Background: Cladribine is an antimetabolite used for the treatment of relapsing-remitting multiple sclerosis. At present, there are no data available on its use in breastfeeding mothers and its transfer in human milk.
Objective: We present a case of a lactating mother who donated her milk samples to study the transfer of cladribine following a 20-mg oral dose.
Methods: Analysis was done using liquid chromatography-mass spectrometry.
Results: The relative infant dose calculated in this study was 3.06%.
Conclusion: This is the first case report suggesting the transfer of cladribine in human milk in measurable quantities. However, caution should be advised during lactation.
Keywords: Multiple sclerosis; antimetabolite; breastfeeding; cladribine; human milk; relative infant dose.