A stability-indicating HPLC method for the determination of isoxsuprine indosage forms. Application to kinetic studies of isoxsuprine

A simple, rapid, and stability-indicating HPLC method has been developed fo r the determination of isoxsuprine in the presence of its degradation produ cts. Acetonitrile: potassium dihydrogen phosphate (0.01 M solution) adjuste d to pH 2.2 +/- 0.1 with phosphoric acid (18:82 v/v), was used as the mobil e phase, at a flow rate of 2.5 mL/min. A mu Bondapak(TM) C-18 10 mum column (3.9 mm i.d. x 150 mm) was utilized as a stationary phase. Detection was affected spectrophotometrically at 275 n m. Methyl p-hydroxybenzoate was used as an internal standard. The method wa s applied for the determination of isoxsuprine in the presence of its main degradation products, namely: 4-hydroxy-benzaldehyde, 4-hydroxybenzyl alcoh ol, 4-hydroxybenzoic acid, and 4-hydroxyacetophenone. Linearity range for i soxsuprine was 2-40 mug/mL with correlation coefficient (r) of 0.9998 and m inimum detectability was 0.2 mug/mL (similar to 6 x 10(-7)M). The proposed method was further applied to the analysis of commercial table ts containing the drug, the percentage recoveries +/- SD were 99.60 +/- 0.7 6 and 99.78 +/- 0.88, and these values were in agreement with those given w ith the official methods. The method was also adopted to detect isoxsuprine in spiked human plasma at its therapeutic level of concentration (0.4 mug/ mL). The proposed HPLC method was successfully applied to study the degrada tion kinetics of isoxsuprine. The photothermal degradation of isoxsuprine u pon exposure to UV light was first-order with regard to its concentration.