Thionamides alter the efficacy of radioiodine treatment in patients with Graves' disease.

Thionamides are often used acutely to control the symptoms of thyrotoxicosis associated with Graves' disease before definitive treatment with radioiodine. Several reports have suggested that pretreatment with thionamides reduces the efficacy of radioiodine therapy in patients with Graves' disease, but other data refute this. This study retrospectively reviewed the records of 95 patients with Graves' disease treated with radioiodine. Pretreatment with thionamides resulted in significantly greater (2 1/2-fold) treatment failure rate than in patients not pretreated with thionamides but given a comparable dose of radioiodine. Higher serum thyroxine concentration at the time of diagnosis was also an independent factor associated with radioiodine treatment failure.