Pain Flashcards
Chronic pain duration definition
More than 3 months
Nociceptive pain definition
Caused by inflammatory response to noxious stimuli, not categorical so can overlap with neuropathic
Neuropathic pain definition
Initiated/caused by primary lesion or disease in PNS/CNS, not categorical so can overlap with nociceptive
What is allodynia
innocuous stimulus now painful
NSAID MOA
Ibuprofen, aspirin, naproxen blocks COX non-specifically (so COX-1 and 2) producing prostaglandins which sensitises pain fibres, also anti-inflammatory and anti-pyretic due to PG inhibition
NSAID use
Anti-inflammatory, anti-pyretic and analgesic, not used for visceral pain
NSAID SE
GI damage
Selective COX-2 SE
Celecoxib, etoricoxib, lumiracoxib are associated with increased incidence of MI
Paracetamol use
Analgesic when there’s no inflammation, MOA not really known but acts partly by reducing cytoplasmic peroxide tone so only effective when leucocyte infiltration is low
Neuropathic pain treatment
Ion channel modifiers e.g. Ca channel blockers (Gabapentin, pregabalin), Na channel blockers (carbamazepine, lignocaine)
AMPA receptors in pain
acute touch and pain
NMDA receptors effect on pain
rapidly enhance it
Ketamine MOA
Blocks NMDA-R, powerful analgesic but has cognitive/memory effects so used in extreme pain
Opioid pain relief works on
Mu opioid receptor for endomorphins, delta is similar but no drugs for it
Kappa opioid receptor effects
Odd side-effects, maybe gender effects
ORL-1 opioid receptor effects
analgesic but can also enhance pain
Mu opioid types
Morphine gold standard
Codeine - weaker prodrug for morphine
Fentanyl - fast on/off, often for short surgical procedures
Pethidine - childbirth
Heroin - diacetylmorphine as so prodrug, fast
Naloxone - antagonist for all opioids
Opioid MOA
GPCR activated, inhibits N-type Ca channels, opens K channels for hyperpolarisation, inhibitory on pain pathways ascending and descending
Cell body in dorsal root makes opioids which presynaptically inhibit glutamate/substance P release, post synaptically inhibits neuronal activity (a delta and c fibres) so less nociceptor excitation
Epidural opioid MOA
Same as normal but just blocks spinal pain pathway, not descending controls so blocks pain below level of epidural
Role of emotion in pain
Emotion areas have off cells to reduce pain and on to increase, antidepressants work on NA/5HT descending pain pathways as well as mood
Antidepressant use in pain
Helps with neuropathic pain, useful in diabetes
Opioid painkillers SE
Sedation
Resp depression (brainstem less sensitive to CO2)
Anti-tussive
Constipation
Nausea/vomiting
Addiction if not used when pain pathways active
Opioid painkillers useful SE
Anxiety relief, anti-tussive, constipation
Triptans MOA and use
5HT1B/D agonist used for headaches e.g. sumatriptan
