Pharmacokinetics of ciprofloxacin: intravenous and increasing oral doses

The pharmacokinetics of ciprofloxacin, after administration of single oral doses of 100, 250, 500, and 1,000 mg, and an intravenous dose of 100 mg, were determined in 12 healthy volunteers (six women and six men). Serum concentrations were determined by high-pressure liquid chromatography, and urine samples were assayed microbiologically. The peak serum concentrations and the total areas under the serum concentration curves increased in proportion to the size of the oral dose. The pharmacokinetics of ciprofloxacin were described by a dose-independent linear relationship. The apparent oral bioavailability was 85 percent, based on comparison of the total areas under the serum concentration curves of the 100-mg dose. The serum concentrations during steady state were not significantly higher than after the first dose. The serum half-life ranged from 3.0 to 3.4 hours after the oral doses, and was 2.9 hours after the intravenous dose. The elimination-phase apparent distribution volume coefficient, delta d,area, was 2.76 liters/kg, and the total body clearance was 42.0 liters/hour. The 24-hour urinary excretion was 42.2 +/- 15.6 percent after the 100-mg intravenous dose and 42.5 +/- 17.6 percent after the 500-mg twice-daily oral dose during steady state.