Background: Tacrolimus is commonly prescribed for immunosuppression, yet it can cause acute and chronic kidney injury. Continuous intravenous nicardipine (CIVN), prescribed for posttransplant hypertension, inhibits tacrolimus metabolism by cytochrome P450 (CYP) 3A4 and could lead to tacrolimus overexposure in patients genetically lacking the alternative pathway for tacrolimus metabolism, CYP3A5.
Methods: We compared maximum 12-hr tacrolimus trough levels (MaxC0) and dose-adjusted MaxC0 in 12 cases treated with CIVN immediately after kidney transplantation with 26 controls (no CIVN). CYP3A5 genotype was determined for all cases.
Results: Eight cases not expressing CYP3A5 (CYP3A5*3/*3) had higher median MaxC0 (24.3 ng/mL) than four cases expressing CYP3A5 (CYP3A5*1/*1; 13.9 ng/mL, P=0.028) and controls (14.6 ng/mL, P=0.003). Compared with the other two groups combined, CYP3A5*3/*3 cases had higher median dose-adjusted MaxC0 (330 vs. 175, P=0.012), less time to MaxC0 (42 vs. 72 hr, P<0.001), and more scheduled tacrolimus doses held per patient (1.75 vs. 0.4, P=0.007). Six of eight (75%) CYP3A5*3/*3 cases had potentially toxic MaxC0 (>20 ng/mL) compared with none of four CYP3A5*1/*1 cases and 3 of 26 (11.5%) controls (P<0.001, CYP3A5*3/*3 cases vs. all others).
Conclusion: CYP3A5 nonexpressors simultaneously treated with tacrolimus and CIVN may be at increased risk for tacrolimus toxicity.