Contains Nonbinding Recommendations 
 
 
#178 
Guidance for Industry  
 
Recommended Study Design and Evaluation of Effectiveness 
Studies for Swine Respiratory Disease Claims 
FINAL GUIDANCE 
 
Comments and suggestions regarding this guidance should be sent to the Division of Dockets 
Management (HFA-305), Food and Drug Administration, 5630 Fishers Lane, Room 1061, Rockville, 
MD  20852.  Comments may be submitted electronically on the Internet at  
http://www.regulations.gov.  All comments should be identified with Docket Number 2006D-0138.   
 
For questions regarding this document, contact Michelle L. Stull, Center for Veterinary Medicine 
(HFV-133), Food & Drug Administration, 7500 Standish Place, Rockville, MD 20855, 240-276-
8351, E-mail: michelle.stull@fda.hhs.gov. 
Additional copies of this final guidance document may be requested from the Communications Staff 
(HFV-12), Center for Veterinary Medicine, Food and Drug Administration, 7519 Standish Place, 
Rockville, MD  20855, and may be viewed on the Internet at 
http://www.fda.gov/AnimalVeterinary/GuidanceComplianceEnforcement/GuidanceforIndustry/defau
lt.htm.   
  
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Veterinary Medicine 
October 1, 2007 
  Contains Nonbinding Recommendations 
 
TABLE OF CONTENTS 
 
INTRODUCTION  Page 3 
SECTION 1:  RECOMMENDED STUDY DESIGN AND EVALUATION OF 
EFFECTIVENESS STUDIES FOR SRD 
1.  Recommended Study Design  Page 5 
2.  Selection of Study Animals   Page 9 
3.  Inclusion/Exclusion Criteria  Page 9 
4.  Post-inclusion Removal of Sites, Pens, or Pigs from the Study  Page 10 
5.  Assessment of Effectiveness   Page 12 
6.  Statistical Methods   Page 14 
SECTION 2:  RECOMMENDED STUDY DESIGN AND EVALUATION OF 
EFFECTIVENESS STUDIES FOR SRD ASSOCIATED WITH 
MYCOPLASMA HYOPNEUMONIAE  
1.  Model Study Considerations   Page 15 
2.  Field Study Considerations   Page 16  Contains Nonbinding Recommendations 
 
SECTION 1:  Swine Respiratory Disease 
 
Guidance for Industry 
Recommended Study Design and Evaluation of 
Effectiveness Studies for Swine Respiratory Disease 
Claims1 
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.  
 
 
 
INTRODUCTION 
This guidance provides recommendations to industry relating to study design and describes 
the criteria that the Center for Veterinary Medicine (CVM) intends to use to evaluate 
effectiveness studies for swine respiratory disease (SRD) claims. 
Section 1 of the guidance suggests designs for studies intended to demonstrate the 
effectiveness of a new animal drug intended for the treatment or control of SRD.  CVM uses 
the term SRD to refer to the component of acute respiratory disease in swine associated with 
bacterial pathogens such as Actinobacillus pleuropneumoniae, Bordetella bronchiseptica, 
Haemophilus parasuis, Pasteurella multocida, or Streptococcus suis. 
For the purposes of this guidance, SRD is not considered synonymous with Enzootic 
Pneumonia, Porcine Respiratory Disease Complex (PRDC), or any other complex or 
syndrome.  Enzootic Pneumonia is a common term used to describe Mycoplasma 
hyopneumoniae co-infection with other bacterial respiratory pathogens (such as 
P. multocida).  PRDC is mixed viral and bacterial infection of two or more respiratory 
pathogens, such as M. hyopneumoniae, A. pleuropneumoniae, S. suis, P. multocida, 
Pseudorabies virus, Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), and/or 
Swine Influenza Virus (SIV).   
Section 2 of the guidance describes study design recommendations and criteria CVM intends 
to use to determine the effectiveness of a new animal drug intended for 1) treatment or 
                                                 
1 This final guidance has been prepared by the Office of New Animal Drug Evaluation in the 
Center for Veterinary Medicine. 
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SECTION 1:  Swine Respiratory Disease 
 
control of SRD associated with Mycoplasma hyopneumoniae and other bacterial pathogens; 
or 2) reduction in severity of effects of respiratory disease associated with Mycoplasma 
hyopneumoniae.  
FDAs guidance documents, including this guidance, do not establish legally 
enforceable responsibilities.  Instead, guidances describe the Agencys current thinking 
on a topic and should be viewed only as recommendations, unless specific regulatory or 
statutory requirements are cited.  The use of the word should in Agency guidances 
means that something is suggested or recommended, but not required. 
 
