Thyroid hormones and Antithyroid drugs

Question 1

Iodine is present in what cells in the thyroid

Answer 1

follicular epithelial cells

Question 2

how is iodide transported into the thyroid

Answer 2

active transport via Na/I symporter

Question 3

what inhibits iodide transport into thyroid

Answer 3

• uncouplers of oxidative phsophorylation (lose ATP production)
• thiocyanate
• perchlorate

Question 4

Iodine trapping is stimulated by what hormone

Answer 4

TSH

Question 5

What happens to the iodine once in follicular cells? where does it enter

Answer 5

• oxidized by thyroid peroxidase in presence of hydrogen peroxide
• iodide forms I2
• follicular lumen

Question 6

What process occurs to I2 in the follicular lumen

Answer 6

organification: thyroglobulin react with I2

- forms MIT and DIT

Question 7

how is T3 and T4 formed?

Answer 7

coupling of MIT and DIT by thyroid peroxidase

Question 8

thyroglobulin that contains T3 and T4 are stored as what

Answer 8

colloid in lumen of follicle

Question 9

During the release of thyroid hormone, what role does TSH play

Answer 9

• stimulates thyroglobulin back into follicular epithelial cells
• lysosomal enzymes digest thyroglobulin and release T3 and T4

Question 10

what molecule inversely modulates thyroid hormone secretion

Answer 10

iodide concentration

Question 11

what molecule inhibits thyroid hormone release

Answer 11

lithium

Question 12

What is the predominant thyroid hormone in blood circulation

Answer 12

T4

Question 13

What is the most potent thyroid hormone in circulation

Answer 13

T3

Question 14

In circulation, what is T3 and T4 bound to

Answer 14

both - TBG (thyroxine binding globulin)

T4 - Transthyretin

Question 15

what converts T4 to T3

Answer 15

5’-deiodinase

Question 16

where is D1 isozymes of 5’-deiodinase located

Answer 16

liver
kidney
thyroid

Question 17

D1 isozymes of 5’-deiodinase responsibilites

Answer 17

• majority of circulating T3

- conversion of T4 to T3

Question 18

D2 isozymes of 5’-deiodinase is expressed where

Answer 18

brain
pituitary
skeletal
cardiac

Question 19

D2 isozymes of 5’-deiodinase role

Answer 19

• influences intracellular T3 levels in certain tissues

Question 20

what inhibits D1 isozymes of 5’-deiodinase

Answer 20

propylthiouracil

Question 21

where is 5’-deiodinase highest activity

Answer 21

liver

Question 22

what metabolizes thyroid hormones

Answer 22

P450

Question 23

How will enzyme induces of P450 impact thyroid hormone

Answer 23

• increases conversion of T4 to T3

Question 24

what is an autoimmune disease that is the most common cause of hypothyroidism in the U.S

Answer 24

Hashimoto’s thyroiditis

Question 25

what is secondary hypothyroidism

Answer 25

pituitary hypothyroidism due to TSH deficiency

Question 26

what is the drug of choice for thyroid supplementation? why?

Answer 26

Levothyroxine (T4) - T4 longer duration of action - can be taken once a day

Question 27

What is another thyroid hormone supplementation

Answer 27

Liothyronine (T3)

Question 28

oral levothyroxine is used to treat what

Answer 28

- hypothyrodism - suppression of TSH - Hashimoto's thyroiditis

Question 29

IV Levothyroxine is used to treat what

Answer 29

- Myxedma coma ( severe hypothyroidism)

Question 30

Levothyroxine interacts with what drugs

Answer 30

1. agnets that reduce thyroxine 2. agents alter thyroid binding globulin 3. agents inhibit 5'-deiodinase 4. Warfin

Question 31

name agents that reduce thyroxine bioavailability

Answer 31

- Calcium carbonate - aluminum hydroxide - cholestyramine - Colesevelam

Question 32

which hormone increase serum thyroid binding globulin

Answer 32

estrogen

Question 33

What molecule decreases serum thyroid binding globulin

Answer 33

Glucocroticod | anabolic steroids

Question 34

Name agents that inhibit 5'-deiodinase

Answer 34

propylthiouracil | amiodarone

Question 35

what is the interaction of Levothyroxine and Warfin

Answer 35

- thyroxine increases anticoagulant activity

Question 36

Adverse effects of Levothyroxine

Answer 36

cardiovascular: increase palpitations, tachycardia, increased blood pressure

Question 37

What is a common cause of hyperthyroidism

Answer 37

Grave's disease

Question 38

What is Grave's disease

Answer 38

- autoimmune disorder | - antibodies bind to thyroid follicular cell or TSH receptor increasing T4 production

Question 39

what used to treat symptoms of inflammation only for hyperthyroidism

Answer 39

- NSIADS | - aspirin

Question 40

what drugs are used to treat hyperthyroidism

Answer 40

- Propanolol - propylthiouracil - methimazole - radioiodine (I131)

Question 41

radioiodine (I131) is contraindicated in who

Answer 41

pregnancy

Question 42

MOA for Propylthiouracil and Methimazole

Answer 42

- inhibit iodide incorporation into tyrosine residues | - inhibit iodotyrosyl coupling to form iodothyronine

Question 43

what is a specific MOA for Propylthiouracil

Answer 43

inhibit peripheral 5'-deiodinase (D1) conversion of T4-T3

Question 44

what antithyroid drug is preferred during pregnancy

Answer 44

- Propylthiouracil

Question 45

compare the half lives of the anti-thyroid drugs

Answer 45

Methimazole 6 hours | Propylthiouracil 1 hour

Question 46

side effects of Methimzaole

Answer 46

agranulocytosis | aplastic anemia

Question 47

side effect of Propylthiouracil

Answer 47

hepatic necrosis and nephritis

Question 48

what is the black box warning for Propylthiouracil

Answer 48

- liver injury and failure

Question 49

what is iodine-131 used for

Answer 49

1. hyperthyroidism 2. thyroid carcinoma 3. grave's disease

Question 50

when is iodide used

Answer 50

preoperative to reduce vascularity of thyroid prior to surgery

Question 51

who should not use iodide and why

Answer 51

pregnant women | - induce goiter, suppress thyroid function in fetus, induce hypothyroidism