Exam II: Thyroid Pharmacology

Question 1

Where is T4 best absorbed?

Answer 1

In the duodenum and ileum

Question 2

Hypothyroidism does what to the clearance of T3 and T4?

Answer 2

It decreases the clearance (half-life increased) so the dose must be adjusted

Question 3

Which drug is the drug of choice for hypothyroidism?

Answer 3

Levothyroid sodium (L-thyroxin, T4)

Question 4

Why is Liothyronine sodium (L-triiodothyronine, T3) not used much?

Answer 4

It has a shorter half-life than T4, so it has to be given multiple times/day. More expensive, harder to monitor, greater risk of cardiotoxicity.

Question 5

Why is Liotrix (T4:T3 at 4:1) not really used?

Answer 5

Because the body will naturally convert T4 to T3

Question 6

How would you adjust the dose of medications for hypothyroidism in the pregnant and elderly?

Answer 6

Pregnancy: increase the dose
Elderly: decrease the dose, they may not absorb the meds as well

Question 7

What are some of the sequelae of infantile hypothyroidism?

Answer 7

Neurological impairment, deaf-mutism, developmental delays

Question 8

Methimazole (MMI) and Propylthiouracil (PTU) fall into what drug class?

Answer 8

Thioamides

Question 9

What is the MOA of thioamides?

Answer 9

Prevent hormone synthesis by inhibiting TPO-catalyze reactions to block iodide organification. Drug binds and inactivated TPO.

Question 10

Your patient has Grave’s disease and just found out she is pregnant. How will we manage her?

Answer 10

She will start on PTU in the first trimester, then MMI for the rest of her pregnancy.

Question 11

What are some of the adverse effects of Thioamides?

Answer 11

• Skin rash
• Joint Pain
• Agranulocytosis
• Hepatotoxicity, worse with PTU

Question 12

What is the purpose of an ion inhibitors?

Answer 12

Blocks thyroidal uptake of iodide in patients with iodide induced hyperthyroidism

Question 13

Why are anion inhibitors no longer used?

Answer 13

The side effects….APLASTIC ANEMIA

Question 14

Mechanism of action of potassium iodide.

Answer 14

Inhibition of organification and hormone release, and decreases the size of the hyperplastic gland.

Can be used in combination with PTU and B-blockers when the patient is having a thyroid storm

Question 15

Your 39 year old patient is scheduled for a subtotal thyroidectomy in 10 weeks. How will you manage him before surgery?

Answer 15

• Thioamide drug until euthyroid (about 6 weeks)
• KI 10 days before surgery to reduce size and vascularity
• Give B-blocker to antagonize catecholamines

Question 16

Indications for radioactive iodide

Answer 16

Treatment of thyrotoxicosis (this will destroy the gland)

Question 17

How does radioactive iodide work?

Answer 17

Rapidly concentrates in thyroid follicle cells, where B particles selectively destroy gland w/o injury to adjacent cells

Patient becomes euthyroid in 6-8 weeks

Question 18

Adverse effects or radioactive iodide…

Answer 18

80% of patients will develop hypothyroidism, but this is bound to happen anyway after thyroidectomy

Question 19

Who cannot receive radioactive iodide???

Answer 19

Children and pregnant women

Question 20

Why can you not give iodides in pregnancy?

Answer 20

Risk of fetal goiter

Question 21

Adverse effects of potassium iodide

Answer 21

Acneiform rash, swollen salivary glands, mucous membrane ulceration

The are reversible once the drug is stopped