High-performance liquid chromatographic method for the determination of cloxacillin in commercial preparations and for stability studies

A reversed-phase column liquid chromatographic method was developed for the assay of cloxacillin and its preparations. The linear calibration range was 0.2-3.0 mg/ml (r=0.9998) and recoveries were generally greater than 99%. The relative standard deviation was 0.13% (n= 10). The high-performance liquid chromatographic assay results were compared with those obtained from a microbiological assay for bulk drug substance, capsule, injection and syrup formulations containing cloxacillin and degraded cloxacillin. At the 99% confidence level, no significant inter-method differences were noted for the paired results. Commercial formulations were also analysed and the results obtained by the proposed method closely agreed with those found by the microbiological method. The results indicated that the proposed method is a suitable substitute for the microbiological method for assays and stability studies of cloxacillin preparations.