Pharmacology Of Thryroid Disease

Question 1

Thyroid hormone actions

Answer 1

Elevate BMR

Increase cardiac rate and contractility
(Upregulate B1 adrenergic receptors)

Physical and mental maturation during infancy and childhood

Question 2

What is synthetic T3 and T4 called

Answer 2

T3 = liothyronine

T4 = levothyroxine

T4 has a substantially longer half life than T3 (7 days: 1.5 days) because T4 can bind to thyroglobulin binding proteins in blood (TBG)

Question 3

Where is the primary feedback located in the HPT axis?

Answer 3

Anterior pituitary on TSH (thryotropin)

Question 4

Two most common cause of Hyperthyroidism

Answer 4

1) Graves’ disease

2) overcorrection of hypothyroidism

Question 5

Treatment modalities for hyperthyroidism

Answer 5

1) anti thyroid drugs
- this urea drugs (PTU and methimazole which block the enzyme in the thyroid cells used to generate T3/T4

2) B-blockers (slow symptoms down)
3) surgical removal of thyroid gland (last resort)
4) give radioactive iodine

Question 6

PTU and methimazole

Answer 6

MOA: inhibits TH synthesis by blocking oxidation of iodide and coupling of iodinated tyrosine into MIT and DIT molecules (cant make T3/T4)
- PTU also prevents peripheral conversation of T4 -> T3

PK = PO within 30-60 minutes

Uses = Graves’ disease (both to induce remission and control symptoms)
- also thyrotoxic crisis (storm/adenoma/etc)

ADRs:

• methimazole is contraindicated in first trimester
• DONT give in lactation as well
• arthralgia and rashes

Question 7

Propranolol and B-adrenergic antagonists

Answer 7

MOA: blocks B1 and B2 receptors throughout body

Uses in thyroid issues
- reduced or reverse tachycardia, palpitations, dysrhythmias, tremors, anxiety, irritability, heat intolerance, sweating, diarrhea, muscle weakened

good in immediate action in thyroid storms

Question 8

SSKI and Lugol solution (KI)

Answer 8

MOA: saturated solutions of potassium iodide and elemental Iodide

• this induces a paradoxical inhibition of thyroid hormone release from the thyroid gland due to “overloading of iodide receptors, tyrosine iodination and coupling reactions and inhibts TH release altogether”
• this is caused by the body’s innate built in resistance to overloading the thyroid in order to prevent complete metabolism of body. So instead in turns it off until high levels of iodide are removed
• this is referred to as the “Wolff-Chaikoff effect”

Uses: adjuvant therapy to TH suppression in hyperthyroidism
- rarely used alone however since tachyphylaxis development almost always
occurs
- ALSO must limit use to 3-14 days
- can also be used in radiation emergencies (radioactive iodine suppression) and acute management of throtoxic crisis

ADRs:

• metallic taste and burning sensations in mouth
• GI distress and diarrhea
• CONTRAINDICATED in pregnancy*

Question 9

Radioactive iodine MOA

Answer 9

Is delivered orally and is a tasteless and colorless liquid or pill

Concentrates solely in the thyroid gland and emits B/Y particles to destroy thyroid follicular cells (can be partial or complete based on dose)

Half-life = 8 days

• *use require substantial commitment for use**
• must avoid others for 1-11 days
• must sleep alone and not go to work and be 6 ft away from children and pregnant women at all times
• cant share foods and needs extensive toilet flushing protocols
• all of this is to prevent radioactive bystander damage

Is only used for severe goiter and severe hyperthyroidism and is often Cl administered with B-blockers

CONTRAINDICATED in pregnancy

also remember this use always induces hypothyroidism as a side effect

Question 10

What is the results of severe hypothyroidism

Answer 10

Myxedema

• shows cold insensitive
• thickened puffy skin around eyes and hands
• menstration irregularities
• drowsiness
• cardiac and metabolic problems

If left untreated = hypoglycemia, weakness, stupor and shock

Question 11

What are symptoms of congenital hypothyroidism (cretinism)

Answer 11

Mental retardation and stunted growth with bone deformations

Low body temp and dulled activity

Poor appetite and dry/.thickened skin

Difficulties breathing

**macroglossia

Excessive fatigue and constipation

treatment = HRT

Question 12

Levothyroxine PK

Answer 12

Only given in hypothyroidism

Is taken orally without food

Half life = 7 days and remains in a steady state for 4 weeks
- ** this is why levothyroxine is more commonly prescribed than liothryonine**

• *MUST start low and titrate up while monitoring TSH/T4 levels in patients**
• increase monthly until appropriate response is achieved

IV loading dose is required for emergency treatment of a myxedema coma