Drugs for Thyroid Disorders

Question 1

What are :

a) Levothyroxine [T4]
b) Liothyronine [T3]
c) Liotrix [a 4:1 ratio of T4:T3]
d) Thyroid desiccated

Answer 1

Thyroid agents used in hypothyroidism

Question 2

What are:

a) Radioactive iodine (131I)
b) Potassium iodide
c) Methimazole
d) Propylthiouracil [PTU]

Answer 2

Anti - thyroid drugs used in Hyperthyroidism

Question 3

What can be used in Thyrotoxicosis (thyroid storm or symptomatic hyperthyroidism) when there is:

1. Excess of thyroid hormone (T4 & T3) production and secretion
2. Increases in heart rate, tremors and nervousness

Answer 3

Propranolol

non-selective beta-1 and beta-2 blocker

Question 4

What is used to reduce heart rate and tremor during thyroid storm? How ?

Answer 4

Propranolol

1. Inhibits conversion of T4 to T3 (more active) in the periphery
2. May help reverse reduced systemic vascular resistance

Question 5

What is Amiodarone- Induced Thyrotoxicosis?

Answer 5

Hyperthyroidism from amiodarone

Type 1: patients with an underlining thyroid disease (Grave’s or Multi-modular goiter) get iodine from amiodarone and goes crazy with hormone production

Type 2: Amiodarone causes a subacute thyroiditis in patients without an underlying thyroid illness–> release of preformed thyroid hormones into circulation–> thyrotoxicosis
- actually causes destruction of thyroid tissue

Question 6

What is Amiodarone prescribed for? What should you measure while using it?

Answer 6

• Prescribed for arrhythmia
• each 200mg tablet releases 7.4 mg of iodine per day and daily recommended iodine intake is 0.15 mg–> TOXIC
• leads to increased hormone production and release

Question 7

What is more potent, Propylthiouracil or methimazole?

Answer 7

Methimazole is 10X more potent than PTU

-Carbimazole converted–> Methimazole

Question 8

What is Methimazole? MOA

Answer 8

Thioamide used to treat hyperthyroidism (ie Grave’s_

• blocks iodide organification
• Inhibits thyroperoxidase (TPO) (necessary to make T3 and T4)

Question 9

What is Potassium Iodide?

Answer 9

Stable form of iodine that blocks iodine uptake via Wolf Charikoff effect

-SSKI is a saturated solution of K iodine to such down T4 production

Question 10

What is Wolff-Chaikoff effect?

Answer 10

negative feedback when there is too much iodine

Question 11

What is the use of Potassium Iodide

Answer 11

1. Shrinks the thyroid gland to protect the thyroid from radiation exposure
2. Decreases thyroid hormone production

Does not affect heart rate or cause irregular heartbeat*

Question 12

What is Propothiouracil use?

Answer 12

Thioamide used in

1. Graves Disease
2. Toxic multi-nodular goiter
   - intolerant of methimazole
   - can’t do surgery

Question 13

What is MOA of Propothiouracil?

Answer 13

1. Inhibit synthesis of thyroid hormones in hyperthyroidism
2. inhibit the conversion of thyroxine to triiodothyronine in peripheral tissues
   - does not inactivate preexisting T4 and T3 in the thyroid or circulating in the blood

Question 14

What is the most sensitive screening test for hyperthyroidism and primary hypothyroidism?

Answer 14

TSH

Question 15

What is Levothyroxine?

Answer 15

• used to treat hormone deficiency
• manufactured from of T4 that gets converted to T3
• can take 6 weeks to take effect and dosing is based on regular measurements of TSH and T4 levels in the patient’s blood

Question 16

What drugs can impair levothyroxine absorption?

Answer 16

1. Sucralfate anti-ulcer med
   
   • *** Cholestyramine
   • Orlistat
   • PPI
2. Antacids
3. Iron

Question 17

Who should not have Radioactive iodine therapy?

Answer 17

Pregnant women