N‐FORMIMIDOYL THIENAMYCIN: IN VITRO COMPARISON WITH CEFOXITIN AND TOBRAMYCIN AGAINST CLINICAL, BACTERIAL ISOLATES

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Abstract
The in vitro activity of the novel .beta.-lactam antibiotic, N-formimidoyl thienamycin (N-f-thienamycin) was compared with those of cefoxitin and tobramycin. An agar dilution method was employed. N-f thienamycin was active against all Enterobacteriaceae isolates (MIC [minimum inhibitory concentration] .ltoreq. 4 mg/l). All Pseudomonas aeruginosa isolates were inhibited by 2 mg/l. N-f thienamycin was also active against Acinetobacter calcoaceticus (95% inhibited by 0.5 mg/l) and gram-positive cocci. All enterococci were inhibited by 2 mg/l. The drug was active against Haemophilus influenzae (MIC .ltoreq. 1 mg/l) and the Bacteroides fragilis group (MIC .ltoreq. 0.5 mg/l). Cefoxitin was inactive against most Enterobacter and A. calcoaceticus isolates and all P. aeruginosa and enterococcal isolates. Tobramycin was virtually inactive against gram-positive cocci other than Staphylococcus aureus. Thus, N-f thienamycin has a broad spectrum of in vitro activity, greater than that of cefoxitin and tobramycin, and may be useful in the treatment of serious infection, particularly when the etiology is unknown.