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Outline
1. Pain Receptors 2. WHO Pain Ladder3. Pain Treatment
-> Types of Analgesics- NSAIDs- Opioids
What are the 2 main types of pain?
Neuropathic pain
Nociceptive pain• arises from stimulation of specific pain receptors – free nerve
endings• ‘groan’ pain from C fibres and ‘ouch’ pain from A-delta fibres• Tx: NSAIDS & Opioids
• E.g. phantom limb pain, trigeminal neuralgia, post-stroke pain• arises from PNS and CNS• Tx: Tricyclic antidepressants (TCAs) & Antiepileptic drugs
(AEDs)
WHO Pain Ladder
Step 1 - Mild To Moderate non-opioids = NSAIDs (e.g. aspirin) and paracetamolStep 2 - Moderate To Severemild opioids like codeine +/- non-opioids Step 3 - Severestrong opioids like morphine with or without non-opioids
NSAIDs
Main Uses1. Anti-inflammation2. Anti-pyretic3. Analgesic4. Anti-coagulant
Mechanism Of Action• block prostaglandin (PG) production by inhibiting COX
enzymes• COX enzymes normally breakdown arachidonic acid to
produce PGs
NSAIDs - Examples
• aspirin • ibuprofen = considered to have quite weak action• naproxen = strong, low side effects • diclofenac • indomethacin = strong, high side effects • COX 2 inhibitors:
- Celecoxib- Parecoxib
NSAIDs - Side Effects
• can delay healing so not used post-operatively or post-partum• GI = vomiting, nausea, diarrhoea, bleeding/ulceration• CV = thrombosis • reye’s syndrome is specific to aspirin and is why not recommended
<16 use aspirin
Intoxication • salicylism = acute or chronic digestion of NSAIDs• auditory, pulmonary, CV, CNS, GI, renal failure, coma• treatment = fluid replacement, haemodialysis, activated charcoal,
lorazepam/diazepam for seizures
Opioids
Main Uses1. Analgesic2. Anaesthesia 3. Cough suppressant 4. Anti-diarrhoeal
Routes Of Administration • IV = rapid effect• IM • Rectal = decreases N&V but slow• Oral = easy to administer but slow • Sublingual • Epidural• PCA = need a catheter (invasive)• Patches = can cause local irritation
Opioids - Types
Pure Agonists • strong activity = morphine, diamorphine and tramadol• weak activity = codeine and dihydrocodeine
Partial Agonists• buprenorphine • pentazocine
Antagonists• naloxene (1/2 hours half-life)• naltrexone (10 hour half-life)
Opioids – Mechanism Of Action decrease neuronal transmissions by:● decrease opening of voltage
dependent calcium channels (VDCC)
● which decreases calcium release from intracellular stores
● increase potassium outflow of cells ● decrease exocyotosis
metabolism: primarily in the liver the metabolites are highly water
soluble and excreted in urine
Opioid Side Effects & Overdose
● Miosis ● Respiratory
depression● Decreased
consciousness
3 cardinal signs of intoxication:
● Nausea/Vomiting● Decreased gastric motility =
constipation● Anaphylaxis● Psychiatric changes, especially
tramadol (often have hallucinations)● Tolerance & dependence -
addiction/withdrawal● AND the major 3….
Treatment for OD:
● opioid antagonists = naloxone & naltrexone (whichever is appropriate re: half-life)
● coma cocktail = naloxone, oxygen, glucose and thiamine