SECTION 1:  Recommended Study Design and Evaluation of Effectiveness 
Studies for Swine Respiratory Disease  
 
Effectiveness must be demonstrated by substantial evidence consisting of one or more 
adequate and well-controlled studies [21 USC 360b(d)(1)(E) and (d)(3); 21 CFR 
514.1(b)(8)(ii); 21 CFR 514.4(a); and 21 CFR 514.117].  CVM recommends use of an 
adequate and well-controlled field study to demonstrate effectiveness of a new animal drug 
intended for use in the treatment or control of SRD.  A sponsor may propose an induced 
infection or other model study that mimics field conditions.  The protocol should include 
justification for the choice of study design. 
CVM recommends that sponsors submit protocols for review and concurrence prior to 
beginning studies that CVM and the sponsor agree are essential to CVM's decision to 
approve or deny an application. Although sponsors are not required to submit study protocols 
for review, CVMs concurrence with a protocol represents a fundamental agreement between 
CVM and the sponsor that we agree with the design, execution, and analyses proposed in the 
protocol we reviewed, and that we will not later alter our perspectives on these issues unless 
public or animal health concerns are evident that we did not recognize at the time we 
reviewed the protocol. (See Animal Drug User Fee Act Performance Goals and Procedures, 
http://www.fda.gov/ForIndustry/UserFees/AnimalDrugUserFeeActADUFA/ucm042936.htm.  
Protocol concurrence does not guarantee that the results of the study will support a particular 
finding or approval of the new animal drug.  
CVM recommends that sponsors follow closely the format for writing protocols that is 
presented in CVM Guidance for Industry No. 85: Good Clinical Practices: VICH GL9, Final 
Guidance, 05/09/01, section 6, available on the CVM website.  The following information 
does not cover every aspect of a protocol.  The information that follows supplements 
Guidance 85.  It provides CVMs recommendations specific to studies designed to evaluate 
effectiveness against swine respiratory disease.   
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SECTION 1:  Swine Respiratory Disease 
 
1.  Recommended Study Design 
The overall design of the study should be thoroughly described in the protocol.  A 
reasonable design should provide a valid and precise estimate of the effectiveness of the 
investigational drug.  The study design should also be reasonably robust in the face of 
circumstances that may arise during the course of a study, such as loss of animals at a 
field site.   
a.  Site Selection 
CVM recommends a multi-site field study to demonstrate effectiveness.  CVM 
recommends that sponsors select the number and geographic location of sites that will 
represent the target population of animals that may be exposed to the new animal 
drug after approval.  The protocol should include a rationale for the number and 
geographic locations of the sites chosen for the study.  The production system type 
and facility location(s) should be specified in the protocol.  
A well-designed field study may include sites that have multiple facilities, multiple 
rooms within a facility, multiple pens within a room, and multiple animals within a 
pen.     
The organization of the facility is very important because there is a potential for 
common influences to result in statistical dependencies among the observed 
responses that should be included in the statistical model.  For example, pigs within a 
pen may influence each others response to treatment by reinfecting each other.  Pens 
within the same room may share some common influences in response to treatment.   
The sponsor should select site(s) for a field study based on a recent history of SRD in 
the herd or on the farm.  CVM recommends that the sponsor confirm that the target 
pathogen(s) are present in the study pig population prior to including a site.  The 
target swine respiratory pathogen(s) should usually be identified through pre-
treatment samples.  Pre-treatment samples should be obtained by sacrifice and culture 
of lung tissues, serology, polymerase chain reaction (PCR), or other appropriate 
diagnostic tests.  Nasal swabs are not recommended for providing a definitive 
identification of organisms causing acute SRD. 
b.  Experimental Unit 
The experimental unit is the smallest unit of organization in the study design to which 
the experimental groups (treatments) are randomized, independent of how the 
individual pigs are assigned.  For example, if pigs are individually randomized to 
experimental groups and pigs from all groups are commingled within each pen, then 
the individual pig is the experimental unit.  If a pen of pigs is assigned at random to 
an experimental group, then the pen is the experimental unit, even though the pigs 
have been assigned at random to the pen.  Likewise, if a room with multiple pens is 
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SECTION 1:  Swine Respiratory Disease 
 
