Influence of CYP2C9 and CYP2A6 on plasma concentrations of valproic acid: a meta-analysis.

Cytochrome P450 (CYP) is involved in the metabolism of valproic acid (VPA). Specifically, CYP2C9 and CYP2A6 are the main enzymes responsible for VPA metabolism. However, the correlation between plasma VPA concentrations and CYP2C9 and CYP2A6 gene variations is uncertain. This meta-analysis aimed to investigate the relationship between CYP2C9 and CYP2A6 variants and plasma concentrations of VPA. The PubMed, Web of Science, and EMBASE databases were searched for qualifying studies published until July 2019. Cohort studies that included standardized plasma VPA concentrations and CYP2C9 and CYP2A6 genotypes were reviewed. The mean difference and 95% confidence intervals (CIs) were evaluated to assess the strength of the relationship. Data analysis was performed using Review Manager (version 5.3) and RStudio (version 3.6). In total, we analyzed data from six studies involving 807 patients. We found that CYP2C9*3 was associated with standardized plasma VPA concentration; *3 allele carriers had a 0.70-μg/mL higher concentration per mg/kg than non-carriers (95% CI 0.25, 1.15; P = 0.002). We also found a significant association between the CYP2A6*4 and standardized trough VPA concentration; patients with the *4 allele had a 0.48-μg/mL higher concentration per mg/kg than patients without the *4 allele (95% CI 0.10, 0.86; P = 0.01). This meta-analysis demonstrated that CYP2C9*3 and CYP2A6*4 genetic variants affect plasma VPA concentrations. For epilepsy patients with these genotypes, dose adjustment may be necessary to ensure VPA's therapeutic effect.