Initial Dosage Adjustment for Oral Administration of Tacrolimus Using the Intestinal MDR1 Level in Living-Donor Liver Transplant Recipients

Abstract

The role of intestinal P-glycoprotein (encoded by the MDR1/ ABCB1 gene) and/or metabolic enzyme CYP3A4 for tacrolimus therapy was examined in recipients of living-donor liver transplantation (LDLT), under the hypothesis that these proteins are factors for pharmacokinetic variability. The intestinal mRNA expression level of MDR1 and CYP3A4 was evaluated by real-time polymerase chain reaction (PCR), using the upper jejunum from a part of the Roux-en-Y limb for biliary reconstruction at LDLT. For 7 days postoperatively, good inverse correlation was found between the tacrolimus concentration/dose (C/D) ratio and the intestinal mRNA level of MDR1 ( r = −0.776), but not of CYP3A4 ( r = −0.096), in the 46 cases. After classifying the patients according to median of the intestinal MDR1 mRNA expression, the oral dose of tacrolimus in the high-MDR1 group was approximately twofold higher than in the low-MDR1 group ( P < .001), whereas its trough level was similar between the two groups. In addition, the correlation between the intestinal MDR1 mRNA level and the tacrolimus C/D ratio was confirmed with a larger population ( r = −0.645, n = 104). Using the regression line between the intestinal MDR1 mRNA level and tacrolimus C/D ratio, we could prospectively predict the individual C/D ratio of tacrolimus immediately after LDLT. Known genetic variations of the MDR1 gene had no effect on intestinal MDR1 mRNA level and tacrolimus C/D ratio in LDLT patients. This suggests that the intestinal mRNA level of MDR1 is a useful molecular marker for determination of the personalized oral dose of tacrolimus in recipients of LDLT immediately after surgery.