randomized to an experimental group, then the room is the experimental unit, even 
though a randomization process has been used to assign pigs to pens within the room.     
For products administered in feed or water, the pen should be the experimental unit.  
For injectable products, the individual pig should be the experimental unit if pigs 
from all experimental groups are commingled within each pen.     
The sponsor should select an appropriate experimental unit and provide appropriate 
replication of the experimental unit for each of the experimental groups in the study.  
For example, if the pen is the experimental unit and pens are grouped into rooms, 
then it may be possible to have several pens in a room assigned to each experimental 
group.  
The pen is considered an important grouping factor, even if it is not considered the 
experimental unit.  We recommend that pens mimic commercial conditions (as 
closely as practical) in terms of square feet per pig, pen size, number of pigs per pen, 
and number of pens per house. 
c.  Number of Animals 
We recommend that sponsors provide a rationale for the number of pigs they plan to 
use in the study, the number of pigs per experimental treatment, the number of sites, 
the number of experimental units and the number of pigs per experimental unit, and 
the numbers associated with any other organizational levels in the study.   
There may be numerous considerations in deciding the number of pens and the 
number of pigs per pen at each site.  Practical limitations and the need to mimic 
commercial conditions may be constraints.  Within these constraints, we recommend 
the following: 
  Estimate the amount of variation in the primary response variables at each level of 
organization in the study.  Factors such as variation among animals in the 
response to treatment, variation among sites in the severity of disease, and 
variation in response among breeds under different environmental conditions, 
may all tend to influence the number of pigs that should be used in a study.  
Attention to these points should aid in the statistical calculations used to allocate 
resources in the study.    
  Aim for balance.  For example, we recommend using approximately the same 
number of pigs per pen within and among sites.  If experimental groups are 
commingled within each pen, then we recommend using the same allocation ratio 
of pigs per experimental group for each pen, such as a 1:1 ratio for test article to 
placebo control in each pen.  For a control claim, we recommend that the ratio of 
pigs with the disease or condition to healthy pigs be as similar as possible among 
pens and among experimental groups.   
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SECTION 1:  Swine Respiratory Disease 
 
  Include an adequate number of pigs per pen to accommodate losses during the 
study and to provide adequate precision for pen-based outcomes, such as the 
percentage of pigs that are cured or improved in a pen.  In situations where 
experimental groups are commingled in a pen, this applies to the number of pigs 
per experimental group per pen.   
Thus, we encourage the sponsor to provide a statistical justification for their study 
numbers based on assumptions from prior knowledge of the factors listed above and 
other factors deemed critical.   
d.  Experimental Groups 
CVM recommends that the experimental groups (treatments) include the treated 
group(s) (receiving the test article at the proposed label dose(s) for the proposed 
frequency and duration) and a control group.  CVM recommends that the sponsor 
use a placebo concurrent control (referred to as placebo control in the remainder of 
this guidance) so that the control group pigs receive the same handling and 
procedures as the treated group pigs.  Using a placebo may also help maintain the 
masking of the pigs as to experimental group.   
For SRD field studies, CVM recommends a superiority comparison of the test article 
to a placebo control group.  If a sponsor would like to propose a field study with a 
non-inferiority comparison to an active treatment concurrent control group (referred 
to as active control in the remainder of this guidance), they are encouraged to 
discuss this further with CVM.  Issues that the sponsor should be prepared to address 
include, but are not limited to:  (1) the selection of an appropriate active control 
article; (2) the statistical justification of study numbers, including number of sites, 
pens, pigs and other organizational units; and (3) the use of a valid statistical model 
for a non-inferiority evaluation that incorporates important elements of the study 
design such as dependencies previously discussed and the establishment of a delta, 
the maximum allowable difference between test article and active control.  
e.  Randomization 
Randomization is recommended to reduce bias in the process of selecting animals and 
assigning them to experimental units.  The experimental unit may be an 
organizational level that has subunits, for example, pigs as subunits within the 
experimental unit of pen.  In this case, it is also recommended to reduce bias in the 
allocation of subunits to that unit, for example, allocating pigs to the pens. 
Randomization in a study design with multiple levels of organization usually includes 
at least two recommended steps.  For example, if the pen is the experimental unit (all 
pigs within the pen will be assigned to the same treatment), then the first step should 
be to randomly assign pigs to pens.  The second step should be to randomly assign 
each pen to an experimental group.  If the pig is the experimental unit and all 
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SECTION 1:  Swine Respiratory Disease 
 
