Functional Pharmacological Validation of Betahistine Release from Chitosan Microspheres Using an Isolated Guinea-Pig...

Background: Betahistine-loaded chitosan microspheres have previously demonstrated formulation-dependent drug release; however, conventional in vitro release testing does not establish whether the drug incorporated into the delivery system retains pharmacological activity. Methods: This study evaluated the time-dependent functional activity of four previously characterized betahistine-loaded chitosan formulations using isolated guinea-pig gastric smooth muscle strips. Microsphere quantities corresponding to an equivalent nominal amount of 10 mg betahistine were compared with free betahistine. Spontaneous contractile activity was continuously recorded and mean peak contractile force (Favr) and the area under the Favr-time curve were evaluated. Results: Free betahistine produced a pronounced early response followed by progressive attenuation. In contrast, all microsphere formulations produced gradually increasing and sustained responses, with higher observed Favr values than free betahistine at later observation times. Time-matched analysis revealed positive formulation-dependent associations between cumulative betahistine release and Favr (R² = 0.8384-0.9914), whereas functional performance did not follow the rank order of drug loading. Conclusions: These findings provide functional evidence consistent with sustained availability of pharmacologically active betahistine from the chitosan microsphere formulations and support ex vivo functional assessment as a complementary approach to conventional in vitro release characterization.