Adjunctive treatment with propylthiouracil or iodine following radioiodine therapy for Graves' disease

Abstract

The effect of radioiodine therapy in Graves' disease is gradual in onset and the subjects continue to be hyperthyroid for several weeks after such therapy. In a prospective study of 112 patients, we compared the usefulness of two commonly employed antithyroid drug regimens in controlling hyperthyroidism in the period immediately following radioiodine therapy. They received propylthiouracil (PTU, 100 mg orally three times a day), saturated solution of potassium iodide (10 drops once a day) or no drugs starting 5 days after radioiodine therapy. Thyroid status was monitored clinically and by serum thyroxine index and TSH measured at 4-6 week intervals over a 6-month period. The control or drug-treated groups did not differ in thyroid status 6 weeks after radioiodine. The PTU-treated group had greater incidence of hyperthyroidism and a lower incidence of hypothyroidism at 6 months. However, the differences were explained on the basis of a greater incidence of large goiters that appeared to confer relative radioresistance in the PTU group. We conclude that patients with mild to moderate hyperthyroidism do not benefit from adjunctive treatment with PTU or potassium iodide immediately after radioiodine therapy.