by Ashley Sanchez, BS, Senior Project Manager, Analytical Sciences
Potency is a required measurement to determine the amount of active ingredient contained in a preclinical dose formulation. Assessing potency ensures that the test system receives the appropriate amount of active ingredient based on predetermined specifications. Potency determinations are made using a validated analytical method. We have identified some factors for consideration in order to have the most effective sample preparation that result in accurate potency measures.
Preclinical Dose Formulation Potency
Assessing the potency of preclinical dose formulation is completed by sampling the prepared formulation and assaying, using a validated analytical method. Each dosing concentration is sampled and assayed; typically, assays are completed in duplicate. The observed concentration is compared to the theoretical amount and a percent of the theoretical concentration is determined. In the event that a dose formulation does not meet the predetermined acceptance criteria, the result must be investigated for laboratory error. If an analytical error cannot be discovered, the effect on the study must be determined.
Potency of a dose formulation is an essential and crucial component in ensuring that the test system receives the appropriate amount of active ingredient based on predetermined specifications. If the correct potency is not achieved, the toxicological effects of the drug may not be observed. Failure to achieve accurate potency levels may be affected by many factors including weighing and mixing procedures, use of laboratory equipment, filtration, and even compound characteristics and storage. When these problems occur, it is important to isolate and investigate each variable to identify the root cause.
Mixing and Filtration
Proper and appropriate mixing of a compound is essential to ensure adequate potency and homogeneity of the ingredient in the formulation. However, assumptions regarding solubility frequently exist when preparing a simple formulation. For example, a formulation prepared as a solution may appear soluble; however, results can dictate otherwise.
Another factor to consider in achieving accurate potency is the effect of laboratory glassware and/or equipment. Interactions may occur between the analyte and surface of the volumetric flask used. Such an observation was discovered in preparation of samples in plastic versus glass (see Table III). Solutions were only left in plastic for 30 minutes. As demonstrated, the analyte possessed a high affinity for plastic. Furthermore, an assessment made using a glass serological pipette yielded higher recoveries, compared with using a positive displacement pipette, containing a plastic tip.
If potency issues exist after assessing most potential mixing complications, it is important to refer back to the compound characteristics. If a compound is micronized, problematic weighing may exist because of the static, cohesiveness, and/or lightness of the material. Alternatively, the material may be highly hygroscopic and require the use of a desiccant in storage. When weighing a hygroscopic material, it is essential to consider the amount of water being absorbed, as this can cause uncertainty during the weighing process. It is also significant to account for a correction factor in consideration of salt factors and purity. This is important when considering manufactured lots used in in vivo studies that do not undergo purification processes that are performed for clinical trials.
A final factor in achieving correct potency is a consideration of storage and stability of the formulated compound. It is necessary to have data to support conditions and duration of storage. Degradation of a compound can be seen at different temperature conditions (e.g., ambient, refrigerated, frozen or ultra-frozen). Yellow light versus ambient light may also affect potency if the formulated test article requires protection from light. Analysis of potency of a formulated drug in specified storage conditions, extending longer than the dose formulation, should be performed before dosing. Covering the time window from preparation to dosing ensures that the proper potency of drug is delivered to the test system.
Failure to achieve accurate potency levels may be affected by many factors including weighing and mixing procedures, use of laboratory equipment, filtration, and even compound characteristics and storage. When these problems occur, it is important to isolate and investigate each variable to identify the root cause.
1 Code of Federal Regulations Title 21, Food and Drug Administration (Government Printing Office, Washington DC), Part 58
2 Whitmire M et al., The AAPS Journal, 12(4), 628–634 (2010).