From the Guidelines
Propylthiouracil (PTU) is the equivalent of methimazole for treating hyperthyroidism, particularly in pregnancy. According to the American College of Obstetricians and Gynecologists (ACOG) practice bulletin on thyroid disease in pregnancy 1, both propylthiouracil and methimazole are thioamides used to treat hyperthyroidism in pregnant women. The goal of treatment is to maintain FT4 or FTI in the high-normal range using the lowest possible thioamide dosage.
Key Considerations
- Propylthiouracil and methimazole have been found to have no significant differences in mean FT4 or TSH levels in newborn cord-blood samples, as well as no cases of aplasia cutis and similar rates of fetal anomalies for both agents 1.
- Women treated with propylthiouracil or methimazole can breastfeed safely.
- The medications require regular monitoring of thyroid function tests and awareness of potential side effects including rash, joint pain, and rarely, agranulocytosis.
Treatment Approach
- The typical starting dose of PTU is not specified in the provided evidence, but it is essential to use the lowest possible thioamide dosage to maintain FT4 or FTI in the high-normal range.
- Measuring the FT4 or FTI every two to four weeks can be helpful in adjusting the dosage.
- A beta blocker (e.g., propranolol) can be used to reduce symptoms until thioamide therapy reduces thyroid hormone levels.
From the Research
Equivalent of Methimazole
The equivalent of methimazole can be found in other antithyroid medications used to treat hyperthyroidism. Some of these alternatives include:
- Propylthiouracil (PTU) 2, 3, 4
- Potassium perchlorate 2
- Beta blockers 5, 2
- Iodine 2
- Lithium carbonate 2
- Glucocorticoids 2
- Rituximab, a monoclonal antibody directed against human CD20 2
Comparison of Methimazole and Propylthiouracil
Studies have compared the efficacy of methimazole and propylthiouracil in patients with hyperthyroidism caused by Graves' disease. The results show that:
- Methimazole 30 mg/d normalized FT4 in more patients than PTU 300 mg/d and MMI 15 mg/d at 12 weeks 3
- Methimazole 15 mg/d is suitable for mild and moderate GD, whereas MMI 30 mg/d is advisable for severe cases 3
- PTU is not recommended for initial use 3
- A single daily dose of 15 mg of MMI was much more effective in the induction of euthyroidism than a single daily dose of 150 mg of PTU 4
Treatment Options for Hyperthyroidism
The treatment options for hyperthyroidism include: