Comparative stability of first, second and third generation cephalosporins and N-formimidoyl thienamycin against gram-negative beta-lactamases.

The susceptibility of cefamandole, cefoxitin, cefotaxime, moxalactam, and N-formimidoyl thienamycin to different gram-negative beta-lactamases was determined by the UV-spectrophotometric method and two microbiological techniques in comparison with that of first generation cephalosporins. In general, the microbiological methods were more sensitive than the UV-assay. Cefamandole was rapidly hydrolyzed by all enzymes tested. The beta-lactamase stability of the other compounds was significantly higher, but clearly proved to be not absolute. With the aid of the "double-disc technique", the most sensitive of the methods used, cefotaxime was shown to be susceptible to all enzymes, whereas cefoxitin, moxalactam and N-formimidoyl thienamycin showed some susceptibility to 6, 3 and 7 enzymes, respectively. Moxalactam appeared to be the most stable of the compounds tested.