<prompt> Which of the following is true of propylthiouracil?It is used in the treatment of myxedemaIt has a long half-life in the circulationIt increases proteolysis of thyroglobulinIt blocks thyroxine synthesis  <response>: Ans. is d i.e., It blocks thyroxine synthesis o Propylthiouracil blocks thyroxine synthesis by inhibiting thyroid peroxidase, and preventing 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 Propylthiouracil also inhibit the peripheral conversion of T4 to T3. About other options o It is a hypothyroid drug, cannot be used in myxedema hypothyroidism. It has a sho VA - 1-2 hours. It does not increase proteolysis of thyroxine. 