Drugs and The Thyroid?

Question 1

How is thyroid hormone release stimulated?

Answer 1

• trigger = stress, cold or trauma
• stimulates release of TRH by hypothalamus
• TRH stimulates thyrotrophin from pituitary gland
• thyrotrophin stimulates release of thyroid hormone into blood and synthesis of thyroid to be stored

Question 2

What is the mechanism of action of superfamily 4 receptors?

Answer 2

• intracellular
• messenger diffuses across cell membrane as lipid soluble
• binds to receptor in cytoplasm
• substrate-receptor complex binds to hormone response element of DNA
• can increase or decrease:
• Gene transcription, activity of RNA polymerase or translation of mRNA

Question 3

How do the thyroid hormones act on the cell?

Answer 3

• bind to thyroid receptor in cytoplasm of cell (S4)
• bind to DNA to stimulate nuclear transcription of target genes, increases mRNA and protein synthesis
• this increases metabolic processes around the body which will increase heat and O2 consumption

Question 4

What are the symptoms of hyperthyroidism?

Answer 4

• Nervous
• Shaky
• Palpitations
• Heat intolerance
• Increased appetite
• weight loss
• Manic levels of energy
• tachycardia

Question 5

Symptoms of hypothyroidism?

Answer 5

• cold intolerance
• weight gain
• loss of appetite
• droopy eyelids
• tired
• slow comprehension
• hair loss
• delayed reflexes

Question 6

What can goitre indicate?

Answer 6

hyper or hypothyroidism usually Graves but can also be normal level of thyroid being produced

Question 7

What is a risks of thyroid surgery?

Answer 7

cutting of left laryngeal nerve

Question 8

Where would you see a scar if someone had thyroid surgery?

Answer 8

lower part of anterior neck

Question 9

How is hyperthyroidism usually treated?

Answer 9

• can be treated with surgery if goitre is compressing trachea
• usually pharmacologically treated
• can either block thyroid production, block and replace thyroid hormone, radioactive iodine to kill off thyroid cells or use surgery if have tumour for example

Question 10

Why do you need to treat symptoms of hyperthyroidism even after stopped thyroid production?

Answer 10

need to treat symptoms for a few weeks even after initial medication or surgery as has lots of thyroid stored in colloid

Question 11

What drugs are used to block thyroid production?

Answer 11

Thioureylenes

Question 12

What is the most common Thioureylenes?

Answer 12

Carbimazole and propylthiouracil

Question 13

What do Thioureylenes do?

Answer 13

Inhibit iodination of tyrosine in thyroglobulin

Question 14

How are Thioureylenes given and how quickly do they act?

Answer 14

• orally
• inhibit almost all iodination within 12h
• but symptoms only go away in around 4 weeks due to stores

Question 15

How is the dose of Thioureylenes changed?

Answer 15

• initially very high dose
• then gradually reduce dose until back to normal maintenance levels
• remain at maintenance for around 18 month
• then encourage discontinuation and most will remain in remission

Question 16

If after Thioureylenes or block and replace if don’t go into remission what is the go to treatment?

Answer 16

Radioactive iodine

Question 17

What are the adverse effects of Thioureylenes?

Answer 17

Common
- rash
- pruritus 
- nausea 
- low energy
Rare
- risk of agranulocytosis, if develop sore throat, cold then must report to doctor 
- can cause goitre and hypothyroidism in foetus if pregnant

Question 18

What are the benefits of propranolol use?

Answer 18

• rapid symptomatic relief as switches off lots of sympathetic overdrive
• inhibits T4 to T3 conversion in the peripheral tissue
• can be used in early weeks to relieve symptoms especially palpitations, arrhythmias and tremors

Question 19

When is propranolol contraindicated?

Answer 19

Asthma as non-selective beta blocker

Question 20

What are the benefits of the block and replace regime?

Answer 20

Less TSH so goitre reduced quickly

Question 21

In block and replace regime what are the medications given?

Answer 21

give enough carbimazole to completely block
Give as much levothyroxine as patient needs to replace
usually try to discontinue after 18 months

Question 22

How does the radioactive iodine work?

Answer 22

• radioactive Iodine absorbed by the gut
• travels to the thyroid where releases its beta particles
• causes follicle cells to die off

Question 23

What is the risk of using radioactive iodine and how long does it last?

Answer 23

• small chance radiation can move into area around neck
• important if have a baby and need to nurse it as baby will be around the neck a lot
• radiation gone in 2 months

Question 24

What needs to be taken if you get radioactive iodine treatment?

Answer 24

must take thyroid tablets for the rest of their life

Question 25

Treatment for hypothyroidism?

Answer 25

Levothyroxine which is T4

• dose can be adjusted based in symptoms
• tend to start lower and increase

Question 26

When is Lugol’s iodine given to patients?

Answer 26

Given in patients with hypothyroid goitre to shrink goitre before surgery to help make removal easier

Question 27

What drugs can affect thyroid hormone synthesis?

Answer 27

• Lugol’s iodine (iodine concentrate)
• Amiodarone (contains iodine and concentrates in thyroid), can cause hypo or hyper
• iodinated contrast media (used fo CT scans)
• lithium can reduce thyroid function

Question 28

What is amiodarone used for?

Answer 28

Anti-arrhytmic

Question 29

When is lithium used?

Answer 29

Schizophrenics

Question 30

Why does excess iodine do to thyroid synthesis?

Answer 30

Can cause hypo or hyperthyroidism

• excess iodine has negative feedback loop reducing thyroid hormone synthesis
• but if don’t reach that level of excess lots of iodine can mean more thyroid production