Analgesics Flashcards
describe acute / nociceptive pain
short term pain with easily identifiable cause. warning of present damage to tissue
describe chronic/ neuropathic pain
pain persists
constant/ intermittent
pain has outlived its purpose
describe allodynia pain
pain from stimulus that doesn’t normally cause pain eg. blanket on diabetic foot
describe parasthesis pain
painful feelings eg. pins and needles with no apparent stimulus
describe the body’s own analgesic system
pain is detected and relayed to brain, brain uses inhibitory pathways stimulated by opiods, serotonin and noradrenaline to secrete local analgesics (opiod, y-aminobutyric acid, encephalins)
name the classes of drugs which are used in analgesia
opiods
antidepressants
antiepileptic’s
local anaesthetic
what is the mechanism of action of opioids?
blocks pain signals going up to the brain - decreases neurotransmitter release / blocks postsynaptic receptors
enhances body’s own analgesic effect at inhibitory pathways
what are the side effects of opioids?
N & V constipation drowsiness resp. depression hypotension sedation dependency
what are the cautions /contraindications of opioids?
acute resp. depression
acute alcoholism
head injury
what are the interactions with opioids?
alcohol - increased hypotension
MAOI - increased CNS excitation/ inhibition
SSRI/ TCA - increased sedation
carbamazepine - decreased plasma conc. of methadone
cimetidine - inhibit opioids
what do opioids mimic?
endogenous ligard “enkephalins” - beta-endorphin, leu-enkeplin, met-enkepalin, dynorphin
name the 3 opioid receptor types that opioids agonise and the subtypes
nu, kappa, delta
nu, kappa 1,2,3, delta 1,2
which opioid receptor is responsible for most analgesic effects?
nu - CNS, spinal cord, peripheral sensory neurons, GI tract
name a pure opioid agonist
morphine - high affinity to nu (low for kappa and sigma)
name a mixed opioid agonist
nalorphine - mixed effects on nu receptors
name to partial opioid agonists
pentazocine
cyclazocine - (-) effect at nu but partial (+) at sigma and kappa receptors
name 2 opioid antagonist and describe when it would be used
naloxone
naltrexone - blocks actions of opioids
used in heroin and morphine overdose
name 2 types of antidepressants used as analgesics
serotonin and noradrenaline reuptake inhibitors (SNRI)
selective serotonin reuptake inhibitors (SSRI)
describe the mechanism of action of SNRI and SSRI
inhibiting the reuptake of neurotransmitters released naturally in response to pain the effect can be prolonged
mediate descending inhibition of ascending pain pathway
what type of pain are SNRI effective in treating?
neuropathic pain (doesn’t work for all)
what type of pain are SSRI effective at treating?
diabetic or HIV neuropathy
name 2 SNRI
venlafaxine
duloxetine
name 2 SSRI
paroxetine
citalopram
what type of pain is duloxetine used to treat and what are the side effects?
peripheral neuropathy (esp. diabetic neuropathy) SE: nausea, somnolence, insomnia, dizziness
what type of pain is venlafaxine used to treat and what are the side effects?
diabetic neuropathy
SE: nausea, sedation, headache, dizziness
what are the cautions of used SNRI
epilepsy, cardiac disease, diabetes, angle closure glaucoma, pregnancy, b/feeding
what do SNRI interact with?
alcohol - increase sedation
NSAIDs/ aspirin - increase bleeding
tramadol - increase CNS toxicity
increased sedation with opoiods
why should SSRI not be given with antiepileptic medication?
antagonise effect
what is the mechanism of action of antiepileptic’s used as analgesics?
inhibit voltage gated Na+ and Ca+ channels
inhibit glumate, y-aminobutyric acid (GABA), glycine receptors
inhibit action potential firing - prevent nerve transmission
limit neuronal excitation - enhance neuronal inhibition
name 2 antiepileptic’s used as analgesics
carbamazepine
gabapentin
what types of pain is carbamazepine used to treat?
glossopharyngeal neuralgia
postherpetic neuralgia (nerve damaged caused by varicella zoster virus)
trigeminal neuralgia
diabetic neuropathies
what types of pain is gabapentin used to treat?
neuropathic pain: complex regional pain syndrome neuropathy of face postherpetic neuralgia sciatic pain
what are the side effects of carbamazepine?
dizziness diplopsia fatigue nausea hepatotoxicity renal impair
what cautions are there when using carbamazepine?
renal impairment
cardiac disease
pregnancy
what are the side effects of gabapentin?
anorexia
dyspepsia
tremor
what cautions are there when using gabapentin?
elderly
renal failure
diabetes
pregnancy
name 2 local anaesthetics used as analgesics
lidocaine
ketamine
what is the mechanism of action of local anaesthetics?
inhibits voltage gated Na+ channels and NMDA receptors - prevent nerve to nerve communication
inhibit firing - prevent impulse transmission
what type of pain are local anaesthetics useful for treating?
severe intractable pain or crescendo neuropathic pain
what is the route of administration and the side effects of lidocaine?
IV CNS effects (confusion) depression convulsions hypotension bradycardia
what are the cautions when using lidocaine?
epilepsy hepatic/ resp. impairment atrial fibrillation heart block heart failure
what is the route of administration and the side effects of ketamine?
injectable hypertension tachycardia tremor diplopia myocardial depression
