Thyroid Drugs

Question 0

The enzyme thyroperoxidase is responsible for what reaction in the thyroid?

Answer 0

Covalently binding iodine to tyrosine residues in the thyroglobulin molecules

Question 1

Which cells in the thyroid secrete calcitonin?

Answer 1

Parafollicular cells

Question 2

What is triiodothyronine? Name and what forms it

Answer 2

T3 - MIT + DIT

Question 3

What is thyroxine? Name and what forms it

Answer 3

T4 - DIT + DIT

Question 4

Name three actions of thyroxine

Answer 4

Increases BMR (inc Na/K ATPase activity) (inc respiration, temp, oxygen use)
Potentiates effects of catecholamines (inc HR and CO)
Promotes CNS development

Question 5

What is the source of most T3 in the body?

Answer 5

Formed from deiodination of T4 in the target tissues

Question 6

Short child is mentally retarded with protruding tongue and umblicus. Diagnosis? Causes (3)

Answer 6

Cretinism - iodine deficiency, defect in T4 synthesis, thyroid didn’t develop

Question 7

Name the two thioamides that treat hyperthyroidism. What can they both cause?

Answer 7

Propythiouracil
Methimazole

Goiter

Question 8

Patient is treated with propythiouracil or methimazole. What is their mechanism of action and how long before you see effects? Why?

Answer 8

They block iodination of thyroglobulin and inhibit coupling of DIT and MIT (decrease T4 and T3 syn). Takes 2-3 weeks for full effect because they don’t affect preformed thyroid hormone

Question 9

What effect does eating cabbage have on thyroid?

Answer 9

Hypothyroidism

Question 10

What is the drug of choice in thyroid storm? Why?

Answer 10

Propythiouracil (PTU) - decreases conversion of T4 to T3 (methimazole can’t do this)

Question 11

Which antithyroid drug is preferred in pregnancy? Why?

Answer 11

Propythiouracil (PTU) - extensively protein bound

Question 12

What is the preferred antithyroid drug in clinic? Why?

Answer 12

Methimazole - way fewer adverse effects

Not preferred in pregnancy because its a possible teratogen

Question 13

Patient on thyroid medication develops rash, agranulocytosis, and aplastic anemia. What drug was she likely taking?

Answer 13

Propythiouracil

Also causes hepatotoxicity and vasculitis

Question 14

High levels of iodine have what effect on the thyroid? How long does this effect last? When would you give iodine to a patient?

Answer 14

They paradoxically inhibit thyroid hormone synthesis, but only for 10-14 days (Wolff-chaikoff effect). Given before thyroid excision surgery

Question 15

Patient is experiencing angioedema, swelling of larynx and eyelids, burning of the teeth and gums and has a brassy taste in her mouth. What drug(s) was she most likely taking?

Answer 15

These are adverse effects of iodide intoxication so probably lugol’s solution (iodine + potassium iodide) or just soln of potassium iodide

Question 16

Patient with graves disease has had a partial thyroidectomy and is on conventional antithyroid meds but isn’t responding to them. What can you give her? MOA? Most important adverse effect?

Answer 16

Radioactive iodine (131 I)

Taken up and sequestered by thyroid gland where it causes local damage only (no other tissue affected)

Dosing is difficult and may see hypothyroidism

Question 17

What is the only antithyroid drug that produces a permanent reduction in thyroid activity?

Answer 17

Radioactive iodine (133 I)

Question 18

Which beta blocker can prevent conversion of T4 to T3?

Answer 18

Propranolol

Question 19

Besides iodine and a beta blocker, what can be given during thyroid storm to prevent peripheral conversion of T4 to T3?

Answer 19

Glucocorticoids

Question 20

What two drugs used in iodinated radioconstrast media are good at rapidly reducing the T3 concentrations in thyrotoxicosis due to their ability to block conversion of T4 to T3 and inhibiting release from thyroid gland?

Answer 20

Diatrizoate (oral)

Iohexol (oral or IV)

Question 22

Which three antithyroid drugs block transport of iodine into the cell? Major adverse effect?

Answer 22

Perchlorate
Thiocyanate
Pertechnetate

Aplastic anemia

Question 23

What inhibits conversion from T3 to T4

Answer 23

Corticosteroids
Propranolol
Amiodarone
PTU
NaI inhibitors

Question 24

What happens to TSH and T3/T4 with Lithium

Answer 24

Increased TSH

Decreased T3/T4