CONTAINS NON-BINDING RECOMMENDATIONS 
#135 
 
Guidance for Industry 
Validation of Analytical Procedures for Type C 
Medicated Feeds 
 
 
This guidance discusses characteristics that may be considered during the validation of non-
microbiological analytical procedures for the analysis of drugs in Type C medicated feeds 
included as part of original and supplemental new animal drug applications (NADAs) and 
abbreviated new animal drug applications (ANADAs) for Type A Medicated Articles submitted 
to the Food and Drug Administration (FDA). It provides guidance and recommendations on 
considering various validation characteristics for each analytical procedure used in medicated 
feed assays and indicates the data that may be included in the applications. 
 
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. All comments should be identified with the Docket No. 2004D-0146. 
Comments may also be submitted electronically on the Internet at  http://www.regulations.gov.  
 
For questions regarding the guidance document, contact Rebecca Owen, Center for Veterinary 
Medicine (HFV-141), Food and Drug Administration, 7500 Standish Place, Rockville, MD 
20855, 240-276-9842, E-mail: Rebecca.owen@fda.hhs.gov.  
 
Additional copies of this 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/
default.htm. 
 
According to the Paperwork Reduction Act of 1995, a collection of information must display a 
valid OMB control number. The existing valid OMB control numbers for this information 
collection are 0910-0032 (expires 12/31/07) and 0910-0154 (expires 12/31/07). This guidance 
contains no new collections of information. 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Veterinary Medicine 
November 7, 2005 
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TABLE OF CONTENTS 
 
INTRODUCTION........................................................................................................................3 
DISCUSSION..............................................................................................................................4 
1. SPECIFICITY...................................................................................................................4 
2. LINEARITY.....................................................................................................................5 
3. RANGE.............................................................................................................................6 
4. ACCURACY....................................................................................................................6 
5. PRECISION......................................................................................................................6 
6. LIMIT OF DETECTION..................................................................................................7 
7. LIMIT OF QUANTITATION..........................................................................................8 
8. ROBUSTNESS / RUGGEDNESS...................................................................................9 
9. SYSTEM SUITABILITY TESTING.............................................................................10 
10. RECOMMENDED DATA...........................................................................................10 
GLOSSARY..............................................................................................................................12 
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 Validation of Analytical Procedures for Type C Medicated Feeds1 
 
 
This guidance represents the agencys 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 statute(s) and regulation(s). 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 
The purpose of this guidance is to provide recommendations on how to consider the various 
validation characteristics for each analytical procedure used in medicated feed assays. This 
guidance is written primarily for chromatographic methods; however, the guidance does not 
limit the analytical technique to chromatographic procedures, as other techniques may be 
appropriate. In some cases (for example, demonstration of specificity), the overall capabilities 
of a number of analytical procedures in combination may be investigated in order to ensure the 
quality of the 
medicated feed. 
 
Section 512(b) of the Federal Food, Drug, and Cosmetic Act (21 U.S.C.  360b) establishes the 
requirements for new animal drug approval. 21 C.F.R.  514.1 specifies the information 
required to be submitted as part of the application and the proper form for the submission. 
Section 514.1(b)(5)(vii) requires an applicant to describe analytical procedures that should be 
capable of determining the active component(s) within a reasonable degree of accuracy and of 
assuring the identity of such components. Section 514.1(b)(5)(vii)(a) states that a description of 
practicable methods of analysis of adequate sensitivity to determine the amount of the new 
animal drug in the final dosage form should be included. 
 
 
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. 
 
                                                 
1 This guidance has been prepared by the Office of New Animal Drug Evaluation in the Center for 
Veterinary Medicine at the Food and Drug Administration. 
 
