Laboratory determination and thermodynamic analysis of alendronate solubility in supercritical carbon dioxide

Alendronic acid, with the commercial name of Alendronate, is a bisphosphonate medicine which is generally used orally to treat the osteoporosis and Paget's disease of bones. However, its absorption is poor, and its oral bioavailability is <1%. So, development of novel delivery systems to enhance its bioavailability and reduce its side effects is essential. The design a modern drug delivery systems, through supercritical carbon dioxide (scCO2) as a green solvent, which is known as an efficient solution to increase the drug bioavailability, reduce toxicity and side effects. Solubility of pharmaceutical substances in scCO2 is an essential parameter that must be determined for this purpose. Here, solubility of Alendronate was experimentally studied in the span of 0.01 × 10−4 to 1.5 × 10−4 (equilibrium mole fraction), at 308–338 K and 120–300 bar. Also, obtained experimental values were correlated by two fugacity coefficient models (PR-EoS and SRK-EoS), and two activity coefficient models (modified Wilson and UNIQUAC). All these models could successfully correlate the Alderonate solubility values. Meanwhile, the solubility data obtained from the SRK-EoS (AARD% = 10.11) and modified Wilson's model (AARD% = 11.52) are more accurately fitted to the experimental data.