experimental groups are represented in each pen, then the first step should be the 
random allocation of pigs to experimental groups.  The second step should be the 
random allocation of pigs within each experimental group to pens.   
Blocking and stratification may be used to maintain balance in the study design.  
Blocking is recommended as a means to remove variation associated with variables 
other than the experimental treatment so that the error variation is less.  The success 
of the blocking procedure is measured by the percent of the overall variation that is 
accounted for.  Typical blocking variables are location in a pig house, severity of 
disease or condition, or weight.  Stratification is recommended when one pre-sets 
classes and one wants to be sure that pigs are included in the study from each pre-set 
class in a specified ratio.  For example, one might pre-set weight classes and specify 
the percent of pigs that should be enrolled in each class.  Blocking is more commonly 
recommended in SRD studies.   
CVM recommends that the sponsor include the following information in the protocol 
concerning the process of randomization:  
 Identify all of the steps to be used in the process of randomization.  
 Describe the method(s) to be used to generate random assignments.  
 Describe the relationship between the experimental unit, the process of 
randomization, and other organizational levels of the study design.  
 Identify any blocking variables, restrictions to randomization, and stratification 
variables that are part of the randomization process.  
f.  Masking 
Masking is recommended to decrease bias in the management and the evaluation of 
the animals in the study.  We recommend that the masking methods planned for the 
study, including which personnel will have access to treatment assignments, be 
thoroughly described in the protocol. 
  Treatment assignments.  We recommend that each pig and each pen be assigned a 
unique identification (ID) number.  A code for pen, room, and facility may be 
included as part of the pig ID number.  However, the ID numbers should not 
include a number or letter code that references the pigs treatment assignment.  
For example, A and B should not be used as part of the ID numbers to 
reference the treatment and the placebo control groups.  Similarly, color or other 
grouping codes should not be used to reference the pigs or the pens treatment 
assignment.  Personnel who are not involved in caring for the pigs or conducting 
clinical evaluations should maintain the list that matches the pig ID code or pen 
ID to the experimental group assignment.  By following this practice, evaluators 
may be less likely to guess the experimental group assignment based on the 
responses of several pigs.  Also, if one treatment assignment is accidentally 
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SECTION 1:  Swine Respiratory Disease 
 
unmasked, the masking assignments of all the other experimental units in that 
same group are less likely to be revealed.   
  Clinical evaluations and necropsies.  We recommend that a separate sheet be used 
to record observations for each evaluation period (for example, day) so that 
observations/scores will not be influenced by the previous evaluations.  Within 
the same evaluation period, it is acceptable to list data for multiple animals on the 
same sheet.  Personnel involved in caring for the pigs and conducting clinical 
evaluations of the pigs should not be aware of treatment assignments.  Personnel 
conducting necropsies and making observations that are intended to be used as 
decision variables (scoring lung lesions or evaluating extent of lung involvement, 
for example) should not be aware of treatment assignments.   
  Evaluation of histopathological data.  If histopathological data will be examined, 
appropriate techniques to minimize the introduction of bias should be used.  
Appropriate methods may include, but are not limited to, informal peer review, 
targeted masked review, or review by a pathology working group.  We 
recommend that personnel evaluating the histopathological data not be aware of 
treatment assignments.   
2.  Selection of Study Animals 
For SRD studies, we recommend that study pigs be representative of U.S. commercial 
production and the intended use population in terms of production class, breed, and 
gender, as follows: 
a.  Class/size:  Weaned to finishing pigs with weight range being representative of the 
production class. 
b.  Breeds:  Representative of U.S. production, including large white or other 
commercial crossbred animals. 
c.  Gender:  Both sexes should be represented.  If the drug is intended for use in 
replacement breeding animals the sponsor should contact CVM for guidance on 
additional target animal safety (TAS) studies. 
d.  Other Information:  Pig source, treatment and vaccination history, herd health status, 
and other pertinent information should be described.  
3.  Inclusion/Exclusion Criteria 
The sponsor should propose and state in the protocol the specific minimum criteria used 
to enroll a pig in the study, and specific criteria for exclusion.   
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SECTION 1:  Swine Respiratory Disease 
 
