By
Rex Roberts, Ph.D.
This article presents an
overview of stability studies from initial, preclinical development of the drug
substance and drug product to routine manufacture of the FDA approved drug
substance and drug product. Proper design, implementation, monitoring and
evaluation are crucial for obtaining useful and accurate stability data.
Stability studies are linked to the establishment and assurance of safety,
quality and efficacy of the drug product from early phase development through
the lifecycle of the drug product. Stability data for the drug substance are
used to determine the physico-chemical stability profile for the compound. From
this information, optimal storage and packaging conditions can be assessed; the
appropriate retest intervals and criteria can be established for bulk lots of
the material. The stability studies for the drug product are designed to
determine the expiration date (or shelf life). In order to assess stability, the
appropriate physical, chemical, biological and microbiological testing must be
performed. Usually this testing is a subset of the release testing. The
specifications for stability testing may be different from release
specifications if properly justified.
The
drug substance characterization and stability is usually determined as part of
pre-formulation studies. Studies are setup to degrade the solid drug substance
and appropriate solutions and determine the degradation profile. The drug
substance is usually challenged under a variety of accelerated environmental
conditions to evaluate its intrinsic stability and degradation
profile.
HPLC is the predominant tool
used to analyze the drug substance and the impurities, particularly for small
molecules. Frequently, the same HPLC method may be used for drug substance and
drug product, although different sample preparation methods would normally be
required. Often the assay and impurity testing can be performed using a single
HPLC method. However, the assay and purity determinations may also be separate
methods. At least in the US, full validation of the analytical method is not
required until the end of Phase 2 clinical trials. However, establishment of specificity,
linearity and limit of quantification (for impurities) are important at the
earliest stages, since verification of stability hinges on a suitable method for
separating impurities from the active ingredient and at least quantifying the
impurities relative to the drug substance.
Stress studies at elevated
temperature (e.g. 50°C, 60°C and 70°C) for several weeks may be
performed to assess thermal stability. Provided the degradation mechanism is the
same at the different temperatures used, kinetic or statistical models can be
used to determine the rate of degradation at other temperatures (e.g.,
25°C). The solid stability
should also be performed in the presence and absence of water vapor to assess
the dependence of stability on humidity.
Degradation studies should
also be performed in solution. The solvent used for the solution testing will
depend on the solubility of the drug substance and should include water, if the
drug substance is water-soluble. Other solutions or solvent systems may be
evaluated depending on the anticipated formulation or the synthetic process. A
series of buffered solutions in the pH range 2-9 are useful in assessing the
impact of solution pH on the degradation. Photostability should also be
evaluated. A xenon light source can be used as a stress condition.
Alternatively, one can use an accelerated version of either Options 1 or 2 as
described in the ICH guideline for determination of
photostability.5
Oxidation of the drug substance under accelerated conditions (e.g.
hydrogen peroxide), may also be performed to establish oxidation products that
could be formed and sensitivity to oxidative attack.
Early drug product stability
studies are designed to help establish a suitable formulation for delivery of
the drug substance. Compatibility studies of the drug substance with excipients
should be performed to eliminate excipients that are not compatible with the
drug substance. Factorial design may be useful to reduce the number of
experiments. Studies similar to the solid drug substance stress studies may be
performed. In addition, thermogravimetric analysis (TGA) and differential
scanning calorimeter (DSC) may be used to assess the stability of
formulations.
Stability testing must be
continued throughout clinical trials to support the safety, quality and efficacy
of materials released for clinical trials. Stability data must be submitted as
part of the IND filing prior to initiating the Phase 1 clinical trial. Prior to
the first Phase 1 stability study, the pre-clinical studies should provide
information on the appropriate long-term condition and the appropriate
container/closure system. ICH Q1A6 provides the guidance for
design of clinical stability studies. Selection of batches, the container
closure system, specifications, testing frequency and storage conditions are the
most important issues to consider when designing a stability study.
