 

direct assessment of immediate clinical outcomes for an acute uncomplicated illness. In 

addition, virologic parameters have not been shown to reliably predict clinical outcomes in 

influenza trials. If situations arise in which sponsors wish to propose development under 

accelerated approval regulations, the proposals submitted for discussion and feedback should 

address the issues related to efficacy assessment and endpoint selection outlined in other sections 

of this guidance, and should also indicate how the subpart H requirements for subsequent clinical 

endpoint confirmation of benefit would be fulfilled. 

10. Risk-Benefit Considerations 

The balance between potential risks and benefits of influenza interventions has been discussed 

elsewhere in this guidance, and should be considered throughout the influenza drug development 

process. Risk-benefit considerations are likely to be affected by the public health need (e.g., 

severity of an influenza epidemic or pandemic, virulence of circulating influenza strains, 

epidemiology of illness and complications, and availability of vaccine), the status of antiviral 

drug and vaccine supplies, and the apparent effect of other available anti-influenza drugs. 

Emergence of drug resistance and viral strain susceptibility should also be part of risk-benefit 

assessments. 

C. Other Considerations 

1. Relevant Nonclinical Safety Considerations 

Although influenza treatment is usually short-term and prophylaxis often lasts no more than a 

few weeks, the possibility of multiple courses of treatment or prophylaxis over a series of 

influenza seasons should be taken into account in determining the nature and duration of 

nonclinical safety studies. For instance, if the indication for a drug is treatment of influenza, 

long-term carcinogenicity studies in rodents usually are not needed. If, on the other hand, the 

drug is indicated for the prophylaxis of influenza, carcinogenicity studies in rats and mice should 

be carried out before approval because drugs used frequently in an intermittent manner in the 

treatment of chronic or recurrent conditions generally should be supported by such studies. The 

ICH guidance for industry S1A The Need for Long-Term Rodent Carcinogenicity Studies of 

Pharmaceuticals provides detailed information concerning the conditions under which 

carcinogenicity studies should be conducted. 

2. PK and PD Considerations 

a. PK measurement 

Several administration routes have been considered for influenza drugs: oral, parenteral, 

inhalation, and intranasal. For oral and parenteral administration, plasma drug concentrations are 

presumed to be correlated with concentrations at site of action, although prediction of clinical 

22 Similar considerations apply to therapeutic proteins or monoclonal antibodies that might be proposed for 

development under the corresponding biologics regulations in 21 CFR part 601, subpart E. 

23 
 

Contains Nonbinding Recommendations 

effect cannot be assumed in this setting. However, for inhalation and intranasal administration in 

prophylaxis or in treatment of typical influenza, drug concentrations at the epithelial layer of 

trachea, bronchi, bronchioles, and lung may better correlate with the drug’s antiviral activity. 

Avian influenza or novel influenza strains may have a tendency to replicate outside the 

respiratory system, necessitating systemic exposure of an antiviral drug. 

Concentrations in the nasal cavity, respiratory tract, and lung can be estimated from nasal wash, 

sputum (by sputum induction), and bronchioalveolar lavage, respectively. Imaging also can be 

applied during influenza drug development. Technetium-99 scintigraphy is a technology 

currently used to quantify the percentage of dose or mass of drug deposited in the lungs, 

oropharynx, and nasopharyngeal cavity after inhalation or nasal drug delivery. The main 

purpose of a technetium-99 scintigraphy study is to select devices, formulations, and 

administration routes during drug development. Fluorescent imaging (e.g., fluorine-19 imaging) 

may estimate drug concentrations in the respiratory tract. All of the above methods are 

somewhat exploratory and have not been shown to be directly suitable for regulatory purposes 

such as labeling or approval decisions. However, comparing drug concentrations in a targeted 

organ to cell culture EC50 values or antiviral activity data from animals with similar 

concentrations in a targeted organ may help select doses for clinical trials. 

b. PD measurement 

Virologic response or clinical endpoints can be used as response metrics in the exposureresponse evaluations. Viral titer in nasal wash has been used as a measure of virologic response; 

however, viral titer reduction in nasal wash should not be used as a primary endpoint supporting 

drug approval. For prophylaxis trials, the clinical endpoint should be used (i.e., percentage of 

subjects developing symptomatic, laboratory-confirmed influenza during prophylaxis). 

Relationships between each of these assessments and the primary efficacy endpoints should be 

assessed based on all available data. 

Viral samples from the throat and rectum can be analyzed for sporadic human infections with 

avian influenza strains, because avian influenza viruses generally show highest affinities for α-2-

3 linked sialic acid, which is the dominating receptor type in epithelial tissues of gut and lung in 

influenza-infected birds. In addition, there have been recent human avian influenza case reports 

of gastroenteritis without respiratory symptoms.23 If additional novel strains of influenza (of 

avian or other origin) show other patterns of viral distribution, other sample types might be 

considered if appropriate. 

