Thyroid and Anti-thyroid Drugs

Question 1

What thyroid hormone is formed in greater amounts?

Answer 1

T4 (90%)

Question 2

What are the 3 main proteins that transport T4?

Answer 2

• Transthyretin
• Thyroid Binding Globulin
• Albumin

Question 3

What enzyme converts T4 to T3?

Answer 3

5’-deiodinase

Question 4

What is the effect of thyroid hormone on GH?

Answer 4

Increases GH

Question 5

What is the function of thyroid hormone on uncoupling protein?

Answer 5

Increases it - generates heat

Question 6

What is the effect of thyroid hormone on the beta-adrenergic receptors?

Answer 6

It will increase their number in the heart

Question 7

What is the treatment for hypothyroidism?

Answer 7

T3 or T4

Question 8

Levothyroxine

Answer 8

Mainly T4 so it is less potent and also safer but takes several weeks for action

Question 9

What is the effect of T4 on warfarin?

Answer 9

Increases the effects of warfarin from protein displacement

Question 10

What are the treatments for hyperthyroidism?

Answer 10

• Surgery or radiation
• Thioureylenes
• beta-blockers
• Corticosteroids
• Iodide

Question 11

Thioureylenes (Methimazole/Propylthiouracil)

Answer 11

Inhibit iodide organification via iodination and coupling

Question 12

What is a unique action of PTU peripherally?

Answer 12

Inhibits peripheral conversion of T4 into T3

Question 13

What is the more potent thioureylene?

Answer 13

Methimazole

Question 14

What is the DOC for hyperthyroid pregnant women?

Answer 14

PTU

Question 15

What are the main SE of PTU and methimazole?

Answer 15

• Agranulocytosis
• Granulocytopenia
• Rash
• Hypothyroidism

Question 16

Iodide

Answer 16

At high doses it inhibits iodide uptake in the thyroid

Question 17

What is iodide particularly useful for treating?

Answer 17

Thyroid Storm

Question 18

Radioactive Iodide MOA

Answer 18

Iodide is taken up and concentrated in the thyroid and the radiation leads to destruction of the gland to reduce activity

Question 19

Radioactive Iodide SE

Answer 19

Delayed hypothyroidism

Question 20

Beta Blockers

Answer 20

Blocks the beta receptors on the heart and decreases conversion of T3 to T4

Question 21

Anion Inhibitors (ClO4-, SCN)

Answer 21

Used only for diagnostic tools as they are highly toxic - compete with iodide uptake

Question 22

Thyroid Storm

Answer 22

Life threatening situation with large amounts of thyroid hormone - heat intolerance, sweating, tachycardia, etc.

Question 23

What is the treatment for thyroid storm?

Answer 23

• Acetaminophen - anti-fever
• beta-blockers
• PTU

Question 24

Levothyroxine MOA

Answer 24

T4 analog converted into T3 which acts as an agonist of VDR

Question 25

Levothyroxine Indications

Answer 25

Hypothyroidism

Question 26

Levothyroxine SE

Answer 26

- Hyperthyroidism with overdose - Risk of atrial fibrillation - Bone loss in postemenopausal women

Question 27

Liothyronine MOA

Answer 27

T3 analog and is active hormone that acts as an agonist of the VDR transcription factor

Question 28

Liothyronine Indications

Answer 28

Hypothyroidism when rapid onset of action is required - myxedema coma or radio iodine therapy for thyroid cancer

Question 29

Liothyronine SE

Answer 29

Risk of thyrotoxicosis with over dose

Question 30

What is a physiological example where TBG is increased and what is the response?

Answer 30

Pregnancy will have increased estrogen with increases TBG and leads to decreased T4 that is free reducing the effects of thyroid hormone.

Question 31

What is the DOC is almost all cases of hypothyroidism?

Answer 31

Levothyroxine

Question 32

Myxedema Coma

Answer 32

Decreased mental status, hypothermia, hypotension, bradycardia, hypoglycemia and hypoventilation - often precipitated by an acute stressor

Question 33

Propanolol MOA in Hyperthyroidism

Answer 33

- Ameliorate adrenergic symptoms | - Inhibits the deiodinase enzyme that converts T4 into T3 (small effect/slow onset)

Question 34

Thioureylenes MOA

Answer 34

- Inhibit Thyroid Peroxidase organification coupling | - PTU partially inibits peripheral deiodination of T4 to T3

Question 35

Thioureylenes SE

Answer 35

* Skin Reactions – pruritus, rash and urticaria * Joint Pain‐ arthralgias and arthritis * Fever * ANCA * Hepatotoxicity

Question 36

Wolf-Chaikoff Effect

Answer 36

‐ negative feedback mechanism | ‐ inhibits organification by inhibiting thyroid peroxidase

Question 37

How can cholestyramine be used in thyroid storm?

Answer 37

Blocks thyroid hormone reabsorption

Question 38

Amiodarone-induced Thyroid Disease

Answer 38

‐ high iodine content causes Wolff‐Chaikoff effect ‐ inhibits the deiodination of T4 to T3 ‐ blocks binding of T3 to Thyroid Hormone Receptor ‐ direct toxic effect on thyroid follicular cells

Question 39

What is the treatment for thyroid carcinoma?

Answer 39

Complete surgical removal

Question 40

Thioureylenes (MMI/PTU) MOA

Answer 40

Inhibit Thyroid Peroxidase Organification Coupling