Pharmacological treatment of hyperthyroidism during lactation: review of the literature and novel data

Antithyroid drugs (ATD) are used as a first line treatment in thyrotoxicosis. Propylthiouracil (PTU), carbimazole (CMZ) and methimazole (MMI) are available. During absorption CMZ is bioactivated to MMI. Initially, mothers were not allowed to breastfeed during treatment with ATD. Newer studies minimized the risk for mother and infant. PTU should be preferred over MMI due to its lower milk concentration. Recent studies have shown severe hepatic dysfunction for both ATD, but especially for PTU, in hyperthyroid patients. Most of those cases were idiosyncratic, not-dose related and presented a latent period of occurrence. No biomarkers could predict hepatic damage. The American Thyroid Association (ATA) has recommended that PTU should not be prescribed as the first line agent in children and adolescents. Its use might be accepted in the first trimester of pregnancy for severe thyrotoxicosis or for patients with previous MMI adverse reactions. Considering the potential harmful effects of PTU, MMI should be used instead during lactation.