Opioid Pharmacology Flashcards
How is 50% of oral morphine metabolised
First pass metabolism in the liver
What does 50% metabolism of morphine mean for prescription
We have to double the dose (10mg morphine = 5mg really)
How long does a single dose of morphine last
3-4 hours
How often is morphine given for ‘slow release’ palliative care
Twice a day
Benefits of diamorphine vs morphone
Diamorphine is more potent and passes across blood-brain barrier more quickly
What class are opioids categorised as
Class A drugs
Why are opioids difficult to get a hold of
- Secure storage
2. CD (controlled drug) books need two signatures
Dihydrocodeine vs codeine
1.5 x more powerful
How do opioids work physiologically
- Inhibits release of pain transmitters at spinal cord and midbrain by binding to G-coupled receptors
- Modulate pain perception at higher centres and emotional response
What two hormones do opioids inhibit to bring bout decreased pain perception
Natural endorphins
Enkephalins
How do Opioids work
Descending inhibition of pain
Do opioids bring about sustained activation
No
What is the problem of sustained activation due to opioids
Leads to tolerance and addiction
Name of the four receptors
MOP
KOP
DOP
NOP
What do Kappa morphine receptors do which is different to the other three
Causes depression instead of euphoria
What receptor do all drugs currently act on
M(u) receptors
Define Potency
How well the drug binds to the receptor
Define efficacy
How well receptor is activated
Which is more potent, Morphine or Diamorphine
Morphine (10mg) vs Diamorphine (5mg for same effect)
Why does Tolerance occur
Down-regulation of receptors with prolonged use
Need higher doses to reach same effect
Define dependance
Psychological response to tolerance - craving
When does opioid withdrawal take place
24 hours and lasts 72 hours