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DISCUSSION 
The objective of the analytical procedure should be clearly understood since this will govern the 
validation characteristics that are evaluated. Typical validation characteristics that may be 
considered are listed below: 
 
- Specificity 
- Linearity 
- Range 
- Accuracy 
- Precision 
- Limit of Detection 
- Limit of Quantitation 
- Robustness 
 
Each of these validation characteristics is defined in the attached Glossary.  Approaches other 
than those set forth in this guidance may be acceptable. It is the responsibility of the applicant 
to choose the validation procedure and protocol most suitable for the product. However, it is 
important to remember that the main objective of validation of an analytical procedure is to 
demonstrate that the procedure is suitable for its intended purpose. 
 
It is recommended that a well-characterized reference standard, with documented purity, be 
used throughout the validation study. The degree of purity necessary depends on the intended 
use. 
 
For the sake of clarity, this document considers the various validation characteristics in distinct 
sections. The arrangement of these sections reflects the process by which an analytical 
procedure may be developed and evaluated. In practice, it is recommended to design the 
experimental work such that the appropriate validation characteristics can be considered 
simultaneously to provide a sound, overall knowledge of the capabilities of the analytical 
procedure. 
 
Appropriate validation characteristics may include: specificity, linearity, range, accuracy, and 
precision. 
 
1. SPECIFICITY 
It is recommended that an investigation of specificity be conducted during the validation of the 
medicated feed assay. The procedures used to demonstrate specificity will depend on the 
intended objective of the analytical procedure. Identification of the analyte may be made by 
means of retention time of the standard. 
 
For chromatographic procedures, it is recommended that representative chromatograms be used 
to demonstrate specificity, and individual feed components and drug products be appropriately 
labeled. The chromatographic profile using peak shape and tailing criteria may be used to 
indicate either co-eluting peaks or sample matrix effects. The peak parameters should be in 
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agreement between the standard and analyte peaks. In addition, to ensure that the peaks are 
single components, a diode array detector may be used to obtain peak purity information 
for the analyte peaks in a variety of feed matrices. Similar considerations may be given to other 
separation techniques. 
 
For the assay, it is recommended that there be a demonstration of a lack of interference by feed 
ingredients or other drug products that may be in the feed. This may be done by demonstrating 
that the responses of a blank placebo made from the feed ingredients and/or drug products, 
either separately or in combination, are either different from the absorbance (for Ultraviolet 
(UV) methods) or retention time (for Gas Chromatography (GC) and High Performance Liquid 
Chromatography (HPLC) methods) of the analyte of interest or not significant (i.e., that the 
signal measured as a percent concentration is not greater than 10%). It is recommended that 
additional information be provided showing that common feed ingredients do not interfere with 
the detection system. If potential interference is observed, it is recommended that the ingredient 
be evaluated by the complete method. Some examples of interfering ingredients are clay agents 
(for flowability) and pellet binding, molasses, grass meals (e.g., alfalfa), high mineral content, 
corn cob meal, cottonseed by product meal, meat and bone meal, and fish meal. Many methods 
developed to give good recovery in a simple corn-soy feed do not work well when the analyte is 
added to high mineral feeds, and are not recommended. 
 
Typically, 2-3 feed mixtures, based on the species that will be medicated, geographical location 
where the feed may be prepared, and life cycle of the species (e.g., starter, finisher), should be 
tested. For drug products, it is recommended that  applicants consider the most common 
products that may typically be present within the feed. 
 
Applicable literature references demonstrating non-interference may be supplied in lieu of 
actual testing. 
2. LINEARITY 
It is recommended that a linear relationship be evaluated across the range (see section 3) of the 
analytical procedure. It may be demonstrated directly on the drug substance by separate 
weighings (two separate weighings preferred) and/or dilution of a standard stock solution, using 
the proposed procedure. 
 
