Determination of cefetamet and its orally active ester, cefetamet pivoxyl, in biological fluids by high-performance liquid chromatography.

Two different, simple and rapid high-performance liquid chromatographic methods with ultraviolet detection, using a common sample work-up procedure, were developed for the determination of cefetamet, an in vitro active cephalosporin, and its orally absorbed pivaloyloxymethyl ester, cefetamet pivoxyl. After protein precipitation with perchloric acid, plasma samples were analysed on C18 reversed-phase columns with 4 mM perchloric acid-acetonitrile (83:17, v/v) and 0.1 M phosphate buffer (pH 6.5)-acetonitrile (60:40, v/v) as mobile phases for the determination of cefetamet and cefetamet pivoxyl, respectively. Urine samples were diluted with water and analysed in the same manner, using 4 mM perchloric acid-acetonitrile (85:15, v/v). The limits of quantification were 0.2, 0.5 and 20 micrograms/ml for the determination of cefetamet and cefetamet pivoxyl in plasma and cefetamet in urine, respectively. The intra-assay precision was less than or equal to 1.5% for cefetamet and less than or equal to 2.3% for cefetamet pivoxyl. The inter-assay precision for cefetamet was less than or equal to 2.4%. Cefetamet was stable in human plasma when stored at -20 degrees C for three months or at 22 degrees C for 24 h. For the determination of cefetamet pivoxyl, which was extremely unstable in plasma (greater than 70% degradation in 1 h), samples were drawn into vacutainers containing citric acid and immediately added to sodium fluoride. The method for cefetamet was successfully applied to several thousand plasma and urine samples from humans, dogs and rats. No unchanged drug could be detected in human or dog plasma after the administration of cefetamet pivoxyl.