The aim of this study was to examine the usefulness of a pH-dependent copolymer - Eudragit FS - for employment in the technology of preparing modified release metronidazole matrix tablets. In addition, in our work, Eudragit RL and Eudragit RS were included in the composition of some formulations, as well as sodium lauryl sulfate and polysorbate 80. As part of the study of the dissolution test, the similarity coefficient (f2) for the obtained profiles was calculated, and mathematic models were used to estimate the kinetics and mechanism of active substance release. In our work, it was observed that the inclusion of polymer Eudragit FS alone in the tablet composition ensured a modified release of the active substance for 10 h. After this time period, the amount of metronidazole determined in the acceptor fluid was 71% - 81% of the declared dose. Modification of the composition by the addition of surfactants resulted in an increased release of the active substance of up to 98%. This effect was dependent on the type of surfactant and its quantitative ratio to the Eudragit FS. Similar release profiles were obtained for tablets containing Eudragit RS and sodium lauryl sulfate, as well as Eudragit RS and polysorbate 80. Depending on the composition of tablets, metronidazole release proceeded in accordance with either first or second-order kinetics. We calculated as well, that the differing masses of Eudragit FS in the studied formulations correlates with the order of release kinetics (p < 0.002). Such an effect was validated using the Weibull model, wherein, in all the studied formulations, the release rate was seen as a decreasing function of time. An analysis of data according to the Ritger-Peppas model and the Peppas-Sahlin model for some formulations, indicated that the mechanism of active substance release from matrix tablets is diffusion.
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