Effect of anionic water-soluble dyes on film coating properties of chitosan acetate.

Solution of chitosan in dilute acetic acid was prepared to have an apparent viscosity of 125 mPa s and mixed with solution of anionic water-soluble dye. The effects of concentration and type of dye and molecular weight and percentage deacetylation of chitosan on their miscibility and physical stability were investigated. High concentration of dye and high molecular weight and percentage deacetylation of chitosan resulted in precipitation or colloidal dispersion due to ionic interaction between dye and the polymer. The effect was more prominent upon storage. The miscibility of dye and the polymer depended on the molecular configuration and ionic group in the dye molecule. It was ranked brilliant blue approximately euqal to green FS > fast green > ponceau SX approximately euqal to green sunset yellow > erythrosine approximately euqal to green tartrazin > indigo carmine. Solutions of low molecular weight chitosan with and without green FS were then used as coating formulations onto propranolol hydrochloride core tablets. There was no color migration on coated tablets even after storage for 1 year. Disintegration and drug dissolution from tablets coated with colored film were slightly slower than those from tablets coated with plain film and core tablet, respectively. This was corresponding to the results of swelling and dissolution of cast films. However, all tablets conformed to the specification in monograph of USP XXIV.