The study compared the pharmacokinetics and pharmacodynamics of ciprofloxacin and ofloxacin in 12 healthy male volunteers with normal renal function. Each volunteer received oral ciprofloxacin 500 mg, intravenous (i.v.) ciprofloxacin 400 mg, oral ofloxacin 400 mg, or i.v. ofloxacin 400 mg in a randomized, double-blind, crossover design with a one-week 'washout' period between doses. Mean peak serum concentrations were 4.48 and 5.44 mg/L for i.v. ciprofloxacin and ofloxacin, respectively. For the oral regimens, mean peak serum concentrations were 2.45 mg/L for ciprofloxacin and 4.44 mg/L for ofloxacin. Minimum bactericidal concentrations (MBC) and serum bactericidal activity (SBA) for each drug were measured against five strains of each of the following species: Escherichia coli, Klebsiella pneumoniae, Enterobacter aerogenes, Pseudomonas aeruginosa, Acinetobacter anitratus, Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pneumoniae, using the microdilution method of the National Committee for Clinical Laboratory Standards (NCCLS). Ciprofloxacin was more active in vitro than ofloxacin against the tested species of Enterobacteriaceae and P. aeruginosa, while ofloxacin was slightly more active against A. anitratus. MBCs for the two drugs were similar for H. influenzae and S. aureus. Oral and i.v. ciprofloxacin in the doses given resulted in nearly equivalent SBA. Similarly, oral and i.v. ofloxacin had nearly equivalent SBA. For the i.v. and oral regimens of both agents, peak SBA was > or = 2 throughout the 12-hour test period against the Enterobacteriaceae and H. influenzae. At peak concentrations, both drugs had modest SBA against P. aeruginosa, A. anitratus, and S. aureus but little or no activity 8 and 12 h after dosing.(ABSTRACT TRUNCATED AT 250 WORDS)