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.