Thyroid Hormone Pharmacology

Question 1

What is used to treat Hypothyroidism?

Answer 1

Thyroid hormone replacement preparations. Levothyroxine (T4), Liothyronine (T3)

Question 2

What is radioactive iodine 131I used for?

Answer 2

Thyroid ablation

Question 3

What is radioactive iodine 123I used for?

Answer 3

Thyroid imaging

Question 4

What is used to treat hyperthyroidism?

Answer 4

Thioamides (aka Thionamides)

Question 5

What is used to prepare patients for thyroid surgery and prevent iodide organization and thyroid peroxidase reactions to iodinate Tyrosines?

Answer 5

Thioamides (aka Thionamides)

Question 6

What are the three Thioamides?

Answer 6

Methimazole (and Carbimazole - metabolizes to methimazole), Propylthiouracil (PTU), Potassium Iodide (KI)

Question 7

What should you know about Levothyroxine (T4)?

Answer 7

Once daily dose. Narrow toxic and therapeutic index. Long half life (7 days), takes 6-8 weeks to reach steady state levels. Absorption variable and incomplete. Dec iron and calcium, AlOH, soy. Lower doses in elderly and those with cardiac risk factors.

Question 8

What must you do with Levothyroxine in pregnancy?

Answer 8

Increase dose by 30-50 percent.

Question 9

What are adverse effects of iatrogenic hyperthyroidism?

Answer 9

Palpitations, tremors, anxiety, weight loss, tachycardia, inc number of bowel movements. Arrhythmia, angina and MI in patients with heart disease. Atrial fibrillation in elderly. Bone loss with chronic over supplementation.

Question 10

What should you know about Liothyronine, T3?

Answer 10

Short onset of 4-6 hours. Half life is about 2 days. Greater potency. Used when quick onset desirable.

Question 11

What are 6 types of antithyroid drugs?

Answer 11

Anion inhibitors, Thioamides, Iodides, Iodinated contrast media 123I, Beta blockers, Radioactive 131I.

Question 12

What are anion inhibitors?

Answer 12

Drugs that impair trapping of iodide

Question 13

What are Thioamides?

Answer 13

Drugs that inhibit thyroid synthesis

Question 14

What are Iodides?

Answer 14

Drugs that impair release and proteolysis of thyroid hormones

Question 15

What is Iodinated contrast media 123I?

Answer 15

Drugs that interfere with T4 to T3 conversion.

Question 16

What are beta blockers?

Answer 16

Drugs that alleviate peripheral symptoms of thyrotoxicosis.

Question 17

What is Radioactive 131I?

Answer 17

Drug that destroys the thyroid gland

Question 18

What are the three Thioamides?

Answer 18

Methimazole, Carbimazole, Propylthiouracil

Question 19

What are Thioamides used for?

Answer 19

Used to treat hyperthyroidism and prepare for thyroid surgery.

Question 20

What is the mechanism of Methimazole and PropylThioUracyl?

Answer 20

Inhibit thyroid peroxidase - oxidation of iodide and conjugation reactions producing T3 and T4

Question 21

What is a secondary action of Propylthiouracyl?

Answer 21

It also inhibits Deiodinase 1 (thereby inhibiting peripheral conversion of T4 to T3)

Question 22

What other things should you know about Thioamides?

Answer 22

Rapid and complete oral absorption. Accumulate in thyroid - duration of action 12 hr for PTU and 24 hr for methimazole. Takes about 2 weeks for effect. First line of defense for Graves’ disease.

Question 23

What is Iodine used for?

Answer 23

Preparation for thyroidectomy, to treat thyroid storm and protection from radioactive iodine.

Question 24

What do high concentrations of iodine cause?

Answer 24

Inhibits almost all aspects of iodine metabolism including transport, synthesis or iodotyrosines and iodotyronines, and release of thyroid hormone.

Question 25

What are the effects of Iodine treatment?

Answer 25

'Escape' from iodine treatment can occur. Side effects include allergic reactions, sore teeth and gums, excess salivation.

Question 26

What is 123I?

Answer 26

Used to scan thyroid. Thyroid cancer incidence has doubled since 2008, largely attributed to the increased use of thyroid scans. Some critics claim that the increased diagnosis is not beneficial to patients.

Question 27

What is 131I?

Answer 27

Used to destroy thyroid. Painless, easy to administer, cheap and effective. Main disadvantage of 131I is too much destruction. Need to supplement Thyroid Hormones after treatment.

Question 28

What remain the cornerstone of treatment in Graves Disease?

Answer 28

Antithyroid hormones

Question 29

What is generally recommended for patients with Graves' disease?

Answer 29

A course of 12-18 months of anti-thyroid drugs.

Question 30

What is the recurrence rate of Graves disease?

Answer 30

High after discontinuation of anti-thyroid drugs. 30-50 percent of adults are in permanent remission (normal TSH) after drugs. 30 precent of children.