Stability study of cloxacillin in an oily suspension, by high performance liquid chromatography

A high performance liquid chromatography method, using spectrophotometric detection (254 nm) has been developed for the analysis of cloxacillin in an oily suspension. Analysis was performed by isocratic elution with 0.02M potassium dihydrogen phosphate solution, methanol, 50/50 (V/V). The method was specific, linear, accurate (99.8 +/- 1.4%) and precise (less than 1.0%). A stability study of cloxacillin in the formulation, showed that about 10% degradation occurred for 6 months storage at room temperature, when lyophilized sodium cloxacillin was used. On the contrary, when sodium cloxacillin obtained by precipitation from non aqueous solvent was used, about 6% degradation appeared in the drug for 3 years storage in the same conditions.