INCREASING THE SOLUBILITY OF LEVODOPA AND CARBIDOPA USING IONIZATION APPROACH

Aim of this study is to increase the solubility of levodopa and carbidopa in order to improve loading quantity of both drugs for oral pullulan thin film preparation. Solubilisation technique via ionization was employed to measure the solubility for pH range of 1.5 to 3.5 and molar concentration at 0.1 and 0.2. Quantitative determination of solubilized levodopa and carbidopa in various solvents showed the highest solubility in pH 1.5, the lowest solubility in pH 3 and 3.5 since zwitterion characteristic of amino and carboxyl group of both drugs. High concentration of proton is able to from cation at carboxylic moiety after ionization. Higher level of molar concentration provided the higher solubility because of the increment of ionic strength. Therefore, suitable solvent for maximizing solubility was found to be either 0.2 M hydrochloric acid/0.1 M citric acid pH 1.5 or 0.1 M hydrochloric acid/0.1 M citric acid pH 1.5. They were subsequently employed as the solvent of levodopa and carbidopa for oral pullulan thin film preparation. Utilization of 0.1 M hydrochloric acid/0.1 M citric acid pH 1.5 provided less tackiness, thinner with less weight/unit film sheet compared to that of 0.2 M hydrochloric acid/0.1 M citric acid pH 1.5. It might be due to lower solid fraction of HCl provided the higher integrity of polymer network formation after drying.