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) 
toT(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.