a.  Inclusion Criteria:  
Eligible pigs should be enrolled in the study when they meet the minimum criteria 
specified in the protocol.  For a treatment claim, all pigs enrolled should meet the 
criteria.  In general, for a control claim, at least 15% of pigs in an experimental unit 
should meet the criteria.  The minimum disease threshold may vary based on the 
dosage form or other drug properties.  Use of a threshold other than 15% should be 
justified in the protocol.  In addition, CVM recommends that for a control claim, the 
proportion of pigs meeting entrance criteria be as similar as possible among pens and 
among experimental groups.   
The scoring system to identify pigs for inclusion should contain comprehensive, non-
overlapping descriptors that allow a uniform evaluation among multiple observers 
and multiple sites.  
CVM suggests the following minimum criteria: 
  Body temperature  104F, and 
  Respiratory score  2 (0 = Rate and pattern normal, no abnormal nasal discharge; 
1 = Mild  Slightly increased respiratory rate, some roughness in breathing; 
2 = Moderate  Increased respiratory rate, some abdominal breathing; 3 = 
Severe  increased respiratory rate with abnormal effort - open mouth breathing, 
grunting, dog sitting), and 
  Depression score  2 (0 = Normal - Alert, active, normal appetite, well-hydrated, 
coat normal; 1 = Mild  moves slower than normal, slightly rough coat, may 
appear lethargic but upon stimulation appears normal; 2 = Moderate  inactive, 
may be recumbent but is able to stand, gaunt, may be dehydrated; 3 = Severe  
down or reluctant to get up, gauntness evident, dehydrated).  
b.  Exclusion Criteria:  
The sponsor should state in the protocol the criteria to be used to exclude pigs from 
enrollment in the study.  Examples of exclusion criteria include pre-existing 
conditions or diseases unrelated to SRD (such as enteric disease, lameness, 
neurological disease, septicemia, etc.), outside weight range, unthrifty appearance, 
abnormal conformation, or history of treatment with any antimicrobial, including 
antimicrobials in feed, typically within 14 days of the start of the study. 
4.  Post-inclusion Removal of Sites, Pens, or Pigs from the Study   
The protocol should state the circumstances that would cause a site, pen, or pig to be 
removed from the study after the study has started.  CVM suggests that the primary 
investigator decide if a site, pen, or pig should be removed from the study.  
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SECTION 1:  Swine Respiratory Disease 
 
a.  An exit examination should be conducted on any pig removed from the study.  The 
results of the examination may serve as documentation of the reason for removal.  
Pigs removed from the study for undocumented reasons should be considered 
treatment failures.   
b.  The following are examples of events that might lead to removal of pigs after the 
study has started.  
  While the study is in progress but prior to the final evaluation, a pig is 
determined to be a treatment failure.  Pigs showing severe clinical signs of SRD 
may be removed from the study for humane reasons and treated with appropriate 
therapy.  These pigs should be counted as treatment failures and be included in 
the effectiveness evaluation.   
  While the study is in progress but prior to the final evaluation, a pig develops 
signs of other diseases or conditions unrelated to SRD.  Pigs exhibiting signs of 
other diseases or conditions unrelated to SRD that are considered confounding to 
the study may be removed.  Documentation (for instance, results of microbiology, 
serology, necropsy, histopathology, and other diagnostic tests) and a rationale for 
removal should be provided.  If any pigs are excluded from the effectiveness 
evaluation, justification for the exclusion of these pigs should be provided. 
  While the study is in progress, a pig experiences a test article-related adverse 
event.  All adverse events should be documented, regardless of severity or cause.  
If a pig experiences a test article-related adverse event that is severe enough to 
result in removal from the study, the pig should generally be analyzed as a 
treatment failure.  CVM will evaluate the circumstances of such withdrawals on a 
case-by-case basis to consider other options with regard to the effectiveness 
evaluation.     
  While the study is in progress, a pig dies or needs to be euthanized.  All pigs that 
die or are euthanized during the study should be necropsied and representative 
lung tissues from all pigs should be cultured.  Positive cultures should be 
identified and minimum inhibitory concentrations (MICs) should be determined 
from isolates.  A pig that dies or is euthanized that has gross lesions of 
pneumonia, with or without a positive culture of an organism associated with 
SRD should be considered a treatment failure and should be included in the 
effectiveness evaluation. 
c.  The protocol should state whether a pig should stay in the study pen after the pig is 
removed from the study.  Pigs removed from the study pens for treatment of severe 
SRD, adverse events, or other diseases should not be added back to the pen during the 
study. 
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SECTION 1:  Swine Respiratory Disease 
 
