Abstract
We established an in vitro drug release test for ointments, using oxybenzone as a model drug. At first, we concentrated upon the reproducibility of the results, the effects of the receiver solution composition, and the effects of the sample loading weight to fix the conditions for the in vitro drug release test.Once the conditions for the test were fixed, we examined the validity of the test by evaluating ointments containing oxybenzone at concentrations of 0.11-15.1%. In this study, we applied T. Higuchi's equation directly to the soluble-type ointment to maintain continuity.Then, for crystal-dispersion type ointments, the diffusion coefficient was calculated by applying the solubility determined by cone mesh filtration method to T. Higuchi's equation. For soluble-type ointments, the diffusion coefficient was calculated by applying a modification of T. Higuchi's equation. Consequently, apparent diffusion coefficient (Dapp) showed constant values, irrespective of the state of the drug (soluble or crystal dispersion). Thus, a validity of Dapp was suggested.Moreover, the theoretical curve of slope fitted well to the observed values in practical drug concentration levels up to 10%. It was suggested taht this in vitro drug release test for ointments is a useful and practical method for quality assurance specifications.
