The Basics
What is Carbimazole?
used to treat an overactive thyroid gland (hyperthyroidism)
Brand names for Carbimazole
Neo-Mercazole
How Carbimazole is classified
Antithyroid Agents, Thionamides
Carbimazole During Pregnancy
Carbimazole pregnancy category
Category N/ANote that the FDA has deprecated the use of pregnancy categories, so for some medications, this information isn’t available. We still think it’s useful to list historical info, however, given what a common proxy this has been in the past.
What we know about taking Carbimazole while pregnant
N/A
Taking Carbimazole While Breastfeeding
What are recommendations for lactation if you're taking Carbimazole?
Carbimazole is not approved for marketing in the United States by the U.S. Food and Drug Administration, but is available in other countries. It 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. Doses of carbimazole of 30 mg daily or 50 mg weekly have not adversely affected the few breastfed infants studied and no cases of thyroid function alteration has been reported among infants exposed to methimazole via breastmilk. 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.[1] 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.
Maternal / infant drug levels
Carbimazole is not approved for marketing in the United States by the U.S. Food and Drug Administration, but is available in other countries. It 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. Doses of carbimazole of 30 mg daily or 50 mg weekly have not adversely affected the few breastfed infants studied and no cases of thyroid function alteration has been reported among infants exposed to methimazole via breastmilk. 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.[1] 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.
Possible effects of Carbimazole on milk supply
Relevant published information was not found as of the revision date.
Possible alternatives to Carbimazole
Methimazole, Propylthiouracil.
List of References
Lactation sources: Drugs and Lactation Database (LactMed) [Internet]. Bethesda (MD): National Library of Medicine (US); 2006-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK501922/1. Alexander EK, Pearce EN, Brent GA et al. 2016 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease during Pregnancy and the Postpartum. Thyroid. 2017;27:315-89. PMID: 28056690
2. Low LC, Lang J, Alexander WD. Excretion of carbimazole and propylthiouracil in breast milk. Lancet. 1979;314:1011. Letter. PMID: 91730
3. Johansen K, Andersen AN, Kampmann JP. Excretion of methimazole in human milk. Eur J Clin Pharmacol. 1982;23:339-41. PMID: 6897386
4. Rylance GW, Woods CG, Donnelly MC et al. Carbimazole and breastfeeding. Lancet. 1987;329:928. Letter. PMID: 2882332
5. Lamberg BA, Ikonen E, Osterlund K et al. Antithyroid treatment of maternal hyperthroidism during lactation. Clin Endocrinol (Oxf). 1984;21:81-7. PMID: 6744638
6. Verd S, Cardo E. Well-being of a baby breast fed by her mother on carbimazol treatment. J Hum Lact. 1998;14:206-7. Letter. PMID: 10205431
Disclaimer: This material is provided for educational purposes only and is not intended for medical advice, diagnosis, or treatment. Consult your healthcare provider with any questions.
