Context: Metyrapone is an inhibitor of endogenous adrenal corticosteroid synthesis which has been proven to be a viable and safe option in controlling maternal serum cortisol concentrations during pregnancy. The infant exposure to maternally ingested metyrapone through breast milk is, however, largely unknown.
Case Description: We report the excretion of metyrapone into breast milk and subsequent infant exposure from a lactating woman on 250mg of metyrapone three times daily. At steady state, the average concentrations in milk and absolute and relative infant doses (AID and RID) were 176 ug/L, 26.45 ug/kg/d, and 0.7% respectively for metyrapone, and 310 ug/L, 46.52 ug/kg/d, and 1.21% for its active metabolite rac-metyrapol. The breastfed infant was found to have a plasma metyrapone concentration of 0.05 ug/L, with no evidence of disruption to his adrenocortical axis biochemically.
Conclusion: These findings indicate that maternal metyrapone use during breastfeeding did not pose a significant risk to the breastfed infant.