Multivariate modeling of encapsulation and release of an ionizable drug from polymer microspheres.

In the formulation of polymer microspheres (MSs) loaded with verapamil hydrochloride (VRP), a low molecular weight ionizable drug, by W/O/W emulsification, the pH of the external aqueous phase proved to be a primary determinant of both IE and drug release behavior. Increasing the pH of the external aqueous phase enhanced IE (approximately 100% at pH 8.4).