Any drug exposure-related toxicity should be explored to assess the relationship of exposure to 

the adverse event, to define the highest tolerable exposure, and to determine the probability of an 

adverse event with a given exposure. This information can also guide dose adjustments for 

special populations. 

23 Beigel, JH, 2005, Avian Influenza A (H5N1) Infections in Humans, N Engl J Med, 353-1374-85. 

24 
Contains Nonbinding Recommendations 

c. Modeling considerations 

Exposure-response modeling of phase 2 and/or phase 3 data should be included in a new drug 

application (NDA) to characterize relationships between drug concentrations and efficacy and 

safety. Data from cell cultures, animal studies, and from trials of other drugs from the same class 

should be considered when an exposure-response model is developed. Disease progression and 

response in a placebo group should be incorporated into the modeling. Demographic data (e.g., 

sex, race, age, body weight, and vaccination status) should be collected and incorporated into the 

exposure-response model. To increase understanding of exposure-response relationships, we 

recommend collection of viral genotype information to assess relationships between genetic 

variants (genotypes), exposure, and response outcomes, such as drug response, efficacy, safety, 

toxicity, and overall survival. If measurable baseline factors are deemed to be clinically 

significant covariates, dose adjustment and individualization may need to be considered. 

3. Labeling Considerations 

Patient labeling is important for influenza drugs because of the possibility of extensive use by 

persons unfamiliar with the drugs. Whether a patient package insert or MedGuide should be 

considered for this purpose depends on the extent of safety concerns and the specific 

circumstances expected for use. If the drug may be purchased for stockpiling, see section 

III.C.6., Stockpiled Drug Products, for labeling issues related to stockpiled drugs. 

4. Animal Rule (Subpart I) and Animal Model Considerations 

Because of the intense interest in the use of animal models for influenza drug development, this 

section discusses several specific uses of animal data. 

Data from animal studies can provide supporting information for human trial design or, in some 

cases, supportive information contributing to regulatory decisions (see examples in section 

III.A.1., Nonclinical and Early Phase Clinical Development Considerations). Together with 

ongoing clinical trial development plans, animal data also can facilitate access to investigational 

drugs under IND or emergency use authorization (EUA) mechanisms. However, because human 

clinical trials in influenza are feasible, ethical, and the best approach for characterizing safety 

and efficacy, the animal rule (21 CFR 314, subpart I, and corresponding biologics regulations in 

21 CFR 601, subpart H) is not an appropriate mechanism for approval of influenza drugs. 

Animal models in general have not been fully characterized or shown to be reliably predictive 

for influenza. Even though the value of clinical trial data of previous strains in predicting 

outcomes for novel strains is uncertain, it is not clear that animal data with a new prevalent strain 

would be more useful than clinical data of previous strains. In addition, a strain used in animal 

studies may differ substantially from the strain that subsequently causes widespread human 

illness or a pandemic. Thus, treatment trials in virus-challenged animals are not a substitute for 

clinical trials. 

25 
Contains Nonbinding Recommendations 

5. Emergency Access Considerations 

a. IND use 

To prepare for use of antiviral drugs in a potential public health emergency, we encourage 

sponsors of approved or investigational antiviral drugs to prepare protocols that might be 

adaptable in a pandemic or other emergency setting and that can be rapidly finalized and 

implemented in a form appropriate to the circumstances. These protocols should be designed 

both to guide use of the drug and to collect data that can contribute to improvements in use, 

including support for assessment of both efficacy and safety wherever appropriate. However, 

given the conditions under which the drug may be administered in these protocols, protocol 

design should be simple and streamlined to answer a few relatively simple questions. Reasons 

for advance preparation of such protocols for use in an emergency situation include: 

•	 Advance consideration of protocols may help facilitate emergency readiness and data 

collection 

•	 Protocols may benefit patients in an emergency by guiding clinical decisions about the 

continuation or modification of treatment interventions 

•	 Protocols may support revisions of other ongoing protocols or development of future 

protocols 

•	 Protocols may help avoid continued diversion of resources into use of investigational 

interventions that subsequently show lack of efficacy or unacceptable toxicity 

•	 Protocols may enhance understanding of other potentially important interventions as the 

pandemic extends through its phases 

•	 Protocols may remind health care professionals of dose adjustments and basic safety 

follow-up that can contribute to patient management and draw attention to major new 

safety or resistance concerns that can improve management of subsequent patients 

•	 Data from a suitably designed protocol in an emergency situation may help support future 

regulatory actions 

When designing protocols, sponsors should consider collection of natural history information for 

illness caused by a novel strain, flexible designs to encompass widespread mild or severe 

disease, and incorporation of monitoring and stopping rules to facilitate trial modification as 

more is learned about a novel viral strain and associated disease. 

