U.S. DEPARTMENT OF AGRICULTURE 

Marketing and Regulatory Programs

Animal and Plant Health Inspection Service

Veterinary Services 

VS Memorandum (VSM) 800.127 

1 | Page

Guidelines for Conducting Product Stability Studies 

1. Purpose and Background 

 

This memorandum provides guidance for studies intended to support the stability criteria

of biological products. It recommends certain aspects of stability study design that the 

Center for Veterinary Biologics (CVB) recognizes as important. It also applies to products 

administered to animals; it does not apply to veterinary diagnostic products.

Title 9, Code of Federal Regulations(9 CFR), 114.13 requires establishment of a dating 

period for every veterinary biological product in accordance with the stability of each of its 

fractions. This document communicates the CVB’s general approach to the concept of 

product stability and provides guidance for designing and conducting stability studies.

 

2. Document Status 

 

A. Issue Date: 03/04/2021

B. This is a new document. This memo is intended to help further clarify 9 CFR 114.13

published in March 2018.

 

3. Authority and References 

 

A. Authorities 

• 9 CFR 101.5

• 9 CFR 113

• 9 CFR 114.13

 

B. References 

• VSM 800.112, Guidelines for Validation of In Vitro Potency Assays 

• VSM 800.124, Guidelines for Potency Specifications of Biological Products 

Administered to Animals 

• CVB Data Guide 

 

C. Definitions 

• Confirmation of dating: In this document, the terms confirmation of dating 

(COD) study and stability study will be used interchangeably.

• Potent or potency: Relative strength of a biological product as determined by 

test methods or procedures as established by the Animal and Plant Health 
U.S. DEPARTMENT OF AGRICULTURE 

Marketing and Regulatory Programs

Animal and Plant Health Inspection Service

Veterinary Services 

VS Memorandum (VSM) 800.127 

2 | Page

Inspection Service (APHIS) in Standard Requirements or in the approved 

Outline of Production for such product.

• Potency degradation profile: The potency degradation profile is the 

mathematical relationship between time and the potency of a product.

• Practical standard deviation (PSD). The PSD is intended as a measure of the 

variability of the potency due to manufacture and testing.

• Stability: Stability refers to the effect of time on the relevant qualities of a 

product stored under specified conditions. This document deals with the 

stability of a product’s potency.

• Stability-indicating assay: A stability-indicating assay is a validated quantitative 

analytical procedure that can detect changes over time in a pertinent 

property of the product. 

4. Audience 

VS employees and members of the biologics industry. 

5. Guidance 

A. Preliminary Stability Criteria 

The stability criteria are the length of the dating period, the potency specification 

throughout dating, and the potency specification at release. The stability criteria are 

related to each other by the potency degradation profile. Before the COD study is 

completed, set preliminary criteria as follows. Setting preliminary potency 

specifications may also be necessary if a major change is made to the potency test 

(e.g.,the measure of potency changes).

1. The length of the dating period.

The firm shall propose a dating period for the product based on preliminary 

information available about the stability of each of its fractions. In the absence of 

such preliminary information, products will typically be assigned an initial dating 

period of twenty-four (24) months for nonviable products and eighteen (18)

months for products intended to replicate in the host animal. The dating period is 

then confirmed or possibly modified based on the COD study. Subsequent 

changes to the dating period may be requested when supported by a stability 

study. Generally dating up to thirty-six (36) months will be considered. Products 

that are licensed prior to confirming the dating period must include a statement 

in Section VI.C. of the Outline of Production that dating has not been confirmed 

and that appropriate data are being collected.
U.S. DEPARTMENT OF AGRICULTURE 

Marketing and Regulatory Programs

Animal and Plant Health Inspection Service

Veterinary Services 

VS Memorandum (VSM) 800.127 

3 | Page

2. The specifications for potency throughout dating.

Set the throughout-dating specification(s) in accordance with VSM 800.124 or in 

accordance with 9 CFR Standard Requirements for the fraction. The throughoutdating potency specifications are the minimum requirements for potency when 

tested at any time within the dating period. They are based on the pivotal 

potency (potency of the serial used in the pivotal efficacy study) and the PSD. 

