Ocular Physiologically Based Pharmacokinetic Modeling for Ointment Formulations

Purpose The purpose of this study is to show how the Ocular Compartmental Absorption & Transit (OCAT (TM)) model in GastroPlus(R) can be used to characterize ocular drug pharmacokinetic performance in rabbits for ointment formulations. Methods A newly OCAT (TM) model developed for fluorometholone, as well as a previously verified model for dexamethasone, were used to characterize the aqueous humor (AH) concentration following the administration of multiple ointment formulations to rabbit. The model uses the following parameters: application surface area (SA), a fitted application time, and the fitted Higuchi release constant to characterize the rate of passage of the active pharmaceutical ingredient from the ointment formulations into the tears in vivo. Results Parameter sensitivity analysis was performed to understand the impact of ointment formulation changes on ocular exposure. While application time was found to have a significant impact on the time of maximal concentration in AH, both the application SA and the Higuchi release constant significantly influenced both the maximum concentration and the ocular exposure. Conclusions This initial model for ointment ophthalmic formulations is a first step to better understand the interplay between physiological factors and ophthalmic formulation physicochemical properties and their impact on in vivo ocular drug pharmacokinetic performance in rabbits.