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Pharmacology > Thyroid drugs > Flashcards

Thyroid drugs Flashcards

1
Q

What are the three approaches to treatment of hyperthyroidism

A

Interfere with thyroid hormone production

Modify tissue response to thyroid hormone

Destroy thyroid gland via radiation or surgery

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2
Q

Name the nine classes of drugs used to tx hyperthyroidism

A 
Iodide uptake inhibitors (anion inhibitors)
Inorganic Iodide
Radioactive Iodine
Thioamides
Beta-adrenergic Antagonists
Radiocontrast agents
Corticosteroids
Lithium
Amiodarone
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3
Q

Name the three Iodide uptake inhibitors and its MOA

A

Thiocyanate
Perchlorate
Pertechnetate

  • competes with iodid for uptake into the thyroid gland follicular cells
  • causes aplastic anemia, so use is limited
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4
Q

Name the inorganic iodide used to treat hyperthyroidism and it’s MOA

A

Lugol’s solution

MOA is to cause Wolff-Chaikoff effect (high concentration of iodide inhibits T4/T3 synthesis/release via negative feedback loop)

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5
Q

Lugol’s solution works in three ways by

A

inhibiting iodide organification (oxidation)

inhibiting release of thyroid hormones

decreasing the size and vascularity of enlarged thyroid gland for easier surgical excision

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6
Q

In order for the autoregulatory phenomenon of Wolff-Chaikoff effect to work, what pathway must be intact

A

negative feedback loop

*usually the case thyroid dysfunction not previously treated

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7
Q

What are the five disadvantages of administering Lugol’s solution

A

Increases the intraglandular stores of iodine

  • delays onset of thionamide therapy
  • delays radioactive treatment

Must be used with other therapies
-gland can “escape” from iodide block to produce severe thyrotoxicosis

Crosses placenta

  • can cause fetal goiter in large doses adminisitered over prolonged times
  • avoid in pregnancy

Irritating and destructive to mucosa

Causes Jod-Basedow phenomenon

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8
Q

What is the Jod-Basedow phenomenon

A

Hyperthyroidism following administration of iodine or iodide which could lead to thyrotoicosis in people who have thryoid abnormalities that cause the gland to function without the control of the pituitary.

*The Jod-Basedow effect does not occur in persons with normal thyroid glands who ingest extra iodine in any form.

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9
Q

What is the difference between Wolff-Chaikoff effect and Jod-Basedow phenomenon

A

some ways the Jod-Basedow phenomenon is the opposite of the Wolff-Chaikoff effect, which refers to the short period of thyroid-hormone suppression which happens in normal persons and in persons with thyroid disease, when comparatively large quantities of iodine or iodide are ingested. However, unlike the Wolff-Chaikoff effect, the Jod-Basedow effect does not occur in persons with normal thyroid glands, as thyroid hormone synthesis and release in normal persons is controlled by pituitary TSH secretion, which does not allow hyperhyroidism when extra iodine is ingested.

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10
Q

Radioactive Iodine is used to treat

A

thyrotoxicosis

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11
Q

Radioactive iodine’s MOA includes

A

Rapid absorption and concentration by the thyroid, and incorporation into storage follicles

*the thyroid tissue is destroyed within a few weeks

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12
Q

What is the goal of radioactive iodine

A

to administer enough to result in Euthyroid state without precipitating hypothyroidism

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13
Q

Radioactive iodine can only be used in adults of what age

A

> 35 years of age

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14
Q

Radioactive iodine is not used in which patient population

A

pregnant or nursing mothers

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15
Q

The incidence of hypothyroidism after 2 years and 10 years of therapy include

A

after 2 years up to 30%

after 10 years up to 50%

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16
Q

Name the two thioamides used to treat hyperthyroidism

A

Prophylthiouracil (PTU)

Methimazole (Tapazole)

