Resistance to cefamandole: a collaborative study of emerging clinical problems.

Cefamandole resistance in five patients was studied. Microorganisms emerged resistant to cefamandole during therapy with the drug in three patients with complicated infections. This resistance was associated with an enhanced production of beta-lactamase and/or with a change in the substrates and the isoelectric focusing patterns of the enzymes. Cross-resistance to other beta-lactam antibiotics developed concurrently in isolates from these patients. Disk diffusion tests did not detect resistance to cefamandole in the pretreatment isolate from the fourth patient; this isolate produced inactivating enzymes, and resistance was detected only in broth dilution tests. In the fifth patient, infection with a cefamandole-resistant Enterobacter developed during postoperative therapy with the drug. Resistance to cefamandole in the isolate from this patient was unstable and was associated with inducible beta-lactamase activity. These examples emphasize the need for close monitoring of patients who are given cefamandole and for thorough in vitro evaluation of isolates from the patients both before and after treatment.