Comparative evaluation of erythromycin release and mechanical properties in gelatin, hydrolyzed carrageenan, and carrageenan–maltodextrin hard-shell capsules

The mechanical behavior, formulation performance, and erythromycin release kinetics of hard-shell capsules prepared from gelatin, hydrolyzed carrageenan (HC), and hydrolyzed carrageenan–maltodextrin (HC-MD) systems were comparatively evaluated. Capsules were produced using a dip-coating method and assessed for weight variation, mechanical strength, degree of swelling, disintegration time, dissolution profile, drug release kinetics, and surface wettability via contact angle measurements. Erythromycin release at pH 1.2, 4.5, and 6.8 followed diffusion- and surface-area-controlled kinetics, consistent with zero-order, first-order, Higuchi, and Hixson–Crowell models. Both HC and HC-MD capsules exhibited faster disintegration, greater swelling, and higher drug release than gelatin capsules, particularly under neutral and basic conditions. The HC-MD formulation demonstrated superior wettability and lower contact angles, which enhanced drug diffusion across the capsule surface.