Can Dimethyl fumarate be given to a lactating mother?

Dimethyl Fumarate Use During Lactation

Dimethyl fumarate can be given to a lactating mother, as the active metabolite monomethyl fumarate (MMF) transfers into breast milk in extremely low amounts, with relative infant doses of only 0.007-0.22%, well below the 10% safety threshold. 1, 2, 3

Evidence from FDA Drug Label

The FDA label for dimethyl fumarate explicitly states there are no data on the presence of DMF or MMF in human milk, and that the effects on the breastfed infant and milk production are unknown. 1 The label recommends considering the developmental and health benefits of breastfeeding alongside the mother's clinical need for the medication and any potential adverse effects on the infant. 1

Direct Human Milk Transfer Data

Recent pharmacokinetic studies demonstrate minimal infant exposure:

• Two lactating patients at 5-6 months postpartum showed relative infant doses of 0.019% and 0.007% after one week of standard dosing (240 mg twice daily). 3
• A third case at 3 months postpartum demonstrated MMF concentrations in milk ranging from 5.5-83.5 ng/mL, with relative infant doses of 0.16-0.22%. 2
• The milk-to-plasma ratio was measured at 0.059, indicating poor transfer into breast milk. 2

These relative infant doses are far below the generally accepted 10% threshold for safety in breastfeeding. 2, 3

Clinical Decision Algorithm

When considering dimethyl fumarate in a lactating mother:

1. Assess disease activity: If the mother requires DMF for active multiple sclerosis, the medication should not be withheld due to breastfeeding, given the minimal infant exposure. 1, 2

2. Timing considerations: The limited data available comes from mothers at 3-6 months postpartum; earlier postpartum use has less supporting evidence but the pharmacokinetic properties suggest similar low transfer. 2, 3

3. Monitoring approach: Observe the infant for any unusual symptoms, though adverse effects are unlikely given the extremely low exposure levels. 1

4. Counseling points: Inform the mother that while human data are limited, available evidence shows minimal drug transfer and no reported adverse infant effects. 2, 3

Important Caveats

Variability in milk concentrations: There is notable intra- and inter-patient variability in MMF concentrations in breast milk (ranging from 5.5-83.5 ng/mL in one patient over 24 hours), though all measured levels remain very low. 2

Limited long-term data: All published cases involve short-term assessment (after 6 days to 1 week of treatment); long-term breastfeeding data during continuous DMF therapy are not available. 2, 3

Pregnancy safety data: The completed TecGistry registry of 397 pregnancies showed no adverse effects on pregnancy outcomes, with birth defects (2.2%), preterm birth, and spontaneous abortion rates consistent with the general population, supporting overall drug safety. 4

Practical Recommendation

Breastfeeding should not be discontinued when dimethyl fumarate is medically necessary for the mother. The combination of extremely low relative infant doses (all <0.25%), poor milk-to-plasma transfer ratio (0.059), and absence of reported adverse infant effects supports continuation of both therapy and breastfeeding. 1, 2, 3