Entrapment of bioactive compounds within native albumin beads: III. Evaluation of parameters affecting drug release

A simple and easily controlled method for preparing microbeads has been developed using a w/o emulsion technique. Under constant process variables (temperature, stirring, etc.), the formulation variables associated with the oil phase that can be altered that affect the size of beads produced are density, viscosity, and interfacial tension. Viscosity and interfacial tension were found to be important factors. Increasing the viscosity of the oil phase decreases the mean size and size distribution of the microbeads produced and results in an increase in the release rate of l-norgestrel. Decreasing the interfacial tension results in an increase in release rate. Since simple mixtures of oleic acid and light mineral oil offer a series of oil phases with different interfacial tensions but similar viscosity, it should be possible to prepare microbeads having a desired release rate by simply varying the mixture of oils. Decreasing temperature translates into an increase in release rate of drug through a viscosity effect. Increasing the amount of drug added decreases release rate.