Futscher and
Schumacher12 proposed that the world could be divided into
four zones based on temperature and humidity: Zone I (temperate), Zone II
(Mediterranean, sub-tropical), Zone III (hot dry), Zone IV (hot humid). The
United States, European Union and Japan are primarily Zone II.13 The provisions for Zones
I and II as stated in ICH Q1A are summarized in Tables 1 and 2.
|
Material |
Selection of
Batches |
Container
Closure |
Specifications |
Testing
Frequency |
|
Drug
Substance |
at least 3 batches,
minimum pilot plant scale, simulates production scale
process |
the same as or simulates
container for storage and distribution |
acceptance criteria for
physical, chemical, biological and microbiological attributes that measure
changes in quality, safety and/or efficacy. See ICH Q6A and Q3A
7,8 |
Longterm (months):
0,3,6,9,12,18,24,36...
intermediate: 0,6,9,12
accelerated: 0, 3, 6 |
|
Drug
Product |
at least 3 batches,
minimum of two pilot plant scale, one can be smaller if
justified |
the same container
closure system proposed for marketing |
acceptance criteria for
physical, chemical, biological and microbiological attributes that measure
changes in quality, safety and/or efficacy. See ICH Q6A and
Q3B9 |
See above. Reduced
designs by applying bracketing and matrixing which can be used if
justified |
The container closure system must be evaluated for compatibility with the drug substance and drug product to ensure that the container does not contribute to degradation or contamination. 10
The testing frequency represents the minimum data required for filing. It may be advisable to pull and test a one-month sample for each storage condition to ensure that the study is proceeding as expected.
During Phase 1 it may be necessary to evaluate multiple formulations, dosage strengths and container closure systems. Using bracketing and/or matrixing can frequently reduce the resource allocation for these studies. These two design approaches are discussed in ICH Q1D.14 Bracketing uses the extremes to provide data for the entire study. For example, if dosage strengths of 10, 25, 50 and 100 mg are to be evaluated the study may include testing of all strengths at the initial and final time points with only the 10 and 100 mg strengths being tested at the intermediate time points. Matrixing might be used to evaluate the same strength in multiple container/closure system by selecting only certain container closure systems for testing at each time-point. This selection is usually done in a random fashion.
At the end of Phase 1, the process for manufacture of the drug substance, and the drug product should be established (although refinements will typically continue for much longer).
The
time period in Table 2 represents the minimum data required for the NDA. The
studies must continue until the longterm stability study is completed for the
shelf life and retest period proposed in the NDA submission. Temperature
cycling studies and in-use stability studies may be needed for certain types of
formulations (particularly liquid and semisolid formulations). In early Phase 3
studies one should expect to be placing the batches on stability (at
least three drug substance and drug product lots) that will be used for filing
the NDA. These may be the validation batches if process validation is performed
early enough. Process validation may be performed near the end of Phase 3 and
adequate stability data for these batches may not be available at the time of
filing. shelflife and retest periods may be determined statistically with
adequate quantitative data.
|
Study |
Storage
Condition |
Minimum Time
Period |
Comments |
|
General Case:
Long-term |
25 °C ± 2°C/60% RH ±5% RH or 30°C ±
2°C/65% RH ± 5% RH |
12
months |
Must cover retest or
shelflife period at a minimum and includes storage, shipment and
subsequent use. |
|
General Case:
Intermediate |
30°C ± 2°C/65% RH ± 5% RH
|
6
months |
Must cover retest or
shelflife period at a minimum and includes storage, shipment and
subsequent use. |
|
General Case:
Accelerated |
40°C ± 2°C/75% RH ± 5%
RH |
6
months |
Must cover retest or
shelflife period at a minimum and includes storage, shipment and
subsequent use. |
|
Refrigeration:
Long-term |
5°C±
3°C |
12
months |
Must cover retest or
shelflife period at a minimum and includes storage, shipment and
subsequent use. |
|
Refrigeration:
Accelerated |
25°C ± 2°C/60% RH ± 5%
RH |
6
months |
Must cover retest or
shelflife period at a minimum and includes storage, shipment and
subsequent use. |
|
Freezer:
Long-term |
- -20°C±
5°C |
12
months |
Must cover retest or
shelflife period at a minimum and includes storage, shipment and
subsequent use. |
Aqueous products stored in
semi-permeable containers must undergo studies designed to determine if water
might be lost during storage. Storage conditions for these studies are
summarized in Table 3.
