Drug release profiles of ophthalmic formulations. 1. Instrumentation

An experimental method is described for measuring time-release profiles of drugs from various ophthalmic dosage forms. This in vitro method is carried out under conditions nearly representative of those observed in vivo. Specifically, we have reproduced in vitro the small volume and the slow exchange rate of the human precorneal tear reservoir. Volumes on the order of 8-30 microL are achievable. The concentration of drug downstream from the sample reservoir is analyzed nearly continuously and the entire release profiles are appropriate for modeling. This analytical system has been used to study drug release kinetics from controlled release formulations such as gels and suspensions. The method is compared with alternative techniques.