Acta Pharm. 57 (2007) 429-439

full paper

Original research paper


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



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 (mDMAPS), pH and ionic strength has been considered responsible for the differences observed in the swelling kinetics. The results obtained prove that mDMAPS 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