Bactericidal activity of ciprofloxacin in serum and urine against Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus and Streptococcus faecalis.

Ten volunteers received three doses of 500 mg ciprofloxacin, orally every 12 hours. After the last dose, mean serum levels were (mg/l +/- SD) 2.4 +/- 0.83 at 1 h; 0.91 +/- 0.30 at 4 h and 0.18 +/- 0.04 at 12 h. At 1 h the median serum bactericidal activity was satisfactory only against the Escherichia coli (1:256) and Klebsiella pneumoniae (1:128). In urine collected from 0 to 4 h and 8 to 12 h after the last dose, the mean ciprofloxacin level was respectively 482.5 +/- 324.7 and 80.9 +/- 48.2 mg/l +/- SD. Bactericidal activity in urine was high even against the least susceptible species tested: Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus faecalis. A post antibiotic effect was demonstrated in 22 out of the 29 strains tested, ranging mainly from 1 to 3 h. Ciprofloxacin 500 mg orally twice a day is a bactericidal regimen against a wide range of urinary pathogens but has a limited systemic activity.