Estimation of Atenolol Transfer Into Milk and Infant Exposure During Its Use in Lactating Women.

Background: Atenolol lactation information is limited, and controversy exists over the safety of its use during breastfeeding. In this study, important parameters including milk-to-plasma ratio, ratio of infant plasma to maternal plasma, infant daily dosage, and relative infant dose were investigated. The findings from this study add information to existing data about atenolol transfer in human milk. This may help guide health professionals in decision making regarding the safety of beta blockers used by mothers during breastfeeding. Research aim: The aims of the study were to quantify concentrations of atenolol in human plasma and milk, to evaluate atenolol pharmacokinetics in lactating women, and to investigate subsequent infant exposure to atenolol via mother's milk.

Methods: In this prospective, longitudinal observational study, participants were lactating mothers ( N = 3), 1 to 4 months postpartum, who had been taking atenolol for therapeutic reasons, and one 4-month-old breastfed infant. Eight milk samples were collected over 24 hr at different time points, together with a single blood sample from each lactating mother and the infant, and quantified using a new sensitive liquid chromatography mass spectrometry method developed for this study.

Results: Peak milk concentrations of atenolol were observed in the women at 4 hr (T) after oral administration. The dose-normalized maximum concentrations (C) of all patients were similar. The mean milk-to-plasma ratio of the patients who were taking 25 to 100 mg of atenolol was 8.57%. In the mother-infant pair study, the ratio (%) of infant plasma drug concentration to maternal plasma drug concentration observed (18.87%) was similar to the relative infant dose estimated (18.20%). The relative infant dose values (13.96%-18.20%) for all patients were within 10% to 25% of maternal dosage.

Conclusion: Atenolol use during breastfeeding should be undertaken with some precaution. If clinically indicated, an alternate beta blocker may be preferred.