Treatment Of Hyperthyroidism

Question 1

What is the MOA of thioamides?

Answer 1

Inhibit thyroid peroxidase and block iodine organification.
Block coupling of iodotyrosines (MIT, DIT)
Propylthiouracil > Carbimazole inhibits peripheral deiondination of T4 and T3

Question 2

What are the shared pharmacokinetics of the thioamides?

Answer 2

Cross the placenta

Have a slow onset, 3-4 weeks before T4 stores are depleted.

Question 3

What are the pharmacokinetics and use of Carbimazole?

Answer 3

Has a slower excretion than Propylthiouracil.
Half-life of 6hrs
Methimazole 10X more potent
It’s the drug of choice in young patients.
Does not block T4 to T3 conversion

Question 4

What are the pharmacokinetics and uses of Propylthiouracil?

Answer 4

Rapidly absorbed. Half-life of 1.5 hrs -> useful in thyroid storm
Reserved for use in 1st trimester of pregnancy.

Question 5

What are the side effects of Thioamides?

Answer 5

Maculo-papular pruritic rash
Agranulocytosis
Hepatitis (Propylthiouracil increases risk)

Question 6

Name the anion inhibitors.

Answer 6

Perchlorate ClO4
Pertechnetate TcO4
Thiocyanate SCN

Question 7

What is the MOA of anion inhibitors

Answer 7

Block iodide uptake by gland through competitive inhibition. Can be overcome by large doses of iodide.

Question 8

What are the uses of anion inhibitors?

Answer 8

To treat drug induced hyperthyroidism.

Rarely used because perchlorate causes aplastic anaemia.

Question 9

What is the MOA of Lugol’s iodine?

Answer 9

Inhibits organification of iodine
Inhibits release of T4 from thyroglobulin (proteolysis of thyroglobulin)
Reduces vascularity.
TSH independent 
Intrathyroidal

Question 10

What are the uses of Lugal’s iodine?

Answer 10

Short term use:
Thyroid storm for up to 7 days
Pre-surgery

Question 11

What are the adverse effects of Lugal’s iodine?

Answer 11

Skin rashes
Metallic taste in mouth
Over long periods can increase thyroid production by becoming a substance for hormone production.

Question 12

What is the MOA of Radioactive Iodine?

Answer 12

It’s taken up and concentrated in the thyroid, results in destruction of parenchyma.
Does not affect already formed T3 and T4, therefore effects only manifests after 2-3 months

Question 13

What are the contraindications of Radioactive Iodine?

Answer 13

Pregnancy
Breast feeding
(Crosses placenta and secreted in breast milk)

Question 14

What are the adverse effects of radioactive iodine?

Answer 14

Thyroiditis
Hypothyroidism (guaranteed to develop after 10yrs)
No evidence of carcinogens is.

Question 15

Name the Thioamides.

Answer 15

Methimazole (Carbimazole covered to methiazole in vitro)

Propylthiouracil

Question 16

Why use Beta-blockers in hyperthyroidism?

Answer 16

Negates symptoms caused by sympathetic activation via thyroxine.
Prevents peripheral conversion of T4 into T3.

Question 17

What radioactive medium can be used in asthmatics instead of Beta-blockers?

Answer 17

Ipodate.

Prevents peripheral conversion of T4 to T3