A comparison of propylthiouracil versus methimazole in the treatment of hyperthyroidism in pregnancy

Abstract

Objective: Our purpose was to demonstrate that propylthiouracil and methimazole are equally effective and safe in the treatment of hyperthyroidism during pregnancy.

Study design: Between 1974 and 1990 records were available on 185 pregnant patients with a history or diagnosis of hyperthyroidism. Ninety-nine patients were treated with propylthiouracil and 36 with methimazole. The response to therapy was compared with respect to the time to normalization of the free thyroxine index and the incidences of congenital anomalies and hypothyroidism.

Results: The time to normalization of the free thyroxine index was compared in the two groups by means of survival analysis. The median time to normalization of the free thyroxine index on propylthiouracil and methimazole was 7 and 8 weeks, respectively (p = 0.34, log-rank test). The incidence of major congenital malformations in mothers treated with propylthiouracil and methimazole was 3.0% and 2.7%, respectively. No neonatal scalp defects were seen. One infant was overtly hypothyroid at delivery.

Conclusion: Propylthiouracil and methimazole are equally effective and safe in the treatment of hyperthyroidism in pregnancy.