The iodine-containing oral cholecystographic contrast agents (OCAs) include sodium ipodate (Oragrafin), iopanoic acid (Telepaque), tyropanoic acid (Bilopaque), and iocetamic acid (Cholebrine).They all inhibit D1 and D2. These actions make OCAs useful as adjunctive therapy with other antithyroid drugs by promoting a rapid fall in the plasma T3 concentration of the seriously thyrotoxic patient.
In addition, the metabolism of OCAs results in the release of large amounts of I~ into the circulation. As described for KI, I~ released from OCAs may have effects at the thyroid gland and if used alone to treat hy-perthyroidism, OCAs carry the same potential to induce increased secretion of thyroid hormone and exacerbation of thyrotoxicosis. When an OCA is used in the treatment of hyperthyroidism, large doses of an-tithyroid agents are usually administered concomi-tantly. However, the combination of OCAs and antithy-roid drugs may cause resistance to the antithyroid drugs with time, presumably because of the elevation in in-trathyroidal I~ content. Thus, it is recommended that the use of OCAs be reserved for short-term treatment of patients with severe thyrotoxicosis and significant comorbidity (e.g., myocardial infarction, sepsis, stroke) for rapid control of plasma T3 concentrations.
When the OCAs are used for these purposes, they are administered at much lower doses than when used for cholecystography. At the higher doses, the major adverse effects of these compounds are acute renal failure, thrombocytopenia, and athrombocytosis; possible minor adverse reactions include diarrhea, nausea, vomiting, and dysuria.
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