3. The specification for potency at release.

Set the release specification(s) in accordance with VSM 800.124 or in accordance 

with the 9 CFR Standard Requirements for the fraction. Set the preliminary 

release specification(s) higher than the throughout-dating specification to 

account forpotential potency loss during the length of the dating period. Base the 

difference between the two specifications, release and throughout-dating, on 

information available about the anticipated loss of potency for each fraction for 

the proposed dating period of the product. Release potency specification(s) will 

be necessary before completing the initial COD study.

B. Stability Study Requirement 

The stability criteria of each fraction of each product shall be confirmed or modified 

based on the results of a stability study. An initial stability study is necessary to 

confirm product dating but may result in changes to the release and throughout 

dating potency specifications. A stability study may be required when there is a major 

change to the product’s composition, manufacturing method, or potency test that is 

likely to impact product stability or to support changes to the stability criteria.

C. Stability Study Design and Analysis 

1. Protocol

Submit a protocol prior to initiating any stability study. Submit the initial COD 

study protocol prior to licensure.

2. Test articles

Use a minimum of three (3) serials for each product code produced in a 

manufacturing facility according to the Outline of Production. For product lines, 

use a minimum of three (3) serials of the largest combination and at least one (1) 

serial from each fallout product. Create each serial from a different lot of bulk 

antigen (e.g., Lot A, Lot B, Lot C) for each fraction. When initial potency testing is 

conducted on final containers, select final containers of production serials for the 

study using a defined, documented process. Fully describe the process in a 

protocol prior to study initiation. Use the same serials for all fractions for the 
U.S. DEPARTMENT OF AGRICULTURE 

Marketing and Regulatory Programs

Animal and Plant Health Inspection Service

Veterinary Services 

VS Memorandum (VSM) 800.127 

4 | Page

initial stability study. There may be instances in subsequent stability studies 

where it is not necessary to test all fractions on all serials.

In those instances in which the use of a stability-indicating assay is not required (9 

CFR 114.13 (d)), at least one (1) serial in the stability study should be batched 

near the minimum according to Section IV. I. of the Outline of Production.

3. Number of tests

The number of potency tests conducted on each fraction of each serial at each 

time point should be no less than that required for serial release according to the 

Outline of Production (e.g., if three (3) vials are tested for serial release, no fewer 

than three (3) vials should be tested at each time point in a stability study).

4. Initial test

The first test in the sequence shall be as close as practical to the day of filling into 

final containers or the date of final formulation if the potency of the product is 

tested in bulk form. The report and electronic data should indicate whether final 

containers were or bulk material wastested.

5. Subsequent tests

Conduct all remaining potency tests on material obtained from final containers. 

The number of final containers tested for each serial should be no fewer than that 

required for serial release as specified in the Outline of Production. The CVB 

recommends, but does not require, conducting testing of different serials on 

different calendar days. 

D. Stability-Indicating Assay 

Stability studies must be conducted with a stability-indicating assay except those 

instances specified in 9 CFR 114.13 (d).

1. Quantitative and quantal assays

Quantitative potency assayssuch as one that produces a live bacterial count, or a 

quantal assay such as a live virus titration, will be considered stability indicating if 

the test method has been validated in accordance with VSM 800.112. Additional 

test methods validated according to VSM 800.112 that quantify the concentration 

of the sample may be considered quantitative (and hence stability indicating) as 

well.
U.S. DEPARTMENT OF AGRICULTURE 

Marketing and Regulatory Programs

Animal and Plant Health Inspection Service

Veterinary Services 

VS Memorandum (VSM) 800.127 

5 | Page

2. Relative potency assays

Relative potency assays validated in accordance with VSM 800.112 Appendix III 

will be considered stability indicating if the same reference is used for all testing 

during the stability study and no critical reagents (e.g., capture antibody, detector 

antibody, etc.) have changed during the stability study. If a reagent is nearing 

depletion, the firm may save sufficient quantity to finish the stability study even if 

the reagent is replaced for routine serial release. The initial test should be 

planned so that the reference remains in-dating for the length of the stability 

study.

