Week 10: Pain and Musculoskeletal - Opioids, Non opioids, NSAIDs, Arthritis Flashcards
What is pain?
- Signalling system - mechanical and nerve
- Unpleasant sensory and emotional experience
- Perception (independent of person experiencing it)
- No objective measuring system
- Symptom of underlying disease/injury (bodies warning system)
Pain is the activation of pain receptors
- A delta and C sensory fibers
- May be due to misfiring/dysfunction of nerves
Classification of pain
- Acute and chronic
- Types of pain
Acute
- Usually has anxiety and hyperactivity of SNS causing tachycardia, increased respiratory rate and increased blood pressure
Chronic
- Usually no sympathetic hyperactivity and may have depressed mood, fatigue, loss of appetite
Types of pain:
Nociceptive
- Pain related to damage of somatic or visceral tissue due to trauma or inflammation
- Examples = rheumatoid arthritis, osteoarthritis, gout
Non-nociceptive Neuropathic pain
- Pain related to damage of peripheral or central nerves
- Examples = painful diabetic peripheral neuropathy, postoperative neuralgia
Sensory hypersensitivity
- Pain without identifiable nerve or tissue damage
- Thought to result from persistent neuronal regularization
- Examples = fibromyalgia
Non pharmacological management of pain
- PT/OT
- CBT, meditation, counseling
- Mobility aids
- Heat
- Rest
- Ice
- Compression
- Elevation
Treating pain - WHO analgesic ladder
Step 1
- Non opioid +/- adjuvant
- E.g. aspirin, paracetamol or NSAID
Step 2:
- Weak opioid for mild to moderate pain +/- nonopioid +/- adjuvant
- E.g. codeine
Step 3
- Strong opioid for moderate to severe pain +/- non opioid +/- adjuvant
- E.g. morphine
Opioids
- MOA
- Pharmacological effects
- Unwanted effects
MOA
- Act on opioid receptor on neuronal cell membrane in CNS and PNS (specifically mu receptor)
- Mimic endogenous opioid such as b endorphin to reduce transmission of pain impulse
- Produce analgesia, respiratory depression, sedation and constipation
- Reduce transmission of pain impulse by acting pre and post synaptically in spinal cord and by modulating descending inhibitory pathway from brain
Pharmacological effects
- Analgesia/cough suppression/antidiarrheal (codeine)
Unwanted effects
- Analgesic tolerance
- Physical dependence
- Respiratory depression
- Constipation
- Nausea, vomiting, sedation (tolerance often develops)
Weak opioids
- Codeine (metabolism, contraindications and cautions)
- Dextropropoxyphene
Codeine
- Metabolised by kidney to morphine
- Not proven to be effective at OTC dosages (prescription only)
- Contraindications and cautions
> Elderly (reduce dose due to increase risk of cognitive impairment, sedation, respiratory depression and falls)
> Hepatic impairment (reduce dose and monitor)
> Children (usually contraindicated under 12 use with caution)
> Pregnancy (caution close to delivery)
> Breastfeeding (Do not use)
> Renal impairment (avoid)
> Contraindicated in comatose, epilepsy, hypotension, shock and neonates
Dextropropoxyphen
- Lots of ADR
- Prescribe must write special application
Examples of strong opioids
- Tramadol
- Fentanyl
- Morphine
- Hydromorphone
- Oxycodone
- Pethidine
- Methasone (for opioid addiction)
- Buprenorphine (partial agonist - longer onset of action)
Strong opioids - Tramadol
- MOA
- Contraindications and cautions
MOA
- Technically not an opioid
- Structurally not opiate but exhibits opioid characteristics
- Binds mu receptor but 10 time less affinity than codeine
- Inhibits reuptake of NA and 5HT
Contraindications and cautions
- Elderly (avoid over 75; avoid CR)
- Hepatic impairment (reduce dose in severe impairment; avoid CR)
- Children (avoid use except under specialist)
- Pregnancy (caution close to delivery)
- Breastfeeding (avoid)
- Renal impairment (avoid CR)
- Contraindicated within 14 days of stopping MAOI or other serotonergics
- Same contraindications as codeine
Strong opioids - morphine
- ADR
- Contraindications and cautions
