Purpose: Because of the large interindividual variability of afatinib pharmacokinetics and adverse events, we evaluated the effects of polymorphisms in pregnane X receptor (NR1I2) and ABC transporters (ABCB1, ABCG2, and ABCC2) on the pharmacokinetics of afatinib.

Methods: The steady-state area under the concentration-time curve (AUC)_0-24 of afatinib was analyzed using blood sampling just prior to and at 1, 2, 4, 6, 8, 12, and 24 h on day 15 after administration.

Results: The median oral clearance (CL/F) of afatinib in patients with the NR1I2 7635A allele was significantly lower than those in patients with the 7635G/G genotype (42.0 and 60.0 L/h, respectively, P = 0.025). There were no significant differences in afatinib CL/F between genotypes for NR1I2 8055C > T, -25385C > T, ABCB1, ABCG2, and ABCC2 polymorphisms. Based on the area under the receiver-operating characteristic curve, the threshold afatinib AUC_0-24 value for prediction of dose reduction or withdrawal was 689 ng·h/mL at the best sensitivity (81.0%) and specificity (72.7%). In multivariate logistic regression analysis, an afatinib AUC_0-24 above 689 ng·h/mL was independently associated with increased risk of dose reduction or withdrawal (OR: 11.66, P = 0.012).

Conclusions: The NR1I2 7635A allele was related to a lower afatinib CL/F. Based on the AUC of 689 ng h/mL and CL/F, the optimal doses for patients with the NR1I2 7635G/G genotype and 7635A allele were recommended to be set at 40 and 30 mg/day, respectively, and subsequent adjustment of the maintenance dose based on the plasma concentrations of afatinib may be necessary to avoid afatinib-related adverse events.