Radioiodine therapy in patients with Graves’ disease and the effects of prior carbimazole therapy

The use of radioiodine as the first line of treatment in Graves’ disease is restricted in India because of its limited availability and an unrealistic risk perception associated with it. Additionally, the effectiveness of radioiodine ablation in Graves’ disease is influenced by many factors. Prior medical antithyroid therapy is one such important factor. AIMS: To analyze the efficacy of low dose radioiodine therapy (5 mCi) in treatment of naive patients of Graves’ disease in comparison to that in which it was already primed with an antithyroid drug, carbimazole. SETTINGS AND DESIGN: A non-randomized, interventional study conducted in the Department of Medicine and Endocrinology of a tertiary care institute in South India. MATERIALS AND METHODS: The study had two groups; Group A (36 treatment naive, uncomplicated Graves’ disease patients) and B (34 Graves’ disease patients on carbimazole prior to radioiodine therapy). Both groups had baseline clinical, biochemical evaluation and were reassessed at 3 and 6 months for evaluating the clinical status for possible documentation of cure. RESULTS: The cure rate was 61.1% in drug naive group and 58.8% in pretreated group at 6 months following radioiodine (P = 0.845). Higher baseline 999m technicium (99m Tc) uptake, male gender, BMI and higher baseline free thyroxine (fT4) level predicted treatment failure following radioiodine therapy. CONCLUSIONS: Administration of carbimazole prior to low dose radioiodine therapy does not alter the efficacy of radioiodine. Low fixed dose (5 mCi) of radioactive iodine may be a safe and effective primary therapeutic option in Graves’ disease patients pretreated with antithyroid drugs.