drugs for thyroid disorders

Question 1

Drugs for hyperthyroidism

Answer 1

1. anti-thyroid drugs
   a) inhibitors of hormone synthesis/ thioamides: propylthiouracil PTU, methimazole (carbimazole is converted to methimazole in the body)
   b) inhibitors of hormone release: Lugol’s iodine, potassium iodide
   c) radioactive destruction of thyroid tissue: radioactive iodine 131 I
   d) inhibition of peripheral conversion of T4 to T3: PTU
2. drug to reduce sympathetic activity: propranolol

Question 2

Drugs for thyroid hormone replacement/hypothyroidism:

Answer 2

levothyroxine
liothyronine

Question 3

Which one is more commonly used to treat hypothyroidism? WHY?

Answer 3

levothyroxine. It is cheaper than liothyronine. It has longer half life.

Question 4

Liothyronine is useful in?

Answer 4

myxedema coma

Question 5

Which thioamide is preferred in treating hyperthyroidism?

Answer 5

carbimazole is preferred over PTU due to carbimazole being more potent, slower metabolised, longer half life and taken once daily dose.

Question 6

MOA of carbimazole and PTU

Answer 6

-prevent thyroid hormone synthesis by inhibiting TPO
-block iodine organification
-block coupling of iodotyrosines
-PTU inhibits peripheral deiodination by deiodinase D1 of T4 to T3

NO EFFECTS ON RELEASE OF PREFORMED HORMONES THAT ARE ALREADY STORED IN COLLOID

Question 7

indications for carbimazole

Answer 7

Grave’s hyperthyroidism due to its
-longer duration of action
-rapid result in euthyroid

Question 8

Indications for PTU

Answer 8

thyrotoxicosis/thyroid storm due to its effect
-to block conversion of T4>T3

suitable for hyperthyroidism in pregnancy
-less freely crosses placenta
-less associated with birth defects

Question 9

Contraindications for carbimazole

Answer 9

nursing mothers
pregnancy (risk category D): cross placental barrier, cause fetal hypothyroidism & congenital malformations

Question 10

Which drug is used prior to thyroidectomy to decrease vascularity of thyroid gland?

Answer 10

saturated solution of potassium iodide (SSKI)
Lugol’s solution

Question 11

MOA of iodides: SSKI, Lugol’s solution

Answer 11

-inhibits hormone release via acute Wolff-Chaikoff effect
-inhibits iodine trapping
-inhibits thyroperoxidase (TPO)

Question 12

Which drug emits beta rays that destroy thyroid parenchyma?

Answer 12

radioactive iodine 131 I

Question 13

AE of radioactive iodine 131 I

Answer 13

hypothyroidism
radiation thyroiditis
CI in pregnancy, causing fetal hypothyroidism
not associated with tumours and birth defects

Question 14

beta blocker propranolol helps relieve what symptoms in hyperthyroidism?

Answer 14

non-selective beta blockers are preffered over selective as they help in relieving hypermetabolic state& related symptoms, as well as decreasing cardiac activity