Methimazole vs. Propylthiouracil for Hyperthyroidism

Methimazole was superior overall, and lower doses seemed sufficient for patients with mild-to-moderate hyperthyroidism.

Both methimazole and propylthiouracil (PTU) are used to treat hyperthyroidism. To compare these drugs, Japanese researchers randomized 396 patients with Graves hyperthyroidism to receive 15 mg of methimazole once daily, 30 mg of methimazole daily (given as 15 mg twice daily), or 100 mg of PTU three times daily.

At each of three time points (4, 8, and 12 weeks), the proportion of patients with normalized free thyroxine (T4) levels was higher in the 30-mg methimazole group than in the other two groups. The differences were of borderline statistical significance at 4 and 8 weeks but significant at 12 weeks (normal free T4 achieved in 97%, 86%, and 78% of patients in the 30-mg methimazole, 15-mg methimazole, and PTU groups, respectively). In patients with mild or moderate hyperthyroidism, normal free T4 was achieved at similar rates in the three groups. However, in patients with severe hyperthyroidism (i.e., free T4 7 ng/dL), higher-dose methimazole was more effective than lower-dose methimazole or PTU. Transaminase elevations and leukopenia occurred less commonly with both doses of methimazole than with PTU. Rash was less common with lower-dose methimazole than with higher-dose methimazole or PTU.

Comment: Based on these results, the authors favor methimazole — at doses of 15 mg/day for those with mild-to-moderate hyperthyroidism, and 30 mg/day for those with severe hyperthyroidism. Because other studies have reached similar conclusions, most U.S. experts already favor methimazole. One exception is that PTU is recommended during pregnancy.

— Allan S. Brett, MD

Published in Journal Watch General Medicine June 19, 2007

Citation(s):
Nakamura H et al. Comparison of methimazole and propylthiouracil in patients with hyperthyroidism caused by Graves’ disease. J Clin Endocrinol Metab 2007 Jun; 92:2157-62.