Neurology: neurological drugs, pain and analgesia Flashcards
Define pain:
unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
What is nociceptive pain?
caused by stimulation of intact primary afferent nerves responding to stimuli approaching or exceeding harmful intensity (nociceptors)
What is neuropathic pain?
pain signal is generated ectopically and often in the absence of ongoing noxious events by pathologic processes in the peripheral or centra nervous system e.g. phantom limb
What is psychogenic pain?
no apparent organic basis / strict diagnostic criteria
What does allodynia mean?
central pain sensitization following normally non-painful stimulation.
it can lead to the triggering of a pain response from stimuli which do not normally provoke pain.
What are the targets for pain control?
source of pain nociceptive substances e.g. prostaglandins, cytokines nerve transmitter e.g. serotonin modulators of spinal cord and brain emotional reaction to pain
What are the basics of the WHO pain ladder?
1 - Non-opioid
2- Weak opioid
3 - strong opioid
plus adjuvant analgesia if required e.g. anticonvulsants / anti-depressants
What factors are important to find out to help treat pain?
SOCRATES - helpful to determine aetiology
- important to start at an appropriate level of the pain ladder
- titrate up and down
What are the principles of good pharmacological control of pain management?
Pre-emptive treatment is useful e.g. post-operative pain relief
Regular administration times will reduce breakthrough pain
Later in the course, PRN treatment may be more suitable
Re-evaluate treatment changes regularly so that patient’s don’t suffer unnecessarily
What are the key facts about paracetamol?
analgesic effects - ? inhibits prostaglandins in CNS additional anti-pyretic effects no anti-inflammatory actions minimal interactions / side effects different forms - oral, rectal and IV suitable for children at right dose Uses: - mild/moderate pain on own - moderate / severe pain in combo
What is the dosage of paracetamol for mild to moderate pain in adults?
adults >50kg
500mg - 2 tablets taken every 4-6 hours with max of 8 tablets per day
if low body weigh <50kg then consider only 1 tablet at a time
What the beneficial side effect of paracetamol and NSAIDs?
antipyretic effect - useful for febrile illness - can be used to control ongoing pyrexia
What are the key facts about NSAIDs?
inhibitors of prostaglandin synthetase (cyclo-oxygenase)
- COX-1 constituitive - protects gastric mucosa
- COX-2 inducible, inflammtory
anti-inflammatory activity leads to pain relief
GI side effects common
examples: ibuprofen and diclofenac
What is the dosing of ibuprofen in adults?
tablets 400mg
1 tablet to be taken four times a day preferably after food
can be increased if necessary to a max dose of 2.4g per day
maintenance dose of 600mg to 1.2g may be adequate
What is the dosing of diclofenac in adults?
diclofenac sodium tablets - 50 mg
1 tablet 3 x a day preferably after food
dont exceed recommended daily dose (150mg/day)
sustained release preparations are available
not recommended in children
What are the main risks of NSAIDs?
risk of bleeding
- potentiated by anti-platelets and anti-coagulants (even lose dose aspirin)
- increased risk of bleeding with SSRIs (drug interaction)
can increase risk of AKI when used with nephrotoxins
Other SE:
- cardiovascular risk
- renal dysfunction
- GI - gastritis, bleeding
- hypersensitivity reactions - rashes, angioedema, bronchospasm
How can you prevent the problems with NSAIDs?
prescribe NSAIDs associated with lower risk start at lowest recommended dose don't use more than one NSAID avoid in pts with previous hypersensitivity to whom aspirin or any other NSAID avoid in pts with previous or active peptic ulcer prescribe PPI (lanzopraole) (gastro protection)
What are some examples of weak opioids and how do they work ?
codeine phosphate, dihydrocodeine
act on CNS to alter perception of pain but have no anti-inflammatory effect
moderate to severe pain
adverse effects can be unpleasant = constipation, nausea
not suitable or long term use due to ADRs
What is the dosing of weak opioids?