It is recommended that linearity be evaluated by visual inspection of a plot of signals as a 
function of analyte concentration or content. If there is a linear relationship, it is recommended 
that test results be evaluated by appropriate statistical methods, for example, by calculation of a 
regression line by the method of least squares. Data from the regression line itself may be 
helpful to provide mathematical estimates of the degree of linearity. It is recommended that the 
correlation coefficient (R) be at least 0.995. The regression line intercept should not differ from 
zero if a single point calibration technique is used. This may be demonstrated if the confidence 
limits of the intercept include zero or if the intercept value is a small percentage of the target 
level. If the intercept is significantly different from zero, then a single point calibration 
technique is not recommended. 
 
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For the establishment of linearity, a minimum of 5 concentrations, covering the intended dosing 
range with one concentration 50% of the lowest dose, is recommended. It is recommended that 
the sponsor contact CVM if other approaches are used. 
3. RANGE 
The specified range should be derived from linearity studies and depends on the intended 
application of the procedure. It may be established by confirming that the analytical procedure 
provides an acceptable degree of linearity, accuracy, and precision when applied to samples 
containing amounts of analyte within or at the extremes of the specified range of the analytical 
procedure. 
 
For the assay of a drug in a medicated feed, the range should be from 50 to 150 percent of the 
labeled concentration. 
4. ACCURACY 
It is recommended that accuracy be established across the specified range of the analytical 
procedure used for medicated feed assays. 
 
It is recommended that two (2) typical feed matrices with known quantities of the drug added 
be analyzed. 
 
It is recommended that accuracy be assessed using a minimum of 15  20 determinations over 
the concentration levels covering the specified range for each feed matrix tested (e.g. 3 - 4 
concentrations (depending on the dose range) / 5 replicates each of the total analytical 
procedure). Recovery from fortified blank matrix samples should be between 80 - 110%. 
5. PRECISION 
Validation of tests for assay of medicated feeds should include an investigation of precision. 
 
5.1. Repeatability 
 
For fortified medicated feed samples, it is recommended that repeatability be assessed using a 
minimum of 15 determinations covering the specified range for the procedure (e.g., 3-4 
concentrations / 5 replicates each).  
 
For drugs incorporated into medicated feeds at greater than 10 ppm, the within laboratory 
variation coefficient should be less than 5.0%. For drugs incorporated into medicated feeds at 
less than 10 ppm, the within-laboratory variation coefficient should be less than 7.5%. 
 
5.2. Intermediate Precision 
 
The extent to which intermediate precision should be established depends on the circumstances 
under which the procedure is intended to be used. It is recommended that the applicant establish 
the effects of random events on the precision of the analytical procedure. It is recommended 
that variations to be studied include days, analysts, equipment, etc. It is not recommended to 
study these effects individually. Instead, the use of a statistical experimental design (matrix) is 
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encouraged (see Statistical Manual of the AOAC by W.J. Youden and E.H. Steiner, 1975, page 
33 for more information on statistical design of experiments). The performance of the method 
by a second independent laboratory is encouraged. 
 
5.3. Reproducibility 
 
It is recommended that reproducibility be assessed by means of an interlaboratory trial. It is 
recommended that reproducibility be considered in the case of standardization of an analytical 
procedure. 
 
5.4. Proof of Performance 
 
It is recommended that proof of performance of the assay be demonstrated by testing two (2) 
batches of the proposed medicated feed manufactured in mixing equipment of the appropriate 
size and under conditions representative of typical commercial processing. When feasible, 
batches should be manufactured using different configurations of mixers. 
 
It is recommended that a minimum of 10 determinations covering the specified range for the 
procedure be made (e.g., 2 concentrations (high and low) / 5 replicates each). If the feed is 
pelletized, it is recommended that the mash and the pelletized feed be tested separately. Results 
should be reported in both concentration and percent label claim. 
6. LIMIT OF DETECTION 
There are several approaches for determining the limit of detection (LOD), depending on 
whether the procedure is non-instrumental or instrumental. Approaches other than those listed 
below may be used. 
 
6.1. Based on Visual Evaluation 
 
Visual evaluation may be used for non-instrumental or instrumental methods. The detection 
limit may be determined by the analysis of samples with known concentrations of analyte and 
by establishing the minimum level at which the analyte can be reliably detected. 
 
