Determination of ceftiofur in bovine plasma by HPLC-DAD

Ceftiofur sodium is a third generation broad-spectrum cephalosporin, formulated as an intramuscular injection, which is used to treat respiratory diseases in swine, ruminants and horses. The thioester bond on ceftiofur is rapidly cleaved to give desfuroylceftiofur which is further metabolized to a disulfide dimer and various desfuroylceftiofur-protein and amino acid conjugates. Methods of analysis of ceftiofur rely on cleavage by dithioerythritol to produce desfuroylceftiofur, which is further stabilized by derivatization to desfuroylceftiofur acetamide using iodoacetamide. Previous analytical methods have extracted derivatized analyte from plasma and tissue using solid-phase extraction clean-up steps followed by HPLC analysis with results reported as ceftiofur-free acid equivalents (CFAE). The simplified method presented here involves direct HPLC injection of a cleaved and derivatized sample following a protein precipitation step with calibration by external standardization and selectivity achieved based on chromatography and diode-array detection (DAD). The assay was linear over the calibration range 0.4-40 microg/ml in plasma. Intra-batch reproducibility R.S.D. was 10.3% and intra-batch sample repeatability R.S.D. was 2.1% at the 5 microg/ml level. The mean accuracy over the range of the calibration curve was -4.2% and the detection limit was 0.15 microg/ml. The assay was successfully applied to bovine plasma following intramuscular injection of ceftiofur sodium. This simplified method is suitable for pharmacokinetic applications involving ceftiofur at normal therapeutic levels.