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

Context: Thionamides have various side effects. Objective: The effectiveness of potassium iodide (KI) was evaluated in hyperthyroid patients who experienced side effects to thionamides. Design and Setting: An observational study was conducted at an academic medical center. Patients: 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. Main Outcome Measures: The primary endpoint was the initial response to KI, and the secondary endpoint was the long-term prognosis. Results: 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). Conclusions: 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.