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Pharm > Thyroid Hormones > Flashcards

Thyroid Hormones Flashcards

1
Q

triiodothyronine

A

T3

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2
Q

thyroxine

A

T4

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3
Q

Thyroid hormone preparation of T4

A

Levothyroxine (given orally, long half life)

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4
Q

T3 aka

A

triiodothyronine

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5
Q

T4 aka

A

thyroxine

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6
Q

Thyroid hormone preparation of T3

A

Liothyronine (more potent, faster acting but short half life, injectable)

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7
Q

When do you give T3?

A

T3 given only when an immediate response is needed (E.g. in myxodema coma)

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8
Q

MOA of thyroid hormones

A

➢ Thyroid hormones are attached to plasma carrier proteins.
• Hormones dissociate from carrier proteins enter the cell by active transport

➢ Within the cell T4 converted to T3 – enters nucleus- bind to thyroid hormone receptor - localized in the nucleus –> Stimulates transcription of particular genes

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9
Q

Levothyroxine

A

T4 hormone prep

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10
Q

Effects of Thyroid hormones on growth & development

A

• Essential for normal physical & mental growth, hence cretinism - mental retardation

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11
Q

caloric effects of thyroid hormones

A
  • ↑ BMR and

* ↑ manitain body temperature

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12
Q

Liothyronine

A

T3 hormone prep

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13
Q

cardiovascular effects of thyroid hormones

A
  • ↑ HR and

* ↑ peripheral resistance

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14
Q

metabolic effects of thyroid hormones

A
  • ↑ blood sugar,
  • ↑ synthesis of fatty acids and
  • decrease plasma CH and TG levels
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15
Q

Use of thyroid hormones

A

➢ Hypothyroidism caused by:

  • Hashimoto’s disease
  • Myxedema
  • Following surgical ablation of thyroid gland
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16
Q

hypothyroidism signs and symptoms

A
  • anemia;
  • hyponatremia,
  • galactorrhea,
  • goiter;
  • hard, pitting edema of the lower extremities
  • delayed return of deep tendon reflexes
  • Any combination of a few or many signs and symptoms may occur at any given time.
  • Some signs and symptoms, such as galactorrhea, anemia, and skin changes are seen in individuals in later stages of hypothyroidism.
17
Q

Thyroid Inhibitors:

A
  • Perchlorate,
  • thiocyanate,
  • goitrin
18
Q

Thyroid Hormone Synthesis

A
  1. Uptake of Iodide (iodide trapping)
  2. Iodide organification
    • (oxidation and iodination)
  3. Coupling of MIT and DIT
  4. Secretion of thyroid hormones
  5. Conversion of T4 to T3
19
Q

Ionic Inhibitors

A

Affects uptake of Iodine

  • Perchlorate (ClO4- )
  • thiocyanate (SCN- )

➢ No Therapeutic use: only Diagnostic

20
Q

Monovalent anions

A

Affects uptake of Iodine

  • Resemble Iodide
  • Inhibit transport of iodide into thyroid

➢ No Therapeutic use: only Diagnostic

21
Q

Thyroid peroxidase

A

Oxidizes iodide to iodine

22
Q

Thioamides

A

Antithyroid drug!

➢ Iodine rapidly iodinates tyrosine residues in thyroglobulin forming MIT (mono-iodotyrosine) and DIT (di-iodotyrosine)

• Inhibited by: Thioamides

23
Q

Coupling of MIT and DIT

A

➢ Coupling reaction involves oxidation by:
• Thyroid peroxidase

  1. MIT + DIT –> T3
  2. DIT + DIT –> T4

➢ Stored in thyroglobulin in colloid matrix
• Inhibited by thioamides -

examples:
• Methimazole
• Propylthiouracil

24
Q

Thioamides MOA

A

➢ Inhibit thyroid peroxidase :
• Block iodine oxidation
• Coupling of MIT and DIT

25
Q

Propylthiouracil MOA

A

Inhibit peripheral conversion of T4 to T3

• Block synthesis T3 and T4 not release, therefore slow onset of action

26
Q

Thioamides A/E

A 
➢  Relatively low incidence (3 – 12%) 
•  Maculopapular pruritic rash
•  Hypothyroidism 
•  Gastrointestinal intolerance
•  Agranulocytosis (
27
Q

Secretion of T4 and T3 Inhibited by:

A

Iodine and Iodides

28
Q

Secretion of T4 and T3

A

➢ Proteolysis - release of T4 and T3 stored within thyroglobulin (TG)
• MIT and DIT deiodinated; iodine reutilized
➢ Inhibited by Iodine and Iodides

29
Q

Iodides

A

➢ Inhibit TH release - thyroid constipation
➢ Decreased size & vascularity of gland
➢ Improvement of thyrotoxic symptoms occurs rapidly – used in thyroid storm

30
Q

Conversion of T4 to T3 Inhibited by

A
  • Propranolol
  • Propylthiouracil
  • Glucocorticoids (prednisolone)
31
Q

Conversion of T4 to T3:

A

➢ 80% of T4 converted to T3 in peripheral tissues

• De-iodination of T4 (thyroxine) to active T3 (triiodothyronine)

32
Q

Lugol’s Iodine and Na/K Iodide:
• use
• toxicity

A

Use:
• Preoperatively- thyroidectomy
• Thyroid storm

Toxicity:
• Iodism- rash, rhinorrhoea, ulcers, conjuctivitis

33
Q

Radioactive Iodine

  • what
  • half life
A

I-131

➢ Rapidly absorbed (orally)
➢ Concentrated in thyroid
➢ Emits b radiation –> destruction of thyroid gland

• half life (5 days)

34
Q

Use of radioactive iodine
• advantages
• disadvantages
• contraindicated

A

Use: Hyperthyroidism

Advantage:
• Inexpensive, simple, outpatient basis
• No surgical risk
• Permanent cure

Disadvantage:
• response slow
• Hypothyroidism

Contraindicated:
• pregnancy,
• young patients

35
Q

Treatment of Hyperthyroidism

A

➢ Antithyroid drug therapy
• Propylthiouracil, methimazole
➢ Thyroidectomy
➢ 131Iodine

36
Q

Thyroid Storm
• triggers
• treatment
• what is it

A

aka thyrotoxic crisis
• high mortality

Triggers:
• Acute illness, surgery, radioiodine in an untreated thyroid.

Treatment:
• Large doses of Propylthiouracil: inhibit the peripheral conversion
• Propranolol - control cardiac manifestations
• Potassium iodide – inhibit release of thyroid hormones
• Glucocorticoids- protect against shock, block conversion of T4 to T3

37
Q

What is Thyroid Storm

A

Thyroid storm is a crisis or life-threatening condition characterized by an exaggeration of the usual physiologic response seen in hyperthyroidism.

Whereas hyperthyroidism can cause symptoms such as sweating, feeling hot, palpitations and weight loss - symptoms of thyroid storm are more severe, resulting in complications such as:

  • fever
  • dehydration
  • rapid heart rate
  • nausea/vomiting
  • diarrhea
  • irregular heart beat
  • weakness
  • heart failure
  • confusion/disorientation
  • death
38
Q

Propranolol

A

beta blocker

➢ Many symptoms of thyrotoxicosis - sympathetic stimulation- palpitation, nervousness, tremors

• b-blockers - Block physiological effects of sympathetic nervous system stimulation

Pharm (32 decks)

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