Comparison of in vitro activity of cefotaxime and desacetylcefotaxime alone and in combination against 320 gram-negative clinical isolates.

The antimicrobial activity of cefotaxime and its intermediate metabolite, desacetylcefotaxime, against 320 Gram-negative bacterial strains was analysed to investigate whether combination of the 2 substances led to increased bactericidal activity. The in vitro study of the minimum inhibitory concentration (MIC) showed the combination to be more effective against Escherichia coli, Klebsiella spp., Enterobacter spp. and Proteus mirabilis, requiring less than or equal to 50% of the concentration of cefotaxime alone to inhibit 90% of strains. For other micro-organisms the MIC90 for the combination was equal to or within 1 dilution of that for cefotaxime alone.