Cefotetan: antibacterial activity against Staphylococcus aureus in the presence of human serum

Cefotetan is a broad spectrum cephamycin antibiotic with a long serum half-life (3-4.5 h): this is explained, in part, by serum-protein-binding (SPB) of 88%. The rate of kill of Staphylococcus aureus by cefotetan was assessed in human serum or broth containing reducing concentrations of drug simulating those seen following a 1 g intravenous dose to man. Cefotetan was bactericidal in serum despite the assumed concentration of unbound drug never reaching the minimum inhibitory concentration (MIC) for the test strain. In a separate study, ceftriaxone (SPB 96%) was more active in broth (MIC 4 mg/1) than cefotetan (MIC 16 mg/1). In 100% serum the minimum bactericidal concentration (MBC) of ceftriaxone was 64 mg/1 whilst the MBC for cefotetan was 16 mg/1.