Effects of Maternal Flecainide Use in the Nursed Infant—A Case Report

INTRODUCTION: Flecainide is a class 1c antiarrhythmic drug used to manage ventricular and supraventricular arrhythmias. Its use in women of childbearing age is limited due to concerns about adverse outcomes. However, existing data suggest that flecainide may be safely used during pregnancy for maternal and neonatal arrhythmias. Its pharmacokinetic properties allow placental and breastmilk passage, but data on neonatal exposure via lactation remain scarce. This case report investigates the safety of maternal flecainide use during breastfeeding by analysing clinical and biochemical data in one nursed infant. METHODS: A 33-year-old primigravida with a history of right ventricular outflow tract tachycardia was maintained on flecainide 200 mg/day throughout pregnancy and lactation. The infant, delivered at term with no complications, was exclusively breastfed initially and later received a reduced volume. RESULTS: The infant underwent clinical and biochemical evaluations and ECG monitoring at 5, 7, and 30 days postpartum. All assessments, including heart rate, rhythm, and QT intervals, remained within normal ranges. Maternal plasma flecainide levels were within the therapeutic range. Despite significant flecainide concentrations in breastmilk, neonatal plasma levels remained below the lower limit of detection, and no adverse effects were observed.Relative infant dose calculations remained under the recommended 10% threshold. CONCLUSION & DISCUSSION: This case report supports the safe use of flecainide during lactation. Despite detectable flecainide in breastmilk, infant exposure remained subclinical. These findings align with prior case studies. Clinicians may safely recommend breastfeeding in the case of maternal flecainide use.