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When designing stability protocols, formulation, storage, and dosing conditions must be assessed.
Establishing adequate stability of a preclinical dose formulation is a crucial component of drug development because it ensures that the test system receives the appropriate amount of test article based on protocol specifications. Considerations for designing adequate stability protocols must include assessment of formulation, storage, and dosing conditions.
Dose-formulation stability analysis
Determination of dose-formulation stability is required for all preclinical regulated studies used to assess the safety of drugs. Stability assessments are completed by the analytical testing laboratory. These assessments, however, cannot be completed in isolation of the analytical laboratory because formulation, storage, and dosing conditions must all be considered to adequately support data collected for preclinical studies.
Analytical methods for assessing concentrations of preclinical dose-formulation analysis are typically less rigorous and are validated using less stringent criteria than those for drug substance or drug products. Methods for preclinical dose formulations are developed for assay potency at concentrations appropriate for dosing in vivo studies. Moreover, the scope of validation used to support these methods is dependent upon the phase of preclinical drug development. Traditional impurity and related substance assays, which focus on quantitative analysis of impurity and degradant products, are not typically used because of long analysis run times and the resources that would be required to develop and validate these types of methods. Forced-degradation studies, which are used in the development of standard impurity and related substance assays, are not required for preclinical dose-formulation methods.
Assessment of stability for preclinical dose formulations is completed by comparing a potency value obtained at time zero (or a nominal concentration) with a potency value obtained following a specified amount of time and corresponding storage conditions. The observed difference is then compared to predetermined specifications to assess the stability of the formulated dosing material. For example, a formulation is validated using acceptable accuracy criteria of 100 ± 10% of nominal concentration. When the formulation was subsequently evaluated for stability, the results shown in Table I were observed.
Based on the specifications for stability being 100 ± 10% of nominal concentration, the 1.0 mg/mL formulation at six hours is acceptable for dosing while the same formulation at 24 hours would not. The data indicate that considerations would need to be made to ensure that dosing of the formulation was completed within six hours of preparation.
While the primary analyte peak is generally used to assess stability, known degradant peaks may be included in the assessment. Known degradant peaks are generally included with the potency value and may be quantitated as a percentage of total observed peak response. In the example previously cited, if a known degradant peak is being monitored along with the primary analyte peak, one would expect the degradant peak to increase inversely relative to the primary analyte peak as a function of time. The specifications may include a requirement that the degradant peak area remains below a specific percentage of the primary analyte peak area. For materials that are well characterized, this provides more stringent information on dose formulation stability. As is often the case during the early stages of drug development, analyte degradants are not well characterized and the comparison of concentrations determined from the primary analyte peak is sufficient and fit for purpose.
Stability assessments may not be performed at all dose levels, which is in contrast to a finished pharmaceutical product (i.e., drug product) whereby stability is assessed at each dose level. Typically, stability assessments are performed using low and high concentrations that encompass the range of possible dosing concentrations.
Stability assessments of preclinical dosing formulations need to consider conditions that are representative of the formulation process used for preparing the dose preparation. Specifically, preparations manufactured in an analytical laboratory to evaluate method performance may not be representative of the process used in the formulation laboratory and, therefore, may not be appropriate for use in assessing stability. Differences in scale, equipment, and mixing methods may need to be considered. For example, heat generated from the use of high-speed mixers in a dosing batch may not have been apparent during the preparation of a small-scale batch. As such, direct heating of the dosing batch may be required. Extended or overnight mixing times also may be required for a dosing batch where they may not be required for a small-scale validation batch. These variables need to be considered when establishing an appropriate stability protocol to ensure stability batches are representative of dosing batches.
Stability data need to cover the conditions encountered during dosing in the in vivo studies. Related to dosing, physical stability becomes just as crucial as chemical stability. Questions related to maintaining a viable suspension or homogeneous mixture during the dosing period may need to be considered and addressed. In situations where dosing formulations have known stability issues, either chemical or physical adjustments may be needed for dosing. Conditions such as preparing the dose formulation under yellow light, temperature control, continuous stirring, and timed dosing are all strategies that may be used to ensure that the integrity of the dosing formulation material remains intact. For example, a dose formulation was found to be chemically stable for 48 hours at ambient temperature and observed recoveries were near 100% of the time-zero value. An optimal dosing viscosity, however, could not be maintained at ambient temperature and the material required heating before and during dosing. As a consequence, heating was incorporated into the original stability assessment.
Consistent with stability assessment for drug products, storage of preclinical dose formulations needs to be considered when evaluating stability. This evaluation may range from a simple assessment of material at ambient or refrigerated conditions or for material being used over multiple dosing days and include evaluation of freeze/thaw cycles. Extensive stability programs, comparable to those designed for drug substances and drug products, are not required as storage and use are tightly controlled.
Stability studies on dose formulations are required to support preclinical regulated studies. While stability protocols for preclinical dose formulations are not as comprehensive as their subsequent drug-substance and drug-product programs, the information they provide to support an in vivo study is critical. Development of stability studies requires consideration of formulation, dosing, and storage to ensure the stability data collected are directly relevant to the in vivo study conditions.
Amy Smith is director of analytical laboratory operations, and Melissa Whitsel is analytical manager both with MPI Research; headquarters located at 54943 North Main Street, Mattawan, MI 49071.
1. FDA, 21 CFR Part 58 Good Laboratory Practice Regulations Final Rule (Rockville, MD, 1987).
2. M.B. Whitmire, AAPS Jrnl. 12 (4), (2010).
3. ICH, Q1A(R2) Stability Testing of New Drug Substances and Products (2003).
4. ICH, Q2(R1) Validation of Analytical Procedures: Text and Methodology (1996).