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Pharmacology > Medications for Hyperthyroidism and Hypothyroidism > Flashcards

Medications for Hyperthyroidism and Hypothyroidism Flashcards

1
Q

_______ is an essential component of T3 and T4

A

Iodine

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2
Q

What is the more active form of thyroid hormone?

A

T3

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3
Q

Describe the synthesis and release of thyroid hormone:

A

The hypothalamus releases TRH
TRH causes release of TSH from the anterior pituitary
TSH acts on the thyroid which is controlling all aspects of thyroid hormone synthesis and release

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4
Q

The thyroid gland secretes more ____ than _____

A

T4, T3

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5
Q

Where is T4 converted to T3?

A

The periphery

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6
Q

Drugs used to treat hyperthyroidism (Grave’s Disease) include which antithyroid drugs (thioamines)?

A

Propylthiouracil (PTU)

Methimazole (Tapazole)

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7
Q

How do PTU and Methimazole work?

A

Block organification process (production of T3 and T4) by competing with thyroglobulin for oxidized iodide
Reduces synthesis of thyroid hormones
(meds are only useful in overproduction of thyroid hormones)

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8
Q

What is the onset of action of PTU and Methimazole and why?

A

1-2 weeks d/t thyroid gland stores

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9
Q

In addition to blocking the synthesis of the T3 and T4 what else can PTU block?

A

Peripheral conversion of T4 to T3

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10
Q

PTU and Methimazole can result in the formation of what? and why?

A

Goiter
Inhibition of thyroid hormone production leads to an upregulation of TSH release, the TSH is unable to increase thyroid hormone because of the medication, elevated TSH levels stimulate hypertrophy of the thyroid gland in an attempt to increase thyroid hormone synthesis

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11
Q

What common AE associated with PTU and Methimazole?

A

Pruritic rash early in treatment

Arthralgias (common reason for discontinuation)

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12
Q

What are rare but serious AE of PTU and Methimazole?

A

**Agranulocytosis- usu. w/in first 90days of treatment, monitor WBC at baseline and if patient has sore throat
Hepatotoxicity (assoc. w/allergic reaction)
Vasculitis (drug induced lupus)

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13
Q

What is the preferred treatment of hyperthyroidism?

A

Methimazole

Longer half life for once daily dosing
More potent
Less common serious AE than PTU

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14
Q

How often is PTU dosed?

A

TID (short half life)

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15
Q

PTU can lead to increased tendency to:

A

bleed d/t depletion of prothrombin levels

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16
Q

What two cases is PTU the preferred method of treatment?

A

Pregnancy

Acute management of hyperthyroidism (thyroid storm) d/t inhibition of T4 to T3 conversion in the periphery

17
Q

Most patients respond to treatment with thioamines within ___-____ months.

A

6-12

18
Q

For patients who do not respond to thioamines for the treatment of hyperthyroidism what two invasive options do they have?

A

Radioactive Iodine- Thyroid Gland Ablation

Surgical removal followed by thyroid hormone replacement

19
Q

When are beta blockers used in the treatment of hyperthyroidism?

A

While waiting for thioamines to work

20
Q

How do beta blockers work to provide symptomatic treatment in hyperthyroidism?

A

Blocks hyperadrenergic effects of thyroid excess (tachycardia, tremors, nervousness)
Blocks peripheral conversion of T4 to T3

21
Q

What beta blocker should be used during thyroid storm and why?

A

Esmolol

quick onset of action and short half life

22
Q

How are iodide salts used to treat hyperthyroidism?

A

Block conversion of T4 to T3
Quickly but temporarily blocks thyroid hormone release from the thyroid gland (gland is so busy trying to uptake the iodine it can’t make/release thyroid hormone- after it’s all taken up large amounts of T3/T4 release)

23
Q

Corticosteriods are available as symptomatic treatment for hyperthryoidism because:

A

Block peripheral conversion of T4 to T3
Suppresses thyroid receptor Ab and inflammation
(prednisone or methylpred)

24
Q

Two type of hypothyroidism include:

A
  1. Primary hypothyroidism (Hashimoto’s Thyroiditis)- autoimmune d/o in which antibodies are produced against TSH receptors, blocking TSH
  2. Iatrogenic- Ablation, drugs containing iodine, pituitary tumor
25
Q

What is the drug of choice for hypothyroidism?

A

Levothyroxine (prodrug of T4)

26
Q

What is levothyroxine and how does it work?

A

L-isomer of T4(prodrug)
Body converts it to T3 as needed

Long half-life (6-7days) allows for once daily dosing, wide availability of strengths=ease of titration

27
Q

What lab values should be monitored in patients taking levothyroxine?

A

TSH, free T4

s/s of hyperthyroidism indicative of too high a dose

28
Q

What could an allergic reaction d/t levothyroxine be secondary to?

A

Dye

29
Q

Why is T3(Cytomel) not usually given?

A

Better to have a reservoir of T4 (prodrug) to normalize metabolism over a wide range of conditions
Short half life, 1 day

30
Q

When is T3 (Cytomel) given?

A

Life threatening hypothyroidism (myxedema coma), where onset of T3 is more useful

31
Q

Levothyroxine has many _____ ______.

A

Drug interactions

32
Q

Phenobarb, phenytoin, rifampin, and carbamazepine all affect levothyroxine how?

A

Potent inducers= increase metabolism of drug

33
Q

PTU, beta blockers, amiodarone, and glucocorticoids all affect levothyroxine how?

A

Block levothyroxine, decrease T4 to T3 conversion

34
Q

Which drugs decrease levoythyroxine’s absorption from the gut?

A

Cholestyramine, sucralfate, kayexelate, FeSO4, Al(OH)3

administer at different time

35
Q

Drugs/condition that increase thyroid binding globulin (bind T3 and T4 include:

A

Estrogen (oral contraceptives)

Pregnancy

36
Q

What three drugs alter thyroid status?

A

Amiodarone
Lithium
Metoclopramide (Reglan)

37
Q

How does amiodarone affect the thyroid?

A

Structurally resembles thyroid hormone
When amiodarone is metabolized it releases iodine which is taken up by the thyroid gland and can suppress the gland (hypo) or increase synthesis of thyroid hormone as well as act on thyroid receptors (hyper)

38
Q

How does lithium affect the thyroid?

A

Actively concentrated in the thyroid gland
Body thinks it is iodine
Can inhibit thyroid synthesis leading to hypothyroidism

39
Q

How does reglan affect the thyroid?

A

Increases TSH production/release= incr T3 and T4 release

Pharmacology (48 decks)

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