Kruse: thyroid drugs

Question 1

What are the thyroid agents

Answer 1

• Levothyroxine (T4)
• Liothyronine (T3)
• Liotrix (4:1 ratio of T4:T3)
• Thyroid desiccated

Question 2

Antithyroid agents

Answer 2

• Radioactive iodie (131 I) Sodium
• Methimazole
• Potassium iodide
• Propylthiouracil (PTU)

Question 3

What transports iodide iodide into the thyroid gland

Answer 3

NIS

Question 4

What is an apical cell iodide transport enzyme that controls the flow of iodide across the membrane?

Answer 4

pendrin

Question 5

where else is pendrin found? clinical implications?

Answer 5

Cochlea; if deficient or absent a syndrome of deafness and goiter called pendred syndrome occurs

Question 6

Iodide is oxidized by what in the apical cell membrane

Answer 6

thyroidal peroxidase

Question 7

Agents that inhibit the conversion of T4 to T3 and increase reverse T3 levels include what

Answer 7

• Radiocontrast agents: iopanoic acid and ipodate
• amiodarone
• Beta blockers
• corticosteroids

Give to those with thyroid storm

Question 8

Drugs that decrease T4 absorption

Answer 8

• Anacids
• ferrous sulfate
• cholestyramine
• colestipol
• ciprofloxacin
• PPI
• bran
• soy
• coffee

Question 9

Of the T4 and T3 preparations available, what is the preparation of choice for thyroid replacement therapy and why

Answer 9

• T4: levothyroxine

- stability, low cost, lack of allergic foreign protein, easy lab measurement, long half lift so once daily

Question 10

Which of the antithyroid drugs is not completely absorbed and has large first pass effect

Answer 10

PTU

Question 11

Which antithyroid is completely absorbed and has slower renal excretion than PTU

Answer 11

methimazole

Question 12

Describe the antithyroid therapy in pregnancy

Answer 12

• PTU in first trimester

- Methimazole in second and third

Question 13

Toxicity of methimazole and PTU

Answer 13

• most common: maculopapular pruriis rash at times accompanied by systemic signs such as fever, nausea, and GI distress
• Rare: urticarial rash, vasculitis, a lupus like reaction, lymphadenopathy, hypoprothrombinemia, acute arthralgia, hepatitis (more common with PTU), and cholestatic jaundice (methimazole)

Question 14

What are the most serious complications of PTU and methimazole

Answer 14

-agranulocytosis (<500)

Question 15

What are the monovalent anions that block thyroid gland uptake of iodide by competitively inhibiting the iodide transport mechanism

Answer 15

• Perchlorate
• Pertechnetate
• Thiocyanate

Question 16

What is the MOA of iodides

Answer 16

• inhibit organification and hormone release

- decrease in size and vascularity of hyperplastic thyroid glands

Question 17

Clinical use of iodide

Answer 17

• Thyroid storm- thyrotoxic symptoms improve rapidly
• Preoperative reduction of a hyperplastic thyroid gland
• Block thyroidal uptake of radioactive isotopes of iodine in a radiation emergency or other exposure

Question 18

Toxicity of Iodides

Answer 18

-uncommon. Can include: acneiform rash, swollen salivary glands, mucous membrane ulcerations, conjunctivitis, metallic taste

Question 19

Iodides and pregnancy?

Answer 19

should be avoided since they can cross placenta and cause a fetal goiter

Question 20

What is the only isotope used for treatment of thyrotoxicosis

Answer 20

(131)I

Question 21

radioactive iodine is contraindicated in who

Answer 21

Pregnant women or those breast feeding

Question 22

Beta blockers and management of thyrotoxicosis

Answer 22

• Those without sympathomimetic activity (metoprolol, propranolol, and atenolol)
• improve symptoms but do not typically alter thyroid levels (high doses of propranolol have been shown to reduce T3 levels by about 20%)

Question 23

What Beta blocker is most commonly used

Answer 23

propanolol

Question 24

Treatment of myxedema coma

Answer 24

• preparations given IV

- Large loading dose of T4 followed by smaller IV dosing

Question 25

Treatment of Myxedema and coronary artery disease

Answer 25

-Correction with T4 must be done cautiously to avoid provoking arrhythmia, angina, or acute MI

Question 26

Treatment of hypothyroidism and pregnancy

Answer 26

- Women who are hypothyroid are typically infertile until restoration of normal thyroid levels - Maintenance of normal levels is crucial due to fetal brain development dependence on maternal T4

Question 27

When do you use antithyroid drug therapy in Graves

Answer 27

- most useful in young patients and mild disease - Methimazole and PTU until remission - Methimazole is preferred except in pregnancy

Question 28

treatment of choice in Graves in patients with very large glands or multinodular glands

Answer 28

- thyroidectomy | - 80-90% will require thyroid supplementation

Question 29

When do u use Radioactive iodine in Graves

Answer 29

- most over 21 - in pts with underlying heart disease or severe thyrotoxicosis and in elderly patients, treatment with antithyroid drugs until patient is euthyroid is preferred

Question 30

Describe the adjuncts to antithyroid therapy in Graves

Answer 30

- B-blockers w/o sympathomimetic activity - these control tachycardia, HTN, and Afib - Diltiazem (calcium channel blocker) can be used to manage tachycardia in pts who Beta blockers are contraindicated

Question 31

Management of thyroid storm

Answer 31

- Beta blocker to control arrhythmia - Potassium iodide to prevent release of thyroid hormones - PTU or methimazole to block hormone synthesis - IV hydrocortisone to protect against shock and to block conversion of T4 to T3 in peripheral tissue - Supportive therapy - in rare situations where the above is inadequate, plasmapheresis or peritoneal dialysis may be used to lower levels of T4