Acta Pharm. 57 (2007) 429-439

full paper

Original research paper

New co-polymer zwitterionic matrices for sustained release of verapamil hydrochloride

BISTRA KOSTOVA and DIMITAR RACHEV

bistrakostova@abv.bg

Department of Pharmaceutical Technology and Biopharmacy, Faculty of Pharmacy, Medical University, Sofia-1000, Bulgaria

Accepted November 9, 2007

Stable co-polymer [vinyl acetate-co-3-dimethyl(methacryloyloxyethyl)ammonium propane sulfоnate, p(VA-co-DMAPS)] latex of different compositions has been synthesized for the first time by emulsifier-free emulsion copolymerization. The unusual “overshooting” behavior of the co-polymer tablets has been explained by the formation of specific clusters from the opposite oriented dipoles - zwitterionic species. The change of their concentration with the DMAPS unit fraction (m_DMAPS), pH and ionic strength has been considered responsible for the differences observed in the swelling kinetics. The results obtained prove that m_DMAPS and ionic strength could be used to control the swelling degree of the p(VA-co-DMAPS) matrices. In this way, p(VA-co-DMAPS) matrices could be effectively used to control the sustained release of drugs with basic properties like verapamil hydrochloride from model tablets.

Keywords: co-polymer [vinyl acetate-co-3-dimethyl(methacryloyloxyethyl)ammonium propane sulfоnate, emulsifier-free emulsion copolymerization, polyzwitterion, dipole-dipole clusters, swelling degree, matrix tablets, drug delivery