Abstract
Both cyclosporine and tacrolimus display a narrow therapeutic index as well as high interindividual pharmacokinetic variability. We approached the effect of the CYP3A4*18B and CYP3A5*3 polymorphisms and haplotypes on the whole blood cyclosporine or tacrolimus concentration in Chinese renal transplant patients during the first month after transplantation. A total of 83 recipients receiving tacrolimus or cyclosporine was genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The whole blood concentration was measured by enzyme-multiplied immunoassay technique. Both CYP3A4*18B and CYP3A5*3 polymorphisms affected the tacrolimus dose-adjusted trough concentration (C0/D). The tacrolimus C0/D was higher in carriers of haplotype GG compared with the non-carriers. The cyclosporine dose-adjusted 2-hour post-dose concentrations (C2/D), dose-adjusted C0 + C2 ((C0 + C2)/D) and C2/C0 during Days 15 - 21 displayed significant difference among the three genotypes. Statistical difference was observed between CYP3A4*1/*1 and CYP3A4*18B/*18B groups and between CYP3A4*1/*18B and CYP3A4*18B/*18B groups, but no difference was detected between CYP3A4*1/*1 and CYP3A4*1/*18B groups. No difference was found in C0/D among the three genotypes of CYP3A4*18B polymorphism, and neither CYP3A5*3 polymorphisms nor CYP3A haplotype-derived genotypes affected the cyclosporine dose-adjusted concentration. Genetic polymorphisms of CYP3A5*3 and CYP3A4*18B may be partly responsible in large interindividual variability of cyclosporine and tacrolimus blood levels in Chinese renal transplant patients during the first month after transplantation. A patient carried combined genotype of CYP3A4*1/*1-CYP3A5* 3/*3 might require lower tacrolimus doses to achieve target concentration levels. Genotyping of CYP3A4*18B and CYP3A5*3 before transplantation is of benefit in determining a suitable initial dose for each patient.
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