Evaluation of the Effect of Uridine Diphosphate-Glucuronosyltransferases (UGT) Inhibition by Valproic Acid on Vixotrigine Pharmacokinetics in Healthy Volunteers

Background and Objective Vixotrigine is a voltage-dependent and use-dependent sodium channel blocker in development for the treatment of neuropathic pain. Metabolism of vixotrigine is primarily through glucuronidation, resulting in the major M13 metabolite. Two additional major metabolites formed are M14 and M16. This study was designed to evaluate the effects of a uridine diphosphate-glucuronosyltransferase inhibitor, valproic acid, on vixotrigine pharmacokinetics. Methods This open-label, fixed-sequence, phase I study enrolled 30 healthy volunteers who received a single dose of vixotrigine 150 mg on day 1 and day 16 following an 8-h fast. On days 8–22, volunteers received valproic acid 500 mg three times daily. A mixed-effects model was used to analyze the effect of valproic acid on the natural log-transformed pharmacokinetic parameters of vixotrigine and its metabolites including maximum concentration and area under the concentration–time curve from time zero to infinity. Results Vixotrigine systemic exposure (area under the concentration–time curve from time zero to infinity) was increased by approximately 70% following the addition of valproic acid with a negligible effect on maximum concentration. Valproic acid administration also impacted vixotrigine metabolites: M13 exposure decreased by approximately 50% and M13 maximum concentration decreased by approximately 70%; increased exposure was noted for the M14 (approximately 100%) and M16 (approximately 70%) metabolites. Conclusions Valproic acid, a uridine diphosphate-glucuronosyltransferase inhibitor, significantly increased vixotrigine systemic exposure. Clinical Trial Registration ClinicalTrials.gov Identifier: NCT03385525.