3. Dichotomous outcome animal tests

Animal tests that provide only a dichotomous (satisfactory/unsatisfactory) 

outcome (such as eight (8) of ten (10) lab animals meeting a requirement) are 

unsuitable to test potency for a stability study except for the exceptions listed in 9 

CFR 114.13 (d). 

4. Other in vivo tests

An in vivo potency test that measures a response in the laboratory animal model 

that is related in a dose-responsive manner to efficacy in the target species and 

the product’s antigen concentration may be considered stability indicating. 

E. Analysis for In Vitro Assays 

Analyze the data to obtain a final estimate of the mean potency loss (MPL) and verify 

the appropriateness of the PSD.

1. Model

Fit a suitable regression model to the potency values obtained from testing of 

final containers to describe the potency degradation profile. When appropriate, 

use the logarithm of the potency estimates as the response variable in the 

regression model. Use a linear regression model when the degradation rate is 

fixed. Use a nonlinear regression model when the degradation rate is time 

dependent. When degradation cannot be distinguished from assay and vial 

variability, use an intercept only model.

2. Final PSD

PSD may continue to be used if the estimate of root mean square error (RMSE) 

from the model fit to the data from the stability study does not exceed 3 x PSD. If 

the RMSE exceeds 3 x PSD, there is an indication the PSD estimate is too low to 

appropriately account for all sources of variation. In such instances, the PSD will 
U.S. DEPARTMENT OF AGRICULTURE 

Marketing and Regulatory Programs

Animal and Plant Health Inspection Service

Veterinary Services 

VS Memorandum (VSM) 800.127 

6 | Page

need to be reevaluated or the throughout-dating specification can be adjusted 

using RMSE in place of PSD.

3. Final MPL

Use the appropriate regression model to determine the expected amount of 

potency decline when stored in final containers during the dating period. The 

potency decline is determined as the difference between the potency estimated 

from the regression model at time 0 and at the time equal to the proposed dating 

period (e.g., eighteen (18) months). Alternatively, the difference between the 

preliminary release and throughout-dating specifications along with the observed 

mean potency loss through time can be used to determine the dating period.

4. Submission to CVB

Submit a report describing the study design, analysis, and final conclusions to the 

CVB. Include all raw data and calculated potency test results in accordance with 

the CVB Data Guide. Submit reports within eight (8) months of the final potency 

test. If Option 31 (VSM 800.124) is selected and the product is licensed prior to 

the completion of the COD study, the COD must be completed no later than the 

date of licensure + product dating + eight (8) months.

F. Monitoring Stability of the Product 

As described in 9 CFR 114.13 (i), product stability must be monitored for products 

licensed after April 13, 2018. Test three (3) percent of serials produced in a calendar 

year with a minimum of one (1) serial and a maximum of three (3) serials. For 

determining the number of serials, all subserials can be classified as the same serial. 

All serials tested for monitoring should be unique (i.e., not different subserials). Each 

of these serials should be tested within thirty (30) days of expiration to monitor the 

stability of the product. For product lines, only the largest combination needs to be 

tested. Submit a monitoring plan to the CVB that describes how serials will be 

selected for monitoring. It may be possible to use the same general plan for multiple 

products.

Submit all data (cumulative) every three (3) years for review. Results should be 

available for the CVB’s review upon request. 

G. Implementation/Applicability 

Updated policy as it relates to stability studies initiated after the date of the 

memorandum is effective immediately. Submit the stability monitoring plans and 

implement testing within one (1) year from the date of this memorandum. 

1 Option 3 from VSM 800.124 requires testing 6 vials initially, after one month, and at expiration.