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 substances 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.
Concentration versus stability.
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 characterised, 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 characterised 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.