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Thiamazole and breastfeeding

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  • Thiamazole and breastfeeding

    I have a patient with hyperthyroism and thyroid nodules, breastfeeding 8 month old baby. Endocrynologist prescribed Thiamazole 10mg 3 times a day and suggested 3h break between taking medicine and nursing. Other endocrynologist ordered to stop breastfeeding at once. As I failed to find any useful information on this medicine (accept that generally thyroid treatment is safe during breatfeeding) in LactMed, M&MM, and other databeses I searched, I hope to get some guidance here.
    Thank you in advance.
    Best regards,
    MoP Karolina Morze

  • #2
    Karolina Morze,

    Thiamazole (methimazole) is rated an L2-limited data-probably compatible. The amount that transfers is 5.88-14.7% of yours dose. You are on the upper dose at 30mg a day. "In a large study of over 134 thyrotoxic lactating mothers and their infants, even at methimazole doses of 20 mg/day, no changes in infant TSH, T4 or T3 were noted in over 12 months of study. The authors conclude that both propylthiouracil and methimazole can safely be administered during lactation. However, during the first few months of therapy, monitoring of infant thyroid functioning is recommended." (Medications and Mothers' Milk, Dr Thomas Hale PhD). We would say it is probably ok to nurse as long as your dose does not increase and your infants thyroid functions are within normal limits.

    Sandra Lovato R.N.
    InfantRisk Center