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Repro-Endo (Additional) > Thyroid Pharmacology > Flashcards

Thyroid Pharmacology Flashcards

1
Q

What is the first line treatment for hypothyroidism?

A

Levothyroxine (LT4)

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2
Q

Why do we treat patients with hypothyroidism with T4 instead of T3?

A

T4 has a much longer half life

Peripheral conversion in liver and skeletal muscle anyway

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3
Q

What are situations in which T3 is used

A

Myxedema coma

During withdrawal for thyroid cancer (don’t worry about this)

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4
Q

What causes side effects in thyroid replacement therapy

A

Inappropriate dosing (not from another mechanism of action)

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5
Q

For a patient on thyroid replacement therapy, what is the frequency of monitoring for TSH?

A

Approximately every 6 weeks due to T4 long half life

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6
Q

Why would the TSH be higher than expected for someone on replacement therapy?

A

Noncompliance

Drugs that decrease LT4 absorption (iron, calcium)

Conditions that decrease LT4 absorption (small intestine disease)

Drugs that increase LT4 metabolism

Increase in TBG (OCPs, estrogens, hepatitis)

Progression of endogenous thyroid disease

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7
Q

Why would the TSH be lower than expected for someone on replacement therapy?

A

Dopamine (directly acts to decrease TSH)

High dose glucocorticoids

Decrease in TBG (androgens, chronic liver disease)

Self administration of excess LT4 in hopes of losing weight

Reactivation of Graves’ disease (more feedback)

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8
Q

What is the mechanism of anti-thyroid drugs?

A

interfere with two steps of thyroid synthesis by affecting TPO

  • iodine utilization
  • coupling
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9
Q

Between the anti-thyroid drugs, why is methimazole better than PTU?

A

Methimazole has longer half life

Methimazole is not protein bound (PTU is)

PTU decreases T4 to T3 conversion

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10
Q

What are exceptions for methimazole use in Graves’ disease patients?

A

Can’t use in patients who are pregnant, have adverse reactions or are undergoing thyroid storm

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11
Q

What is the main side effect of anti-thyroid medications? Why is it so dangerous

A

Agranulocytosis (can kill patient)

Can occur at any time or with any dose

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12
Q

What do you do/how do you counsel patients suspected of agranulocytosis from anti-thyroid meds?

A

Stop drug use and check WBC with diff if fever and sore throat

If granulocyte count is

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13
Q

What drugs did we discuss that inhibit T4 to T3 conversion?

A

PTU
Glucocorticoids
Propranol (beta blocker)

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14
Q

What other drugs did we discuss that can be used to treat hyperthyroidism?

A

Beta blockers (thyroid hormones rev up the heart, and beta blockers slow the heart down - has nothing to do with thyroid pathway)

NSAIDs

Iodine or glucocorticoids

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15
Q

What drugs do you use for treatment of thyroid storm?

A

PTU (or methimazole)

Propranol (or other beta blockers)

Hydrocortisone

Potassium iodide drops (inhibits thyroid iodide organification)

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16
Q

FACT: beta blockers can be used in any form of thyrotoxicosis

A

Yep

17
Q

FACT: the effect of iodide on the thyroid gland depends on the state of the underlying gland…whether it is normal or abnormal

A

Yep

18
Q

Explain the Wolff-Chaikoff Effect in normal thyroid

A

Excess iodide transiently inhibit iodide organification but the gland will eventually recover from this inhibitory effect

19
Q

Explain the Wolff-Chaikoff Effect in patient with autoimmune thyroid disease (Hashimoto or Graves’)

A

Excess iodide will inhibit iodide organification and the suppressive effect will persist (gland will not recover)

20
Q

What is the Jod-Basedow Phenomenon?

A

Thyrotoxicosis caused by iodine exposure

occurs in nodular thyroid glands

21
Q

How does radioiodine therapy to ameliorate Grave’s disease or other cause hyporthyroidism?

A

Results in hypothyroidism by ablating the thyroid gland or toxic nodule

Necrosis of follicular cells followed by disappearance of colloid and fibrosis of gland (over months)

22
Q

What is amiodarone and how does it relate to thyroid dysfunction?

A

Normally used to treat arrhythmias BUT 37% is organic iodide

23
Q

How does amiodaraone cause hypothyroidism?

A

Exacerbates hypothyroidism in patients who have it already

24
Q

What is Type 1 hyperthyroidism caused by amiodarone?

A

Patients with underlying thyroid nodular disease or Graves’ disease –> increased thyroid hormone production (iodide effect)

25
Q

What is Type 2 hyperthyroidism caused by amiodarone?

A

Patients with normal thyroids –> amiodarone causes destructive thyroiditis –> increased thyroid hormone release (leakage): direct toxic effect of amiodarone

26
Q

Who is not allowed to get radioiodine?

A

breast feeding or pregnant women, children

Repro-Endo (Additional) (5 decks)

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