Prophylactic-Dose Rivaroxaban Transfer Into Human Milk.

Direct oral anticoagulants are increasingly used for postoperative thromboprophylaxis, but use is limited in postpartum populations in the absence of data informing transfer into human milk. We evaluated the excretion of prophylactic-dose rivaroxaban into the milk of 20 low-risk lactating individuals from April through September 2024. Participants received two doses of prophylactic-dose rivaroxaban and provided blood and milk samples, with rivaroxaban concentrations quantified by liquid chromatography-tandem mass spectrometry. Pharmacokinetic metrics were evaluated, and the relative infant dose was calculated. Maternal plasma and milk rivaroxaban concentration peaked 2 hours after the second dose. At maximum maternal milk concentration of rivaroxaban, the relative infant dose was 2.9%, below the 10% safety threshold for drug use during breastfeeding. Findings suggest that neonatal exposure is likely low risk for use of prophylactic-dose rivaroxaban in lactating individuals.