The effect of the drug/polymer ratio on the properties of the verapamil HCl loaded microspheres

In this study, the microspheres containing verapamil hydrochloride (VRP) were prepared with Eudragit RS 100 by solvent evaporation method. In the solvent evaporation method one of the parameters which affect to the formation and properties of the microspheres is the variations of drug/polymer ratios. The aim of our study is to examine the effects of this parameter on the VRP loaded microspheres. To achieve this purpose, only drug/polymer ratio was altered while the other formulation parameters were kept constant and percentage yield value, incorporation efficiency, particle size and distribution of the microspheres were analyzed and micrographs of the microspheres were taken to determine the effects of the increase in the polymer amount of formulations. All the dispersed phase viscosities were evaluated by comparing them with the variations in particle size and distribution of the microspheres. In vitro dissolution tests were done by using dissolution media with three different pH in sequence as half-change method with flow through cell and the effect of the variation in polymer ratio on drug dissolution was evaluated according to dissolution test results. As a result of our study, it is thought that the variation in drug/polymer ratios might have an influence on the physical characteristics of the microspheres and the increasing amount of polymer might be result in decreased drug dissolve. (C) 2002 Elsevier Science B.V. All rights reserved.