Thyroid drugs

Question 1

Which drug is pure T4

Answer 1

levothyroxine

Question 2

Which drug is pure T3

Answer 2

liothyronine

Question 3

What are the important differences between levothyroxine and liothyronine

Answer 3

Levo has a slower onset than lio, but a longer duration. Dose for levo is 100ug and lio 25ug, lio is 4x more potent

Question 4

Considerations for thyroid hormone replacement in elderly/ cardiac disease

Answer 4

small dose initially, increase slowly

monitor cardiac function

Question 5

Considerations for pregnant women

Answer 5

maintain therapy, may need to increase

Question 6

therapy for myxedema coma

Answer 6

levothyroxine IV to fill plasma binding sites, followed by oral maintenance

Question 7

Drug interactions with thyroid hormone replacement

Answer 7

many other drugs alter thyroid function and absorption, drugs that bind plasma protein

Question 8

What are the thioamides

Answer 8

Propylthiouracil (PTU), and Methimazole (MMI)

Question 9

What is the MOA of thioamides

Answer 9

Inhibit peroxidases involved in thyroid hormone synthesis

Question 10

What is one difference in the mechanism between propylthiouracial and methimazole

Answer 10

Propylthiouracil inhibits T4 to T3 transition, but methimazole does not, this makes it the preferred drug for thyroid storm

Question 11

Therapeutic use of antithyroid drugs

Answer 11

use to control hyperthyroidism for 1 year, reevaluate to determine if destructive surgery is needed (remission only 30%)

Question 12

What are the pharmacokinetics of antithyroid drugs

Answer 12

absorbed orally, rapidly cleared from circulation and concentrated in thyroid. Metabolism by conjugation and excretion in urine

Question 13

What are the differences in pharmacokinetics of the two antithyroid drugs

Answer 13

Propylthiouracil is less potent and has short half life. Generally methimazole is better since only one pill per day is required.

Question 14

What is the most concerning adverse effect of antithyroid drugs

Answer 14

agranulocytosis, discontinue and treat with antibiotics, switch to definitive therapy

Question 15

What is an important, but minor side effect of propylthiouracil that affects drug choice

Answer 15

Liver toxicity and failure in .1% of patients

Question 16

What is the DOC for antithyroid drugs for pregnant women

Answer 16

propylthiouracil, due to rare fetal problems with methimazole

Question 17

Therapeutic uses of radioactive iodine 131I

Answer 17

destruction of thyroid

Question 18

What Isotype and radioactivity does radioactive therapy

use

Answer 18

I-131 which is a weak beta emitter, only acts locally

Question 19

What is the MOA of Iodides

Answer 19

Acute inhibition of synthesis and RELEASE of THs

Question 20

Therapeutic uses of Iodides

Answer 20

during thyroid storm to inhibit synthesis and release , not useful for long term therapy
Before thyroidectomy to reduce size of thyroid
Radiation emergencies to compete for radioactive iodine

Question 21

Drug interactions of iodides

Answer 21

should not be used prior to radioiodine therapy due to competition for uptake.

Question 22

Strategies for for hyperthyroidism

Answer 22

try to achieve a euthyroid state with thioamides. 2 weeks prior to surgery use iodide therapy, they surgical removal, replacement levothyroxine to treat hypothyroidism

Question 23

Treatment strategy for thyroid storm

Answer 23

propylthiouracil to prevent conversion, iodides to decrease release