Solubilities of anti-cancer and anti-AIDS drugs in supercritical carbon dioxide

Abstract

Solubility data for pharmacological drugs in supercritical fluids (SCFs) is of great importance, because there is an environmental and cost effective need for alternative specialty separation methods. This research was focused on the study and determination of solubilities of some anticancer (e.g., Taxol, 5-Fluorouracil) and anti-aids drugs (e.g., Azodicarbonamide, Thymidine and 2-Phenyl-4H-3,1-benzoxazin-4-one) in supercritical carbon dioxide. These measurements were made using a Supercritical Fluid Chromatograph (SFC) coupled to a high pressure UV detector online. The solubility of these drugs were studied as a function of temperature (35.1°C ñ 55.1°C) and pressure (100 ñ 300 bar). This technique was initially validated using phenanthrene and compared with the data of several other investigators. The technique proved to be fast, reliable and reproducible. The order of magnitude of the obtained solubilities was 10-6 to 10-4 mole fraction. The drug with the highest solubility was 2-Phenyl-4H-3,1-benzoxazin4-one and the less soluble was taxol. These results correlated well with the volatility of the drugs (indicated by their melting point). This research also studied the effect of pressure (100 ñ 300 bar) and temperature (35.1°C ñ 55.1°C) on the solubility of the drugs. The effect of pressure on the solubility of the drugs followed the expected trend of increasing solubility with an isothermal increase in the pressure for all temperatures studied. This is explained since as pressure is increased, carbon dioxide density increases, and the intermolecular mean distance of carbon dioxide molecules decreases; thereby, increasing the specific interaction between the solute and solvent molecules. The temperature effect always showed a proportional effect in solubility. This indicated that the temperature effect in solute volatility (proportional effect) was more significant than the temperature effect in solvent density (inversely proportional effect). This study showed that it is possible to determine relatively fast a large number of solubility measurements for the studied systems by retention in SFC.