Vedolizumab Levels in Breast Milk of Nursing Mothers With Inflammatory Bowel Disease.

INTRODUCTION There are no data on the transfer of vedolizumab in breast milk of nursing mothers. We aimed to assess the presence of vedolizumab in breast milk of nursing inflammatory bowel disease [IBD] patients. METHODS This was a prospective observational study of vedolizumab-treated breastfeeding patients with IBD. Serum and breast milk samples were obtained at pre-defined tim -points. The in-house developed enzyme-linked immunosorbent assay [ELISA] for measuring vedolizumab in blood was adapted and validated for measurement of the drug in breast milk. The level of vedolizumab was also measured in breast milk of a control group of nursing healthy mothers. RESULTS Vedolizumab was undetectable in breast milk in IBD patients before the first infusion of vedolizumab [n = 3] and in all of the healthy controls [n = 5]. Vedolizumab was measurable in all lactating women who received vedolizumab [n = 5]. However, on serial measurements in breast milk after an infusion, drug levels did not surpass 480 ng/ml, which was roughly 1/100 of the comparable serum levels. CONCLUSIONS Vedolizumab can be detected in the breast milk of nursing mothers. Although more data are imperative, the concentrations of vedolizumab in breast milk are minute and are therefore unlikely to result in systemic or gastro-intestinal immune-suppression of the infant.