Iopanoic acid as an adjunct to carbimazole in the management of hyperthyroidism.

BACKGROUND: The thiourea drugs take a few weeks to control the symptoms of hyperthyroidism whilst iodine containing radiographic contrast agents (iopanoic acid and sodium ipodate) have a more rapid effect. There is no report on the use of iopanoic acid administered in conjunction with carbimazole, so we evaluated the efficacy of this combination in the early medical management of patients with hyperthyroidism. METHODS: Thirty hyperthyroid patients diagnosed by clinical and biochemical criteria were randomized into two treatment groups. Group A (n = 16) received iopanoic acid (500 mg orally twice a day for the first 3 weeks) and carbimazole (30 mg orally in three divided doses) while group B (n = 14) received carbimazole alone. Clinical examination and estimation of serum total T3, total T4 and TSH were done by radioimmunoassay at the start of therapy, weekly for 4 weeks and then at 6, 8 and 12 weeks. RESULTS: In the initial 3 weeks, iopanoic acid induced a significantly greater fall in mean serum total T3 levels (Z = 2.298, p < 0.02) and a slower fall in mean serum total T4 (Z = 2.396, p < 0.05) in group A patients compared to those in group B. This was accompanied by earlier clinical improvement in group A patients. The mean serum total T3 and T4 values rose to higher levels in group A at 4 weeks, one week after discontinuation of iopanoic acid. At the end of 12 weeks, however, there was no significant difference in the mean serum total T3 and T4 levels between the two groups (p > 0.05). Biochemical euthyroidism (i.e. total T3 < 3 nmol/L and total T4 < 170 nmol/L) was achieved later in group A patients than in group B (10.4 +/- 5.0 weeks v. 3.6 +/- 1.2 weeks, p < 0.0001). CONCLUSIONS: Iopanoic acid given together with carbimazole induces rapid clinical improvement in hyperthyroid patients than carbimazole alone. However, the delayed achievement of euthyroidism may preclude its routine use in the management of patients with hyperthyroidism except in those with thyrotoxic emergencies.