Antibacterial activity of desacetylcefotaxime alone and in combination with cefotaxime.

Cefotaxime is metabolized to 3-desacetylcefotaxime. The antibacterial activity of desacetylcefotaxime is four- to eightfold less than that of cefotaxime. The activity of desacetylcefotaxime is species- and strain-specific. Although desacetylcefotaxime is less active than cefotaxime, it is more active than cefazolin, cefamandole, or cefoxitin. Desacetylcefotaxime does not inhibit many strains of Morganella, most strains of Pseudomonas aeruginosa, some strains of Serratia marcescens, some strains of Providencia, and many strains of Bacteroides fragilis at clinically achievable concentrations. Cefotaxime and desacetylcefotaxime act synergistically against 72% of strains tested, and antagonism between the two compounds is seen only with strains of Morganella and Proteus vulgaris. The presence of the metabolite desacetylcefotaxime increases rather than decreases the activity of cefotaxime.