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.
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.
Typical acceptance criteria are listed in Table I.
Table I: Typical acceptance criteria for different formulation types.
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.
Each dosage concentration, including control samples, should be assessed for the first and last test batches of in vivo studies, at a minimum. Theoretical concentrations considering displacement factor and density will aid in achieving the targeted
concentration, but measuring the actual result of a formulation will detect the true potency level of the drug in vehicle.
Conversely, achieving the correct potency level is not always a simple addition of active ingredient to vehicle. The use of
laboratory equipment, filtration, compound characteristics, storage, and chemical instability, including weighing and mixing
procedures, are factors that can affect potency.
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. Such an occurrence was observed
in a high-range quality control sample preparation shown in Table II.
Table II: Low recovery observed in a high-range quality control sample preparation.
A laboratory investigation was conducted to identify an assignable cause for the low recoveries. A secondary dilution was
prepared from the primary dilution as the method instructed. This time, however, recoveries were within specification of 100%
±10. Although the solution appeared to be a true solution, it was clear that the formulation presented problematic mixing
and/or dissolution. Furthermore, in a consecutive run, precipitate was later observed in the primary dilution, indicating
the potential problem was dissolution of the analyte in the primary dilution. The analytical method was updated to include
in the processing procedure that adequate mixing must be performed after the primary dilution to assure complete dissolution,
because particles of the analyte may be present. Thereafter, all samples passed the solution criterion. In this instance,
the formulation itself achieved the targeted potency; the problem arose during sample processing for analysis. Though the
test system did receive the correct dosage potency, it is necessary to have the analytical data to support this conclusion.
Equally important when carrying out many mixing procedures, especially sonication, is allowing the formulation to cool before
performing any additional aliquots. Neglecting this in itself can cause low recoveries when diluting. Special mixing considerations
are also necessary when working with analytes that are not small molecules. Cautious inversion can effectively mix large molecules
and proteins, without potential destructive effects observed from vigorous mixing procedures.