Thyroid Pharmacology Flashcards Preview

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Flashcards in Thyroid Pharmacology Deck (36):
1

What are the relative half lives and potency of thyroid hormone?

T4: half life is 7 days
T3: half life is only 1 day but it is 4x more potent

2

Are there greater levels of free T4 or free T3? About how much is there?

There is about 10x more free T3. Unbound T3 constitutes .4% of the total thyroid hormone

3

What are the three classes of thyroid hormone preparations?

Levothyroxine: LT4
Liothyronine: LT3
T4/T3 Mixes: just don't use them

4

Why is hypothyroid treated with T4? (2)

Longer half life and peripheral conversion via deiodination

5

When is T3 use indicated? (2)

Myxedema coma
Withdrawal for thyroid cancer radioactive iodine treatment

6

When do you see side effects from thyroid treatment?

Only from inappropriate dosing

7

What are some dosing considerations when starting therapy?

Starting dose depends on age, degree of thyroid failure of patient

8

How often is TSH levels monitored?

What is the target range? Does this change for people of different ages?

Check TSH about every 6 weeks

Target TSH normal range (.5-5) with target usually below 2.5. The target is usually higher in older people

9

What are reasons for TSH levels being higher than expected? (6)

Noncompliance
Drugs that decrease LT4 absorption
Conditions that decrease LT4 absorption: SI disease
Drugs that increase LT4 metabolism
Increased TBG
Progression of thyroid disease

10

Name some drugs that increase LT4 metabolism.

Name some factors that increase TBG

Drugs: phenytoin, rifampin, phenobarbital, carbamazepine

Increased TBG seen during pregnancy, estrogens, hepatitis

11

Why would TSH on therapy be lower than expected? (5)

Dopamine
High dose glucocorticoids
Decreased TBG
Self-administration of excess LT4
Reactivation of Grave's disease or development of autonomous nodules

12

What are some factors that decrease TBG? (4)

Androgens
Nephrotic syndrome
Chronic liver disease
Severe systemic illness

13

What are drugs that cause hypothyroidism? (5)

Primary: amiodarone, lithium, INFa, aminoglutethimide

Secondary bexarotene

14

For what conditions should you involve a endocrinologist to monitor TSH levels? (2)

Pregnancy
Thyroid cancer

15

What do you do to treat myxedema coma? Why?

First IV hydrocortisone to fix adrenal

Give LT4/LT3 IV--decreased metabolism for most medications

16

What is the mechanism of antithyroid drugs?

interfere with two steps of thyroid hormone synthesis via TPO
1. Intrathyroidal iodine utilization
2. Iodotyrosine coupling

17

When do you use antithyroid drugs?

Graves disease
To cool patient down prior to RAI or surgery

18

What are two antithyroid drug? Which is preferred? Why? (3)

PTU and Methimazole.
Mithimazole has longer half life-- longer duration of action.
Mithimazole is not protein bound.
PTU decreases T4-T3 conversion

19

When do you use methimazole? When do you use PTU? (3)

Use methimazole in all Grave's disease patients except:
First trimester of pregnancy
Thyroid storm
AE to methimazole

20

What are the main side effects of antithyroid drugs? (6)

Agranulocytosis, severe hepatitis (just PTU), cholestasis (MMI), vasculitis, polyarthritis, skin rxns

21

What is the greatest concern with antithyroid drugs?

How is it monitored?

Agranulocytosis, which occurs in .1-.5% patients at any time.

They should stop antithyroid drug and check WBC if fever or sore throat.

22

Which drugs inhibit T4-T3 conversion? (3)

PTU
Glucocorticoids
Propanolol

23

Which other drugs can you use in hyperthyroidism? (3)

Beta-blockers
NSAIDs in subacute thyroiditis
Iodine/glucocorticoids in severe thyrotoxicosis

24

Which drugs do you use in treatment of Thyroid Storm? (4)

PTU
Propanolol or esmolol
Hydrocortisone
Potassium iodide drops

25

How is iodide uptake mediated? How does it correspond to dietary supply?

Iodide uptake is mediated by the Na/I symporter (NIS).

Low iodide increases NIS; high iodide decreases NIS

26

Where is NIS expressed?

High levels in thyroid
Low levels in salivary glands, lactating breast, placenta

27

What is optimal iodide intake? What are effects of prolonged decrease? (2)

Optimal intake is 100-150 mcg/day
Prolonged decrease results in endemic goiter and cretinism

28

What is the Wolff-Chaikoff Effect? What is the clinical implication?

Excess iodide transiently inhibits thyroid iodide organification.

In individual with normal thyroid, gland escapes inhibitory effect. But if underlying autoimmune thyroid disease, suppressive effect may persists.

29

What is the Jod-Basedow Phenomenon? When is it observed?

The Jod-Basedow Phenomenon describes thyrotoxicosis produced by iodine exposure.

It occurs in nodular thyroid glands

30

Describe the uses for radioiodine. (2)

When is it contraindicated

Can be used in low doses for diagnostic purposes or high doses for therapy

It should not be given to breast-feeding/pregnant women or children

31

When do you use radioiodine therapy? What is the long-term effect?

Use it in Grave's disease to create hypothyroidism. The result of radioiodine therapy is necrosis of follicular cells followed by disappearance of colloid and fibrosis of gland

32

What is amiodarone?

Drug used to treat arrhythmias

33

Describe the iodine effect of amiodarone: when do you observe it?

In patients with underlying thyroid nodular disease or Grave's disease, amiodarone results in increased thyroid hormone production.


This is called the iodine effect

34

Describe the direct toxic effect of amiodarone: when do you observe it?

In patients with normal thyroids it induces destructive thyroiditis-->
There is increased release of preformed thyroid hormone from colloid

35

When do you use recombinant TSH?

Use in thyroid cancer patients: stimulate thyroid tissue for diagnostic thyroglobulin measurement and radioiodine scanning.

It avoids symptomatic hypothyroidism from radioiodine

36

When does amiodarone cause hypothyroidism?

In patients with predisposition for hypothyroidism such as Hashimotos