Transfer of emicizumab into breast milk in postpartum acquired hemophilia A.

BACKGROUND

Acquired hemophilia A (AHA) is a rare, potentially life-threatening autoimmune bleeding disorder caused by neutralizing autoantibodies against factor (F)VIII. The postpartum period is a recognized risk factor for AHA. Emicizumab is increasingly used for hemostatic prophylaxis in AHA, including in women who may wish to continue breastfeeding. However, data on transfer of emicizumab into breast milk are lacking. This limits evidence-based counseling and shared decision-making.

OBJECTIVE

To assess whether emicizumab is detectable in the breast milk of a patient with postpartum AHA.

METHODS

Plasma and breast milk samples were collected from a woman who developed AHA 4 months after delivery and was treated with emicizumab while breastfeeding. Samples were analyzed for emicizumab using a modified one-stage clot assay and for anti-FVIII immunoglobulin (Ig)G and IgA antibodies using immunoassays.

RESULTS

Emicizumab was measurable in breast milk shortly after treatment initiation and reached concentrations of up to 20 μg/mL. The steady-state plasma concentration of emicizumab was 42 μg/mL. Anti-FVIII IgG and IgA were detected in plasma but not in breast milk samples.

CONCLUSION

In this patient with postpartum AHA, emicizumab was detectable in breast milk, whereas FVIII inhibitors were not. These findings are relevant for counseling breastfeeding women receiving emicizumab. Further studies are needed to determine the extent and clinical relevance of infant exposure.