Drug which inhibits conversion of T4 to T3 is -
Ans. is 'c' i.e., Propylthiouracil DRUGS USED IN HYPERTHYROIDISMThyroid inhibitorsInhibit hormone synthesisInhibit iodine trappingInhibit hormoneDestroy(antithyroid drugs)(ionic inhibitors)releasethyroid tissueo Propylthiouracilo Thiocyanateso Iodineo Radioactiveo Methimazoleo Perchlorateso NaIiodineo Carbimazoleo Nitrateso KI Antithyroid drugs iPropylthiouracil, carbimazole, methimazolefo Conventionally, only the synthesis inhibitors are called antithyroid drugs.o Antithyroid drugs inhibit thyroid peroxidase and prevent oxidation of iodide / iodotyrosyl residues, there by:Inhibit iodination of tyrosine residue in thyroglobulin.Inhibit coupling of MIT and DIT to form T3. & T4.o Action 2 occurs at lower concentration.o Antithyroid drugs do not interfere with iodine trapping and do not modify the action of T4 & T3. on peripheral tissue.o They do not affect release of T4 & T3.o These drugs inhibit the formation of new thyroid hormones but their action manifests only when already stored pool of T4 and T3, is utilized a - lag period of 1-3 weeks is present,o Propylthiouracil inhibits the peripheral conversion ofT4 to T but carbimazol and methimazole do not -for this reason propylthiouracil is preferred in thyroid storm.o Carbimazol acts largely by getting converted to methimazole.o Both carbimazole and propvlthiourcil can be used during pregnancy, but propyl-thiouracil is the drug of choice because its greater protein binding allows low doses of propylthioracil to be transferred across the placenta and therefore less chance of hypothyroidism.o The most common side effect of these drugs is maculopapular pruritic rash, while most serious adverse effect is agranulocytosis which is reversible.o Recently prophylthiouraci) has been found to be hepatotoxic and FDA has declared methimazole as preferred drug over prophylthiouraci! in non-pregnant patients.Goodman cPS Gilman 11th/e 1530o Historically, prophylthiouracil has been preferred over methimazole because transplacental passage was thought to be lower; However, according to recent studies, both propylthiouracil and methimazole cross the placenta equally and either may be used safety in the pregnant patient.Note : However, if you will have to choose one option, prophylthiouracil is still the best because all other books still mention prophylthiouracil as the DOC in pregnancy.Iodine and Iodideso Iodine is the fastest acting thyroid inhibitor.o Most important action is inhibition of hormone release (thyroid constipation)', but all facets of thyroid synthesis may be affected.o Excess iodide inhibits its own transport in thyroid cells and may alter the redox potential of cells, thus interfering iodination - reduced T4/T3, synthesis (Wolff-chaikoff effect).Role of b-blockers in thyrotoxicosiso b-blockers (Propranolol) have emerged as an important form of therapy to rapidly alleviate manifestations of thyrotoxicosis that are due to sympathetic overactivity - palpitation, tremor, nervousness, sweating.They are used in hyperthyroidism in the following situations :While waiting response to carbimazole or I1J].Along with iodide for preoperative preparation before subtotal thyroidectomy.Thyroid storm (thyrotoxic crisis).
Carbimazole
Methimazole
Propylthiouracil
Lugol's iodine
Anti Thyroid