In vitro combination effects of cefotetan with four aminoglycosides, piperacillin and mezlocillin on gram-positive and gram-negative nosocomial bacteria.

The in vitro efficacy of cefotetan in combination with gentamicin, tobramycin, amikacin, netilmicin against Staphylococcus aureus, Staphylococcus epidermidis and Enterobacter cloacae and with piperacillin and mezlocillin against Escherichia coli, Klebsiella pneumoniae, Serratia marcescens and Enterobacter cloacae was compared by use of the checkerboard agar dilution technique. On average, 60% of the gram-negative and 46% of the gram-positive strains were inhibited by additive, but only 22% of the gram-negative and 2% of the gram-positive bacteria were inhibited by synergistic cefotetan-aminoglycoside combinations. Netilmicin combinations were least active. On gram-negative bacteria, 63% of the cefotetan-penicillin combinations were additive and 11% synergistic. No antagonism occurred with any of the combinations.