Synthesis of controlled‐release products in supercritical medium

Abstract

AbstractControlled‐delivery products have recently received considerable attention. They prolong the drug's therapeutic effect, keeping its concentration between the therapeutic and toxicity limit. The final product must be free of residual solvent, even with nontoxic solvents, to provide its constant property that does not change with natural evaporation of the solvent. A major cost item in the synthesis of controlled‐release drugs is to remove this solvent to acceptable limits. To eliminate the production step involving the organic solvent from the overall process, the drug was introduced into the polymer matrix using supercritical carbon dioxide (scCO2) as the carrier solvent and swelling agent. This study focuses on the impregnation of a biodegradable polymer matrix with 5‐fluorouracil for chemotherapy and β‐estradiol estrogen hormone therapy. Swelling of the polymer matrix, solubility of drug components in scCO2 and the adsorption isotherm/partition coefficients in the presence of scCO2 were studied. To investigate the single‐component supercritical adsorptive synthesis of controlled‐delivery products, accurate experimental techniques to measure drug‐component solubilities in supercritical fluids and adsorption isotherms in the presence of supercritical fluids were developed. Solubility data of these drugs in scCO2 at 35–55°C and 101–220‐bar were reported. The adsorption equilibrium constants/partition coefficients were presented for these drug components on poly‐dl‐lactide‐co‐glycolide (PLGA) at the same conditions. To understand the effect of operating variables on the total drug loading and to predict the drug‐loading breakthroughs, a flow over a flat plate model was developed that accounts for the polymer swelling, the partitioning of the drug component between the supercritical and polymer phases, and the polymer diffusivity. Experimental isotherm data with and without the polymer were incorporated into the model to isolate the system response from the polymer response to determine impregnation efficiencies.