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Amiodarone has both direct and indirect effects on thyroid function. The most notable indirect thyroid altering property is that the drug is approximately one-third iodine by weight. As a result, amiodarone therapy elevates free circulating iodine levels up to 40 times greater than the iodine intake from the average American diet. [2]
In some ways the Jod-Basedow phenomenon is the opposite of two physiological compensation mechanisms, the Plummer effect and the Wolff–Chaikoff effect, which in normal persons and in persons with thyroid disease, suppress the thyroid hormone after ingestion of large quantities of iodine or iodide. However, unlike the Plummer and Wolff ...
Thyroid function tests (TFTs) is a collective term for blood tests used to check the function of the thyroid. [1] TFTs may be requested if a patient is thought to suffer from hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid), or to monitor the effectiveness of either thyroid-suppression or hormone replacement therapy.
Both of these factors contribute to the effects of amiodarone on thyroid function. [20] [45] [47] [48] Amiodarone also causes an anti-thyroid action, via Plummer and Wolff–Chaikoff effects, due its large amount of iodine in its molecule, which causes a particular "cardiac hypothyroidism" with bradycardia and arrhythmia. [49] [50]
The recommendation is stronger in pregnant women with subclinical hypothyroidism (defined as TSH 2.5–10 mIU/L) who are anti-TPO positive, in view of the risk of overt hypothyroidism. If a decision is made not to treat, close monitoring of the thyroid function (every 4 weeks in the first 20 weeks of pregnancy) is recommended.
TPP is distinguished from other forms of periodic paralysis (especially hypokalemic periodic paralysis) with thyroid function tests on the blood. These are normal in the other forms, and in thyrotoxicosis the levels of thyroxine and triiodothyronine are elevated, with resultant suppression of TSH production by the pituitary gland .