Which of the following is wrong regarding treatment with iodine?(AIIMS Nov 2013, May 2013)
Correct Answer: Contraindicated in hyperthyroidism
Description: Ans. d. Its use is contraindicated in hyperthyroidism (Ref: KDT 7/e p254-255, 6/e p251-252; Goodman-Gillman 12/e p1152-1153)Iodine is not contraindicated in hyperthyroidism.MC therapeutic indication of 1131 (half life-8 days) is hyperthyroidism due to Grave's disease or toxic nodular goiter.Iodine is not contraindicated in hyperthyroidism.MC therapeutic indication of I131 (half life-8 days) is hyperthyroidism due to Grave's disease or toxic nodular goiter.Uses of Iodine in Hyperthyroidism:In the perioperative period in preparation for thyroidectomyIn conjunction with other antithyroid drugs and propranolol in the treatment of thyrotoxicosis.Inhibit release of thyroid hormones:An important clinical effect of high iodine is inhibition of release of thyroid hormones.This action is rapid and efficacious in severe thyrotoxicosis.Acute inhibition of iodotyrosine and iodothyronine synthesis:High concentration of iodine appears to influence almost all important aspects of iodine metabolism by the thyroid gland.Acute inhibition of the synthesis of iodotyrosines and iodothyronines by iodide is well-known (Wolff-Chaikoff effect)Causes iodism:The severity of symptoms with chronic intoxication of iodine (iodism) is related to dose.Manifestations: Inflammation of mucus membranes, salivation, rhinorrhea, sneezing, lacrimation, swelling of eyelids, burning sensation in mouth, headache, rashes GI symptoms etc.Iodine and IodidesThough iodine is a constituent of thyroid hormones, it is the fastest acting thyroid inhibitor.It is reduced in the intestine to iodide and the response to iodine or iodides is identical.The gland if enlarged, shrinks, becomes firm and less vascular.With daily administration, peak effects are seen in 10-15 days, after which 'thyroid escape' occurs and thyrotoxicosis may return with greater vengeanace.Worsening of hyperthyroidism especially occurs in multinodular goiter.All facets of thyroid function seem to be affected, but the most important action is inhibition of hormone release 'thyroid constipation'.Endocytosis of colloid and proteolysis of thyroglobulin comes to a halt.The mechanism of action is not clear. It appears to be a direct action on thyroid cells, through attenuation of TSH and c-AMP induced thyroid stimulation has been demonstrated.Excess iodide inhibits its own transport in thyroid cells and may alter redox potential of cells, thus interfering with iodination leading to reduced T3/T4 synthesis (Wolff-Chaikoff effect)Uses:Pre-operative preparation for thyroidectomy, generally given for 10 days just preceding surgery. The aim is to make the gland firm, less vascular and easier to operate upon.Thyroid storm: Lugol's iodine (6-10 drops) or iodine containing radiocontrast media orally are used to stop any further release of T3/T4 from the thy roid and to decrease T4 to T3 conversion.Prophylaxis of endemic goiterAntiseptic as tincture iodineAdverse Effects:Acute reaction: Swelling of lips, eyelids and angioedema in sensitive patientsChronic overdose (iodism): Inflammation of mucus membarnes, salivation, rhinorrhea, sneezing, lacrimation, swelling of eyelids, burning sensation in mouth, headache, rashes Gl symptoms etc.Long-term use of high doses can cause hypothyroidism and goiter
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