Gel formation in systems composed of drug containing catanionic vesicles and oppositely charged hydrophobically modified polymer

The aim of this study was to explore if mixtures of drug containing catanionic vesicles and polymers give rise to gel formation, and if so, if drug release from these gels could be prolonged. Catanionic vesicles formed from the drug substances alprenolol or tetracaine, and the oppositely charged surfactant sodium dodecyl sulphate were mixed with polymers. Three polymers with different properties were employed: one bearing hydrophobic modifications, one positively charged and one positively charged polymer bearing hydrophobic modifications. The structure of the vesicles before and after addition of polymer was investigated by using cryo-TEM. Gel formation was confirmed by using rheological measurements. Drug release was studied using a modified USP paddle method. Gels were observed to form only in the case when catanionic vesicles, most likely with a net negative charge, were mixed with positively charged polymer bearing lipophilic modifications. The release of drug substance from these systems, where the vesicles are not trapped within the gel but constitute a founding part of it, could be significantly prolonged. The drug release rate was found to depend on vesicle concentration to a higher extent than on polymer concentration.