Thyroid

Question 1

How does iodide get into the thyroid follicles?

Answer 1

Via a sodium-iodide symporter.

Question 2

Where is the Thyroid Hormone receptor located and what is it composed of?

Answer 2

In the nucleus: retinoic acid receptor and TR monomer.

Question 3

What is the main physiological effect of Thyroid Hormone?

Answer 3

To increase metabolism/BMR

Question 4

What is a T4 replacement?

Answer 4

Levothyroxine Sodium

Question 5

What is a T3 replacement?

Answer 5

Liothyronine Sodium

More rapidly effective and eliminated faster (4x more potent than levothyroxine).

Question 6

What is a mixture of T4 and T3?

Answer 6

Liotrix

Question 7

What is the preferred drug for use in the treatment of hypothyroidism?

Answer 7

Levothyroxine Sodium (T4)

Longer half-life than Liothyronine

Question 8

Who requires a higher dose of levothyroxine? Who requires a lower dose?

Answer 8

Higher: infants/children

Lower: patients with angina pectoris

Question 9

When do you give IV liothyronine?

Answer 9

In acute emergency conditions.

Question 10

Which drug is less desirable for chronic replacement therapy?

Answer 10

Liothyronine (less stable, more costly).

Question 11

TSH levels are usually what in hyperthyroidism?

Answer 11

Decreased

Question 12

What are the anti-thyroid drugs and how do they work?

Answer 12

Propylthiouracil, Methimazole, Carbimazole

They inhibit the organification of iodide and coupling of iodotryrosine, thus inhibiting thyroid hormone synthesis.

Propylthiouracil also reduces the deiodinization of T4 to T3.

Question 13

What is the active metabolite of Carbimazole?

Answer 13

Methimazole

Question 14

When do you give a higher dosage of anti-thyroid drugs?

Answer 14

For thyrotoxicosis.

Question 15

What are the 3 severe side effects of anti-thyroid drugs?

Answer 15

Agranulocytosis (worse in Propylthiouracil), Hepatitis and Lupus-like syndrome

Question 16

How does Methimazole compare to Propylthiouracil?

Answer 16

Lower risk of agranulocytosis, higher concentration in breast milk, longer half-life, slower excretion

Question 17

What is the preferred anti-thyroid drug for pregnancy?

Answer 17

Propylthiouracil: less likely to cross the placenta.

Question 18

What is the purpose of radioactive iodine?

Answer 18

It destroys sufficient thyroid tissue to restore euthyroid.

Question 19

When is radioactive iodine used?

Answer 19

Treatment of choice for relapsed hyperthyroidism after antithyroid drug therapy.

Also, larger doses are used after thyroid cancer surgery to destroy any remaining cancer cells.

[Since effects are not seen for over 4 weeks, patients with severe hyperthyroidism should combine antithyroids or a beta-blocker until it takes effect]

Question 20

What is a side effect of radioactive iodine treatment?

Answer 20

May cause permanent hypothyroidism.

Do not give to pregnant or breast-feeding women. Should not be initial treatment for children (use anti-thyroid drugs).

Question 21

When are beta-blockers used for hyperthyroidism?

Answer 21

Only when symptoms are moderate or severe. They are used as adjunctive agents in Graves’ to control tremor, anxiety, palpitations, etc.