b. Emergency use authorization 

The Project BioShield Act (Public Law 108-276) permits the FDA to authorize the use of an 

unapproved drug or the unapproved use of an approved drug in an actual or potential emergency 

during the effective period of a declaration of an emergency. An EUA may be issued for a 

26 
 

Contains Nonbinding Recommendations 

specific drug if the totality of available scientific evidence indicates that it may be effective for 

diagnosing, preventing, or treating a serious or life-threatening disease or condition.24 We 

anticipate that drugs considered for use under an EUA will have substantially more data than that 

required to support administration to subjects under an early IND protocol so that an appropriate 

risk-benefit evaluation can be made to decide whether an EUA is justified. 

In most instances, the route toward use of a drug under an EUA includes both nonclinical studies 

and clinical trials directed toward influenza drug development. Information from studies in 

animal models, or human challenge trials, in combination with other human clinical trial data 

appropriate to the development stage, contribute to the evaluation of an EUA proposal. EUA 

proposals should contain sufficient information to justify dosing regimens and potential for 

antiviral activity and clinical benefit, and to evaluate potential risks. In EUA proposals, it is also 

important to consider dosing recommendations for populations such as children, pregnant 

women, and individuals with renal insufficiency that may be at higher risk of influenza 

complications. If a potential EUA requestor believes consideration of EUA status is warranted, 

the potential requestor is encouraged to contact the FDA as early as possible, to provide data in 

support of such consideration, and to engage in pre-EUA interactions with the FDA. Such 

interactions can identify additional types of information that might be important to support the 

EUA consideration. Use of a drug under an EUA is not a clinical trial and does not take the 

place of continuing clinical trials to provide information in support of eventual submission of an 

NDA. 

Although INDs and EUAs might be considered either for new antiviral drugs or for new uses of 

existing drugs, the amount of new information needed may differ depending on prior experience 

with the drug, as well as factors such as the intended population (e.g., treatment of seriously ill 

patients without other treatment options versus prophylaxis of low-risk persons likely to have 

good outcome without treatment). 

6. Stockpiled Drug Products 

Approved drugs, or investigational drugs with sufficient safety and efficacy data to consider 

widespread investigational use, can be considered for stockpiling by appropriate entities. We do 

not make decisions regarding selection or purchase of drugs for stockpiling. However, we will 

review sponsor proposals for stockpile-specific manufacturing, labeling, and packaging. 

Information collected during initial trials can be used to develop simplified instructions for 

potential use during a pandemic. The instructions on the container label may need to be assessed 

for clarity based on the anticipated distribution modes and whether it will be possible to provide 

additional instructions (e.g., depending on the course of a specific emergency situation it may not 

be possible for a health care professional to provide appropriate counseling). The inclusion of 

tear-off panels with lot information for record keeping purposes may be useful in some stockpile 

situations. 

Sponsors who wish to propose stockpile-related packaging or instructions should provide 

information about concerns from potential purchasers that affect their packaging or labeling 

24 See the guidance Emergency Use Authorization of Medical Products 

(http://www.fda.gov/RegulatoryInformation/Guidances/ucm125127.htm). 

27 
 

 

Contains Nonbinding Recommendations 

proposals. Documentation should be provided to show how the submitted proposal addresses 

priorities expressed by specified potential purchasers and how the purchasers together with the 

sponsor plan to manage any pitfalls associated with the proposed packaging or instructions. For 

additional packaging issues for stockpiled drugs, see section III.C.7., CMC Considerations, and 

the interim final rule “Exceptions or Alternatives to Labeling Requirements for Products Held by 

the Strategic National Stockpile” (72 FR 73589, December 28, 2007). 

7. CMC Considerations 

We anticipate that the chemistry, manufacturing, and controls (CMC) data for influenza drugs 

will be comparable to the CMC data for other drugs with similar uses and administration.25 We 

strongly recommend a quality-by-design approach to drug development, as well as the principles 

described in ICH guidances for industry,26 although allowances can be made in situations of dire 

need (e.g., reduced or modified expectation for stability data). 

Special CMC considerations may arise for drugs intended for stockpiling. For example, because 

the distribution of stockpiled drugs during some types of pandemic conditions may take place 

rapidly and under less than ideal conditions, it may be advantageous to package such drugs in 

configurations that can be readily dispensed. This type of packaging can include drugs in unitof-use bottles instead of bulk packs that require a pharmacist to dispense the appropriate number 

of tablets or capsules. Similarly, stockpiled drugs that are not taken orally might be packaged in 

kit configurations that include all associated paraphernalia such as diluents, syringes, needles, 

and delivery devices to facilitate quick drug delivery in remote conditions or under emergency 

conditions. Assembly of such a kit from separately stored components may not be feasible 

during some types of pandemic situations. Another factor that can be considered is the use of 

packaging presentations that can be readily relabeled if the expiration dating period of the 

stockpiled drug is extended (e.g., the use of bottles instead of blister packages). 

