MDR-1 C3435T polymorphism influences cyclosporine A dose requirement in liver-transplant recipients

Background. Cyclosporine A (CsA) is characterized by high interindividual variations in oral bioavailability and a narrow therapeutic index. CsA is a substrate for P-glycoprotein, a member of the ABC transporter family, ncoded by the multiple drug-resistant gene MDR1. Methods. Because MDR1 gene exon 26 C3435T polymorphism influences intestinal P-glycoprotein expression, we investigated whether this polymorphism was correlated with variation in CsA dose requirement and concentration/ dose ratio in 44 liver-transplant recipients during 1 month, after, transplantation. CsA concentration was measured 2 hours' after administration, (C-2), according to international recommendations. Results. The MDR-1 wild-type genotype (3435CC) was observed in 15 patients (34%), whereas 21 (48%) patients were heterozygous (3435CT), and 8 (18%) patients were homozygous for the mutation (3435TT). There was no significant difference between,the three groups regarding corticosteroids treatment or renal function during this period. One to 3 days after liver transplantation, when every patient received a similar CsA weight-adjusted dose, the concentration/dose ratio was correlated with exon 26 single nucleotide polymorphism and was significantly higher in subjects homozygous for the mutation (P = 0.012). This was confirmed 1 month after transplantation (P = 0.049), when the dose was adjusted to maintain the. C-2 target level of 1,000 mug/L and we observed that TT patients required approximately 50% lower weight-adjusted CsA dose than wild-type patients (P=0,0333). Conclusions. These findings demonstrate that the MDR1 exon 26 C3435T polymorphism is a major determinant of CsA-concentration/dose ratio in liver-transplant recipients and is predictive of the dose of CsA to be administered to achieve the target C-2 concentration.