Development of a Test Method for in Vitro Drug Release from Soluble and Crystal Dispersion Type Ointments

determining biological equivalence between pioneer and generic products, checking equivalence after change in batch size, detecting changes in components or composition, and checking equivalence after modification of manufacturing equipment or processes. The test method has also been suggested as a possible standard for quality control of topical drug products. We thus established an in vitro drug release test for ointments. The theory of the drug release profile from ointments was established by T. Higuchi and W. I. Higuchi and has been used in various methods. However, there has been no in vitro drug release test for topical drug products aimed at topical action validated like that for oral dosage forms. In the 90’s a test method was described for evaluating transdermal delivery systems (TTS’s) in the Drug Release section in the USP 22 revision. However, this method was not for the purpose of evaluating topical drug products aimed at topical action, but for the purpose of evaluating TTS. The in vitro drug release profile for practical formulation aimed at topical action was reported to be suitable as an evaluation method for bioequivalence. The study used the slope obtained from plotting the cumulative amount of drug released against the square root of time as an index for release, but further analysis was not performed. With respect to practical formulation, there have been few studies analyzing drug release profiles from hydrocarbon bases, which display inferior release results. In the present study, using oxybenzone as a model drug, we performed intensive parameter analysis on in vitro drug release profiles from hydrocarbon bases by applying T. Higuchi’s equation. For analysis of the cumulative amount of drug released, T. Higuchi’s equation: q5{(2Co2Cs)Cs ·D · t} 1/2 and an equation modified for soluble-type ointments: q5Co(2 ·D · t) 1/2