Effect of iopanoic acid on radioiodine therapy of hyperthyroidism: long-term outcome of a randomized controlled trial.

Telepaque [iopanoic acid (IA)] is believed to rapidly ameliorate hyperthyroidism; however, it may preclude subsequent 131I therapy, possibly delaying it for several months. Our objective was to see how early patients, made euthyroid with Telepaque, can be treated with 131I and to compare their short- and long-term outcome with patients treated with 131I, after making them euthyroid with carbimazole and beta-blockers. We conducted a randomized controlled trial. We studied 200 hyperthyroid patients at a tertiary care teaching institute. The IA group received Telepaque, 500 mg/d orally, for 7 d and then no medication for 1 wk followed by 131I therapy if radioiodine neck uptake had recovered. The control group received 30-40 mg oral carbimazole daily until patients became euthyroid followed by 131I. After 1 wk of Telepaque therapy and 6 wk of carbimazole, almost all patients became clinically and biochemically euthyroid, and 86 and 94% of patients were ready for 131I therapy after 1 and 2 wk off Telepaque, respectively. The cure rate, defined as euthyroid plus hypothyroid, after the first dose of 131I in controls and the IA group was 80 and 76.2%, respectively (P = 0.54). Thirty-two percent among controls and 25% in the IA group became hypothyroid within 1 yr (P = 0.33); thereafter, the annual rate of hypothyroidism was about 2% in both groups. After a mean follow-up duration of 11 yr, 58% of patients in the control group and 51% in the IA group were hypothyroid. Telepaque rapidly ameliorates hyperthyroidism without jeopardizing the subsequent radioiodine therapy, and the outcome of radioiodine therapy in this subset of patients is in no way different compared with those prepared by carbimazole.