Development of polysaccharide gel-coated pellets for oral administration. 2. Calcium alginate.

Calcium alginate gel-coated pellets were developed by forming an insoluble gel coat on extruded-spheronized pellets by interfacial complexation. Experiments were designed to investigate the effect of pellet size, alginate type, alginate concentration, and dissolution medium on swelling and drug release behavior. Low swelling in acidic media was related to proton-calcium ion exchange forming insoluble acid gels. In contrast, partial formation of soluble sodium alginate in 0.1M NaCl induced water uptake, resulting in greater swelling. Drug release from coated pellets showed a lag time when the gel coat hydrated and swelled, followed by a zero-order release. Significantly slower release was observed when either the pellet size or the alginate concentration was increased. Alginate with high guluronic acid content gave the slowest release. Different types of alginate with high mannuronic acid content showed different release behaviors that are probably due to the different monomer sequences and botanical sources. The faster drug release in acidic media and 0.1M NaCl compared to water is probably due to reduced calcium cross-linking in the gel. These results suggest that the pellet size, alginate type and concentration and dissolution medium influenced the swelling and drug release behavior of calcium alginate gel-coated pellets.