Antimicrobial activity of ceftriaxone, cefotaxime, desacetylcefotaxime, and cefotaxime-desacetylcefotaxime in the presence of human serum

Eighty-seven organisms were tested against ceftriaxone, cefotaxime, desacetylcefotaxime, and the combination of cefotaxime and desacetylcefotaxime (1:1 ratio) in broth containing 0, 25, or 50% human serum. In the presence of human serum, ceftriaxone MICs were four- to eightfold higher than those obtained in broth, changing 98% of Staphylococcus aureus strains from the susceptible to the moderately susceptible category and 53% of selected gram-negative strains to a more resistant category. The MICs of cefotaxime, desacetylcefotaxime, and cefotaxime plus desacetylcefotaxime were not adversely affected by human serum; in fact, the bactericidal activity was slightly improved.