Carbimazole is not approved for marketing in the United States by the U.S. Food and Drug Administration, but is available in other countries. Doses of carbimazole of 30 mg daily or 50 mg weekly have not adversely affected the few breastfed infants studied. Carbimazole is a prodrug for methimazole which has been studied extensively during breastfeeding; maternal methimazole therapy does not affect thyroid function or intellectual development in breastfed infants with doses up to 20 mg daily. Some experts now recommend that methimazole should be considered the antithyroid drug of choice in nursing mothers.[1-3]
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.[4] 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.