Iopanoic acid

Iopanoic acid is an iodine-containing radiocontrast medium used in cholecystography. Both iopanoic acid and ipodate sodium are potent inhibitors of thyroid hormone release from thyroid gland, as well as of peripheral conversion of thyroxine (T₄) to triiodothyronine (T₃). These compounds inhibit 5'deiodinase (5'DID-1 and 5'DID-2) enzymes, which catalyse T₄-T₃ conversion in the thyroid cell, liver, kidney, skeletal muscle, heart, brain, pituitary. This accounts for the dramatic improvement in both subjective and objective symptoms of hyperthyroidism, particularly when they are used as an adjunctive therapy with thioamides (propylthiouracil, carbimazole). These are less toxic, as iodine is covalently bound in these compounds. They can be used in the treatment of patients with severe thyrotoxicosis (thyroid storm) and significant morbidity (e.g., myocardial infarction, or stroke) for rapid control of elevated plasma triiodothyronine concentrations. The use of iopanoic acid for treatment of thyrotoxicosis has been discontinued in the United States.