**8.2. Iodine and iodine containing components**

Inorganic iodine acts in many ways in thyrotoxicosis. Iodine blocks its own transport in thyroid, inhibits iodine organification and inhibits the release of hormone. Inhibition of iodine organification by inorganic iodide is known as Wolf-Chaikoff effect. Major action of iodine is inhibition of hormone release. Iodine also decreases the vascularity of thyroid gland. All of these effects of iodine are transient and lasts only for a few days or weeks. Now a days iodine is used only for preoperative preparation for Graves' disease and in the management of thyrotoxic crisis. The usual dose of Lugol's solution is 3-5 drops three times per day and that of SSKI is 2-3 drops twice daily. Iodine decreases the effect of subsequently administad thionamides and radioiodine for severe weeks.

Iodinated radio contrast agents like iopanoic acid, and sodium ipodate acts by blocking the peripheral conversion of T4 to T3 and inhibition of hormone release. They are ideally used in emergency situations when rapid control of thyrotoxicosis is needed or in preoperative preparation or while awaiting the response of radioiodine.
