This report describes the policy at our institution to evaluate the safety of breastfeeding during maternal medication use by weekly capillary blood sampling in the infant. Additionally, this is the first report on combined maternal, fetal, breastmilk and neonatal flecainide concentrations in a breastfed infant of a mother requiring flecainide treatment. The low RID, AID, undetectable flecainide concentration in neonatal blood and absent cardiac symptoms, suggest that flecainide can safely be used during lactation, despite flecainide accumulation in breastmilk.
The RID is often used to evaluate the effect of maternal medication use on the breastfed infant, and an RID below 10% is considered safe (5). Two previous studies estimated the RID instead of flecainide quantification in neonatal blood and found proportions of 3.6% and 4.5% (3, 4). Our RID was 5.6%, which is quite comparable with the previous studies. In addition, the AID was 0.15 mg/kg/day which is much lower than the therapeutic dose in neonates of 2–8 mg/kg/day (6). However, it has to be considered that the RID is only a safety threshold for risk assessment and not a toxicity threshold. The drug’s pharmacological action and the infants’ metabolic capicities are not taken into account. Therefore, combined drug concentrations in maternal plasma, fetal plasma (collected from umbilical blood), breastmilk and infant plasma are required to adequately evaluate perinatal drug exposure in relation to its effects and safety. As breastmilk constitution, intake and infant’s intestinal drug absorption evolve over time, repeated measurements are recommended. Neonatal blood sampling can be performed with simple heel prick, or using scavenged blood samples. A previous focus serie on drug exposure in newborns of mothers using medication during pregnancy and lacation also described the added value of measurements of drug concentrations in the newborn in evaluating the safety of breastfeeding (7). However, in our knowledge, this method is hardly applied.
In conclusion, flecainide can be prescribed safely to lactating mothers as neonatal plasma concentrations are undetectable despite accumulation in breastmilk. For essential maternal drugs of which safety during breastfeeding has not yet been established, simultaneous measurement of drug concentrations in maternal blood, fetal blood, breastmilk and infant blood are a valuable aid to acertain neonatal safety and enhance maternal reassurance and comfort with breastfeeding. Systematic collection and pooling of these data will provide valuable evidence to establish the safety of perinatal drug use and allow breastfeeding in the future.