Stability of cefdinir (CI-983, FK482) to extendedspectrum plasmid-mediated -lactamases

Fourteen plasmid-encoded extended-spectrum beta-lactamases were purified from Escherichia coli transconjugants of original clinical isolates. The Vmax, Km and Vmax/Km were each determined for ampicillin, carbenicillin, cephaloridine, cephalexin, cefuroxime, cefixime, cefdinir, ceftazidime and cefotaxime as substrates with eight of these enzymes and with the narrow-spectrum beta-lactamase, TEM-1. The relative rates of hydrolysis of ampicillin, cephaloridine, cephalexin, cefuroxime, cefixime, cefdinir, ceftazidime and cefotaxime were also determined for the remaining six enzymes. Cefdinir had Vmax/Km or relative rates of hydrolysis values either equal to or lower than ampicillin, cephaloridine, cephalexin and cefotaxime for all the enzymes tested. Overall, cefdinir was more stable to the 15 beta-lactamases tested than either cefuroxime or cefixime; however, ceftazidime was more stable than cefdinir to hydrolysis by eight of the enzymes tested.