Abstract OBJECTIVE Oxcarbazepine(OXC) is an antiepileptic drug, which is metabolized to the active 10-monohydroxy derivative(MHD) after oral administration. The half-life period of MHD in children is significantly shorter than that in adults, and the clearance is increased by 30% to 160% compared with that in adults, which indicates that the pharmacokinetics(PK) of MHD in children is obviously different from that in adults, while adults and children exhibit different levels of expression of metabolism enzymes and transporter proteins with the same genotype. At present, there is no study describing the influence of genetic polymorphism of PK-related enzymes on MHD plasma concentrations in children with epilepsy. This study investigates whether the polymorphism of metabolic enzymes and transporter genes have significant effects on MHD plasma concentrations in children with epilepsy in China, so as to provide the reference for individualized application of OXC in pediatric patients. METHODS The plasma samples from pediatric patients with epilepsy aged 0-14 years old at the First Affiliated Hospital of Fujian Medical University who received OXC were prospective collected from June 2021 to June 2023. The MHD blood concentrations of the patients were measured using enzyme amplified immunoassay, and the metabolic enzyme genes UGT2B7 802T>C, UGT1A9 I399C>T, as well as the transporter genes ABCB1 3435C>T and ABCB2 1249G>A polymorphism were detected using dideoxy chain-termination method in epilepsy children. According to Hardy Weinberg's law of genetic balance, the theoretical values of genotype frequency of the patients were calculated, and a Chi-Square test method was used to compare whether there was a significant difference between the theoretical value and the measured value, to examine whether the genotype of the patients included in the study is accordance with the law of genetic balance. One-way ANOVA statistical method was used to analyze the correlation of the four single nucleotide polymorphisms, daily maintenance dosage of OXC, and MHD blood concentrations. Subsequently, Fisher's least significant difference(LSD) test was performed. LSD test is a pairwise comparison of the differences between the mean values of each group, calculated based on the standard error and degrees of freedom to obtain the minimum significant difference between each two groups, while P<0.05 indicated that the difference was significant. RESULTS In this study, 161 trough concentrations were collected from children with epilepsy. The genotype of the included population conformed to the genetic balance law, which indicated that the included patients were representative for the population. Unite analysis of variance showed a significant correlation between the transporter gene ABCB1 3435C>T and MHD blood drug concentration(P<0.05). Subsequently, Fisher's minimum significant difference test was conducted, and MHD plasma concentrations of patients carrying the ABCB1 3435C>T mutation allele were significantly higher than that of non-carriers. No significant association was found between the four single nucleotide polymorphisms and the daily maintenance dosage of OXC, and no significant impact of the other metabolic enzyme and transporter genetic polymorphisms on MHD plasma concentrations was found. CONCLUSION The results of research shows that the ABCB1 3435C>T polymorphism significantly affect the MHD blood concentration of pediatric patients with epilepsy, and the effects of UGT2B7 802T>C, UGT1A9 I399C>T and ABCB2 1249G>A genetic polymorphisms on MHD blood concentration and daily maintenance dosage of OXC are not found. The results suggest that MHD blood concentrations are significantly increased by affecting the expression of the encoded MDR1 transporter protein after ABCB1 3435C>T site mutation, which also may increase the risk of adverse reactions of OXC. The genetic polymorphisms of ABCB1 3435C>T can be detected in children with epilepsy when taking OXC, and the dosage can be adjusted appropriately for patients with genetic mutations. The results of this study can provide the reference for the individualized administration of OXC in clinic.