|
Study |
Storage
Condition |
Minimum Time
Period |
|
Long-term |
25°C ± 2°C/40% RH ± 5% RH
|
12
months |
|
Intermediate |
30°C ± 2°C/60% RH ± 5% RH
|
6
months |
|
Accelerated |
40°C ± 2°C/ NMT 25% RH
|
6
months |
The second revision of Q1A (Q1A (R2)), which addresses stability studies required for Zones I and II, resulted in several changes intended to easily allow incorporation of storage conditions in Zones I, II, III and IV into the same study design. The intermediate storage condition changed from 30°C ± 2°C/60% RH ± 5% RH to 30°C ± 2°C/65% RH ± 5% RH for drug substance storage, drug product and drug products packaged in semi-permeable containers. The 30°C ± 2°C/65% RH ± 5% RH condition may be used as a longterm condition instead of 25°C ± 2°C/60% RH ± 5% RH. However, keep in mind that this would result in no backup condition for the accelerated storage condition of 40°C ± 2°C/75% RH ± 5% RH. Stability studies for Zones III and IV are covered in a separate ICH document. 11
ICH
Q1E15 addresses the evaluation of stability data.
The scenarios for room temperature (RT) and refrigerated (RF) conditions are
summarized in Table 4.
The
time period in Table 2 represents the minimum data required for the NDA. The
studies must continue until the longterm stability study is completed for the
shelf life and retest period proposed in the NDA
submission.
|
Scenario |
Storage
Condition |
Statistical
Analysis |
(RT) Retest Period or
Shelf Life (Y) |
(RF) Retest Period or
Shelf Life (Y) |
|
No significant change
in accelerated condition over 6 mo; little or no change over time and
little or no variability for accelerated and longterm |
Room temperature or
Refrigerated |
Usually not
required |
Y= NMT 2X and NMT X+12
mo |
Y= NMT 1.5X and NMT X+6
mo |
|
No significant change
in accelerated condition over 6 mo, but either change or variability or
both; little or no change over time and little or no variability for
longterm |
Room temperature or
Refrigerated |
Long-term data amenable
to statistical analysis and statistical analysis
performed |
Y= NMT 2X and NMT X+12
mo |
Y= NMT 1.5X and NMT X+6
mo |
|
No significant change
in accelerated condition over 6 mo, but either change or variability or
both; little or no change over time and little or no variability for
longterm |
Room temperature or
Refrigerated |
Long-term data not
amenable or statistical analysis not performed, but relevant supporting
data |
Y= NMT 1.5X and NMT X+6
mo |
Y= NMT 1.5X and NMT X+6
mo |
|
Significant change in
accelerated condition over 6 mo and significant change for
intermediate |
Room Temperature
|
No
extrapolation |
NMT longterm data;
possibly less |
N/A |
|
Significant change in
accelerated condition and no significant
change for intermediate over 6 mo |
Room Temperature
|
Long-term data amenable
to statistical analysis and statistical analysis
performed |
Y=NMT 1.5X and NMT X+6
mo |
N/A |
|
Significant change in
accelerated condition and no significant
change for intermediate over 6 mo |
Room Temperature
|
Long-term data not
amenable to statistical analysis, but relevant supporting
data |
Y= NMT X+3
mo |
N/A |
|
Significant change in
accelerated condition over 6 mo and no significant change for intermediate
over 3 mo |
Refrigerated |
No
extrapolation |
N/A |
NMT longterm data;
possibly less |
|
Significant change in
accelerated condition over 6 mo and significant change
for intermediate over 3 mo |
Refrigerated |
No
extrapolation; |
N/A |
NMT longterm data;
possibly less; data may be needed to support
excursions |
In Table 4,
‘X’ represents the number of months of data
being evaluated. No extrapolation is allowed
if the longterm condition is –20ºC (freezer). In this case, the shelflife
and retest period will not be approved beyond the time period for the available
supporting data. Concepts of change over time, significant change and
variability must be defined in order to determine the retest and shelflife using
Table 4. The concepts of change over time and significant change are defined in
Q1E. A p-value > 0.25 for the slope of the regression line indicates
insignificant change; otherwise, the p-value represents change over time. There
is no definition for variability. Bar16 has recently proposed
that process capability index (Cpk), be used as a measure of variability and
that a value of Cpk > 2.5 indicates little or no data variability.
