Analgesics Flashcards
Opioids - basic overview
Modify the transmission of pain signals and the subjective perception of pain
Antidepressants and Antiepileptics - basic overview
Trigeminal neuralgia Neuropathic pain (which is resistant to opioids)
Local Anaesthetics - basic overview
Particularly effective for severe intractable or crescendo neuropathic pain: emergency medicine
Opioids – Mechanism of Action
Act at the level of the spinal cord and the CNS
- Decrease neurotransmitter release
- Block postsynaptic receptors
- Activate inhibitory pathways
Advantages of Opioids?
Highly effective
Range of duration of effect
various routes
Disadvantages of Opioids?
Side effects = Dose-related; from nausea, vomiting, constipation, drowsiness, to respiratory depression, hypotension, sedation, dependency
Interaction =
- alcohol = increase hypotensive and sedative effects
- MAOI increases CNS excitation/inhibition
- SSRI / TCA increases sedation
- carbamazepine decreases plasma conc. of methadone
cimetidine (ulcer healing) g inhibit opioids metabolism
Opiods working on d receptors inhibit what area?
CNS and peripheral sensory neurons Can contribute to analgesia
Opiods working on μ receptors inhibit what area?
CNS, spinal cord, peripheral sensory, GI tract
Responsible for most analgesic effects and side effects
Most analgesic opioids are μ-receptor agonists
Opiods working on receptors inhibit what area?
CNS, Spinal Cord, Peripheral Sensory Neurons
Sedation & dysphoria, but few side effects
Does not contribute to dependence
Pure Agonists
Typified by morphine-like drugs
Have high affinity for μ-receptors; low affinity for δ & κ
Partial agonists & Mixed Agonist-Antagonists
e. g. nalorphine: mixed effects on μ-receptors
e. g. pentazocine & cyclazocine: (-) at μ-, but partial (+) on δ- & κ-
Antagonists
Block the actions of opiates
e.g. naloxone and naltrexone; treatment of heroin/morphine overdose
Serotonin and Noradrenaline Reuptake Inhibitors (SNRI)
Serotonin and noradrenaline mediate descending inhibition of ascending pain pathways in the brain and spinal cord
Highly effective for neuropathic pain, but not in all patients Actions are independent of their antidepressant effects
Selective serotonin reuptake inhibitors (SSRI)
Serotonin and noradrenaline mediate descending inhibition of ascending pain pathways in the brain and spinal cord
Not particularly effective analgesics
Appear to work well in the disease environment, e.g. diabetic- or HIV-related neuropathy e.g. paroxetine, citalopram
Duloxetine
Prescribed for peripheral neuropathy, particularity diabetic neuropathy.
Side-effects include nausea, somnolence, insomnia, dizziness
Cautions / Contraindications:
Epilepsy, cardiac disease, diabetes, angle closure glaucoma, pregnancy / breast feeding
Venlafaxine
Prescribed for diabetic neuropathy
Side-effects include nausea, sedation, headache and dizziness.
Cautions / Contraindications:
Epilepsy, cardiac disease, diabetes, angle closure glaucoma, pregnancy / breast feeding
Antiepileptic Agents mechanism of action?
Inhibit of voltage gated Na+ channels and Ca2+ channels
Inhibit Glutamate, g-Aminobutyric Acid (GABA) & Glycine receptors
Inhibit action potential firing this prevents impulse transmission
limit neuronal excitation and enhance neuronal inhibition
Carbamazepine
glossopharyngeal neuralgia, post herpetic neuralgia, trigeminal neuralgia, and diabetic neuropathies
Gabapentin
various neuropathic pain states;
complex regional pain syndrome, deafferentation neuropathy of the face, postherpetic neuralgia, sciatic type pain, neuropathy.
Local Anaesthetics mechanism of action?
Inhibit of voltage gated Na+ channels or NMDA receptors
Prevent nerve-nerve cell communication
Inhibit firing and prevent impluse transmission
Lidocaine
Na-Channel Blocker
Effective in non-cancer patients
Given via IV
Side effects: CNS effects (confusion), respiratory depression, convulsions, hypotension, bradycardia
Ketamine
Blocker of Glutamate Receptors (NMDA Subtype).
Injectable, but not favoured due to side effects
Side effects: Hypertension, tachycardia, tremor, diplopia, myocardial depression