6.2. Based on Signal-to-Noise 
 
It is recommended that this approach be applied only to analytical procedures that exhibit 
baseline noise. 
 
Determination of the signal-to-noise ratio may be performed by comparing measured signals 
from samples with known low concentrations of analyte with those of blank samples, and 
establishing the minimum concentration at which the analyte can be reliably detected. A signal-
to-noise ratio of between 3 or 2:1 is generally recommended for estimating the detection limit. 
 
6.3. Based on the Standard Deviation of the Response and the Slope 
 
 
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It is recommended that the LOD be expressed as: 
LOD = 3.3  / S 
 
where  = the standard deviation of the responses and S = the slope of the calibration curve. 
The slope S may be estimated from the calibration curve of the analyte. The estimate of  may 
be carried out in a variety of ways, for example: 
 
6.3.1. Based on the Standard Deviation of the Blank 
 
It is recommended that the measurement of the magnitude of analytical background response be 
performed by analyzing an appropriate number of blank samples and calculating the standard 
deviation of these responses. 
 
6.3.2. Based on the Calibration Curve 
 
It is recommended that a specific calibration curve be studied using samples containing an 
analyte in the range of the LOD. The residual standard deviation of a regression line or the 
standard deviation of y-intercepts of regression lines may be used as the standard deviation. 
7. LIMIT OF QUANTITATION 
Several approaches for determining the limit of quantitation (LOQ) are possible, depending on 
whether the procedure is non-instrumental or instrumental.  
Approaches other than those listed below may be used. 
 
7.1. Based on Visual Evaluation 
 
Visual evaluation may be used for non-instrumental or instrumental methods. The LOQ may be 
determined by the analysis of samples with known concentrations of analyte, and by 
establishing the minimum level at which the analyte can be quantified with acceptable accuracy 
and precision. 
 
7.2. Based on Signal-to-Noise Approach 
 
It is recommended that this approach be applied only to analytical procedures that exhibit 
baseline noise. Determination of the signal-to-noise ratio may be performed by comparing 
measured signals from samples with known low concentrations of analyte with those of blank 
samples, and establishing the minimum concentration at which the analyte can be reliably 
quantified. A signal-to-noise ratio of 10:1 is recommended. 
 
7.3. Based on the Standard Deviation of the Response and the Slope 
 
The LOQ may be expressed as: 
 
LOQ = 10  / S 
 
where  = the standard deviation of the responses and S = the slope of the 
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calibration curve. The slope S may be estimated from the calibration curve of the analyte. The 
estimate of  may be carried out in a variety of ways, for example: 
 
7.3.1. Based on the Standard Deviation of the Blank 
 
Measurement of the magnitude of analytical background response may be performed by 
analyzing an appropriate number of blank samples and calculating the standard deviation of 
these responses. 
 
7.3.2. Based on the Calibration Curve 
 
It is recommended that a specific calibration curve be studied using samples containing an 
analyte in the range of the LOQ. The residual standard deviation of a regression line or the 
standard deviation of y-intercepts of regression lines may be used as the standard deviation. 
8. ROBUSTNESS / RUGGEDNESS 
It is recommended that the evaluation of robustness be considered during the development 
phase and demonstrated during the analytical validation phase. Robustness depends on the type 
of procedure under study. It should show the reliability of an analysis with respect to deliberate 
variations in method parameters. 
 
If measurements are susceptible to variations in analytical conditions, it is recommended that 
the analytical conditions be suitably controlled or a precautionary statement be included in the 
procedure. One consequence of the evaluation of robustness should be that a series of system 
suitability parameters (e.g., resolution test) are established to ensure that the validity of the 
analytical procedure is maintained whenever used. 
 
Examples of typical variations are: 
  -stability of analytical solutions and feed extracts; and 
  -extraction time. 
   
