Enantioselective disposition of ofloxacin in humans

The enantioselective disposition of ofloxacin (OFLX) was studied in healthy subjects after oral administration of (+/-)-OFLX at a dose of 200 mg. S-(-)-OFLX and R-(+)-OFLX concentrations in serum and urine were measured separately by high-performance liquid chromatography, and various pharmacokinetic parameters were calculated from the data. The ratio of S-(-) to R-(+) enantiomer concentrations in serum showed a increase with time, with S/R ratios of 1.01 at 2 h and 1.31 at 24 h. The terminal elimination half-life of S-(-)-OFLX was 6.9 h, which was significantly greater (P less than 0.05) than that of the R-(+) enantiomer (6.3 h). S-(-)-OFLX also revealed a significantly greater area under the concentration-time curve in serum, mean residence time, and total body clearance than the R-(+) enantiomer did. The renal clearance of S-(-)-OFLX (7.14 liters/h/1.73 m2) was significantly lower than that of the R-(+) enantiomer (7.53 liters/h/1.73 m2). Although the difference in the pharmacokinetic parameters of the enantiomers was small, their disposition in humans was found to be stereoselective. The difference between the enantiomers may be explained by the difference in their renal excretion.