Analgesic Drugs Flashcards
Peripheral sensitisation
Increases the action of the nociceptive stimuli in order to reduce subsequent injury to the area
Effect of descending inhibition of nociception
Decreases the pain felt by acting on the spinal cord.
Types of analgesic drugs
Opiate drugs
NSAIDs (non-steroidal anti-inflammatory drugs)
Other analgesics
WHO pain ladder
Mid pain - NSAIDs (aspirin, ibuprofen)
Moderate pain - low potency opioids (codeine, buprenorphine)
Severe pain - high potency opioids (morphine, fentanyl)
Effects of NSAIDs
- Anti-inflammatory (paracetamol is not, we don’t know why)
- Anti-pyretic (decrease fever)
- Analgesic
All effects related to decreased prostaglandin synthesis
Effects are additive, but toxicity is not
Examples of NSAIDs
Aspirin, ibuprofen, diclofenac, paracetamol
Decreased synthesis of prostaglandins does what?
It decreases the action of bradykinins, VGNa And Wr-1.
NSAIDs and COX
NSAIDs inhibit both COX-1 and COX-2
COX converts Arachidonic acid to protaglandin H2 in the production of protaglandin E2
Disadvantage of NSAIDs
PGs are involved in a lot of processes, so decreasing them leads to:
* severe gastric irritation
* kidney disorders
* paracetamol overdose
COX-2
Only COX-2 causes the desired effect.
* COX-1 is widespread throughout the body and causes side effects
* COX-2 is just involved in the inflammatory response
COX-2 inhibitors
Rofecoxib (vioxx) was a very effective treatment for rheumatoid arthritis, but had a small chance of cardiac side effects.
Celecoxib (celebrex) does the same thing but hasn’t been pulled because side effects are known.
Other NSAIDs also have this cardiac risk, but the chances are very low.
Neuropathic pain
Pain unrelated to peripheral nociception
Sometimes called pathological pain
Generally don’t respond to opioids or NSAIDs
Causes of neuropathic pain
Generally by peripheral nerve damage
Peripheral nerve terminal damage or infection
Spinal damage
Thalamic stroke
Tricyclic antidepressants
e.g. imipramine
Work for shingles-caused neuropathic pain
Antiepileptic drugs
e.g. gabapentin
Neuropathic pain
Cannabinoid receptor agonists
Central and peripheral effects
Neuropathic pain (esp. multiple sclerosis)
Glutamate receptor blockers
MK801
Block afferent transmission
Severe side effects
Neurokinin receptor blockers
Block central sensitization
Has to be taken before pain such as before surgery
Nociceptor blockers
TRPV1, P2X3, sodium channel
Block detection of noxious signals