Amdinocillin in combination with beta-lactam antibiotics for treatment of serious gram-negative infections.

Amdinocillin in combination with another beta-lactam antibiotic (ampicillin, cephalothin, cefamandole or cefoxitin) was used to treat 25 patients with pyelonephritis (with or without bacteremia), pneumonia, bacteremia secondary to intravenous devices, and urinary tract infections (with catheter in place) due to gram-negative organisms. The combination resulted in a clinical response in 96 percent of the patients and a bacteriologic response in 100 percent at 72 hours. Few toxic effects were seen. At long-term follow-up, relapse occurred in three of 10 patients with pyelonephritis who were treated with a combination regimen and completed their course of antimicrobial therapy with a beta-lactam antibiotic. Reinfection occurred in one patient who had a urinary tract infection with a catheter in place. In vitro testing showed that the cefamandole-amdinocillin combination most frequently produced synergy against the strains of Escherichia coli isolated. Synergy with the antibiotic combinations was also seen against strains of Klebsiella pneumoniae. It was difficult to correlate the in vitro test results with the in vivo therapeutic effect of these antibiotic combinations.