- Morphine is benchmark for comparing opioid equivalence
- Stronger opioids have higher affinity and/or efficacy for opioid receptors
- Higher incidence of ADR including sedation, respiratory depression, GI effects, addiction/dependence and tolerance
Contraindications and cautions
- Elderly (reduce dose and titrate slowly)
- Hepatic impairment (Avoid in severe)
- Children (avoid in neonates, only when indicated by specialist in older children)
- Pregnancy (caution close to delivery)
- Breastfeeding (avoid repeated doses)
- Renal impairment (reduce dose in mild/mod and avoid in severe)
- Contraindicated in comatose, endocrine abnormalities, epilepsy and hypotension
Opioid overdose and dependence
- Naltrexone
- Opioid overdose can be hard to treat due to severe withdrawal symptoms
> Use methadone in step wise manner
Naltrexone - opioid antagonist
- Reversibly blocks effects of opioid for 24-72 hrs
- After it wears of patient more susceptible to effects of opioids (fatal overdose)
Non opioid analgesics
- Indications
- Causes
Indications - Neuropathic pain (described as burning, electric shock, shooting pain) > Hyperalgesia > Allodynia > Hyperpathia
Causes
- Phantom limb pain
- Diabetic neuropathy
- Postherapetic neuralgia
- Herpes zoster
- Fibromyalgia
Non opioid analgesic treatment options
Neuropathic pain treatment options
- Paracetamol
- Topical capsaicin
- Antidepressant - may inhibit nociceptive transmission via inhibition of NA and 5HT reuptake (TCA, SSRI, SNRI)
- Antiepileptic - decrease excitability of neurons by modifying action of voltage gated Ca2+ channels - reduced release of P, NA, and glutamate (gabapentin, pregabalin)
Local anaesthetics
- MOA
- Examples
- Practice points
MOA
- Block sodium channels in order to reversibly interrupt peripheral nerve impulse conduction
- Block ability of nerve cell to depolarise and send pain signals to CNS
Examples
- Lignocaine
- Prilocaine
- Cocaine
Practice points
- All cause vasodilation, which can make drug leak into surrounding tissue, limiting duration of action
- Usually given along with adrenaline (powerful vasoconstrictor) to keep anaesthetic localised and increase duration of action
Paracetamol
- Class
- Indication
- MOA
- Practice points
Class
- Analgesic and antipyretic
Indication
- 1st line for mild to mod pain in several situation
- Well tolerated
MOA
- Analgesia MOA may include inhibition of central prostaglandin synthesis and possible effect on serotonergic pain pathways
- Antipyretic effect probably due to reduced production of prostaglandins
- Negligible anti-inflammatory effects
Practice points
- Hepatotoxicity with excessive use and overdose
- Increase risk of adverse effects in hepatitis or chronic alcohol use
- Works best taken regularly at max recommended dose (especially chronic)
- Safe for children approx 4 weeks
- Safe for pregnancy and breastfeeding
- Dangerous in large overdose (liver failure and death)
Overdose of paracetamol
- Factors increasing risk of hepatotoxicity
Factors increasing risk of hepatotoxicity due to paracetamol
- Increased frequency of dosing
- Using higher than recommended doses for prolonged period
- Malnourished or dehydrated
- Fasting or vomiting
- Taking with other drugs such as antiepileptics
Common cause of paracetamol induced liver damage is inadvertently taking 2 paracetamol containing preparations at once
NSAID - Non steroidal anti inflammatory drugs
- Effects
- Examples
Effects
- Analgesic
- Antipyretic
- Anti inflammatory
Examples
- Aspirin
- Ibuprofen
- Diclofenac
- Naproxen
- Indomethacin
NSAID
- MOA
- Practice points
- Contraindications
MOA
- Inhibit synthesis of prostaglandins by inhibiting cyclo-oxygenase (COX) 1 and 2
See diagram
Practice point
- Non is more effective than other
- Dependent on patient response
Contraindications (many)
- CVD
- Asthma
- Therapy with anticoagulants
- Renal impairment
- Dehydration
- PUD/GORD/GIT complication
- Elderly
- Pregnancy
- Impending surgery
