Treatment of type II amiodarone-induced thyrotoxicosis by either iopanoic acid or glucocorticoids: A prospective, randomized study

Amiodarone-induced thyrotoxicosis (AIT) may occur either in the presence of underlying thyroid disease ( type I AIT) or in apparently normal thyroid glands (type II AIT). Type II AIT, a destructive thyroiditis, often favorably responds to glucocorticoids. Iopanoic acid (IopAc) is an iodinated cholecystographic agent that inhibits deiodinase activity and reduces the conversion of T-4 to T-3. It has recently been reported that cholecystographic agents restore euthyroidism in patients with type II AIT. We describe the results of a prospective randomized study conducted in 12 patients with type II AIT treated with either iopanoic acid ( group A, n = 6) or glucocorticoids (group B, n = 6). Serum free T-3 levels normalized rapidly in both groups after 7 d, from 0.75 +/- 0.20 ng/dl (11.5 +/- 3.1 pmol/liter) to 0.46 +/- 0.10 ng/d (7.1 +/- 1.7 pmol/liter), P< 0.01, and from 0.58 +/- 0.10 ng/dl ( 9.0 +/- 1.2 pmol/liter) to 0.34 +/- 0.03 ng/dl 5.2 +/- 0.5 pmol/liter), P< 0.003, in groups A and B, respectively ( P = NS). Serum free T-4 levels reduced at 6 months in group B[ from 2.70 +/- 0.32 ng/dl (35.1 +/- 4.1 pmol/liter) to 1.0 +/- 0.04 ng/dl (13.4 +/- 0.6 pmol/liter), P < 0.0001] but not in group A ( from 2.90 +/- 0.6 ng/dl (38.0 +/- 7.5 pmol/liter) to 2.30 +/- 0.4 ng/dl (35.6 +/- 6.1 pmol/liter, P = 0.39; P = 0.005 group B vs. group A). All patients in both groups became euthyroid and had their amiodarone-induced destructive thyroiditis cured as defined by normalization of both serum free T-4 and free T-3 levels, during both drugs therapy. However, patients in group B were cured more rapidly than patients in group A( 43 +/- 34 d vs. 221 +/- 111 d, respectively, P < 0.002). This study shows that, albeit both drugs are effective, glucocorticoids are probably the drug of choice for more rapidly curing type II AIT.