Pharmacokinetics of Viloxazine ER (Viloxazine Extended-Release Capsules) in Breast Milk of Healthy Lactating Women.

Objective: To evaluate pharmacokinetics of viloxazine extended-release (ER) in breast milk and plasma of healthy lactating women and calculate potential infant exposure. Methods: Healthy lactating women (N=15), who were ≥12 weeks postpartum, received viloxazine ER 600 mg/d (the maximum recommended adult dose, given as 3x200 mg capsules) for 3 days at the same time each morning. Pharmacokinetic parameters describing the timing and amount of viloxazine in plasma and breast milk were measured based on samples collected predose and for 24 hours postdose on Day 3.Measures of potential infant exposure were calculated, including estimated daily infant dose (EDID) and relative infant dose (RID; the percentage of the weight-adjusted maternal daily dose that an infant would likely receive through breast milk). Results: At steady state, the median Tmax, milk in breast milk for viloxazine ER was 5.53 h, and the geometric mean (coefficient of variation [CV]%) breast milk-to-plasma ratio was 0.338 (17.4), indicating limited partitioning of drug into breast milk. Using a standard estimate of 150 mL/kg/d infant milk intake, the geometric mean (CV%) EDID was 0.134 (34.4) mg/kg/d, yielding an RID of 1.53% (27.6)-a value indicating low infant exposure within the commonly accepted <5%-10% RID safety threshold. Mild treatment-related adverse events were reported by 80% of participants, most commonly somnolence (67%), nausea (20%), and dizziness (20%). No participants discontinued. Conclusion: Viloxazine transfer into breastmilk of healthy, lactating women following multiple, once-daily 600 mg viloxazine ER doses was low. Trial Registration: ClinicalTrials.gov identifier: NCT06259331.