Metabolism and in vitro drug–drug interaction assessment of viloxazine

Abstract

Viloxazine is currently being developed as a treatment for attention deficit/hyperactivity disorder (ADHD). The aim of these studies is to update the understanding of the rat and human metabolism and the in vitro drug–drug interaction profile of viloxazine to a degree where it meets current regulatory standards for such investigations. In vivo absorption-distribution-metabolism-excretion (ADME) studies demonstrated that in humans 5-hydroxylation followed by glucuronidation is the major metabolic route. This route was also seen as a minor route in rats where the major route is O-deethylation with subsequent sulfation. In humans, the 5-hydoxylation pathway is mediated by CYP2D6. An estimate for the fraction of the metabolism via this pathway suggests a PM/EM difference of <2-fold, making it highly unlikely that this will be an issue of clinical significance. Viloxazine forms a unique N-carbamoyl glucuronide in humans. The chemical reactivity characteristics of this metabolite are similar to stable glucuronide conjugates and dissimilar from acyl glucuronides; therefore, it is regarded as a stable Phase II conjugate. In vitro drug–drug interaction (DDI) testing indicates that viloxazine is not a significant inhibitor or inducer of CYPs and transporters with the exception of CYP1A2.