Thyroid Pharmacology

Question 1

T/F iodide is the rate limiting step in thyroid hormon syntehsis

Answer 1

T

Question 2

T/F more t4 than than t3 is produced by thyroid

Answer 2

T

Question 3

T/F T4 and T3 are largely protein bound

Answer 3

T

Question 4

T/F TSH is low in hypothyroidism

Answer 4

F

Question 5

T4 half life

Answer 5

7 days –> longer than 1 day T3

Question 6

Why is there high TSH/TRH in hypothyroidism?

Answer 6

body trying to compensate for low T3/T4

Question 7

Goal of thyroid hormone replacement

Answer 7

not a cure, just replacement

Question 8

Why is hypothyroidism treated with T4 vs T3

Answer 8

half life is longer, peripheral conversion of T4 to T3

Question 9

Why do some people have persistence of symptoms after T4 tx?

Answer 9

small studies show no benefit of combo tx, might also depend on polymorphisms of type 2 deoiodinase gene

Question 10

Indications for T3

Answer 10

thyroid cancer pts before radioactive iodine therapy and scans, myxedema coma

Question 11

Side effects of levothyroxin

Answer 11

from inappropriate dosing, can also have coloring dye sensitivity

Question 12

Starting dose of levothyroxin depends on:

Answer 12

age, degree of thyroid failure –> older or cardiac disease, use smaller doses

Question 13

IV dose of levothyroxin

Answer 13

75% of oral dose

Question 14

Target TSH on tx

Answer 14

6 weeks/half lives and TSH target of .5-5 (but best is .5-2.5

Question 15

In which situation can TSH not be trusted?

Answer 15

secondary hypothyroidism –> need to check thyroid hormone levels

Question 16

Why would TSH on tx be higher than expected?

Answer 16

noncompliance, drugs/conditions that decrease LT4 absorption, drugs that increase LT4 metabolism, increase TBG, progression of endogenous thyroid disease

Question 17

Drugs that decrease LT4 absorption:

Answer 17

iron, calcium carbonate, aluminum hydroxide, sucralfate, colestipol, ppi –> can be an issue with maternal supplements

Question 18

Conditions that decrease LT4 absoprtion:

Answer 18

small intestine disease,

Question 19

Drugs that increase LT4 metabolism

Answer 19

phenocarbitol, carbamazepine, phenytoin, rifampin

Question 20

Causes of increase TBG

Answer 20

pregnancy, estrogens, hepatitis

Question 21

Why would TSH on tx be lower than expected?

Answer 21

dopamine, high dose glucocorticoids, decrease TBG, self administration of excess LT4, reactivation of Graves’ or development of nodules

Question 22

causes of decrease TBG

Answer 22

androgens, nephrotic syndrome, chronic liver disease, sever systemic illness

Question 23

Tx of myxedema coma

Answer 23

iv hydrocortisone, LT4 and LT3, tx of precipitating factors like infection

Question 24

Drug to avoid in myxedma coma

Answer 24

sedatives b/c of decrease drug metabolism

Question 25

Antithyroid drugs block:

Answer 25

1. oxidation and iodination of Tg 2. iodotyrosine coupling to form T3/T4 e.g. PTU, tapazole

Question 26

Indications of antithyroid drugs

Answer 26

Graves: cool down pt before RAI or surgery, adults who may achieve remission, children and adolescents

Question 27

Antithyroid drug of choice

Answer 27

methimazole --> longer half life than PTU --> both have latent period of improvement

Question 28

T/F methimazole is protein bound

Answer 28

F --> PTU is which is useful in tx of pregnant women in 1st trimester (can't cross placenta)

Question 29

PTU increases/decreases T4 to T3 conversion

Answer 29

decreases

Question 30

Side effects of PTU

Answer 30

lupus, vasculitis, hepatitis --> more than methimazole

Question 31

T/F frequency of side effects of methimazole are dose related

Answer 31

T --> vs PTU which is pretty random

Question 32

Use methimazole in graves' always except in:

Answer 32

1st trimester pregnancy, thyroid storm, adverse effects to methimazole

Question 33

Major side effects of antithyroid drugs

Answer 33

agranulocytosis, PTU hepatitis, MMI cholestasis, vasculitis, polyarthritis

Question 34

Tx of agranulocytosis

Answer 34

stop antitoyroid drug, broad spectrum ab, hospitalize if granulocyte<500

Question 35

Drugs that inhibit T4 to T3 conversion

Answer 35

PTU, glucocorticoids,propanolol

Question 36

Tx of thyrotoxicosis

Answer 36

beta blockers b/c not an issue of thyroid proliferation but simply higher release of thyroid hormone from cells --> atenolol or metoprolol

Question 37

Tx of subacute thyroiditis

Answer 37

NSAID

Question 38

Tx of thyroid storm

Answer 38

PTU/MMI, propanolol, hydrocortisone, SSKI drops

Question 39

Iodide uptake mediated by ___ in normal thyroid

Answer 39

Na+/I- symporter NIS

Question 40

Wolff-Chaikoff Effect

Answer 40

excess iodide transiently inhibits thyroid iodide organification --> in normal thyroid, gland can regulate this inhibitory effect // in individuals with underlying autoimmune disease, this suppressive effect may persist even after iodine levels normalize

Question 41

T/F wolff chiakoff can be beneficial in tx of graves

Answer 41

T --> persistent suppression can decrease thyroid hormone synthesis, supporting anti-thyroid tx

Question 42

Jod-Basedow effect

Answer 42

thyrotoxicosis produced by iodine exposure --> in nodules

Question 43

I131

Answer 43

emits gamma and beta particles for dx and tx --> dose dependent effect

Question 44

Contraindications of I131

Answer 44

breastfeeding/pregnant women, children

Question 45

T/F goal in graves is hypothyroidism

Answer 45

T

Question 46

Amiodoarone

Answer 46

anti-arrhythmia that is 37% iodine --> can cause hypo or hyperthyroidism Type 1 hyperthyroidism: in pts with underlying thyroid nodular disease, increased thyroid hormone production --> iodine effect Type 2 hyperthyroidism: in pts with normal thyroid --> destructive thyroiditis with increased thyroid hormone release --> direct toxic effect of amiodorone

Question 47

rTSH

Answer 47

used in thyroid cancer pts for dx and imaging --> avoids symptomatic hypothyroidism TSH stimulates uptake of iodine //in pts with residual thyroid cancer, want to stimulate uptake of iodine as much as possible before doing scan --> normally let the pt go hypothyroid and then give iodine to measure effect --> now can give rTSH to avoid hypothyroid effects while still letting endogenous TSH to drop before the test