Analgesia Flashcards
Pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
Types of pain
- nociceptive - stimulation of nociceptors
- neuropathic - pain signal generated by pathological processes in CNS or PNS
- psychogenic - no apparent organic basis
WHO pain ladder
- Non-opioid (paracetamol/NSAID)
- Weak opioid (codeine) & non-opioid
- Strong opioid (morphine) & non-opioid
Plus adjuvant analgesia if required at all steps
paracetamol
Analgesic and antipyretic actions
Minimal interactions or adverse effects
Used alone for mild to moderate pain or in combination for moderate to severe pain
Adult dose paracetamol
500mg tablets
2 tablets every 4-6 hours
Max of 8 tablets a day
In low weight adults - halve dose
Paracetamol dosing for children
Soluble tablets - 500mg
Paracetamol suspension 120mg/5ml or 250mg/5ml
Use age banding and consult child BNF
How do NSAIDs work
Inhibit prostaglandin synthetase (cyclo-oxygenase)
- cox 1 - constitutive - protects gastric mucousa
- cox 2 - inducible - inflammation
Anti-inflammatory activity leads to pain relief
Examples of NSAIDs
Ibuprofen, diclofenac, aspirin (rarely used)
Ibuprofen dosing
Adults: - 400mg tablets, 1 tablet 4x/day - can be increased if necessary to max daily dose of 2.4g - maintenance dose: 600mg-1.2g a day CHILDREN - age banding, consult BNF - tablets 200mg or supsension 100mg/5ml
Diclofenac
- NSAID used for moderate inflammatory or post-op pain
- Adults: 50mg tablets - 1 tablets 3x/day, or sustained rlease preparation
- not recommended for children
- stronger than ibuprofen
Drug-drug interactions with NSAIDs
- increased risk of bleeding with antiplatelets, anticoagulants and SSRI’s
- increased risk of AKI when used with nephrotoxins
Adverse effects of NSAIDs
- GI - gastritis, bleeding, peptic ulcer
- Cardio - MI, stroke
- Renal dysfunction
- Hypersensitivity reactions in a small proportions of asthmatics
How to avoid NSAID problems
- prescribe lower risk drugs at lowest recommended dose
- do not use more than 1
- do not prescribe in patients with hypersensitivity
- prescribe alongside a PPI in patients with previous/active peptic ulcer disease
Action, use and examples of weak opioids
- act on CNS to alter the perception of pain
- used for moderate-severe pain
- e.g. codeine phophate and dihydrocodeine
ADRs of weak opiods
- nausea
- constipation
- dependence
Dosing of weak opiods
ADULTS
- Codeine phosphate 30mg tablets: 1-2 tablets 4x/day (max 240mg/day)
- Dihydrocodeine 30mg tablets: 1 tablet 4x/day (max 120mg/day????)
Not recommended for use in kids due to morphine toxicity
Problems with combination agents
- reduction of scope to titrate individual componenets
- increased with of s/e
- increased danger from overdose
Tramadol - mechanism, use and dose
- opiod analgesic with enhanced 5HT and adrenergic pathways
- for moderate to severe pain
- adult dose: 50-100mg every 4 hours, max daily dose 400mg
Problems with tramadol
- subject to abuse
- s/e: n&v, drowsiness, respiratory depression, hypotension
Strong opiods - use, mechanism and examples
- for severe pain
- act on mu and kappa receptors in CNS
- analgesia/euphoria/sedation –> dependence
- morphine, fentanyl, oxycodone, pethidine
Contraindications to strong opiods
respiratory depression, hypotension, liver impairment
Strong opiods - dosing in adults
pethidine 50mg tablets
- 50-100mg every 4 hours - max 450mg
Problems with pethidine (strong opioid)
- metabolised to norpethidiine which can accumulate in renal impairment
- can stimulate the CNS and cause seizures
Adjuvant agents - what are they, were do they act, what are they used for
- drugs intended for indications other than pain, but are analgesic in select cirmcumstances
- act centrally
- used at lower doses than their usual indications
- e.g. TCA’s for neuropathic pain, AEDs for neuropathic pain and trigerminal neuralgia, Anxiolytics for facial and back pain
Adjuvant agents for neuropathic pain
TCA’s
- amitryptiline - 10mg/day increased up to 75mg
- noritriptyline, dosulepin
Antiepileptics
- gabapentin - 300mg 3x/day, up to 3.6g/day
- carbamazepine - 100mg 1-2x/day, up to 1.6g (requires FBC and LFT monitoring)
Adjuvant agents used for facial and back pain
Anxiolytics
- benxodiazepines (diazepam 2mg 3x/day)
- short course - subject to abuse
Cautions with analgesia in liver disease
- increased risk of bleeding with NSAIDs
- caution with paracetamol
- opiods may be slowly metabolised and precipitate encephalopathy
Cautions with analgesia in renal disease
- NSAIDs may further increase renal impairment
- elimination of some drugs decreased - give lower doses
