Analgesics Flashcards
Define acute/nociceptive pain
short term pain, easily identifiable cause, responds well to medication
Define chronic/neuropathic pain
pain which persists, no longer helps the body to prevent any further injury
Define allodynia
pain from stimulus that does not normally cause pain
Define parasthesis
painful feelings with no apparent stimulus
Pain management
Assessments:
- type of pain (nociceptive/neuropathic)
- form of pain (acute/chronic)
- severity of pain (pain scores)
- routes of admission (iv/oral)
Opioids
modify transmission of pain signal and the subjective perception of pain
act at the level of the spinal chord and CNS to:
- decrease neurotransmitter release and block post-synaptic receptors
- activate inhibitory pathways
mimic our endogenous pain killers ‘enkephalins’
3 types of receptors
act as suppressors
Opioid advantages and disadvantages
Advantages:
- highly effective, variety of routes, range of duration of effects
Disadvantages:
- SE (dose related)
> nausea, vomiting, constipation
> drowsiness, respiratory depression, sedation, dependency
- cautions/contraindications:
> acute respiratory depression, acute alcoholism, head injury
- interactions:
> alcohol increases hypotensive and sedative effects
> MAOIs increase CNS excitation
- Carbamazepine decreases plasma concentration of the membrane
Opioid receptors
Mu = found in CNS, spinal chord, peripheral sensory neurones, GI tract
responsible for most analgesic effects
responsible for SE
Kappa = found in CNS, spinal chord, peripheral sensory neurons
sedation and dysphoria, few SE, no dependance
Delta = found in CNS, peripheral sensory neurons, may contribute to analgesia
Morphine
- opioid
oral, i.v, s.c
treats acute and chronic pain
SE = respiratory depression, sedation, constipation, nausea, vomiting, itching, dependence
Diamorphine
-opioid
oral, i.v
acute and chronic pain
more rapid than morphine, metabolised to morphine
SE = respiratory depression, sedation, constipation, nausea, vomiting, itching, dependence
Hydromorphone
-opioid
oral, i.v
acute and chronic]
less sedative, SE same as morphine
Methadone
- opioid
oral
chronic pain
less euphoric, SE same as morphine
Pethidine
- opioid
oral, i.v, i.m
acute and intense pain
SE = anticholinergic effects, risk of excitement and convulsion, same as morphine
Anti-depressants and analgesia
SNRI = Serotonin and Noradrenaline Re-uptake inhibitors
- highly effective for neuropathic pain but not in all patients
- actions independent of anti-depressive effects
Eg. Venlafaxine, Duloxetine
SSRI = Selective Serotonin Re-uptake inhibitors
- not particularly effective GA
- appear to work well in disease environments eg diabetes
Eg. Paroxetine, Citalopram
Duloxetine
- anti-depressant
prescribed for peripheral neuropathy, particularly diabetic neuropathy SE = nausea, insomnia, dizziness cautions/contraindications: epilepsy, diabetes, cardiac disease, pregnancy/breast feeding interactions: alcohol increases sedation NSAIDS/aspirin increase risk of bleeds Tramadol increase risk of CNS toxicity
Venlafaxine
- anti-depressant
prescribed for diabetic neuropathy SE = nausea, sedation, headache and dizziness cautions/contraindications: epilepsy, diabetes, cardiac disease, pregnancy/breast feeding interactions: alcohol increases sedation NSAIDS/aspirin increase risk of bleeds Tramadol increase risk of CNS toxicity
Anti-epileptics and analgesia
inhibit voltage gated sodium channels inhibit voltage gated calcium channels inhibit GABA and glycerine receptors > inhibit action potential firing > prevent impulse transmission > limit neuronal excitation > enhance neuronal inhibition
Carbamazepine
used to treat glossopharyngeal neuralgia, post hepatic neuralgia, diabetic neuropathies
SE: dizziness, fatigue, nausea, hepatotoxicity, renal impairments
cautions/contraindications:hepatic/ renal impairment, cardiac disease, pregnancy, history of bone marrow disease
Gabapentin
used to treat various neuropathic pain states:
complex reginal syndrome, deafferentation neuropathy of the face,sciatic pain
drug of choice due to limited side effects
SE = anorexia, tremor
cautions: renal impairment, pregnancy
Local anaesthetics
inhibit voltage gated sodium channels to prevent nerve-nerve cell communication
- inhibit firing
- prevent impulse transmission
Eg. Lidocaine, Ketamine
Lidocaine
sodium channel blocker
effective in non-cancer patients
i.v
SE = CNS effects (confusion), respiratory depression, hypotension, bradycardia
cautions/contraindications= epilepsy, hepatic/respiratory impairment, atrial fibrillation, heart failure
Ketamine
blocker of glutamate receptors
injectable, not favourable due to side effects
SE = hypertension, tachycardia, tremor, myocardial depression
cautions/contraindications = angina, hypertension, heart failure, aneurysm, psychotic disorders
What are the 4 anti-depressants effective as analgesics?
Venlafaxine, Duloxetine = SNRI
Citalopram, Paroxetine = SSRI
