Abstract

Sodium alginate was selected as film-forming polymer because of its water solubility and low cost. Metronidazole tablets were coated to mask their bitter taste. The present work was carried out by initially developing aqueous film coating formulae with various concentrations of sodium alginate (4, 6 and 8% w/v). Secondly, the properties of the cast films were evaluated. When compared with dilute solutions, concentrated solutions gave thick films, as the density was more. UV light transmission, water vapour transmission and gas permeability of the films decreased with the increase in the thickness of the films. They were freely soluble in distilled water and simulated intestinal fluids but precipitated in simulated gastric fluid. Thirdly, 2 kg of tablets were coated using solutions of the above concentrations. Some tablets were withdrawn after application of 400, 600 and 800 ml of coating solutions, respectively. Coated and uncoated tablets were evaluated for weight variation, hardness and friability, which were all within the acceptable limits. Coating increased hardness and decreased friability. All the coated and uncoated tablets disintegrated within 10 min in water and complied with the USP and BP limits for the assay. The rate of drug release decreased as the concentration of sodium alginate increased. Only 400, 600 and 800 ml coats of 4% w/v solution and 400 ml coats of 6% and 8% w/v solutions In buffer pH 1.2 met USP dissolution requirements. Based on the results of above work along with statistical analysis and accelerated stability studies, 400 ml coat of 6% w/v solution was chosen as the best.