If specific packaging configurations are developed, they should be described clearly and a 

scientific justification should be provided for their selection. Stability studies should adequately 

address all climate zones where the drug may potentially be stockpiled. Temperature cycling 

studies and humidity variation studies should be carried out to support temperature excursions 

and humidity changes that are typically encountered during stockpiling. 

25 General guidance pertaining to CMC of drug development can be found on the FDA Drugs guidance Web page at 

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

26 See the ICH guidances for industry Q8(R2) Pharmaceutical Development, Q10 Pharmaceutical Quality System, 

and Q9 Quality Risk Management. 

28 
 

Contains Nonbinding Recommendations 

REFERENCES27 

Guidances relevant to general safety and efficacy determinations 

Draft guidance for industry Non-Inferiority Clinical Trials28 

Guidance for clinical trial sponsors Establishment and Operation of Clinical Trial Data 

Monitoring Committees 

Guidance for industry Acceptance of Foreign Clinical Studies 

Guidance for industry Content and Format of Investigational New Drug Applications (INDs) for 

Phase 1 Studies of Drugs, Including Well-Characterized, Therapeutic, Biotechnology-Derived 

Products 

Guidance for industry Patient-Reported Outcome Measures: Use in Medical Product 

Development to Support Labeling Claims 

Guidance for industry Providing Clinical Evidence of Effectiveness for Human Drug and 

Biological Products 

Guidance for industry Using a Centralized IRB Review Process in Multicenter Clinical Trials 

ICH guidance for industry E1A The Extent of Population Exposure to Assess Clinical Safety: 

For Drugs Intended for Long-Term Treatment of Non-Life-Threatening Conditions 

Guidances relevant to clinical pharmacology and exposure-response assessments 

Guidance for industry Exposure-Response Relationships — Study Design, Data Analysis, and 

Regulatory Applications 

Guidance for industry Population Pharmacokinetics 

Guidances relevant to nondrug influenza interventions (vaccines and diagnostics)29 

Guidance for industry Clinical Data Needed to Support the Licensure of Pandemic Influenza Vaccines 

(http://www.fda.gov/BiologicsBloodVaccines/GuidanceComplianceRegulatoryInformation/default.ht 

m) 

27 These guidances can be found on the FDA Drugs guidance Web page at 

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

noted. 

28 When final, this guidance will represent the FDA’s current thinking on this topic. 

29 In addition to these guidances, see the CDRH Laboratory Safety Tip, Cautions in Using Rapid Tests for Detecting 

Influenza A Viruses 

(http://www.fda.gov/MedicalDevices/Safety/AlertsandNotices/TipsandArticlesonDeviceSafety/ucm109356.htm). 

29 
 

 

Contains Nonbinding Recommendations 

Guidance for industry Clinical Data Needed to Support the Licensure of Seasonal Inactivated 

Influenza Vaccines 

(http://www.fda.gov/BiologicsBloodVaccines/GuidanceComplianceRegulatoryInformation/defa 

ult.htm) 

Draft guidance for industry and FDA staff Establishing the Performance Characteristics of In 

Vitro Diagnostic Devices for the Detection or Detection and Differentiation of Influenza Viruses 

(http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/default.htm)30 

Guidance for industry and FDA Staff In Vitro Diagnostic 2009 H1N1 Tests for Use in the 2009 

H1N1 Emergency 

(http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/default.htm) 

Guidance for industry and FDA staff In Vitro Diagnostic Devices to Detect Influenza A Viruses: 

Labeling and Regulatory Path 

(http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/default.htm) 

Guidance for industry and FDA staff — Class II Special Controls Guidance Document: 

Reagents for Detection of Specific Novel Influenza A Viruses 

(http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/ucm0 

78583.htm) 

Guidance relevant to virologic assessments 

Guidance for industry Antiviral Product Development — Conducting and Submitting Virology 

Studies to the Agency and its attachment Guidance for Submitting Influenza Resistance Data 

Guidances relevant to expediting review processes and access to investigational drugs in 

settings of public health need 

Guidance Emergency Use Authorization of Medical Products 

(http://www.fda.gov/RegulatoryInformation/Guidances/ucm125127.htm) 

Guidance for industry Fast Track Drug Development Programs — Designation, Development, 

and Application Review 

30 When final, this guidance will represent the FDA’s current thinking on this topic. 

30