Background: The impact of cytochrome P450 3A5 (CYP3A5) genotype of recipients (intestine) as well as donors (graft liver) on the tacrolimus pharmacokinetics and the incidence of infectious complications was assessed in Japanese living-donor liver transplant (LDLT) adult recipients. Material/Methods: Fifty-six patients were divided into 4 groups based on the CYP3A5 genotype (expression of *1 allele: expressor (EX) and non-expressor (NEX)) in each recipients (R) and donors (D), EX-R/EX-D (n=9), EX-R/NEX-D (n=7), NEX-R/EX-D (n=12) and NEX-R/NEX-D (n=28). Tacrolimus blood concentration and concentration/ dosage ratio (C/D) were evaluated every week until 4 weeks and every month until 12 months after LDLT. The incidences of postoperative infectious complication, acute cellular rejection and tacrolimus adverse effect were compared. Results: The tacrolimus blood concentrations among 4 groups did not significantly differ at each follow-up time period. The C/Ds were significantly lower in EX-R/EX-D (median: 122.3 at 2 weeks) than in NEX-R/NEX-D (389.6 at 2 weeks) until 12 months. The C/Ds in EX-R/NEX-D (163.2 at 2 weeks) have been significantly lower than those in NEX-R/NEX-D until 6 months. Over 6 months, however, those in NEX-R/EX-D showed lower levels (84.1 at 8 months) than those in NEX-R/NEX-D (189.3 at 8 months). Additionally, logistic regression analysis showed that EX-R/EX-D had significantly higher risk for the development of infectious complications than NEX-R/NEX-D (odds ratio 8.67, p=0.03). Conclusions: Preoperative assessment of CYP3A5 genotypes in both recipients and donors would be useful not only for predicting tacrolimus pharmacokinetics but also defining high-risk group of infectious complications after LDLT.
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