Cosolvency – An Approach for the Solubility Enhancement of Lornoxicam

Solubility of lornoxicam in various pure solvents and solvent-cosolvent mixtures was studied to understand drug vehicle interactions and in order to get the required solubility equal to the dose of lornoxicam, i.e., 4 mg/ml for development of solution formulation. Polyethylene glycol (PEG) 400, propylene glycol, ethanol, water, dimethyl formamide, dimethyl sulfoxide, and ethyl acetate were used as solvents and propylene glycol-water, PEG 400-water, PEG 400-propylene glycol, PEG 400-ethanol were used as solvent mixtures. Solubility of lornoxicam was low in water, but increased drastically when semi-polar solvents were added. In PEG 400, dimethyl formamide, dimethyl sulfoxide solubility of lornoxicam was greater than 4.0 mg/ml. The increase in the volume fraction of cosolvent resulted in an increase in solubility of lornoxicam. Based on the solubilization powers, which was determined from slope of their log solubility vs cosolvent volume fraction plots, PEG 400 was found to be a better cosolvent. PEG 400 with the large nonpolar parts and several hydroxyl groups were responsible for enhancing the solubility. The blend of ethanol and PEG 400 provided matching polarity for enhanced solubility of lornoxicam. PEG 400 and ethanol in the ratio of 7:3, 8:2, 9:1 were recommended for achieving minimum required solubility (4.0 mg/ml) and development of the lornoxicam solution formulation.