Analgesics

Question 1

Opioids - basic overview

Answer 1

Modify the transmission of pain signals and the subjective perception of pain

Question 2

Antidepressants and Antiepileptics - basic overview

Answer 2

Trigeminal neuralgia
Neuropathic pain (which is resistant to opioids)

Question 3

Local Anaesthetics - basic overview

Answer 3

Particularly effective for severe intractable or crescendo neuropathic pain: emergency medicine

Question 4

Opioids – Mechanism of Action

Answer 4

Act at the level of the spinal cord and the CNS

1. Decrease neurotransmitter release
2. Block postsynaptic receptors
3. Activate inhibitory pathways

Question 5

Advantages of Opioids?

Answer 5

Highly effective
Range of duration of effect
various routes

Question 6

Disadvantages of Opioids?

Answer 6

Side effects = Dose-related; from nausea, vomiting, constipation, drowsiness, to respiratory depression, hypotension, sedation, dependency

Interaction =

1. alcohol = increase hypotensive and sedative effects
2. MAOI increases CNS excitation/inhibition
3. SSRI / TCA increases sedation
4. carbamazepine decreases plasma conc. of methadone
   cimetidine (ulcer healing) g inhibit opioids metabolism

Question 7

Opiods working on d receptors inhibit what area?

Answer 7

CNS and peripheral sensory neurons Can contribute to analgesia

Question 8

Opiods working on μ receptors inhibit what area?

Answer 8

CNS, spinal cord, peripheral sensory, GI tract
Responsible for most analgesic effects and side effects
Most analgesic opioids are μ-receptor agonists

Question 9

Opiods working on receptors inhibit what area?

Answer 9

CNS, Spinal Cord, Peripheral Sensory Neurons
Sedation & dysphoria, but few side effects
Does not contribute to dependence

Question 10

Pure Agonists

Answer 10

Typified by morphine-like drugs

Have high affinity for μ-receptors; low affinity for δ & κ

Question 11

Partial agonists & Mixed Agonist-Antagonists

Answer 11

e. g. nalorphine: mixed effects on μ-receptors

e. g. pentazocine & cyclazocine: (-) at μ-, but partial (+) on δ- & κ-

Question 12

Antagonists

Answer 12

Block the actions of opiates

e.g. naloxone and naltrexone; treatment of heroin/morphine overdose

Question 13

Serotonin and Noradrenaline Reuptake Inhibitors (SNRI)

Answer 13

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

Question 14

Selective serotonin reuptake inhibitors (SSRI)

Answer 14

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

Question 15

Duloxetine

Answer 15

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

Question 16

Venlafaxine

Answer 16

Prescribed for diabetic neuropathy
Side-effects include nausea, sedation, headache and dizziness.
Cautions / Contraindications:
Epilepsy, cardiac disease, diabetes, angle closure glaucoma, pregnancy / breast feeding

Question 17

Antiepileptic Agents mechanism of action?

Answer 17

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

Question 18

Carbamazepine

Answer 18

glossopharyngeal neuralgia, post herpetic neuralgia, trigeminal neuralgia, and diabetic neuropathies

Question 19

Gabapentin

Answer 19

various neuropathic pain states;
complex regional pain syndrome, deafferentation neuropathy of the face, postherpetic neuralgia, sciatic type pain, neuropathy.

Question 20

Local Anaesthetics mechanism of action?

Answer 20

Inhibit of voltage gated Na+ channels or NMDA receptors
Prevent nerve-nerve cell communication
Inhibit firing and prevent impluse transmission

Question 21

Lidocaine

Answer 21

Na-Channel Blocker
Effective in non-cancer patients

Given via IV

Side effects: CNS effects (confusion), respiratory depression, convulsions, hypotension, bradycardia

Question 22

Ketamine

Answer 22

Blocker of Glutamate Receptors (NMDA Subtype).
Injectable, but not favoured due to side effects
Side effects: Hypertension, tachycardia, tremor, diplopia, myocardial depression