Drugs and The Thyroid? Flashcards
How is thyroid hormone release stimulated?
- 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
What is the mechanism of action of superfamily 4 receptors?
- 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
How do the thyroid hormones act on the cell?
- 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
What are the symptoms of hyperthyroidism?
- Nervous
- Shaky
- Palpitations
- Heat intolerance
- Increased appetite
- weight loss
- Manic levels of energy
- tachycardia
Symptoms of hypothyroidism?
- cold intolerance
- weight gain
- loss of appetite
- droopy eyelids
- tired
- slow comprehension
- hair loss
- delayed reflexes
What can goitre indicate?
hyper or hypothyroidism usually Graves but can also be normal level of thyroid being produced
What is a risks of thyroid surgery?
cutting of left laryngeal nerve
Where would you see a scar if someone had thyroid surgery?
lower part of anterior neck
How is hyperthyroidism usually treated?
- 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
Why do you need to treat symptoms of hyperthyroidism even after stopped thyroid production?
need to treat symptoms for a few weeks even after initial medication or surgery as has lots of thyroid stored in colloid
What drugs are used to block thyroid production?
Thioureylenes
What is the most common Thioureylenes?
Carbimazole and propylthiouracil
What do Thioureylenes do?
Inhibit iodination of tyrosine in thyroglobulin
How are Thioureylenes given and how quickly do they act?
- orally
- inhibit almost all iodination within 12h
- but symptoms only go away in around 4 weeks due to stores
How is the dose of Thioureylenes changed?
- 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
If after Thioureylenes or block and replace if don’t go into remission what is the go to treatment?
Radioactive iodine
What are the adverse effects of Thioureylenes?
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
What are the benefits of propranolol use?
- 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
When is propranolol contraindicated?
Asthma as non-selective beta blocker
What are the benefits of the block and replace regime?
Less TSH so goitre reduced quickly
In block and replace regime what are the medications given?
give enough carbimazole to completely block
Give as much levothyroxine as patient needs to replace
usually try to discontinue after 18 months
How does the radioactive iodine work?
- radioactive Iodine absorbed by the gut
- travels to the thyroid where releases its beta particles
- causes follicle cells to die off
What is the risk of using radioactive iodine and how long does it last?
- 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
What needs to be taken if you get radioactive iodine treatment?
must take thyroid tablets for the rest of their life
Treatment for hypothyroidism?
Levothyroxine which is T4
- dose can be adjusted based in symptoms
- tend to start lower and increase
When is Lugol’s iodine given to patients?
Given in patients with hypothyroid goitre to shrink goitre before surgery to help make removal easier
What drugs can affect thyroid hormone synthesis?
- 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
What is amiodarone used for?
Anti-arrhytmic
When is lithium used?
Schizophrenics
Why does excess iodine do to thyroid synthesis?
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
