Remission after potassium iodide therapy in patients with Graves' hyperthyroidism exhibiting thionamide-associated side effects.

Abstract

Thionamides have various side effects. The effectiveness of potassium iodide (KI) was evaluated in hyperthyroid patients who experienced side effects to thionamides. An observational study was conducted at an academic medical center. Among 1388 patients with Graves' hyperthyroidism treated with thionamides, 204 (14.7%) exhibited side effects, and 44 were treated with KI and followed for 17.6 (median; range, 8.6-28.4) years. The primary endpoint was the initial response to KI, and the secondary endpoint was the long-term prognosis. The conditions of 29 (65.9%) of the 44 patients were well controlled with KI alone (10-400 mg/d) (A group), and 17 (38.6%) patients went into remission after 7.4 (1.9-23.0) years. The conditions of 15 (34.1%) patients were not controlled with KI alone (B group), even at a high dose (100-750 mg/d), but seven patients (15.9%) were controlled with a combination of KI and low-dose thionamides, resulting in remission after 7.2 (2.8-10.8) years. The initial parameters did not predict the response to KI or long-term prognosis. However, remission occurred in 70.8% of the patients treated with less than 200 mg of KI, compared with 35.0% of the patients who required 200 mg or more of KI (P < .05). Among hyperthyroid patients with thionamide-associated side effects, KI therapy was effective in two-thirds of cases, and about 40% of the patients experienced remission after KI therapy alone. The chance of remission was small among the patients refractory to KI.