Impact of Viloxazine Extended-Release Capsules (Qelbree®) on Select Cytochrome P450 Enzyme Activity and Evaluation of CYP2D6 Genetic Polymorphisms on Viloxazine Pharmacokinetics

Background and Objective Viloxazine extended-release (ER) [Qelbree ® ] is a nonstimulant attention-deficit/hyperactivity disorder (ADHD) treatment. In vitro studies suggested potential for viloxazine to inhibit cytochrome 450 (CYP) enzymes 1A2, 2B6, 2D6 and 3A4. This clinical study therefore evaluated viloxazine ER effects on index substrates for CYP1A2, 2D6, and 3A4, and secondarily evaluated the impact of CYP2D6 polymorphisms on viloxazine pharmacokinetics. Methods Thirty-seven healthy subjects received a modified Cooperstown cocktail (MCC; caffeine 200 mg, dextromethorphan 30 mg, midazolam 0.025 mg/kg) on Day 1, viloxazine ER 900 mg/day on Days 3–5, and a combination of viloxazine ER 900 mg and MCC on Day 6. Viloxazine ER effects on MCC substrates were evaluated using analysis of variance. The impact of CYP2D6 genetic polymorphisms on steady-state viloxazine plasma concentrations was evaluated using Student’s t test assessing pharmacokinetic parameter differences between poor versus extensive metabolizers. Results The least squares geometric mean ratio [GMR%] (90% CI) of MCC substrate + viloxazine ER/MCC substrate alone for caffeine maximum concentration ( C max ), area under the plasma concentration-time curve from time 0 to the last quantifiable concentration (AUC t ), and area under the plasma concentration-time curve from time 0 extrapolated to infinity (AUC ∞ ) was 99.11 (95.84–102.49), 436.15 (398.87–476.92), and 583.35 (262.41–1296.80), respectively; 150.76 (126.03–180.35), 185.76 (155.01–222.61), and 189.71 (160.37–224.42) for dextromethorphan C max , AUC t, and AUC ∞ , respectively; and 112.81 (104.71–121.54), 167.56 (153.05–183.45), and 168.91 (154.38–184.80) for midazolam C max , AUC t , and AUC ∞ , respectively. At steady state, viloxazine least squares GMR (90% CI) for poor/extensive CYP2D6 metabolizers were C max 120.70 (102.33–142.37) and area under the plasme concentration-time curve from time 0 to 24 hours (AUC 0–24 125.66 (105.36–149.87)). Conclusion Viloxazine ER is a strong CYP1A2 inhibitor and a weak CYP2D6 and CYP3A4 inhibitor. CYP2D6 polymorphisms did not meaningfully alter the viloxazine ER pharmacokinetic profile.