Stereoselective glucuronidation of ofloxacin in rat liver microsomes.
The stereoselective glucuronidation of ofloxacin [(+/-)-OFLX], a new quinolone antibacterial agent, was studied in vitro using rat liver microsomes. OFLX glucuronidation exhibited Michaelis-Menten kinetics in rat liver microsomes. Stereoselective glucuronidation of the optical enantiomers occurred. S-(-)-OFLX glucuronide was produced 7-fold more than R-(+)-OFLX glucuronide with little or no difference in the values of KM of the enantiomers. The value of Vmax/KM for the glucuronide conjugate of S-(-)-OFLX was 8-fold greater than for the conjugate of R-(+)-OFLX. These results demonstrate that OFLX undergoes stereoselective glucuronidation in vitro. Moreover, we studied the in vivo interaction between enantiomers of OFLX in rats to clarify the effects of R-(+)-OFLX on the metabolism and disposition of S-(-)-OFLX. When the racemate [(+/-)-OFLX (20 mg/kg)] or single enantiomer [S-(-)-OFLX (10 mg/kg)] is administered iv to the rat, the serum concentrations of S-(-)-OFLX were higher after racemate administration than those after enantiomer administration, although the dose of S-(-)-OFLX was identical in both cases. These results indicate that R-(+)-OFLX may compete with S-(-)-OFLX in the in vivo glucuronidation. Furthermore, the results of the enantiomeric inhibition study showed that R-(+)-OFLX competitively inhibited S-(-)-OFLX glucuronidation in vitro with a Ki value of 2.92 mM.
Okazaki
O
O
Drug Metabolism and Analytical Chemistry Research Center, Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan.
Kurata
T
T
Hakusui
H
H
Tachizawa
H
H
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D005965:Glucuronates / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D015242:Ofloxacin / Q000097:blood / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013237:Stereoisomerism
D005965:Glucuronates; D015242:Ofloxacin