Pain & Analgesia

Manpreet &

Olivia

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

Thank you! Any Questions?