  (Note: it is recommended that results of the stability studies of the 
  analytical solutions and feed extracts be included in the procedure) 
 
In the case of high performance liquid chromatography (HPLC), examples of 
typical variations are: 
  -influence of variations of pH in a mobile phase; 
  -influence of variations in mobile phase composition; 
  -different columns (different lots and/or suppliers); and 
  -temperature-flow rate. 
 
In the case of gas chromatography (GC), examples of typical variations are: 
  -different columns (different lots and/or suppliers); and 
  -temperature-flow rate. 
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9. SYSTEM SUITABILITY TESTING 
 
System suitability testing is an integral part of many analytical procedures. The tests are based 
on the concept that the equipment, electronics, analytical operations, and samples to be 
analyzed constitute an integral system that can be evaluated as such. System suitability test 
parameters to be established for a particular procedure depend on the type of procedure being 
validated and may include, for example, data acceptability testing for feed controls. It is 
recommended that system suitability tests and criteria for the HPLC or GC detection system be 
evaluated. Performance specifications for critical reagents and steps, such as solid phase 
extraction, should be included when appropriate. If specific tests and criteria are used, then the 
recommended actions taken if performance does not meet the criteria should be determined. 
Additional information is available in Pharmacopoeias. 
10. RECOMMENDED DATA 
 
It is recommended that data collected during validation and formulae used for calculating 
validation characteristics be submitted for each feed type and discussed as outlined below: 
 
Specificity: 
 
It is recommended that representative sample sets of chromatograms be 
provided so that recalculation can be performed, including: 
    Baseline / mobile phase 
    Extraction solvent 
    Feed ingredient placebo that cause interference 
    Other drug product placebo that causes interference 
    Standards 
    Samples (high and low concentration, different feed mixtures) 
 
  Retention times and a comparison of relative retention times should be provided. 
 
Tabular listing of feed mixture ingredients and other drug products tested 
should be provided. 
 
Linearity & Range: 
 
It is recommended that the correlation coefficient, y-intercept, slope of the 
regression line, and residual sum of squares be submitted. A plot of the data 
should be included. In addition, an analysis of the deviation of the actual data 
points from the regression line may also be helpful for evaluating linearity. 
 
Accuracy: 
 
It is recommended that accuracy be reported as percent recovery by the assay of 
known added amount of analyte in the sample or as the difference between the 
mean and the accepted true value together with the confidence intervals. 
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Tabular listing of feed mixture ingredients used should be provided. 
 
For each feed matrix studied, it is recommended that the complete set of data including 
weighings, sample and standard preparation, chromatography, calculations, and results 
be provided. A representative set of chromatograms should be provided and, for the 
concentration(s) in between, a table of relevant parameters should be provided. All 
individual area or height measurements for controls, standards, and samples and all 
other information such as sample weights, standard concentrations, and dilutions should 
also be provided. 
 
Precision: 
 
It is recommended that the standard deviation, relative standard deviation 
(coefficient of variation), and confidence interval be reported for each type of 
precision investigated. 
 
It is recommended that the complete set of data including weighings, sample and 
standard preparation, chromatography, calculations, and results be provided. A 
representative set of data should be provided and, for the concentration(s) in between, a 
table of relevant parameters should be provided for each type of precision investigated. 
 
Limit of Detection: 
 
It is recommended that the limit of detection and the method used for determining the 
detection limit be presented. If the LOD is determined based on visual evaluation or 
based on signal-to-noise ratio, the presentation of the relevant chromatograms may be 
considered acceptable for justification. In cases where an estimated value for the LOD is 
obtained by calculation or 
extrapolation, this estimate may subsequently be validated by the independent analysis 
of a suitable number of samples known to be near, or prepared at, the LOD. 
 
Limit of Quantitation: 
 
It is recommended that the limit of quantitation and the method used for determining the 
LOQ be presented. The limit should be subsequently confirmed by the analysis of a 
suitable number of samples known to be near, or prepared at, the LOQ. 
 