Postapproval (Marketing
Phase)
At
least one lot of drug substance and one lot of each packaging type for drug product
produced each year should be placed on long-term stability. Additional stability
testing may be required to support process changes for drug substance and/or
drug product. The filing requirements for changes are covered in multiple FDA
guidance documents addressing drug product changes (SUPAC) and drug substance
changes (BACPAC). This is typically an area that requires substantial regulatory
understanding and experience to know how to proceed and is beyond the scope of
this article.
Stability is interwoven through the entire fabric of the drug product lifecycle. A detailed understanding of this area is needed to properly design and evaluate stability studies in order to ensure minimal delays and minimize costs in developing a new drug product. This article presents an overview of stability testing and provides the reader with references to obtain a detailed understanding of the subject. Finally, detailed knowledge of the stability requirements and the impact on other areas (e.g., container closure, process changes) is crucial for selecting the appropriate contract lab to perform stability studies.
References
1.
Grimm, W., “Stability Testing of Clinical Samples”, Drug Development and
Industrial Pharmacy, 22, No. 9&10, 851-871 (1996).
2. Berglund, M., Bystrom, K., Persson, B., “Screening Chemical and Physical Stability of Drug Substances”, Journal of Pharmaceutical & Biomedical Analysis, 8, No. 8-12, 639-643 (1990).
3. Krummen, K., “Stability Testing During Development”, Paperback APV, 16, 209-225 (1987).
4. Witthaus, G. “Drug Stability. Accelerated Storage Tests: Predictive Value”, Top. Pharm. Sci., Proc. Int. Congr. Phar., 275-290 (1981).
5. Federal Register, “Guideline for the Photostability Testing of New Drug Substances and Products”, May 16, 1997, Vol. 62, No. 95, 27116.
6.
ICH Q1A (R2), Stability Testing of New Drug Substances and Products, 6 February
2003.
7.
ICH Q6A, Specifications Test Procedures and Acceptance Criteria for New Drug
Substances and New
Drug Products: Chemical
Substances, 6 October, 1999.
8.
ICH Q3A(R), Impurities in New Drug Substances, Step 4, 7 February
2002.
9.
ICH Q3B(R), Impurities in New Drug Products, Step 4, 5 February
2003.
10.
FDA Guidance, “Container Closure Systems for Packaging Human Drugs and
Biologics”, May 1999.
11. ICH Q1F, Stability Data Package for Registration Applications in Climatic Zones III and IV, Step 4, 6 February 2003.
12. Futscher, N., Schumacher, P., Phar. Ind., 34, 479-483 (1972).
13. Beaumont, T., Paperback APV, 32, 177-190
(1993).
14. FDA Guidance, “Q1D Bracketing and Matrixing Designs for Stability Testing of New Drug Substances and Products”, January 2003.
15. ICH Q1E, Evaluation for Stability Data, Step 4, 6 February 2003.
16. Bar, R., “Statistical Evaluation of Stability”, PDA J. Pharm. Sci. Technol., 57, No. 5, 369-377 (2003).