Supercritical solvent impregnation: A semiquantitative method for the evaluation of affinity between polymers and drugs

A supercritical fluid can be used in substitution of the original organic solvent for the preparation of pharmaceutical forms. The steps involved in the preparation are essentially similar to those of the traditional preparation but in this case the final purification is not required. The interest in the supercritical fluid impregnation of polymeric materials stems from the opportunity to utilize high diffusivity, low surface tension and the ease of solvent recovery for the preparation of new polymeric materials. The partition of organic compounds between a polymer and a supercritical fluid has been studied by different authors and, despite the low solubility of the organic compound in the supercritical phase, high concentrations in the polymeric phase is easily reached. Most of the applications concern the preparation of drug delivery systems using polymers that are also in the glassy state. Despite the increased number of experimental data, the theoretical framework for the complete understanding and description of the process is still not satisfactory especially regarding the interactions between the polymeric drug and the polymers. The use of linear free energy descriptors is proposed to extrapolate experimental information on polymer organic solvents interaction to the evaluation of the interactions with drugs. The method proposed is validated comparing the calculated results with experimental data of drug – polymer impregnation.