Physicochemical and Bioadhesive Evaluation of Eudragit® EPO/L100 Interpolyelectrolyte Complexes as Gastroretentive Drug Delivery Carriers

This study evaluated interpolyelectrolyte complexes (IPECs) formed from Eudragit® EPO and Eudragit® L100 as potential platforms for gastroretentive drug delivery systems (GRDDS), using metronidazole (MZ) and acyclovir (ACR) as representative model drugs. The prepared Eudragit® EPO/L100 IPECs, obtained under different pH conditions, exhibited variable swelling behavior in simulated fasted gastric fluid (0.1 M HCl) while retaining structural integrity for 6 h. Changes in the internal microenvironment of IPEC matrices under acidic conditions were analyzed by FT-IR spectroscopy, complemented by thermal and elemental characterization. The IPEC formulations exhibited notable bioadhesive performance, with no statistically significant difference from the reference material (Carbopol) in mucin compact adhesion testing. Drug release studies indicated that the liberation of metronidazole (class I BCS) from the IPEC matrices was positively correlated with the extent of swelling. After 6 h in simulated gastric medium (0.1 M HCl), IPEC 1 released 49.62% ± 6.20% of metronidazole, whereas IPEC 2 achieved 87.69% ± 5.15%. In contrast, the cumulative release of acyclovir (class III BCS) reached 25.76% ± 5.67% for IPEC 1 and 21.48% ± 5.00% for IPEC 2. The release behavior of both drugs followed a mechanism governed by polymer chain relaxation within the matrix, consistent with the Peppas–Sahlin kinetic model. Overall, the findings indicate that these interpolymer complexes represent promising candidates for further investigation as carriers in gastroretentive bioadhesive drug delivery applications.