BACKGROUND: Single nucleotide polymorphisms (SNPs) in the multidrug resistance (MDR1) gene correlate with the intestinal function of P-glycoprotein (PGP). PGP serves as a hydrophobic export pump that extrudes cyclosporine (CsA) across the luminal membrane thus preventing CsA absorption. These genetic variants may predict CsA exposure levels in the early posttransplantation period. METHODS: CsA absorption profiles were established in 75 renal transplant patients using total daily dose and body weight adjusted 4-hour area under the time-concentration curve, AUC(0-4)/mg dose/kg body weight, on posttransplant day 3. These patients were subsequently genotyped for C3435T and G2677T polymorphisms using real-time polymerase chain reaction. An analysis was conducted to assess the independent impact of C3435T and G2677T SNPs on CsA bioavailability. RESULTS: C3435T polymorphisms were found to be an independent predictor of CsA AUC(0-4)/mg dose/kg levels on postoperative day 3. An inverse correlation was found between the number of T alleles and AUC values such that every T allele was associated with an approximate 15% decrement in AUC(0-4)/mg dose/kg (P = .034). A similar nonsignificant trend was observed for G2677T polymorphisms. CONCLUSIONS: MDR1 SNPs are correlated with CsA exposure in the early post-transplant period. Polymorphisms, in conjunction with other criteria, may become a useful tool to optimize initial drug dosing in renal transplantation.
