Iodinated radiocontrast agents in the treatment of hyperthyroidism
- Douglas S Ross, MD
Douglas S Ross, MD
- Section Editor — Thyroid Disease
- Professor of Medicine
- Harvard Medical School
As of this writing, neither iopanoic acid nor ipodate are available in the United States. It is unclear when, or even whether, they will ever again be marketed in the United States.
Ipodate and iopanoic acid, two oral iodine-containing drugs marketed as oral cholecystographic agents, have been used in the treatment of hyperthyroidism. These drugs are the most potent inhibitors of 5'-monodeiodinase, thereby impairing the extrathyroidal conversion of thyroxine (T4) to the more potent triiodothyronine (T3). The release of iodine in pharmacologic quantities from these agents has the additional benefits of blocking thyroid hormone release and interfering with its synthesis in some patients. (See "Iodine in the treatment of hyperthyroidism".)
These agents are more potent than propylthiouracil in blocking the conversion of T4 to T3, and they result in a rapid reduction in serum T4 and T3 concentrations (figure 1) [1,2]. Doses in most studies have ranged from 500 mg to 1000 mg as a single daily dose.
LIMITATIONS TO USE
Ipodate and iopanoic acid have been used as monotherapy for the treatment of hyperthyroidism caused by Graves' disease . However, they are not as effective as methimazole or propylthiouracil in controlling the hyperthyroidism, and the relapse rate after therapy is discontinued is higher .
There are also several additional problems with the use of these agents:
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