Serum bactericidal activity of aztreonam, cefoperazone, and amikacin, alone or in combination, against Escherichia coli, Klebsiella pneumoniae, Serratia marcescens, and Pseudomonas aeruginosa.

Serum samples from volunteers receiving (per kilogram) 20 mg of aztreonam, 20 mg of cefoperazone, 7.5 mg of amikacin, 20 mg of cefoperazone plus 20 mg of aztreonam, or 20 mg of aztreonam plus 7.5 mg of amikacin were evaluated for bactericidal activity against Escherichia coli, Klebsiella pneumonia, Serratia marcescens, and Pseudomonas aeruginosa. Serum bactericidal activities were similar for aztreonam alone or in combination but were lower for amikacin and cefoperazone alone, especially against S. marcescens and P. aeruginosa. Killing studies, performed with serum samples diluted 1:8, demonstrated a high killing rate for aztreonam plus amikacin, especially against P. aeruginosa.