CYP2C9, but not CYP2C19, polymorphisms affect the pharmacokinetics and pharmacodynamics of glyburide in Chinese subjects.

BACKGROUND

Although cytochrome P450 (CYP) 2C9 was thought to be the main pathway for glyburide (INN, glibenclamide) metabolism in vivo, studies in vitro indicated that CYP2C19 had a more dominant effect. This study investigated the relative influence of CYP2C9 and CYP2C19 genotypes on the pharmacokinetics and pharmacodynamics of glyburide in Chinese subjects.

METHODS

Three groups of healthy male Chinese subjects (n=6 per group) were enrolled, as follows: group I, CYP2C9*1/1 and CYP2C19 extensive metabolizers (EMs); group II, CYP2C91/1 and CYP2C19 poor metabolizers (PMs); and group III, CYP2C91/*3 and CYP2C19 EMs. Subjects received single oral doses of 5 mg glyburide. Multiple blood samples were collected, and the plasma glyburide concentrations were determined by an HPLC method. The plasma glucose and insulin concentrations were also measured up to 2 hours after dosing.

RESULTS

No significant differences in glyburide pharmacokinetics were observed between CYP2C19 EM and PM subjects who had the CYP2C9*1/1 genotype (group I versus group II). Their respective values for area under the plasma concentration-time curve from time 0 to infinity (AUC0-infinity) and elimination half-life (t1/2) were 0.46+/-0.13 microg.h/mL versus 0.57+/- 0.11 microg.h/mL (P=.569) and 2.09+/-0.22 hours versus 2.24+/- 0.27 hours (P=.721). However, significant increases in AUC(0-infinity) (125% and 82%; P=.008 and .024, respectively) and t1/2 (71% and 60%; P=.003 and .007, respectively) were observed when CYP2C91/3 subjects (group III) were compared with CYP2C91/1 subjects in group I or II. Blood glucose reductions at 2 hours after dosing were 41.8%, 23.9%, and 27.7% in groups I, II, and III, respectively (P=.029), and hypoglycemia developed in 3 of 6 CYP2C91/3 carriers and 2 of 12 CYP2C91/*1 carriers.

CONCLUSION

CYP2C9, but not CYP2C19, polymorphism appears to exert a dominant influence on glyburide pharmacokinetics and pharmacodynamics in vivo. Further studies in diabetic patients with long-term dosing are warranted to confirm these findings.