Influence of Propylthiouracil and Methimazole Pre-treatment on the Outcome of Iodine-131 Therapy in Hyperthyroid Patients with Graves' Disease

There is ongoing controversy about potential differences in the influence of the anti-thyroid drugs propylthiouracil (PTU) and methimazole (MMI) on radioiodine treatment of Graves' hyperthyroidism. This retrospective study investigated the influence of PTU and MMI pre-treatment, individually or sequentially, on the outcome of iodine-131 ((131)I) therapy in 199 patients with Graves' disease who had been treated with (131)I for the first time and followed up at 3 and 6 months after treatment. Pre-treatment with PTU, or sequential PTU and MMI pretreatment, increased the failure rate of (131)I therapy and reduced the rate of hypothyroidism. MMI pre-treatment alone had no significant influence on the results of (131)I therapy. Logistic regression analyses indicated that PTU pre-treatment and having a thyroid gland of > 60 g were both significantly related to (131)I therapy failure.