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Year II Pharmacolofy Term III > Thyroid Hormone & Anti-thyroid Drugs > Flashcards

Thyroid Hormone & Anti-thyroid Drugs Flashcards

1
Q

How is thyroxine formed

A

Iodination & couplling of 2 tyrosineresidues

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2
Q

Thyroxine is know as

A

T4

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3
Q

How is thyroxine (T4) convered to T3

A

De-iodination of the outer ring

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4
Q

How can thyroxine (T4) be deactived

A

De-iodination of the inner ring of tyrosine

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5
Q

6 steps of T4 & T3 sythesis

A
  1. Iodine taken into thyroid follicular and out into the lumen where the colloid is located
  2. Iodine added to tyrosine residues inside thyroglobulin (peroxidase enzyme)
  3. T4 formed by joining of diiodotyrosines (DIT) to form tetraiodothyronine (thyroxine, T4) by thyroid peroxidase enzyme
  4. T3 formed by joining DIT and monoiodotyrosine (MIT) to form triiodothyronine (T3) by thyroid peroxidase enzyme
  5. Thyroglobin taken from lumen bought into follicular cell & undergoes proteolysisto yeild T4 & T3
  6. DIT & MIT can be deiodinated
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6
Q

Which (T4 or T3) has a longer half life

A

T4 - 1 week

T3 - 1 day

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7
Q

Which (T4 or T3) is biological active

A

T3 active

T4 is a reservior

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8
Q

Thyroid Hormone Receptor have 2 domains- name them

A

DNA binding

Ligand binding

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9
Q

How does T3 alter gene expression

A

T3 binds to and inactivates CoR (Corepression) to the retinoid X receptor hetrodimer

Co-activator (CoA) canbind & increases mRNA

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10
Q

Side Effects of thyroxine

A

Adverse effects of thyroxine administration: Hyperthyroidism, including cardiac symptoms such as tachycardia, arrhythmias, angina, or infarction.

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11
Q

Treatment options for hyperthyrodism - Radioablation

Mechanism
SE

A

Mechanism

  • Radioactive iodine (I 131)
  • Destroys functional thyroid tissues

SE

  • Hypothyrodism
  • Destroys fetal thyroid
  • NOT carcinogenic
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12
Q

Treatent options for hyperthyrodism - medicinal

Mechanism
How long until effects show up?
How does this alter dosage?
SE
BBW for PTU
A

Methimazole and Propylthiouracil (PTU)

How long until effects are evident
- several weeks must deplete existing thyroid hormone

Dosage
- Start at high doses and then lower dose once euthyroid

SE
- Inhibit thyroid hormone sythesis by inhibiting thyroid peroxidase

BBW for PTU
- Severe liver injury

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13
Q

Treatment options for hyperthyrodism - radioative iodide

What isotope?
Mechanism
How long until effect?
SE (2)

A

Isotope
I 131

Mechanism
- Radioactive iodide concentrated in the thyroid and emits beta particle

How long until effect?
2-3 months

SE

  • Hypothyrodism (treat levothyroxine)
  • Ablation of fetal thyroid
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14
Q

Is radioactive I carcinogenic

A

No

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15
Q

Name one effect that propylthiouracil has that methimazole does not have

A

PTU can stop peripheral conversion of T4 to T3 so it can be used acutely

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16
Q

Thioureas

Mechanism
Use
SE

A

Mechanism
Inhibits thyroid peroxidase & stops deiodination of T4

Use
- Acute states of hyperthyroidsim or thyrotoxic crisis
- Can be used long term for patients with Grave's disease (causes sponatous remission in some)
SE
- Agranulocytosis
- Hepatitis
- Jaundice
- Pruritis
- Rash
17
Q

Which (methimazole/propylthiouracil)

causes agranulocytos or hepatacoxicity

A

propylthiouracil

18
Q

Which (methimazole/propylthiouracil) has a longer half life

A

methimazole

19
Q

Which (methimazole/propylthiouracil) is prefered in 1st trimester of pregancy

A

propylthiouracil

20
Q

Which (methimazole/propylthiouracil) can be used to rapidly control severe hyperthyrodism?

A

propylthiouracil & Thioureas

21
Q

2 drugs used to treat hypothrydoism

How long until patients experece an effect

A

Levothyroxine
Liothyronine

6-8 weeks

22
Q

2 drugs used to treat hyperthyrodism

Duration of action

A

Methimazole: 24 hrs given orally

Propylthiouracil: 6-8 hrs given orally

23
Q

Radioactive iodine

Which isotopes
How long until onset of action
Maximum effect st

A

131

Onset: 6-12 weeks
Maximum effect: 3-6 months

Year II Pharmacolofy Term III (6 decks)

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