In-vitro activity of pefloxacin compared to other antibiotics

Pefloxacin is a new quinolone carboxylic acid with a broad spectrum of antibacterial activity. A comparison was made of the in-vitro activity of pefloxacin and that of nine other antibiotics (ampicillin, ticarcillin, piperacillin, cefazolin, cefotaxime, ceftazidime, gentamicin, amikacin and norfloxacin). The MIC90 of pefloxacin against 500 strains of Enterobacteriaceae ranged from 0.25 mg/l (Escherichia coli, indole + Proteus spp., Enterobacter cloacae, Salmonella spp. and Shigella spp.) to 1 mg/l (Klebsiella pneumoniae). Pefloxacin inhibited 90% of 52 strains of Pseudomonas aeruginosa at 2.5 mg/l (range 0.25 mg/l-4 mg/l). The MIC90 of pefloxacin against 100 Staphylococcus aureus strains (78 oxacillin resistant strains) was 0.4 mg/l (range 0.12-0.5 mg/l). It was markedly less active against Streptococcus faecalis and Str. pneumoniae (37 strains of each species) the MIC90 being 4 mg/l against both species. Overall, pefloxacin was at least as active as the third-generation cephalosporins against Enterobacteriaceae and was more active than any other antibiotic tested against P. aeruginosa, S. epidermidis, and S. aureus. Against E. coli, pefloxacin had a more rapid anti-bacterial activity than piperacillin. A paradoxical effect was observed with pefloxacin. An optimal killing rate was observed at concentrations of pefloxacin compatible with those one can expect in blood of patients treated with this drug.