d.  The reason for dropping any site, pen, or pig from the analysis should be explained in 
the final study report. 
5.  Assessment of Effectiveness  
a.  Measurements and Observations: 
  The sponsor should define in the protocol the primary and secondary variables and 
describe when and how they should be measured.  The measured variables should 
have clinical relevance.  There should be a logical relationship between the 
variables intended to be measured, the timing and frequency of study observations 
and measurements, and the proposed claim.  The protocol should state how each 
variable contributes to the study conclusion. 
  CVM considers success/failure determination as the primary variable for SRD 
studies.   
We recommend that all pigs be classified as a success or failure on the 
predetermined evaluation day(s).  CVM recommends using the following criteria 
to classify a pig as a success or failure.  
 Table 1.  Success/failure criteria for SRD studies. 
SUCCESS  FAILURE 
Alive, and 
T <104F, and  All pigs that do not meet the 
definition of success on the 
Respiratory score = 1 or 0, and 
evaluation day(s). 
Depression score = 1 or 0 
 
  Mortality may be a secondary variable.  
  The time points for measuring variables in a field study should be carefully 
considered.  The most appropriate time points depend on the proposed claim, 
product characteristics or formulation, pharmacokinetics, and treatment regimen.  
  The timing and frequency of study observations should be specified in the 
protocol.  CVM suggests that repeated observations and other measurements be 
done at the same time of day to decrease variation.   
  The sponsor should describe in the protocol any additional procedures and/or tests 
they plan to use for assessment, including the time of sampling and the interval 
between sampling, storage of samples, and the analysis or testing method. 
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SECTION 1:  Swine Respiratory Disease 
 
b.  Microbiological Endpoints: 
(1)  Pathogens Included in the Label Claim (Indications):  Only pathogen(s) obtained 
from the study animals should be included in the proposed claim.  Isolates may be 
obtained by necropsying study animals, identifying lung lesions, and culturing 
SRD pathogens.  The number of isolates needed in order to consider the 
pathogen(s) for inclusion in the label claim should be stated in the protocol.  For 
each pathogen species, CVM recommends that at least 30 isolates be collected 
from a minimum of 30 pigs.  If a sponsor wishes to add pathogens to the claim in a 
later supplement, then CVM may request that additional effectiveness data be 
generated with isolation of the additional pathogen(s) from field studies. 
(2)  In Vitro Minimum Inhibitory Concentration (MIC) Data for the Microbiology 
Section of the Label:  The microbiology section should only include MIC data for 
the pathogen species included in the indication.  MIC data should be obtained from 
field isolates from pivotal effectiveness studies.  CVM recommends that MIC data 
proposed to be included on the label (microbiology section) be obtained from at 
least 30 isolates from a minimum of 30 pigs for each pathogen species included in 
the indication.  Susceptibility testing should be conducted using validated methods 
such as those described by the Clinical and Laboratory Standards Institute 
(formerly the National Committee for Clinical Laboratory Standards).  
Susceptibility testing should include quality control strains to verify that the test 
method is valid.    
c.  Basis for Study Conclusion: 
To have CVM consider a drug and dosage regimen effective, CVM recommends that 
the sponsor demonstrate: 
  that the target pathogen(s) were present and contributed to an acute respiratory 
disease outbreak in the study animals, and 
  the proportion of successes is statistically significantly different (at an  level 
of 0.05) in the treated group compared with the placebo control group, and 
  there was clinically relevant improvement in the treated group compared with 
the placebo control group for the decision variable(s), as stated in the protocol. 
The day(s) selected to evaluate success or failure may vary depending on the 
pathogen, the drug, disease pathophysiology, and supporting arguments, which may 
include data such as pharmacokinetic/pharmacodynamic relationships and the 
existence of a post-antibiotic effect.  CVM generally recommends classifying each 
pig as either a success or a failure 48 hours after drug concentrations drop below 
therapeutic blood levels for the target pathogens.  For drugs with poor correlation 
between drug concentrations in the blood and at the site of infection, the evaluation 
should be made 48 hours after the drug concentrations at the site of infection have 
dropped below the MIC of the target pathogens.   
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6.  Statistical Methods 
For SRD effectiveness studies, the primary response variable should typically be the 
classification of each pig as either a success or a failure.  This variable should be 
measured for each pig in the study.  The sponsor should tabulate the number of pigs in 
each pen that were successes and the number that were failures.  For a design with 
commingled treatments, the summary should separate the responses of pigs from each 
pen into experimental groups.   
The sponsor should conduct a statistical comparison between the investigational drug and 
the placebo control in terms of the proportion of successes in each group.  The null 
hypothesis should be that each group has the same population proportion of successes.  
This should be tested against a two-tailed alternative hypothesis.  The appropriate 
statistical model depends on what the experimental unit is and how it is replicated in the 
study design.  Linear mixed models or generalized linear mixed models may be 
appropriate for the primary response variable as well as secondary variables depending 
on the nature of the response variable. 
Site is considered an important contributor to the inferential value of the study.  The 
sponsor and CVM should agree at the protocol stage on the number and location of sites 
and how information from these sites should be evaluated and combined.   
We suggest that the sponsor work with CVM at the protocol stage to develop an 
acceptable approach to the analysis of data in support of the proposed claim for the 
investigational drug. 
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SECTION 2:  Swine Respiratory Disease associated with Mycoplasma hyopneumoniae 
 
