Pharmacology (Analgesics) Flashcards
ways analgesics can reduce nociception and pain
- decrease nociceptor sensitisation by blocking prostaglandins (NSAIDs)
- suppressing nerve conduction at Na+ channels (lidocaine)
- suppressing synaptic transmission in dorsal horn (opioids)
- activating descending inhibition
- targeting ion channels upregulated
analgesic rungs
3/ strong opioid
2/ weak opioid
1/ NSAIDs or paracetamol
examples of strong opioids
morphine heroin fentanyl oxycodone hydromorphone
examples of weak opioids
codeine
tramadol
dextropropoxyphene
important brainstem regions in pain
periaqueductal grey (midbrain) locus coeruleus (pons) nucelus raphe magnus (medulla)
what does excitation of PAG cause?
profound analgesia
what does NRM cause when activated by PAG?
suppression of nociceptive transmission
what does the LC do?
projects to dorsal horn and are excited inhibiting nociceptive transmission
what receptor do opioids act on?
GPCR
what do opioids do when they bind to GPCR?
inhibit Ca2+ channels (suppressing neurotransmission of nociception) and open K+ (suppress excitation post-synaptically)
adverse of opioids
addictive potential apnoea orthostatic hypotension action on CTZ causing N&V confusion, euphoria, hallucinations
how do opioids cause apnoea?
blunts medulla respiratory centre to CO2 causing hypercapnia responses
how do opioids cause orthostatic hypotension?
reduce sympathetic tone and bradycardia with mast cell degranulation
what do opioid agonists act on?
u-opioid receptors
opioid agonists
morphine diamorphine codeine fentanyl pethidine buprenorphine tramadol methadone
what organ metabolises morphine?
liver
what organ excretes morphine?
kidney
what is diamorphine?
a more lipophilic version of morphine so ha rapid onset
additional properties of codeine?
anti-diarrhoeal
antitussive
higher potency derivatives of codeine
oxycodone
hydrocodone
when is pethidine used?
acute pain, particularly labour
what is buprenorphine used in?
chronic pain with patient-controlled injections
when should you avoid tramadol?
epilepsy
what can methadone be used in?
withdrawal from strong opioids such as heroin
opioid antagonists
naloxone
naltrexone
alvimopan and methylnaltrexone
when is naloxone used?
reverse opioid toxicity associated with overdose
can trigger acute withdrawal episode
may be given to new-borns with opioid toxicity as a result of administration of pethidine during labour
properties of NSAIDs
analgesic
antipyretic
anti-inflammatory
action of NSAIDs
inhibit prostaglandins COX1 and COX2
suppress sensitisation of nociceptors by prostaglandins
decrease recruitment of leucocytes
suppression in dorsal horn
adverse of NSAIDs
GI damage
conditions with neuropathic pain
trigeminal neuralgia
diabetic neuropathy
post-hepatic neuralgia
phantom limb pain
management options for neuropathic pain
gabapentin and pregabalin
amitriptyline
carbamazepine
action of gabapentin and pregabalin
reduce expression of Ca2+ channels which causes a decrease in neurotransmitters (glutamate and substance P)
what neuropathic pain condition is gabapentin used in?
migraine prophylaxis
what neuropathic pain condition is pregabalin used in?
painful diabetic neuropathy
action of amitriptyline
act centrally by decreasing reuptake of NA
action of carbamazepine
block Na+ channels
what neuropathic pain condition is carbamazepine used in?
trigeminal neuralgia
