Antimicrobial activity of desacetylcefotaxime alone and in combination with cefotaxime: evidence of synergy.

The level of antimicrobial activity of 3-desacetylcefotaxime was found to be approximately eightfold lower than that of cefotaxime. Variation in the inhibitory effects of desacetylcefotaxime was species dependent. Desacetylcefotaxime was 1-2 log2 dilutions more active than cefotaxime against Pseudomonas acidovorans and Pseudomonas cepacia. Desacetylcefotaxime and cefotaxime were bactericidal, and their minimal inhibitory concentrations were influenced only slightly by increases in the inoculum concentration. Synergy (complete and partial) of 75.8% was noted with the combination. Only with strains of Morganella morganii was the combination antagonistic, but these results were not clinically significant; i.e., all strains remained susceptible to cefotaxime.