 
SECTION 2:  Recommended Study Design and Evaluation of Effectiveness 
Studies for Swine Respiratory Disease Associated with Mycoplasma 
hyopneumoniae. 
Mycoplasma hyopneumoniae is rarely the only pathogen involved in SRD.  The presence of 
M. hyopneumoniae in the lung tends to decrease the immune defenses in the lung, which 
allows other pathogens to cause clinical signs of respiratory disease.  For this reason, CVM 
suggests several possible claims regarding M. hyopneumoniae  1) reduction in severity of 
effects of respiratory disease associated with M. hyopneumoniae, or 2) a treatment (or 
control) of SRD claim in which M. hyopneumoniae is included in the list of associated target 
pathogens.  Sponsors may also propose (with justification and supporting data) other 
appropriate claims and claim wording. 
The study design concepts and considerations discussed in Section 1 (Swine Respiratory 
Disease) provide guidance for designing field studies to evaluate the effectiveness of a new 
animal drug against SRD associated with bacterial pathogens such as Actinobacillus 
pleuropneumoniae, Bordetella bronchiseptica, Haemophilus parasuis, Pasteurella 
multocida, or Streptococcus suis.  Many of these concepts are also appropriate for studies 
conducted to generate effectiveness data for M. hyopneumoniae-associated claims.  Section 2 
provides additional guidance for designing studies and evaluating the effectiveness of a new 
animal drug for claims associated with M. hyopneumoniae.   
Due to the complexity of M. hyopneumoniae infection in pigs, CVM recommends an 
appropriately validated model study in addition to an adequate and well-controlled field 
study.  The model study should show that the drug has a therapeutic effect specifically 
against M. hyopneumoniae in swine, and the field study should show that the drug is 
effective under field use conditions in an SRD outbreak where M. hyopneumoniae is present. 
1.  Model Study Considerations 
An induced infection model study mimicking natural infection should show that the drug 
is effective against M. hyopneumoniae, for example, by providing evidence that organism 
numbers were reduced in the pigs after the drug was given.  The model study may also 
show that the drug provided a clinical effect (such as decreased lung lesions) in the 
treated animals.  
The sponsor should provide data to support that the inoculating strain used in the model 
study is representative of current (within three years of the start of the study) North 
American field isolates.  The dynamics of infection should have biological relevance for 
field infection in pigs.  
21 CFR 514.4(b)(3)(ii) requires that studies using models be validated to establish an 
adequate relationship of parameters measured and effects observed in the model with one 
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SECTION 2:  Swine Respiratory Disease associated with Mycoplasma hyopneumoniae 
 
