Neurology: neurological drugs, pain and analgesia

Question 1

Define pain:

Answer 1

unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage

Question 2

What is nociceptive pain?

Answer 2

caused by stimulation of intact primary afferent nerves responding to stimuli approaching or exceeding harmful intensity (nociceptors)

Question 3

What is neuropathic pain?

Answer 3

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

Question 4

What is psychogenic pain?

Answer 4

no apparent organic basis / strict diagnostic criteria

Question 5

What does allodynia mean?

Answer 5

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.

Question 6

What are the targets for pain control?

Answer 6

source of pain 
nociceptive substances e.g. prostaglandins, cytokines 
nerve transmitter e.g. serotonin 
modulators of spinal cord and brain 
emotional reaction to pain

Question 7

What are the basics of the WHO pain ladder?

Answer 7

1 - Non-opioid
2- Weak opioid
3 - strong opioid
plus adjuvant analgesia if required e.g. anticonvulsants / anti-depressants

Question 8

What factors are important to find out to help treat pain?

Answer 8

SOCRATES - helpful to determine aetiology

• important to start at an appropriate level of the pain ladder
• titrate up and down

Question 9

What are the principles of good pharmacological control of pain management?

Answer 9

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

Question 10

What are the key facts about paracetamol?

Answer 10

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

Question 11

What is the dosage of paracetamol for mild to moderate pain in adults?

Answer 11

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

Question 12

What the beneficial side effect of paracetamol and NSAIDs?

Answer 12

antipyretic effect - useful for febrile illness - can be used to control ongoing pyrexia

Question 13

What are the key facts about NSAIDs?

Answer 13

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

Question 14

What is the dosing of ibuprofen in adults?

Answer 14

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

Question 15

What is the dosing of diclofenac in adults?

Answer 15

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

Question 16

What are the main risks of NSAIDs?

Answer 16

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

Question 17

How can you prevent the problems with NSAIDs?

Answer 17

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)

Question 18

What are some examples of weak opioids and how do they work ?

Answer 18

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

Question 19

What is the dosing of weak opioids?

Answer 19

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

Question 20

What are the problems with combination agents? (e.g. paracetamol- opioid or NSAID- opioid)

Answer 20

reduction of scope to titrate individual components
increased risk of side effects with low dose combo
increased danger of overdose

Question 21

What are some examples of combo agents?

Answer 21

co-codamol = paracetamol and codeine 
co-dydramol = paracetamol and dihydrocodeine 
co-codaprin = codeine and aspirin 
tramacel = tramadol and paracetamol 
codaden continus = codeine and ibuprofen

Question 22

What is tramadol?

Answer 22

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

Question 23

What are some examples of strong opioids?

Answer 23

severe pain

• morphine
• fentanyl
• oxycodone
• pethidine

Question 24

How do strong opioids work?

Answer 24

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

Question 25

What is the dosing for pethidine?

Answer 25

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

Question 26

What is meant by patient controlled analgesia?

Answer 26

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

Question 27

What are adjuvant agents?

Answer 27

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

Question 28

What are tricyclic antidepressants?

Answer 28

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

Question 29

What are antiepileptics?

Answer 29

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

Question 30

What are anxiolytics?

Answer 30

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

Question 31

When is opioid dependence irrelevant?

Answer 31

generally irrelevant in terminal care and acute pain

only relevant if addicts try to persuade you to prescribe

Question 32

What drugs do you need to be careful of prescribing in liver disease and why?

Answer 32

NSAIDs - risk of bleeding
Paracetamol - caution with regular, high doses
Opioids - slowly metabolised and precipitate encephalopathy in liver failure

Question 33

What drugs do you need to be careful of prescribing in renal disease and why?

Answer 33

NSAIDs - further increase renal impairment

elimination of some drugs decreased therefore lower doses required

Question 34

What are the do’s and don’ts in prescribing analgesics to children?

Answer 34

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

Question 35

What are some other modalities of pain management?

Answer 35

acupuncture
transcutaneous electrical nerve stimulation
topical anaesthesia
nerve block/epidural