Amiodarone-induced elevation of thyroid stimulating hormone in patients receiving levothyroxine for primary hypothyroidism

Article Abstract:

Amiodarone, a drug used to prevent abnormal heart rhythms, has complex effects on the metabolism of thyroid hormones. Because amiodarone antagonizes the effects of the thyroid hormone, 3,5,3'-triiodothyronine (T3), it may be capable of elevating levels of thyroid stimulating hormone (TSH). Two cases are described in which amiodarone increased TSH levels in patients treated with levothyroxine for hypothyroidism, the decreased activity of the thyroid gland. Amiodarone may increase TSH levels through a mechanism involving impaired conversion of the thyroid hormone thyroxine (T4) to T3 in peripheral tissues and pituitary. This mechanism would be consistent with the findings of previous studies. It is also possible that amiodarone may block the entry of the thyroid hormones T3 and T4 into the pituitary, or that it prevents the attachment of T3 to its receptor. However, this second mechanism is not supported by evidence. A third possible mechanism of an amiodarone-induced increase in TSH levels involves the release of iodide from amiodarone, which suppresses thyroid function, thereby lowering T3 levels. It is recommended that patients treated with levothyroxine and amiodarone should be routinely tested for hypothyroidism by measuring TSH levels and by clinical evaluation. (Consumer Summary produced by Reliance Medical Information, Inc.)

Causes of, Amiodarone, Thyrotropin

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Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism

Article Abstract:

Iron supplements in the form of ferrous sulfate may reduce the effectiveness of thyroxine, or thyroid hormone, in patients with hypothyroidism. Hypothyroidism is a disorder characterized by decreased production of thyroxine by the thyroid gland. Fourteen hypothyroidism patients who were being treated with thyroxine were simultaneously treated with 300 milligrams of ferrous sulfate per day over a 12-week period. After 12 weeks of treatment with ferrous sulfate, the patients' average blood level of thyrotropin, or thyroid stimulating hormone (TSH), was approximately three times higher. The average blood level of thyroxine was approximately the same after the 12-week period, but nine patients experienced an increase in symptoms of hypothyroidism. Iron may bind to thyroxine, reducing its effectiveness.

Iron compounds, Thyroxine, Ferrous sulfate

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Normalization of Hyperhomocysteinemia with L-Thyroxine in Hypothyroidism

Article Abstract:

One cause of high homocysteine plasma levels may be hypothyroidism, which is treatable with drugs. High homocysteine levels are a significant risk factor for various cardiovascular diseases, while hypothyroidism is a risk factor for the acceleration of atherosclerosis. Measurement of homocysteine in 24 patients, 14 with chronic hypothyroidism and 10 who had a recent total thyroidectomy, found eight patients with elevated levels. Re-examination after three and nine months of L-thyroxine replacement therapy found that all patients had lowering of homocysteine levels, and those levels had returned to normal in seven of the eight whose had originally been abnormally high.

Health aspects, Cardiovascular diseases, Risk factors, Tryptophan, Homocysteine

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