or more significant effects of treatment.  We recommend that the sponsor provide 
information showing that:   
  the model study method can be reproduced by different investigators, and  
  the model study methods and endpoints would be acceptable to the scientific 
community.  For example, evidence that the model study has been published in a 
peer-reviewed scientific journal may be provided. 
2.  Field Study Considerations 
A field study should demonstrate that the drug has a therapeutic (clinical) effect under 
field use conditions where M. hyopneumoniae is present.  Serology may be used to 
support the presence of M. hyopneumoniae but should not be used alone as verification.  
The following standards are recommended to verify that M. hyopneumoniae is present in 
the study group:   
  Live animal diagnostics:  PCR (nasal swab or tracheal wash)  at least 20% of the 
study pigs should be positive for M. hyopneumoniae; or   
  Necropsy (lung tissue):  fluorescent antibody, immunohistochemistry, PCR, or 
culture of lung tissue  5-10% of the study pigs should be positive for 
M. hyopneumoniae.   
The information below summarizes the additional recommended considerations for a 
field study protocol to test the effectiveness of a new animal drug intended for one of 
the following claims. 
a.  Treatment or Control of SRD associated with M. hyopneumoniae 
A claim for either the treatment or control of SRD where M. hyopneumoniae is 
present may be based on a well designed SRD field study that demonstrates that the 
drug was effective against M. hyopneumoniae in the presence of other bacterial 
pathogens in an acute SRD outbreak.  Design considerations are the same as those 
recommended in Section 1, with the additional recommended step of verification of 
the presence of M. hyopneumoniae as described above. 
b.  Reduction in Severity of Effects of Respiratory Disease associated with 
M. hyopneumoniae 
A reduction in severity claim should be based on the evaluation of the chronic 
effects of M. hyopneumoniae.   
(1) Study Design 
A well designed field study for a reduction in severity claim may follow a 
group of pigs from nursery to slaughter to demonstrate that the drug was effective 
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SECTION 2:  Swine Respiratory Disease associated with Mycoplasma hyopneumoniae 
 
in reducing the chronic adverse (harmful) effects of M. hyopneumoniae (such as 
fewer acute SRD outbreaks with fewer pigs needing treatment, less prevalent/less 
severe lung lesions, or maintenance and uniformity of weight gains).  The sponsor 
may suggest an alternate study length, based on the intended dosing regimen and 
study endpoints.  
(2) Experimental Unit  
In field studies associated with M. hyopneumoniae, there is no recommendation at 
the present time for a typical experimental unit.  The experimental unit may be 
the pig, the pen, the room, the facility, or some other organizational level.  
Therefore, we recommend that the sponsor justify the appropriateness of the 
choice of experimental unit in terms of the field use of the product.  
(3) Enrollment Criteria 
When there is 1) documented evidence of respiratory disease associated with 
M. hyopneumoniae in the herd(s) of origin; and 2) a positive identification of 
M. hyopneumoniae in the group of pigs currently targeted for the study as 
described above, the entire group of study pigs should be enrolled. 
(4) Assessment of Effectiveness  
a) The time points for measuring variables in a field study for a reduction in 
severity claim should be carefully considered.  A field study for this claim 
may be considerably longer than a study for a disease of acute onset and short 
duration.  In addition, clinical signs and lung lesions may vary considerably 
among pigs at different stages of disease. 
b) Serial necropsies should be conducted to compare lung lesions at specific 
points (for example, 4 weeks after therapy begins) relative to the treatment 
period(s).  The number of pigs requiring alternate or additional therapy for 
acute respiratory disease should be recorded.  Physical health parameters such 
as average daily gain (ADG) and uniformity (weight variability) data should 
also be recorded.    
c) Basis for conclusion of study: 
  The decision variables may include dichotomous success/failure 
classifications, a count of the number of pigs requiring additional or 
alternate therapy, a continuously distributed variable such as weight gain; 
and scores of lung lesions.   
  The choice of statistical methodology should consider points covered in 
Section 1.  Linear mixed models or generalized linear mixed models may 
be appropriate depending on the nature of the response variable.   
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SECTION 2:  Swine Respiratory Disease associated with Mycoplasma hyopneumoniae 
 
  For studies with multiple variables (such as mortality, clinical signs and 
lung lesions), the protocol should specifically state how all of the variables 
will be considered in determining effectiveness.  A decision tree or flow 
chart may assist in determining effectiveness if some, but not all, variables 
show significant differences between treated and placebo control groups.   
  Data on physical health variables, such as weight gain, feed intake, and 
feed efficiency may also be analyzed.  Improvement in physical health 
variables without statistically significant improvement in other primary 
decision variables should not be used to demonstrate effectiveness for 
Mycoplasma claims.   
d) To have CVM consider a drug and dosage regimen effective, CVM 
recommends that the sponsor demonstrate: 
  that M. hyopneumoniae was present and contributed to respiratory disease 
in the study animals, and  
  there was a statistically significant improvement (at an  level of 0.05) in 
the treated group compared with the placebo control group for the 
decision variable(s), as stated in the protocol, and  
  there was clinically relevant improvement in the treated group compared 
with the placebo control group for the decision variable(s), as stated in the 
protocol. 
 
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