Thyroid Pharmacology Flashcards Preview

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Flashcards in Thyroid Pharmacology Deck (47):
1

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

T

2

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

T

3

T/F T4 and T3 are largely protein bound

T

4

T/F TSH is low in hypothyroidism

F

5

T4 half life

7 days --> longer than 1 day T3

6

Why is there high TSH/TRH in hypothyroidism?

body trying to compensate for low T3/T4

7

Goal of thyroid hormone replacement

not a cure, just replacement

8

Why is hypothyroidism treated with T4 vs T3

half life is longer, peripheral conversion of T4 to T3

9

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

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

10

Indications for T3

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

11

Side effects of levothyroxin

from inappropriate dosing, can also have coloring dye sensitivity

12

Starting dose of levothyroxin depends on:

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

13

IV dose of levothyroxin

75% of oral dose

14

Target TSH on tx

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

15

In which situation can TSH not be trusted?

secondary hypothyroidism --> need to check thyroid hormone levels

16

Why would TSH on tx be higher than expected?

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

17

Drugs that decrease LT4 absorption:

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

18

Conditions that decrease LT4 absoprtion:

small intestine disease,

19

Drugs that increase LT4 metabolism

phenocarbitol, carbamazepine, phenytoin, rifampin

20

Causes of increase TBG

pregnancy, estrogens, hepatitis

21

Why would TSH on tx be lower than expected?

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

22

causes of decrease TBG

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

23

Tx of myxedema coma

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

24

Drug to avoid in myxedma coma

sedatives b/c of decrease drug metabolism

25

Antithyroid drugs block:

1. oxidation and iodination of Tg
2. iodotyrosine coupling to form T3/T4

e.g. PTU, tapazole

26

Indications of antithyroid drugs

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

27

Antithyroid drug of choice

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

28

T/F methimazole is protein bound

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

29

PTU increases/decreases T4 to T3 conversion

decreases

30

Side effects of PTU

lupus, vasculitis, hepatitis --> more than methimazole

31

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

T --> vs PTU which is pretty random

32

Use methimazole in graves' always except in:

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

33

Major side effects of antithyroid drugs

agranulocytosis, PTU hepatitis, MMI cholestasis, vasculitis, polyarthritis

34

Tx of agranulocytosis

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

35

Drugs that inhibit T4 to T3 conversion

PTU, glucocorticoids,propanolol

36

Tx of thyrotoxicosis

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

37

Tx of subacute thyroiditis

NSAID

38

Tx of thyroid storm

PTU/MMI, propanolol, hydrocortisone, SSKI drops

39

Iodide uptake mediated by ___ in normal thyroid

Na+/I- symporter NIS

40

Wolff-Chaikoff Effect

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

41

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

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

42

Jod-Basedow effect

thyrotoxicosis produced by iodine exposure --> in nodules

43

I131

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

44

Contraindications of I131

breastfeeding/pregnant women, children

45

T/F goal in graves is hypothyroidism

T

46

Amiodoarone

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

47

rTSH

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