Document Type : Original Article
Mashhad University of Medical Sciences, Mashhad, Iran
Hyperthyroidism is a common disease and one of the best methods for its treatment is radioiodine therapy. Treatment with antithyroid drugs brings patients to euthyroidism before radioiodine therapy. Antithyroid drugs should be discontinued before radioiodine therapy to increase thyroid uptake. The purpose of this study was to determine the optimal time of methimazole (MTZ) discontinuation. One hundred eighty four patients, who were referred for radioiodine therapy were classified in 3 groups according to the duration of MTZ discontinuation before thyroid uptake (RAIU) measurement. Group 1, 2 and 3 were patients who discontinued MTZ (48-72 hrs), (72-120 hrs) and more than 120 hrs before RAIU measurement, respectively. Mean thyroid uptake in group 1, 2 and 3 was (64±15.1%), (60.1±14.1%) and (59.3±12.8), respectively. No significant difference was noted in thyroid uptake between these groups (F=1.83, P<0.16). This study shows that 48-72 hrs of MTZ discontinuation before radioiodine therapy is enough and longer term abstention is not associated with higher uptake.