CYP2C19 genotype has a major influence on labetalol pharmacokinetics in healthy male Chinese subjects.

PURPOSE: The pharmacokinetics (PK) of labetalol show wide inter-subject variability, but the genetic causes for this are largely undetermined. This study was performed to examine whether common polymorphisms in UGT1A1, UGT2B7, CYP2C19 and ABCB1 affect the PK of labetalol. METHODS: The PK of labetalol were determined in 37 Chinese healthy male subjects who took a single oral dose of 200 mg labetalol. Plasma concentrations of labetalol were determined by a high-performance liquid chromatographic method. Subjects were genotyped for the CYP2C19 2 and 3, UGT1A1 6, 28 and 60, UGT2B7 2 and ABCB1 1236C>T, 2677G>T/A and 3435C>T polymorphisms. RESULTS: Subjects with the CYP2C19 2/ 2 genotype had a higher peak concentration (255.5 ± 80.1 vs. 156.0 ± 66.3 ng/mL; P < 0.05) and area under the concentration-time curve (AUC0-∞; 1,473.7 ± 493.6 vs. 502.8 ± 176.1 ng[Symbol: see text]h/mL; P < 0.001) than subjects with 60 or 28, and UGT2B7 2 did not result in a significant effect. Subjects with ABCB1 2677TA or TT or ABCB1 3435TT genotypes had higher AUC0-∞ and lower total clearance than the wild-types (P < 0.05), but this appeared to be related to the distribution of CYP2C19 genotypes. The CYP2C19 genotype appeared to be the only predictor of labetalol concentrations, accounting for approximately 60 % of the total variance in the AUC0-∞. CONCLUSION: Our results suggest that the PK of labetalol are significantly affected by the common CYP2C19 polymorphisms in individuals of Chinese ethnicity. Future larger studies are needed to evaluate the effect of CYP2C19 and UGT1A1 polymorphisms on the PK of labetalol stereoisomers and the pharmacodynamic effects.

Impact of CYP2D6 polymorphisms on the pharmacokinetics of lovastatin in Chinese subjects.

PURPOSE: Although CYP3A4/5 enzymes play the predominant role in the metabolism of simvastatin and lovastatin, polymorphisms in CYP2D6 were reported to be associated with the cholesterol-lowering effect and/or tolerability of simvastatin. This study was performed to examine whether common CYP2D6 polymorphisms affect the pharmacokinetics of lovastatin, which is taken as the inactive prodrug lovastatin lactone and converted to active lovastatin acid. METHODS: A single-dose pharmacokinetic study was performed with lovastatin in 23 Chinese healthy male subjects. Plasma concentrations of lovastatin lactone and acid were determined by an LC-MS-MS method in samples collected over 24 h after single oral doses of 40-mg lovastatin. RESULTS: Compared with the CYP2D6 wt/wt group, the area under the plasma concentration-time curve (AUC(0-∞)) values for lovastatin lactone increased (P < 0.01) by average ratios (95% CI) of 1.57 (1.01-2.45), 2.11 (1.36-3.29), 2.52 (1.47-4.32), and 5.84 (3.16-10.78) in the wt/*10, *10/*10, *10/*5, and *5/*5 groups, and the values of lovastatin lactone plasma clearance (CL/F) were reduced on average (95% CI) by 40.4% (10.2-60.5%), 53.1% (29.3-68.9%), 63.8% (40.2-78.1%) and 84.2% (72.1-91.1%) in these genotype groups respectively. The pharmacokinetics of lovastatin acid did not differ among the genotype groups. CONCLUSION: This study demonstrates that CYP2D6 polymorphisms appeared to influence the disposition of lovastatin lactone in these subjects.

Effects of grapefruit juice and SLCO1B1 388A>G polymorphism on the pharmacokinetics of pitavastatin.

Pitavastatin undergoes little hepatic metabolism but it is a substrate for uptake and efflux transporters, particularly OATP1B1 (gene SLCO1B1). A previous study in 8 Japanese healthy subjects showed that co-administration with grapefruit juice (GFJ) resulted in a small increase in systemic exposure to pitavastatin. We examined whether common polymorphisms in SLCO1B1 might influence the pharmacokinetics of pitavastatin or the interaction with GFJ. Twelve Chinese healthy male volunteers took pitavastatin 2 mg orally with water or with GFJ on separate occasions and plasma concentrations of pitavastatin acid and lactone were measured over 48 h. GFJ increased the mean area under the plasma concentration-time curve (AUC0-48 h) for both pitavastatin acid and lactone by 14% (p<0.05). Subjects with SLCO1B1 *1b/*1b haplotype (388GG-521TT) had 47% and 44% higher systemic exposure for pitavastatin acid and lactone than the SLCO1B1 *1a carriers (388AA/AG-521TT, p<0.05 and p=0.005, respectively). The SLCO1B1 388A>G polymorphism, which increases transporter activity for some statins, was associated with higher plasma levels of pitavastatin acid and lactone in subjects with the homozygous variant indicating decreased hepatic uptake. Co-administration of pitavastatin with GFJ resulted in a small but significant increase in plasma levels in healthy Chinese subjects.