The drug release profile from calcium-induced alginate gel beads coated with an alginate hydrolysate.

Calcium-induced alginate gel bead (Alg-Ca) coated with an alginate hydrolysate (Alg), e.g. the guluronic acid block (GB) was prepared and the model drug, hydrocortisone release profiles were investigated under simulated gastrointestinal conditions. Their molecular weights were one sixth or one tenth that of Alg and the diffraction patterns of the hydrolysates resembled that of Alg. The drug release rate from Alg-Ca coated with GB apparently lowered than that of Alg-Ca (coating-free) in the gastric juice (pH1.2). And the coating did not resist the disintegration of Alg-Ca in the intestinal juice (pH 6.8) and the gel erosion accelerated the drug release. On the other hand, for the coated Alg-Ca containing chitosan, the drug release showed zero-order kinetics without rapid erosion of Alg-Ca. The drug release rate from Alg-Ca was able to be controlled by the coating and modifying the composition of the gel matrix.