Calcium alginate microparticles for oral administration: II. Effect of formulation factors on drug release and drug entrapment efficiency.

The release rate of nicardipine HCl from various alginate microparticles was investigated. Manugel A7B618 which has a high guluronic acid content of 70% and a low polymerization degree of 60-400 was used as alginate. A 2(3) factorial design was utilized for the preparation of the alginate microparticles. The effect of drug:polymer weight ratio, CaCl2 concentration and curing time on parameters such as the time for 50% of the drug to be released (t50%) and the drug entrapment efficiency were evaluated with analysis of variance. The mean particle sizes and the swelling ratios of the microparticles were determined. The in vitro release studies were carried out with a flow-through cell apparatus at different media (pH 1.2, 2.5, 4.5, 7, 7.5 buffer solutions). Drug:polymer weight ratio and the concentration of the crosslinking agent were the influential factors on the release of NC from the alginate microparticles. The release of nicardipine was extended with alginate microparticles prepared in a ratio of 1:1 (drug:polymer weight ratio). The release of drug from alginate microparticles took place by both diffusion through the swollen matrix and relaxation of the polymer at pH: 1.2-4.5. However, the release was due to diffusion and erosion mechanisms at pH 7-7.5.