Solubility of Meloxicam in Mixed Solvent Systems
Solubility of meloxicam was determined in polyethylene glycol 400 (PEG 400), water, ethanol, propylene glycol (PG), phosphate buffer pH 7.4, Tween 80 and Brij 35 in order to understand the nature of drugvehicle interactions. Meloxicam exhibited highest solubility (7 mg/ml) in PEG 400 due to possible hydrophobic interaction of the compound with polyethylene chains. The extent of solubility of meloxicam is the same in ethanol and PG, but is higher when compared to its solubility in water, indicating the role of hydrogen bonding in the solubility of meloxicam. The solubility of meloxicam is higher in phosphate buffer (pH 7.4) compared to water, probably due to ionization of the drug. The solubility of meloxicam is marginally enhanced in surfactant systems (Tween 80 and Brij 35) at concentrations higher than cmc, proving the micellar solubilization. Meloxicam solubility studies in PEG 400 and other vehicles provide an idea to understand the nature of interactions between the drug and the solvent system employed. The solubility of meloxicam is highest (12 mg/ml) in PEG 400-phosphate buffer in the ratio of 40:60. This vehicle may have the matching polarity with that of meloxicam. These results were in agreement with the values for cosolvents obtained from Setschenow equation. The functional groups in meloxicam have definite role in the solubilization and that hydrophobic interaction is predominant with PEG 400 vehicles.
Keywords: meloxicam, cosolvency, solubility enhancement, parenteral preparations, ophthalmic drops
Ethiopian Pharmaceutical Journal Vol. 25 (1) 2007: pp. 23-28