Pharmacokinetics and absolute bioavailability of sitafloxacin, a new fluoroquinolone antibiotic, in healthy male and female Caucasian subjects

1. The aim was to compare the pharmacokinetics of sitafloxacin from a capsu le formulation (dose of 500 mg sitafloxacin) and an intravenous (i.v.) form ulation infused over 1 h (dose of 400 mg sitafloxacin) in healthy male and female subjects and to estimate the absolute bioavailability of sitafloxaci n from the capsule formulation. 2. Following oral administration, sitafloxacin was rapidly absorbed, with a mean maximum concentration in plasma (C-max) of 4.65 mug ml(1) occurring a t a median t(max) = 1.25 h giving a mean AUC(0-infinity) = 28.1 mug h ml(1) . For the i.v. administration, a mean C-max = 5.53 mu ml(1) occurred at the end of the 1-h infusion with a mean AUC(0-infinity) = 25.4 mug h ml(1). Th e mean terminal elimination half-life was 7.0 h (oral) and 6.6 h (i.v.). Fo r the oral and i.v. formulations, the mean total plasma clearance was 296 a nd 263 ml min(1), respectively and the mean volume of distribution was 180 and 150 litres, respectively. 3. Within 48 h post-dose, similar to 61% (range 26-86%) of the administered dose was excreted unchanged in urine following capsule administration, com pared with similar to 75% (range 42-101%) following the i.v. formulation. F or both formulations, the renal clearance of sitafloxacin (means of 181 and 198 ml min(1) for the capsule and i.v. doses, respectively) implies active tubular secretion of the drug. 4. The absolute bioavailability of sitafloxacin from the capsule formulatio n was high at 89%, with a 95% CI of 84-94%. The intersubject variability (C V%) in the sitafloxacin AUC(0-infinity) for the capsule was low at 18.6%. 5. Gender differences in the pharmacokinetics of sitafloxacin were small an d would not warrant dose adjustment. 6. The findings show that the capsule formulation offers good oral bioavail ability and merits further clinical evaluation of sitafloxacin as an orally effective fluoroquinolone antibacterial.