Pharma L2 Thyroid & Antithyroid Drugs

Question 1

Which drugs accelerate breakdown of thyroid hormones ?

Answer 1

Phenytoin, phenobarbital, rifampin

Question 2

Which drugs cause primary hypothyroidism ?

Answer 2

Carbimazol, propyl-thyrouracil

Question 3

Liothyronin (T3) & Levothyroxine (T4) PKs

Answer 3

1) TSH levels determine improvement
2) Levothyroxine stronger binding to plasma proteins—> long duration with slow onset
3) Drug if choice is Levothyroxine

Question 4

Levothyroxine Food & drug interactions

Answer 4

1) Given on empty stomach (soybeans & walnuts decrease absorption)
2) 2-4 hrs before or after calcium or iron supplements (since they reduce absorption)

Question 5

Enzyme inhibitors

Answer 5

1) Grapefruit
2) Cimetidine
3) ketoconazol
4) Erythromycin
5) ciprofloxacin
6) omeprazol

Question 6

Enzyme inducers

Answer 6

Alcohol, phenobarbital, carbamazepine, rifampin, phenytoin

Question 7

Which drugs decrease synthesis of hormones?

Answer 7

Thioamides: Carbimazole, propyl-thiouracil, methimazole

Question 8

Thioamines MOA

Answer 8

1) inhibit TPO (inhibits Iodide ion oxidation to iodine)
2) inhibit Coupling
3) PTU inhibits peripheral deiodinase

Question 9

Onset of Thioamines and why?

Answer 9

Delayed & slow because no effect on stored thyroglobulin

Question 10

Which of the thioamines is teratogenic and which isn’t?

Answer 10

Methimazole (long HL) is teratogenic while PTU is not (Short HL highly ionized in blood)

Question 11

What is the active form of carbimazole?

Answer 11

Methimazole

Question 12

Thioamines S/E

Answer 12

Agranulocytosis (granulocyte deficiency), hepatotoxicity

Question 13

Drug of choice in treating Hyperthyroidism ?

Answer 13

Methimazole

Question 14

MOA of iodide (Lugol’s solution)

Answer 14

1) Inhibit T3 & T4 protease enzyme preventing its release from thyroglobulin
2) transient inhibition of iodination
3) reduce size and blood supply to the gland

Question 15

Therapeutic use of Lugol’s solution

Answer 15

Not used as solo, used in thyroid storm and before surgery

Question 16

Thyroidectomy and I-131 treatment

Answer 16

Oral I-131 is given and is selectively taken by follicular cells
Most become hypothyroidic and require Levothyroxine

Question 17

Preparation for surgical thyroidectomy

Answer 17

1) Antithyroid drugs 1-2 months prior
2) Iodide 7-10 days prior (reduce size and vasculation)
3) propranolol 40 mg

Question 18

Thyroid storm treatment

Answer 18

Iodide (fast effect), PTU to prevent deiodination, propranolol (decrease symp. Stimulation), Hydrocortisone (🤷‍♂️)

Question 19

Order of drugs administration during thyroid storm

Answer 19

1: propranolol
2: PTU (better) / methimazol
3: iodide
4: steroids