Analgesics Flashcards
Describe the WHO pain ladder.
1 –> 3
1 = paracetamol ± NSAIDs
2 = weak opioids
3 = strong opioid
Combinations of 1+2 or 1+3 for moderate/severe pain
Analgesic that suppresses nerve conduction by blocking voltage activated Na channel?
local anaesthetics e.g. lidocaine
Analgesic that acts at site of injury to decrease nociceptor sensitisation in inflammation?
NSAIDs block synthesis of prostaglandins
Analgesics that target ion channels unregulated in nerve damage?
many anti epileptics e.g. GABA pentinoids
Examples of weak opioids
codeine
tramadol
dextropropoxyphene
Examples of strong opioids
morphine oxycodone hydromorphone heroin fentanyl
Which efferent pathway from the midbrain is serotonergic?
periaqueductal grey matter
synapses in nucleus raphe magnus which continues serotonergic projection
Which efferent pathway from the pons is a noradreneric projection?
locus ceruleus
Areas of brain involved in pain perception excite ??? by electrical stimulation to produce profound analgesia.
PAG - periaqueductal grey
Where in the spinal cord does nociceptive transmission get suppressed?
dorsal horn
What adverse effect do opioids have on the respiratory system?
Apnoea - they blunt the medullary respiratory centre to CO2
= hypercapnia response
Why should morphine not be used in asthmatics?
causes mast cell degranulation which can trigger bronchospasm
An opioid antagonist produces analgesia mainly through prolonged activation of m-opioid receptors.
T/F?
False
opioid agonist prolongs activation of m-opioid receptors
Acute severe pain and chronic pain = which opioid m receptor agonist?
morphine
IV in acute
oral in chronic
Severe post-op pain = ?
diamorphine aka. heroin
more lipophilic than morphine
Naturally occurring, weaker opioid for mild/moderate pain?
codeine
orally
semi-synthetic derivatives of codeine with higher potency…
oxycodone
hydrocodone
75-100-fold more potent tan morphine
fentanyl
given IV to provide analgesia in maintenance anaesthesia
fentanyl
given for acute pain, especially in labour
pethidine
Why is pethidine not suitable for chronic pain control?
rapid onset but short duration
Partial against for patient-controlled chronic pain; injection or sublingually
buprenorphine - slow onset but long duration of action
Which opioid receptor agonist should you avoid in patients with epilepsy?
tramadol
what is the plasma 1/2-life of methadone?
> 24hrs
uses for methadone?
chronic pain in terminal cancer
assists with withdrawal from strong opioids e.g. heroin
opioid antagonist used to reverse opioid toxicity
naloxone
Newborn baby with opioid toxicity - potential iatrogenic cause and treatment?
giving mother pethidine during labour
give baby naloxone
difference between naltrexone and naloxone?
naltrexone can be given orally and has much longer 1/2 life
drugs to reduce GI effects of surgical and chronic opioid use
alvimopan
methylnaltrexone
why is paracetamol not classed as an NSAID?
no anti-inflammatory activity and only acts centrally
non-selective NSAIDs inhibit COX-1 - why is this an issue if used long term?
PGE2 is produced by COX-1 protects against the acidic nature of stomach = lack of PGE2 = stomach ulcer
disadvantage of COX-2 inhibitors?
prothrombotic
how do gabapentin and pregabalin work?
reduce cell surface expression of Ca2+ channels which have been unregulated in damaged sensory neurones
this decreases neurotransmitter = nociceptive signal terminates.
How does amitriptyline work?
acts centrally by decreasing re-uptake of noradrenaline
