Putting Propylthiouracil in Perspective

Abstract

The antithyroid drugs propylthiouracil (PTU) and methimazole (MMI) have played central roles in the management of hyperthyroidism for more than 50 yr. Although both drugs effectively control hyperthyroidism, observations over several decades have shown that MMI and its prodrug carbimazole are better than PTU in controlling more severe hyperthyroidism, having higher adherence rates, and causing less toxicity, especially when prescribed in lower doses (1). This has led to the recommendation that MMI should be the first-line drug when antithyroid drug therapy is initiated, either for primary treatment or to prepare a patient for radioiodine or surgery. An exception to this rule has been pregnancy, during which PTU has been preferred because of rare reports of birth defects associated with MMI (2). PTU has also been used in patients who had minor reactions to MMI but, nonetheless, preferred to continue antithyroid drug therapy. PTU may also be preferable in patients with life-threatening thyrotoxicosis because of its additional inhibition of T₄ to T₃ conversion.