Physico-chemical analysis of metronidazole encapsulation processes in Eudragit copolymers and their blending with amphiphilic block copolymers

A physico-chemical analysis of metronidazole–Eudragit copolymers L100 and RLPO (a cationic polymeric matrix with an electrophilic character) was carried out in order to explore the drug–polymer interaction and its possible effects on the encapsulation and release profiles. An oil-in-oil encapsulation procedure was designed to obtain more intimate drug–matrix mixtures and to obtain a better insight into the details of the interaction. The encapsulation efficiency obtained in these cases was high (in the range of 85–95%), but the release rates were quite rapid. Solubility and interaction between metronidazole and copolymers are discussed in detail with a view to explaining the results. Amphiphilic block copolymers of poly(ethylene)-b-(polyethylene oxide) (20, 50 and 80% PEO) were tested as a matrix for metronidazole release in order to improve drug profiles. The performance of RLPO as the matrix for drug release was improved by blending it with amphiphilic block copolymer poly(ethylene)-b-(polyethylene oxide) (20% PEO). The release mechanism of metronidazole is governed mainly by the swelling of RLPO, yielding a better fit with the second-order Schott equation.