Robustness/Ruggedness: 
 
It is recommended that tabular representation including conditions tested, retention 
times, tailing factors, effects on resolution, and potency be presented. 
 
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GLOSSARY 
 
1. ANALYTICAL PROCEDURE 
 
The analytical procedure refers to the way an analysis is performed. It describes in detail the 
steps that should be followed to perform each analytical test. This may include, but is not 
limited to, the sample, the reference standard and the reagents preparations, use of the 
apparatus, generation of the calibration curve, and use of the formulae for the calculation. 
 
2. SPECIFICITY 
 
Specificity is the ability to assess unequivocally the analyte in the presence of components that 
may be expected to be present. Typically, these might include impurities, degradation products, 
matrix, other approved drugs, etc. 
 
Lack of specificity of an individual analytical procedure may be compensated for by other 
supporting analytical procedure(s). 
 
This definition includes the following: 
Identification: to ensure the identity of an analyte. 
Assay (content or potency): to provide an exact result which allows an accurate 
statement on the content or potency of the analyte in a sample. 
 
3. LINEARITY 
 
The linearity of an analytical procedure is its ability (within a given range) to obtain test results 
that are directly proportional to the concentration (amount) of analyte in the sample. 
 
4. RANGE 
 
The range of an analytical procedure is the interval between the upper and lower concentration 
(amounts) of analyte in the sample (including these concentrations) for which it has been 
demonstrated that the analytical procedure has a suitable level of precision, accuracy, and 
linearity. 
 
5. ACCURACY 
 
The accuracy of an analytical procedure refers to the closeness of agreement between the value 
that is accepted either as a conventional true value or an accepted reference value, and the value 
found. This is sometimes termed trueness. 
 
6. PRECISION 
 
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The precision of an analytical procedure expresses the closeness of agreement (degree of 
scatter) between a series of measurements obtained from multiple sampling of the same 
homogenous sample under the prescribed conditions. 
 
Precision may be considered at three levels: repeatability, intermediate precision, and 
reproducibility. 
Precision is investigated using homogenous, authentic samples. However, if it is not possible to 
obtain a homogenous sample, it may be investigated using artificially prepared samples or a 
sample solution (although extraction variability will not be measured). 
 
The precision of an analytical procedure is usually expressed as the variance, standard 
deviation, or coefficient of variation of a series of measurements. 
 
6.1. Repeatability: Repeatability expresses the precision under the same operating 
conditions over a short interval of time. Repeatability is also termed intra-assay 
precision. 
 
6.2. Intermediate precision: Intermediate precision expresses within-laboratories 
variations: different days, different analysts, different equipment, etc. 
 
6.3. Reproducibility: Reproducibility expresses the precision between laboratories 
(collaborative or transfer studies, usually applied to standardization of methodology). 
 
7. LIMIT OF DETECTION 
 
The limit of detection of an individual analytical procedure is the lowest amount of 
analyte in a sample that can be detected, but not necessarily quantitated as an exact 
value. 
 
8. LIMIT OF QUANTITATION 
 
The limit of quantitation of an individual analytical procedure is the lowest amount 
of analyte in a sample that can be quantitatively determined with suitable precision 
and accuracy. The quantitation limit is a parameter of quantitative assays for low 
levels of compounds in sample matrices and is used particularly for the 
determination of impurities and/or degradation products. 
 
9. ROBUSTNESS / RUGGEDNESS 
 
The robustness of an analytical procedure is a measure of its capacity to remain unaffected by 
small, but deliberate variations in method parameters. Robustness provides an indication of its 
reliability during normal usage. 
 
10. SYSTEM SUITABILITY 
 
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A procedure run prior to the individual analytical analysis to demonstrate that the instrument, 
column, mobile phase, etc., parameters are within defined criteria. Adequate system suitability 
is demonstrated before proceeding with the analysis. 
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