Which of the following is not true regarding iodine therapy?
Ref: Multiple Sources. Harper, Vasudevan and Sreekumari. Goodman and Giliman and Ganong Principles of Medical Physiology By Sabyasachi Sircar,Page 513Explanation:"The severity of symptoms of chronic intoxication with iodide (iodism) is related to the dose. Fortunately. the symptoms of Ref: Goodman and Gillman within a few days after stopping the administration of iodide," Ref: Goodman and Gillman"Therapeutic Uses: The uses of iodide in the treatment of hyperthyroidism ore in the preoperative period in preparation for thyroidectomy, and in conjunction with antithyroid drugs and propranolol, in the treatment of thyrotoxic crisis. Prior to surgery, iodide is sometimes employed alone, but more frequently it is used after the hyperthyroidism has been controlled by an antithyroid drug." Ref: Goodman and Gillman"In normal individuals, large doses of iodides act directly on the thyroid to produce a mild and transient inhibition of organic binding of iodide and hence of hormone synthesis. This inhibition is known as the Wolff-Chaikoff effect." Ref: Ganong"The inhibition of thyroid hormonogenesis by excess iodine is termed as Wolff-Chaikoff effect." Ref: Principles and Practice of Endocrinology and Metabolism. Page 957, edited by Kenneth L. Becker "The effect of iodine on thyroid is quite complex. The most obvious effect of administering a high dose of iodine is a decrease in the release of thyroid hormones. This effect is very prompt and is quicker than action of antithyroid dings. Hence iodine was used in the treatment of thyrotoxicosis. " Ref: Principles of Medical Physiology By Sabyasachi Sircar. Page 513 Iodine is required for thyroid hormone synthesis.STEPS INVOLVED IN SYNTHESIS(a) Iodine trapping: Pumping of 12 from blood to thyroid cell against cone gradient and down the gradient to colloid.Organification: Oxidation of iodide and bound to tyrosine of thyroglobulin; Thyroid peroxidase.Coupling reactions between MIT imonoiodo- tyrosine) and DIT (diiodotyrosine)DIT + DIT = T4MIT + DIT = T3Uncoupled MIT and DIT - deiodinated(d) Storage: Thyroid cells ingest colloid by endocvtosis, merge with lvsosomes.Secretion: Peptide bonds between iodinated residues and TG broken by proteases in lvsosomes.Release of T^ and T,. MIT. DIT.In hyperthyroidism, the amount of thyroid tissue is reduced by radioiodine (131I) treatment.(See the following Figure)IODINE THERAPYIodine is the fastest acting thyroid inhibitor.It is reduced in the intestine to iodide.Thyroid 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 (Jod- Basedow effect).Figure: Inhibitory Effect of Iodine on Iodine MetabolismWorsening hyperthyroidism especially occurs in multinodular goiter.All facets of thyroid function seem to be affected, hut the most important action is inhibition of hormone release 'thyroid constipation'.Endocytosis of colloid and proteolysis of thyroglobulin comes to a halt.The MOA 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).UsesPre-operative preparation for thyroidectomyo Usually given for 10 days before surgeryo Makes the gland firm. less vascular and easier to operate upon.Thyroid storm: LugoTs iodine or iodine containing radiocontrast media orally are used to stop further release of T3/T4 from the thyroid and to decrease T4 to T3 conversion.Prophylaxis of endemic goiter.Antiseptic as tincture iodine.Adverse EffectsAcute reaction: Swelling of lips, eyelids and angioedema.Long term use of high doses cause hypothyroidism and goiter.Chronic overdosage causes lodism.IODISMSymptoms due to chronic intoxication with iodide (iodism).Dose related severity of symptoms.Unpleasant brassy taste.Burning in the mouth and throat.Soreness of the teeth and gum.Increased salivation.Coryza, sneezing.Irritation and swelling of the eyelids.Severe headache that originates in the frontal sinuses.Productive cough.Pulmonary edema.Painful enlargement of parotid and suhniaxillary glands.Inflammation of the pharynx, larynx and tonsils.Mildly acneform eruptions in the seborrheic areas.Fatal dermal eruptions (ioderma) but reversible.Gastric irritation and bloody diarrhea.Fever, anorexia.Depression.Symptoms disappear spontaneously after stopping iodide.NOTE:Jod-Basedow EffectHyperthyroidism due to administration of iodine or iodide.ft occurs when large amounts of iodine are administered in people from regions deficient in iodine or people with goiter. So this phenomenon does not occur in normal individuals.
Iodine inhibits release of thyroid hormones
Contraindicated in hyperthyroidism
Inhibits synthesis of mono-iodo and di-iodo tyrosine
It causes iodism
Nutrition & Digestion