Clinical Bacteriology of Cephazolin

Abstract

Cephazolin, the latest parenteral cephalosporin produced by substitution of heterocyclic groups on the 7-aminocephalosporanic acid (7-ACA) nucleus, became available for clinical use in the U.K. in 1974. Its history is traced from the original Sardinian mould (1945) through isolation of cephalosporin C (1953) and 7-ACA (1962) to its discovery (1969) and subsequent clinical use. Its mode of action is examined and its bactericidal nature confirmed. MICs of over 500 common pathogens are used to define its spectrum. The cut-off point for sensitivity and resistance is taken as 20 mg. per l. With 30 μg. discs zone sizes ≤ 14 mm. indicate resistance. The clinical relevance of MICs and attainable serum and urine levels is examined by relating them to clinical response in 12 patients. A disc study compares cephazolin with 4 other available cephalosporins, namely cephaloridine, cephalothin, cephalexin and cephradine. Many major discrepancies indicate that they are not interchangeable. The laboratory and clinical implications are discussed, including the need for local policy decisions regarding choice of preparation. The change from a parenteral to an oral form should be preceded by a sensitivity test against the causal organism. The validity of using a single representative disc is questioned and the use of phrases such as ‘sensitive to the cephalosporins’ deprecated. Cephazolin is potent, broad-spectrum and bactericidal and is potentially life-saving in serious hospital infections. The cephalosporins rival the aminoglycosides as ‘best-guess’ primary choice and are preferable in pregnancy, the puerperium and in pulmonary infections. Within the group cephazolin will seriously challenge or even oust cephaloridine and cephalothin.