Propylthiouracil (PTU) had been considered the antithyroid drug of choice during lactation;[1,2] however, findings that the rates of liver injury higher with PTU than with methimazole has altered this judgement. Some experts now recommend that methimazole should be considered the antithyroid drug of choice in nursing mothers.[3-5] No cases of PTU-induced liver damage have been reported in breastfed infants and it is unknown if the small amounts of the drug in breastmilk can cause liver damage. The drug or breastfeeding should be discontinued if liver toxicity is suspected. Dosages of PTU should be limited to 450 mg daily during breastfeeding.[6]
The American Thyroid Association recommends only monitoring infants for appropriate growth and development during routine pediatric health and wellness evaluations and routine assessment of serum thyroid function in the child is not recommended.[6] Rare idiosyncratic reactions (e.g., agranulocytosis) might occur, and the infant should be watched for signs of infection. Monitoring of the infant's complete blood count and differential is advisable if there is a suspicion of a drug-induced blood dyscrasia.