Pain Management Flashcards
What is pain?
An unpleasant sensory and emotional response and a protective and helpful mechanism to prevent further damage.
What is chronic pain?
Pain that lasts longer than 3 months.
No longer helpful.
Remains beyond the normal healing process.
Unpleasant sensory and emotional experience.
It may be associated with actual or potential tissue damage.
Physical and social impact
Biological, psychological and physical factors contribute to and are associated with the pain.
Nociceptive and neuropathic
What is primary chronic pain?
When the cause of the pain is unknown which is the most common concern.
What is secondary chronic pain?
When there is a specific known element causing the pain e.g., inflammation in RA.
What is the analgesic pain ladder?
- Non-opioids
- NSAIDs
- Adjuvant
- Weak opioid
- Strong opioid
What is nociceptive pain?
Response to physical trauma.
What is neuropathic pain?
Pain in nerve endings.
Example of a non-opioid analgesic
Paracetamol.
Example of an NSAID
Ibuprofen.
Examples of an adjuvant analgesic
Tricylics, gabapentoids, pregabalin.
Examples of weak opioids
Codeine, tramadol, dihydrocodeine.
Examples of strong opioids
Morphine, buprenorphine, diamorphine, fentanyl.
When are non-opioid analgesics used?
First line, baseline medication for mild pain.
Benefits of non-opioid analgesics
They are generally safe in long-term use
Have a synergistic effect with other meds
Usually good with other drugs
Cautions / contraindications of non-opioid analgesics
Malnourished patients = dose needs to be reduced in <50kg
Liver impairment = hepatotoxicity can occur in overdose
What do you need to consider if someone is taking effervescent preparations?
They may exceed their daily salt limit if they take paracetamol PRN at max dose = care needs to be taken in hypertensive or cardiovascular diseased patients.
Benefits of NSAIDs
Good where there is inflammation present
Why aren’t NSAIDs typically used in chronic pain?
Because chronic pain isn’t usually associated with inflammation
Contraindications of NSAIDs
When pt. is on warfarin, aspirin or SSRI = increased risk of bleed
History of stomach ulcers
Asthmatics
AKI
Mechanism of action of NSAIDs
Reversibility inhibits COX 1 and 2 enzymes
What does COX 1 inhibition result in and why?
GI side effects
COX 1 is responsible for maintaining the gastric mucosa as the prostaglandins produced by COX 1 inhibit gastric acid secretion. Therefore, inhibition of COX 1 leads to too much acid which will destroy part of the lining, leading to ulceration.
May also experience respiratory issues
Why might NSAIDs cause breathing issues in asthmatics?
Because COX1 is constitutive - which means it is present most of the time in most tissues.
Inhibition in lungs = difficult breathing
What does COX 2 inhibition result in?
Pain relief and anti-inflammatory response
Increased risk of cardiac problems and endothelial damage
Why are NSAIDs contraindicated in patients with an AKI?
COX 1 is responsible for producing prostaglandins.
These prostaglandins are responsible for vasodilation in the glomerulus.
If COX 1 is inhibited = no prostaglandins = no vasodilation.
As vasodilation doesn’t occur, the concentration gradient decreases along with the filtration rate of drugs which can result in kidney injury.
How would you develop a drug that selectively inhibits COX 2?
Add a bulky side chain group to the drug as it would still fit into the pocket of COX-2 but not COX-1 = minimises side effects.
Risk and benefits of Gabapentoids
Risk = abuse potential Benefit = Synergistic effect with opioids
Risks of using antidepressants?
Interactions
Poor side effect profile
How is neuropathic pain treated?
Usually with adjuvant analgesics
When should opioids be used?
For short-term pain when the analgesic ladder has been appropriately adhered to i.e. when pain persists after the lower tiers have been tried.
Also palliative care.
What daily dose of morphine should not be exceeded? Why?
120mg - because there is no increased benefit but there is an increase in the risk of harm.
What action is required if pain persists while taking opioids?
Stop the opioids even if no other treatment is available.
What is codeine?
A weak opioid (prodrug of morphine).
What is a prodrug?
A biologically inactive compound which can be metabolised in the body to produce the active drug.
What are the issues with codeine being a prodrug?
Inter-variations in metabolism between individuals
Slow metabolisers = not much analgesic benefit
Fast metabolisers may overdose
What are the pro’s of giving codeine as a fixed dose with paracetamol?
Reduces tablet burden
Increased adherence
What are the cons of giving codeine as a fixed dose with paracetmol?
Decreased flexibility of dosing
Which opioid receptor produces analgesia?
Mu
Why aren’t opioids used in neuropathic pain?
Because the dose needed for analgesia often produces excessive side effects.
Which opioid has the highest BBB permeability?
Diamorphine (heroin).
Why does buprenorphine have less side effects?
It is a partial agonist so doesn’t fully activate the receptor.
Provides moderate analgesia and less side effects than a full agonist.
