The new extended-release formulation of ciprofloxacin (ciprofloxacin XR) was designed for once-daily administration in the treatment of urinary tract infection (UTI). The aim of this study was to compare concentrations in plasma, urinary excretion (UE) and pharmacokinetic parameters of ciprofloxacin XR (1000 mg) versus those of levofloxacin (500 mg) in healthy volunteers receiving a single oral dose. In this randomised crossover study, 12 volunteers (6 males, 6 females) received a single oral dose of 1000 mg ciprofloxacin XR or 500 mg levofloxacin to assess the concentrations (by high-pressure liquid chromatography) in plasma up to 32 h and the UE at intervals up to 36 h. The following pharmacokinetic parameters were studied: C(max), t(max), t(1/2), AUC(plasma0-->infinity), AUC(plasma0-->last), Cl(ren), maximal urinary concentration (U(max)), AUC(urine0-->last) and UE. Both fluoroquinolones were well tolerated. The plasma concentrations of levofloxacin were significantly higher than those of ciprofloxacin XR throughout the study period. The urinary concentrations of ciprofloxacin XR were significantly higher than those of levofloxacin in the first collection interval (0-4 h), whereas the concentrations of levofloxacin were significantly higher than those of ciprofloxacin XR in the five last collection intervals (12-36 h). The median proportions of cumulative renal excretion of the administered dose of the parent drug up to 36 h were 43.1% for ciprofloxacin XR (range, 13.7-50.8%; mean +/- standard deviation (S.D.), 40.5 +/- 9.9%) and 79.8% for levofloxacin (range, 74.0-88.2%; mean +/- S.D., 80.4 +/- 5.5%). C(max), AUC(plasma0-->infinity), AUC(plasma0-->last) and UE were statistically significantly higher in the levofloxacin than in the ciprofloxacin XR phase; t(max), Cl(ren) and U(max) were statistically significantly higher in the ciprofloxacin XR phase than in the levofloxacin phase; and AUC(urine0-->last) and t(1/2) were not statistically different. After an oral administration of ciprofloxacin XR 1000 mg and levofloxacin 500 mg, C(max) and AUC(plasma0-->infinity) were significantly higher in the levofloxacin phase. UE of ciprofloxacin XR 1000 mg once daily, however, was equivalent to that of levofloxacin 500 mg, and overall comparable urinary concentrations and AUC(urine) were reached by both drugs. Therefore, it can be assumed that the two doses investigated can be considered equivalent for the treatment of UTI.