Medications for Hyperthyroidism and Hypothyroidism

Question 1

_______ is an essential component of T3 and T4

Answer 1

Iodine

Question 2

What is the more active form of thyroid hormone?

Answer 2

T3

Question 3

Describe the synthesis and release of thyroid hormone:

Answer 3

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

Question 4

The thyroid gland secretes more ____ than _____

Answer 4

T4, T3

Question 5

Where is T4 converted to T3?

Answer 5

The periphery

Question 6

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

Answer 6

Propylthiouracil (PTU)

Methimazole (Tapazole)

Question 7

How do PTU and Methimazole work?

Answer 7

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)

Question 8

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

Answer 8

1-2 weeks d/t thyroid gland stores

Question 9

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

Answer 9

Peripheral conversion of T4 to T3

Question 10

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

Answer 10

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

Question 11

What common AE associated with PTU and Methimazole?

Answer 11

Pruritic rash early in treatment

Arthralgias (common reason for discontinuation)

Question 12

What are rare but serious AE of PTU and Methimazole?

Answer 12

**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)

Question 13

What is the preferred treatment of hyperthyroidism?

Answer 13

Methimazole

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

Question 14

How often is PTU dosed?

Answer 14

TID (short half life)

Question 15

PTU can lead to increased tendency to:

Answer 15

bleed d/t depletion of prothrombin levels

Question 16

What two cases is PTU the preferred method of treatment?

Answer 16

Pregnancy

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

Question 17

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

Answer 17

6-12

Question 18

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

Answer 18

Radioactive Iodine- Thyroid Gland Ablation

Surgical removal followed by thyroid hormone replacement

Question 19

When are beta blockers used in the treatment of hyperthyroidism?

Answer 19

While waiting for thioamines to work

Question 20

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

Answer 20

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

Question 21

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

Answer 21

Esmolol

quick onset of action and short half life

Question 22

How are iodide salts used to treat hyperthyroidism?

Answer 22

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)

Question 23

Corticosteriods are available as symptomatic treatment for hyperthryoidism because:

Answer 23

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

Question 24

Two type of hypothyroidism include:

Answer 24

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

Question 25

What is the drug of choice for hypothyroidism?

Answer 25

Levothyroxine (prodrug of T4)

Question 26

What is levothyroxine and how does it work?

Answer 26

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

Question 27

What lab values should be monitored in patients taking levothyroxine?

Answer 27

TSH, free T4 | s/s of hyperthyroidism indicative of too high a dose

Question 28

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

Answer 28

Dye

Question 29

Why is T3(Cytomel) not usually given?

Answer 29

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

Question 30

When is T3 (Cytomel) given?

Answer 30

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

Question 31

Levothyroxine has many _____ ______.

Answer 31

Drug interactions

Question 32

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

Answer 32

Potent inducers= increase metabolism of drug

Question 33

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

Answer 33

Block levothyroxine, decrease T4 to T3 conversion

Question 34

Which drugs decrease levoythyroxine's absorption from the gut?

Answer 34

Cholestyramine, sucralfate, kayexelate, FeSO4, Al(OH)3 | administer at different time

Question 35

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

Answer 35

Estrogen (oral contraceptives) | Pregnancy

Question 36

What three drugs alter thyroid status?

Answer 36

Amiodarone Lithium Metoclopramide (Reglan)

Question 37

How does amiodarone affect the thyroid?

Answer 37

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)

Question 38

How does lithium affect the thyroid?

Answer 38

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

Question 39

How does reglan affect the thyroid?

Answer 39

Increases TSH production/release= incr T3 and T4 release