Analgesia Flashcards
Inflammatory pain
- Presentation
- Indicated analagesia
Presents
- Throbbing, aching
- Localised area
Drugs
- NSAID
- Paracetamol
Nociceptive/ somatic
- Presentation
- Causes
- Indicated analgesia
Sharp pain, localised
- Caused by activation of nociceptors in skin, muscles, bone
Drugs
- NSAIDs
- Paracetamol
- Opioids
Nociceptive- visceral
- Presentation
- Cause
- Indicated analgesia
Deep, aching
Poorly localised
Cramping
- Caused by activation of nociceptors from stretching, distension or inflammation
Drugs
- NSAIDs
- Paracetamol
- Opioids
- Neuropathic agents
Neuropathic
- Presentation
- Cause
- Indicated analgesia
Shooring, burning, hypersensitive
Tingling, numbing
Caused by direct damage to PNS/CNS
Drugs
- Neuropathic agents
Analgesics classifications
Simple
- NSAIDs
- Paracetamol
Opioids
Neuropathic agents
Paracetamol
- Dose
Normal dose
- 1g QDS
Liver impairment/ <50kg
- 500 mg QDS (max 15mg/kg IV)
NSAIDs
- Dosing
Ibuprofen
- 400mg TDS PO
Naproxen
- 250-500mg BD PO
NSAIDs side effects
GI bleeds/ Side effects
Nephrotoxic
- Decreases blood flow
- Na+ and water retension
Reyes syndrom
Drug interactions
- Warfarin
- Methotrexate
- Lithium
Asthma sensitivity
Prescribe PPI for preventative protection
- Lansoprazole 15mg OD
Weak opioids
- Indication
- Examples
- Metabolism
Indication
- Moderate pain
- Anti-diarrhoeal
Examples
- Codeine
- Hydromorphine (first line)
Metabolism
- Pro-drugs, have to be converted to morphine (codeine) or dihydromorphine (hydromorphine)
- Not metabolised in 1 in 10 caucasians or have ultrametabolisers
Weak opioids
- Doses
Codeine
- 30-60mg QDS
Dihydrocodeine
- 30mg every 4-6 hours.
Strong opioids
- Indication
- Examples
- Metabolism
Examples - Morphine - Oxycodone - Fentanyl--> patch more suitable for prolonged pain. Good for renal impariment patients
Strong opioids doses
- Morphine
- Oxycodone
Morphine
Naive- 5-20mg 1-2 hrs PRN
- Elderly= 2.5-10mg 2-4 hrs
- Renal impairment= 2.5-5mg. Not used if eGFR<30
Oxycodone
Naive- 5-10mg 2-4 hrs
Elderly= 1.25-5mg
Renal impairment
- 1.25-2.5mg
Opioid dose equivalents
Morphine IV/IM= 2x oral
Diamorphine s.c= 3x morphine oral
Oxycodone oral= x2 morphine oral
Nefopam
- Drug type
- Dose
- Side effects/ contraindications
Drug type
- Non-opioid/ NSAIDs
- Good alternative for opioid dependent patients.
Dose
- 60 mg TDS (30 in elderly)
Side effects
- Nausea
- Dizziness
- Urinary retention
- Dry mouth
- Pink urine
Ascending pain pathway
Spinothalamic tract:
- Nociceptors at site of tissue (somatic/ visceral)
- A-delta fibres transmits sharp, localised pain quickly.
- C fibers transmits dull, burning pain slowly - First order neurones synapses with second order neurones at dorsal horn
- Second order neurones cross spinal cord and ascending the anterior column to thalamus
- Third order neurones synapse from thalamus into somatosensory cortex.
Descending modulation of pain
- receptors
- Endogenous opioids
- Pain control centres
3 types of opiod receptors
- Mu, kappa, delta
- when activated, they hyperpolarised neurones and reduces their excitibility
Endogenous opioids activate opioid receptors
- Β-endorphins = mu opioid receptors
- Dynorphins = kappa opioid receptors
- Enkephalins = delta opioid receptors
Periaqueductal grey matter (PAG) in midbrain and rostral ventral medulla (RVM)
- Contains high levels of opioid receptors
- Descending fibres from PAG and RVM synapse with spinothalamic tract at dorsal horn via 5HT/NA neurone
- Inhibits communication between 1st and 2nd order neurone
WHO analgesia ladder
- Non-opioid +/- adjuvant
- NSAIDs, paracetamol - Add weak opioid
- Tramadol, codeine, dihydrocodeine - Replace weak opioid with strong opioid
- Morphine
- Oxycodone
- Fentanyl
- Diamorphine
- Alfentanil
- Hydromorphone
Pharmacological adjuvants
Corticosteroids
antidepressants
- Duloxetine
- Amitriptylline
- Mirtazepine
Antimuscarinics
Benzos
Ketammine
Bisphosphonates
Antiepileptics
- Gabapentin
- Pregaballin
Pharmacological effects of opioids
- Examples of use specific to effect
Analgesia
- Inhibition of spinothalamic tract
Psychotrophic
- Anxiolytic and euphoria
Respiratory depression
- Acts on respiratory centre in medulla
- Oramorph can be used in end stage COPD pts SOB
Suppresses cough reflex
- Codeine can be used for cough
Constipation
- Delays gastric emptying
- Inhibits peristalsis
- Codeine can be used for high output stoma.
Pharmacological adverse effects of opioids (5)
- Ways of overcome/ relieve adverse effects
Constipation
- Change medication or ad laxative
- Consider peripherally acting opioid antagonist in severe caes (naloxogel)
Nausea and vomiting
- Anti-emetic
Sedation
- Advice of this
Drug mouth
- Sugar free chewing gum
- Mouthwash
Pruritus
- Antihistamine
Symptoms of opioid toxicity
Drowsiness
Miosis
- Pinpoint pupils
Respiratory depression
Confusion, agitation
Hallucinations
Myoclonic jerks
Management of opioid toxicity
- Mild/ moderate
Mild-moderate
- Reduce/ stop drug
- Check renal + hepatic function
- Ensure adequate hydration
Severe (RR<8, decreased O2, unresponsive)
- Naloxone
Codeine
- Action
- dose
- Major side effect
- Morphine equivalence
Action
- Mu receptor
Dose
- 15-60mg PO QDS
- 240mg Max in a day
Major side effect
- Constipation
Morphine equivalence
- /10
Dihydrocodeine
- Action
- dose
- Major side effect
- Morphine equivalence
Action
- Semi-synthetic analogue of codeine
- Acts on Mu
Dose
- Same as codeine
- 15-60 PO QDS
Major side effect
- Constipation
Morphine equivalent= /10.
