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Organic anion transporting polypeptide 1B1 (OATP1B1), encoded by SLCO1B1, is an influx transporter expressed on the sinusoidal membrane of human hepatocytes. The aim of this study was to investigate whether the SLCO1B1*1B haplotype affects the pharmacokinetics and pharmacodynamics of repaglinide and nateglinide.Eight healthy volunteers with the SLCO1B1*1B/*1B genotype and 16 with the SLCO1B1*1A/*1A genotype ingested a single 0.5-mg dose of repaglinide and, after a washout period of 1 week, a single 60-mg dose of nateglinide. Plasma repaglinide and nateglinide and blood glucose concentrations were measured for 7 h.The AUC0–∞ and Cmax of repaglinide were 32% (P=0.007) and 24% lower (P=0.056) in the individuals with the SLCO1B1*1B/*1B genotype than in those with the SLCO1B1*1A/*1A genotype. The mean blood glucose concentration from 0 to 7 h after repaglinide intake was 10% higher in the SLCO1B1*1B/*1B participants than in the SLCO1B1*1A/*1A participants (P=0.007). The Cmax of nateglinide occurred earlier in the SLCO1B1*1B/*1B participants than in the SLCO1B1*1A/*1A participants (P=0.004), but no differences were seen in the other pharmacokinetic variables of nateglinide.The SLCO1B1*1B/*1B genotype is associated with reduced plasma concentrations of repaglinide, consistent with an enhanced hepatic uptake by OATP1B1, but has limited effects on the pharmacokinetics of nateglinide.