Piperacillin (T-1220), a new semisynthetic penicillin. II. In vitro antimicrobial activity and synergy comparison with carbenicillin and gentamicin.

Piperacillin, a new semisynthetic penicillin, was found to have potent antimicrobial activity against nearly all (405) tested bacterial species. Piperacillin was consistently 4 approximately 16-fold more active than carbenicillin against the Enterobacteriaceae, 16 approximately 32-fold against Pseudomonas aeruginosa and Pseudomonas species, and 16-fold against Streptococcus faecalis. Carbenicillin and piperacillin were equally effective against Staphylococcus aureus, but inactivated by beta-lactamase. A 38% overall synergy rate for the piperacillin-gentamicin combination was identified, a finding similar to that for carbenicillin-gentamicin. Highest incidences of synergy were found for both antibiotic pairs tested on gentamicin-resistant isolates (Ps. aeruginosa and Providencia). In vitro findings suggest that piperacillin alone or in combination with aminoglycosides may be highly efficacious in the treatment of most serious bacterial infections.