Interaction of cefdinir with beta-lactamases.

The interactions of cefdinir, a new orally-active third-generation cephalosporin, with cell-free beta-lactamase preparations were studied in comparison with some other beta-lactams. Cefdinir was very resistant to narrow-spectrum Ambler's class A beta-lactamases, as it was for other oximino beta-lactams: cefotaxime, ceftazidime, cefixime and cefuroxime. Cefaclor showed a low but significant hydrolysis by these beta-lactamases. These class-A enzymes include the widespread plasmid mediated TEM-1, TEM-2, SHV-1 and also the enzymes of Gram-positive penicillinases, such as that produced by S. aureus. The hydrolysis of cefdinir was hardly detectable by the Ambler's class C beta-lactamases (cephalosporinases) produced by E. coli, E. cloacae and M. morganii. A similar conclusion is shown for cefotaxime, ceftazidime, cefixime and cefuroxime: for these beta-lactamases, the hydrolysis of cefaclor was high. The P. vulgaris cephalosporinase differs from the previous cephalosporinases in that it hydrolyses cefotaxime, cefuroxime and cefaclor efficiently. However, the hydrolysis of cefdinir remains too low to be detected. Cefdinir, as other third-generation cephalosporins, showed some hydrolysis by the novel extended-spectrum beta-lactamases (ESBL): SHV-2, TEM-3, TEM-5, MEN-1 and other ESBL.