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17
Q

What is the MOA of the PTU and Methimazole

A

Binds to thyroid-peroxidase thereby inhibiting iodine organification and synthesis of thyroid hormones

prevents coupling of iodotyrosines (DIT)

18
Q

What additional MOA does PTU have that Methimazole lacks

A

PTU also inhibits the peripheral conversion of T4 to T3, unlike methimaxole

19
Q

Name four other drugs whose MOA is similar to PTU (inhibition of T4 to T3)

A

Sodium Thiopental (induction agent)

Propanolol (beta adrenergic antagonist)

Mifepristone (steroid receptor antagonist used to tx cushing’s syndrome)

Sodium Ipodate (radiocontrast agent used in ERCP procedures)

20
Q

Does the thioamides (PTU/Mehtimazole) inhibit the release of stored thyroid hormones

A

NO

21
Q

What is the major SE associated with PTU/Methimazole administration

A

Pruritic rash with fever

22
Q

What is the most life-threatening SE associated with PTU/Methimazole adminsistraton

A 
Severe agranulocytosis (lowered WBC)
bleeding tendancies
23
Q

PTU/Methimazole and pregnacy

A

Both drugs cross the placenta and will effect the fetal thyroid

  • however, PTU is preferred bc it is more highly protein bound and crosses placental less
  • Okay to breast feed
24
Q

Thioamides are sometimes referred to as?

A

Goitrogen

*as TSH levels rise in response to lowered thyroid hormone levels, the thyroid gland hypertrophies

25
Q

Name the main beta-adrenergic antagonist used to tx hyperthyroidism

A

Propanolol

26
Q

What is the MOA of beta-adrenergic antagonists

A

Decreases the peripheral conversion of T4 to T3

*decreases the symptoms of excess sympathetic activity (tachy, tremor, anxiety, sweating, and heat intolerance)

27
Q

beta-adrenergic antagonists must be used with caution in which patient population

A

CHF

Reactive airway disease

28
Q

What is the MOA of corticosteroids

A

inhibits the 5’-deiodinase enzyme that converts T4 to T3, reducing net thyroid activity.

29
Q

What is the MOA of Lithium

A

inhibits thyroid hormone release from thyroid follicular cells, as well as inhibition of synthesis

30
Q

What antidysrhythmic resembles thyroxine

A

amiodarone

*contains a large amount of iodine that accumulates in the thyroid when metabolized

31
Q

What percent of patients taking amiodarone will develop thyroid dysregulation

A

14-18%

32
Q

Amiodarone can cause ——- and ——-

A

hypothyroidism

hyperthyroidism

33
Q

The hypothyroidism caused by amiodarone is a result of what effect

A

wolff-chaikoff

*increased iodine concentration leads to decreased T3/T4 via upregulation of negative feedback loop

34
Q

the hyperthyroidism caused by amiodarone is a result of what phenomenon that is classified as type 1

A

jod-basedow- iodine-induced hyperthyroidism

*Increased concentration of Iodine leads to increased T4/T3

35
Q

The hyperthyroidism caused be amiodarone is categorized as two types, what is the main difference between the two types

A

type 1: doppler shows INCREASED vascularity of gland

type 2: doppler shows DECREASED vascularity of gland
*known as destructive thyroiditis

36
Q

Hypothyroidism is classifed as

A

primary, secondary, tertiary, and thyroid gland hormone deficiency

37
Q

Hashimoto’s thyroidits is classified as what type of hypothyroidism

A

primary

*destructive autoantibodies Destroy the thyroid gland
VS.
* Grave’s disease whereby autoantibodies bind to the gland and stimulate thyroid hormone production

38
Q

What significant consideration must be kept in mind when deciding to tx hypothyroidism

A

replacement must be weighed against the risk of percipitating myocardial ischemia

39
Q

What main drug is used to treat hypothyroidism

A

Levothyroxine (T4)

40
Q

Why is Levothyroxine the most commonly used thyroid supplement

A

Because its GI absorption is predictable up to 75%

Pharmacology (27 decks)

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