Comparative Evaluation of Metformin and Metronidazole Release from Oral Lyophilisates with Different Methods

The aim of this study is to compare three different dissolution methods to assess the drug release from oral lyophilisates, based on interpolyelectrolyte complexes (IPECs). IPECs were prepared by mixing solutions of a linear polymer, Eudragit® EPO, with a polymer with a cross-linked structure, Noveon® AA-1 or Carbopol® 10 Ultrez (in ratios of 1:2 and 1:1, respectively). Metformin or metronidazole were used as model drugs to achieve a systemic or local effect. A comparative assessment of the drug release kinetics was carried out using artificial saliva and three different set-ups: a paddle stirrer (USP apparatus 2), a flow cell (USP apparatus 4) and a Franz diffusion cell. The results demonstrated that oral lyophilisates disintegrated within 1 min. In the case of metformin, the drug release was completed in about 90 min independently of the set-up. The static conditions in the Franz diffusion cell and USP apparatus 2 permitted the aggregation of the IPEC; therefore, the release profiles show a significant difference compared to the USP apparatus 4.