The effect of drug concentration and curing time on processing and properties of calcium alginate beads containing metronidazole by response surface methodology

The purpose of present research work was to prepare calcium alginate beads containing water-soluble drug metronidazole using 3² factorial design, with drug concentration and curing time as variables. Curing time was kept as low as possible to improve entrapment with increasing drug concentration. Mostly the drugs which had been encapsulated were water insoluble to facilitate drug encapsulation; a characteristic drug release as whole process is aqueous based. Entrapment efficiency was in the range of 81% to 96% wt/wt, which decreased with decrease in polymer concentration and increase in curing time. The beads were spherical with size range between 1.4 and 1.9 mm. Scanning electron microscope (SEM) photomicrographs revealed increase in the leaching of drug crystals with increased curing time and high drug concentrations. In acidic environment, the swelling ratio was 200% in 30 minutes, but in basic medium, it increased to a maximum of 1400% within 120 minutes. In acidic medium, the swelling and drug release properties were influenced by drug solubility, whereas in phosphate buffer these properties were governed by the gelling of polymer and exhibited curvilinear and quadratic functions of both the variables, respectively.