Qualitative and quantitative impact of protective glucocorticoid therapy on the effective 131I half-life in radioiodine therapy for Graves disease.

UNLABELLED This aim of this retrospective study was to determine the impact of glucocorticoid therapy on the effective (131)I half-life in radioiodine therapy for Graves disease. METHODS Three hundred fifteen consecutive Graves disease patients undergoing radioiodine therapy at our institution between August 2004 and January 2009 were enrolled. We investigated the influences of thyroid state (hypothyroidism, euthyroidism, hyperthyroidism), antithyroid drug dose before (131)I therapy, thyroid-stimulating hormone receptor antibody (TRAb) level, and qualitative and quantitative factors of prednisolone therapy on the effective (131)I half-life, applying univariate (paired t test) and multivariate (multiple-regression) analyses. RESULTS Multivariate analyses revealed independent significant effects of the thyroid metabolic state (P = 0.004), antithyroid drugs (P < 0.001), presence of TRAb (P = 0.004), and glucocorticoids (P = 0.046) on thyroidal radioiodine half-life. Compared with euthyroidism, thyrotoxicosis and hypothyroidism reduced the effective half-life; high doses of antithyroid drugs and high TRAb levels had the same effect. Also, glucocorticoid therapy shortened the effective thyroidal radioiodine half-life in a dose-dependent manner. Pharmacologically, this effect is attributable to the prednisolone-induced increase of renal plasma (131)I clearance and the resulting reduction of plasma (131)I available for reuptake into the thyroid during radioiodine therapy. CONCLUSION Oral treatment with prednisolone results in a reduction of effective thyroidal (131)I half-life in Graves disease, especially at higher doses.