EXAM #5: THYROID AND ANTITHYROID DRUGS Flashcards Preview

Pharmacology > EXAM #5: THYROID AND ANTITHYROID DRUGS > Flashcards

Flashcards in EXAM #5: THYROID AND ANTITHYROID DRUGS Deck (50):
1

What is the difference between T3 and T4?

T3= active
T4= pro-hormone

2

What are four general functions of the thyroid hormones?

1) Growth
2) Development
3) Body temperature
4) Energy metabolism

3

Outline the steps of thyroid hormone synthesis.

1) Iodide uptake
2) Oxidation of Iodide to Iodine
3) "Iodide Organification" i.e. iodination of tyrosine residues on the thyroglobulin molecule
- MIT
- DIT
4) "Coupling" - MIT and DIT are combined to make T3 and T4

4

What is responsible for Iodide uptake into the thyroid gland?

Sodium-Iodide Symporter (NIS)

5

How are the thyroid hormones secreted?

1) Thyroglobulin is taken up by thyroid cell
2) Degradation of Thyrogobulin releases T3 and T4
- 5:1 ratio of T4:T3
3) Majority is bound to thyroxine-binding globulin in the blood

6

Describe the MOA of the thyroid hormone.

Absence of hormone:
- T3 receptor (TR) has a ligand binding domain and a DNA binding domain
- Dimer of TR is bound to TRE and represses transcription

Hormone:
- Ligand binding causes dissociation of TR from TRE
- Transcription ensues

7

What converts T4 into active T3?

5'-deiodinase

*Note that this is a drug target*

8

Outline the regulation of thyroid hormone release (HPA axis).

1) Hypothalamus= TRH
2) Anterior Pituitary= TRH promotes release of TSH
3) Thyroid= TSH promotes synthesis of T3 and T4

*Thyroid hormone feedsback on Hypothalamus and Anterior Pituitary*

9

How does iodine regulate thyroid hormone synthesis?

- High blood iodine= inhibit thyroid hormone synthesis
- Low blood iodine= promotes thyroid hormone synthesis

10

What are the effects of thyroid hormone on the SNS?

1) Increased B-adrenergic receptors
2) Decreased a-adrenergic receptors

11

What is the effect of thyroid hormone on the respiratory system?

Increased O2 consumption and respiratory rate

12

What is the effect of thyroid hormone on the GI system?

Increased secretions and motility

13

What is the effect of thyroid hormone on glycosaminoglycans?

Prevents accumulation of glycosaminoglycans in the interstitial space

*****These result in edema and puffy/baggy eyes in HYPOTHYROIDISM*****

14

What is the effect of thyroid hormone on LDL receptor expression and cholesterol?

Thyroid hormone:
1) Decreases circulation of cholesterol
2) Increases LDL expression

15

What is myxedema?

Puffy/baggy eyes in HYPOTHYROIDISM

16

What are the causes of Type I/ Primary Hypothyroidism?

1) Congenital defect--Cretinism
2) Autoimmune Thyroiditis--Hashimoto's Disease
3) Iodide Deficiency
4) Other
- Surgery
- Radiation
- Medications e.g. Lithium

17

What causes Type II or Secondary Hypothyroidism?

Impaired TSH production:
- Head trauma
- Cranial neoplasm

...etc.

18

What drugs are used to treat Hypothyroid?

Levothyroxine
Liothyronine
Liotrix

19

What is Levothyroxine?

T4

*Most common b/c it is more stable and cheaper

20

What is Liothyroine?

T3

*More potent with short half-life

21

What is Liotrix?

T3 and T4

22

What do you need to remember about Hypothyroidism and the geriatric population?

Hypothyorid is PROTECTIVE; treating it can be detrimental

23

What are the adverse effects of thyroid replacement in children?

- Restlessness
- Insomnia
- Accelerated bone maturation

24

What are the adverse effects of thyroid replacement in adults?

- Nervousness
- Heat intolerance
- Palpitations
- Tachycardia
- Weight loss

25

What are the adverse effects of thyroid replacement in the geriatric population?

A-fib and osteoporosis

26

What are the causes of Primary Hyperthyroidism?

1) Grave'e Disease
2) Thyroid adenoma/ carcinoma
3) Autoimmune thyroiditis
4) Thyroid storm
5) Excess iodide

27

What is Grave's Disease?

Autoantibodies stimulate TSH receptors to increase T3 and T4

*TSH will be LOW*

28

What is a thyroid storm?

Acute episode of excessive thyroid hormone release e.g.
- Surgery
- Infection
- DKA

****This can be fatal b/c of the cardiovascular effects*****

29

What is the mechanism by which excess iodide causes HYPERthyroid?

*Negative regulatory processes have failed*
- Idiopathic
- More common with UNDERLYING thyroid disease

30

What is Secondary Hyperthyroidism?

Dysfunction of the Hypothalamis of Pituitary leading to elevated thyroid hormones

31

List the thioamides.

Methimazole
Propylthiouracil

32

What is the MOA of the thioamides?

Inhibition of all the processes that are taking place in the colloid of the thyorid follicle

I.e. inhibition thyroid synthesis

33

What is the black box warning with Propylthiouracil (PTU)?

Severe hepatitis

34

What is the adverse effect assocaited with Methimazole?

Altered taste and smell

35

Which thioamide is better to use in pregnancy?

PTU

36

What thioamide is better to use for thyroid storm?

PTU b/c it is absorbed faster

37

What is the MOA of the iodides?

Increased iodine that has a negative regulatory effect on thyroid hormone synthesis

38

List the Iodides.

Potassium iodide
Lugol's Solution

39

What are the drawbacks to the Iodides?

- Will only work for 2-8 weeks
- Sudden withdrawal will cause thyrotoxiosis (burst of thyroid hormone)

40

What are the iodides a good strategy to treat?

1) Thyroid storm
2) Preoperative prep for surgery

41

What key adverse effects are associated with Iodides?

Cold sx.

42

What is the MOA of radioactive iodine?

Emission of beta and gamma rays
- Beta= induces tissue damage
- Gamma= measure levels/ dose

43

What is the most common adverse effect of radioactive iodine?

Complete knockout of the thyroid gland--Hypothyroidism

44

What patient population is radioactive iodine contraindicated in?

Pregnant

45

What is the MOA of the anion inhibitors?

Inhibition of the NIS transporter

46

List the Anion Inhibitors.

Perchlorate
Pertechnetate
Thiocyanate

47

What is the clinical utility of the anion inhibitors?

Treatment of iodide-induced hyperthyroidism

48

What are the key antithyroid adjuncts?

1) Propanolol
2) Diltiazem
3) Barbiturates
4) Bile acid seqestrants

49

Why is propanolol a good drug for hyperthyroid?

1) Blocks sx. of hyperthyroid
2) Prevents conversion of T4 to T3

50

What is the utility of Diltiazem in Hyperthyroid?

Good alternative to propanolol in a patient with asthma

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