codeine phosphate - 30mg adults
- 1-2 tabs 4x day = max 240g daily dose
- can be IM
dihydrocodeine - 30mg tabs
- 1 tab 4x day - max 240g daily dose
What are the problems with combination agents? (e.g. paracetamol- opioid or NSAID- opioid)
reduction of scope to titrate individual components
increased risk of side effects with low dose combo
increased danger of overdose
What are some examples of combo agents?
co-codamol = paracetamol and codeine co-dydramol = paracetamol and dihydrocodeine co-codaprin = codeine and aspirin tramacel = tramadol and paracetamol codaden continus = codeine and ibuprofen
What is tramadol?
opioid analgesic and enhanced 5ht and adrenergic pathways
moderate to severe pain
side effects: N+V, drowsiness, respiratory depression, hypotension
Adult dose: 50-100mg every 4 hours
max dose 400mg per day
What are some examples of strong opioids?
severe pain
- morphine
- fentanyl
- oxycodone
- pethidine
How do strong opioids work?
act on mu and kappa receptors in CNS
many different formulations - tablets, syrup, sub cut, IV
analgesic/ euphoria/ sedation
repeat use associated with dependence
avoid in respiratory depression, hypotension and in liver impairment
What is the dosing for pethidine?
50mg tabs
- orally 50-150mg every 4 hours
- max daily dose - 450mg
- metabolise to norpethidine (can accumulate in renal impairment)
- stimulate the CNS and cause seizures
What is meant by patient controlled analgesia?
delivers boluses of opioid analgesia
dedicated delivery device
careful settings - bolus dose control, time limit control, overrides
allow better control of pain esp following major surgery e.g. major abdo surgery
What are adjuvant agents?
drugs intended for indications other than pain but that are analgesic in select circumstances
inc at every step of ladder as additional consideration
act as centrally acting analgesics
used at lower doses than their usual indications
combo to provide multimodal approah
examples:
- tricyclic antidepressants - amitryptyline, dosulepin
- anti-epileptics - pregabalin, gabapentin
- anxiolytics - diazepam
What are tricyclic antidepressants?
for neuropathic pain - much lower dose than for depression
amitriptyline = unlicensed indication
10mg daily at night, gradually increased to 75mg daily
SE: sedation/drowsiness, antimuscarinics effects
caution - dangerous in overdose
alternatives = nortriptyline, dosulepin
What are antiepileptics?
neuropathic pain e.g. trigeminal neuralgia
- gabapentin= 300mg 3x day, increased gradually according to response, 3.6g max daily dose
- carbamazepine = 100mg one to two x day, increased according to response, 1.6g max daily dose, require bt monitoring, various drug-drug interactions
What are anxiolytics?
adjuvant in various pain conditions including facial pain and back pain
- benzodiazepines - adjuvant to pain disorders
- esp useful to reduce associated muscle spasms
- lower doses than for hypnotic use
- diazepam - 2mg - 1 tab 3x day
- short courses only recommended, susceptible to abuse
When is opioid dependence irrelevant?
generally irrelevant in terminal care and acute pain
only relevant if addicts try to persuade you to prescribe
What drugs do you need to be careful of prescribing in liver disease and why?
NSAIDs - risk of bleeding
Paracetamol - caution with regular, high doses
Opioids - slowly metabolised and precipitate encephalopathy in liver failure
What drugs do you need to be careful of prescribing in renal disease and why?
NSAIDs - further increase renal impairment
elimination of some drugs decreased therefore lower doses required
What are the do’s and don’ts in prescribing analgesics to children?
base it on suitabilty for the condition and the child
NSAIDS and paracetamol usually ok - prescribe based on weight and age
dosing errors are common
do NOT prescribe aspirin - risk of reye’s syndrome
be aware of codeine as people respond very differently
sugar free meds should be prescribed where possible
What are some other modalities of pain management?
acupuncture
transcutaneous electrical nerve stimulation
topical anaesthesia
nerve block/epidural
