W15 53 analgesics and pain management Flashcards
What are the types of pain?
Nociceptive - caused by (mechanical, thermal or chemical) stimulation of peripheral nerve fibres responding to stimuli approaching or exceeding harmful intensity
Neuropathic - caused by aberrant (abnormal) somatosensory activity due to damage or disease affecting the peripheral or central nervous system
Psychogenic - related to emotional state - made up
What are the possible targets for pain control?
Source of pain
Nociceptive substances eg PGs
Nerve transmitter substances eg serotonin
Modulators in spinal cord and brain eg morphine, opioid receptors part of the modulation
Emotional reaction to pain
What is the WHO pain ladder?
Step 1 - non-opioid, eg paracetamol
Step 2 - weak opioid, eg codeine, plus non opioid
Step 3 - strong opioid eg morphine, plus non opioid
What is good pharmacological control of pain post-procedure?
Post-op taking analgesics before LA has worn off can improve pain control
Regular administration times, eg every 6 hrs, will reduce breakthrough pain
Then PRN - pro-ray nata, as and when required
What is analgesia?
The absence of pain in response to stimulation which would normally be painful
What are adjuvant analgesics and give examples?
Medicines that are intended for indications other than the pain, but can also be used as analgesics in select circumstances (eg anticonvulsants and antidepressants).
What is the efficacy of different analgesic agents for pain relief?
Weak opioids may be less effective for odontogenic pain
Aspirin isn’t good for dental pain
A good combination = paracetamol and ibuprofen
What is a beneficial side effect of taking paracetamol in combo with ibuprofen?
Can have a beneficial antipyretic effect
(However this might mask post-opaerative signs of infection)
What are the facts about paracetamol?
Analgesic actions (potentially by inhibition of PGs in CNS)
Additional antipyretic action helpful in some dental conditions
NO anti-inflammatory action
Minimal interactions/adverse effects
Suitable for children (in correct dosing)
Used for mild/moderate pain alone or moderate/severe pain in combination therapy
What do NSAIDs do?
Inhibit prostaglandin synthesis (by inhibiting cyclo-oxygenase)
Anti-inflammatory activity leads to pain relief
What do COX 1 and 2 do?
COX-1 - constitutive protects gastric mucosa (try to avoid targeting)
COX-2 - inducible inflammatory, also renal (more targeted)
When should you restrict ibuprofen usage?
Restrict to less than 5 days in patients taking anti-hypertensive drugs
What odontogenic pain is good to be relieved by NSAIDs?
Inflammatory origin - eg pulpitis
Eg ibuprofen, diclofenac
Aspirin less appropriate due to risk of bleeding following extraction or other minor surgery
Which NSAIDs can you use in children?
Ibuprofen at smaller doses
Not diclofenac or aspirin
What NSAID drug-drug interactions are there?
Main issue is the risk of bleeding:
Potentiated by antiplatelets and anticoagulants
Increased risk of bleeding with SSRIs
What NSAID adverse effects are there?
Renal dysfunction
Gastro-intestinal side-effects (gastritis, bleeding)
Hypersensitivity reactions, eg rashes, angioedema, bronchospasm
What should you prescribe to patients with a history of previous or active peptic ulcer disease who require an NSAID?
Prescribe a proton pump inhibitor (PPI), eg lansoprazole, to be taken once daily during NSAID treatment. To offset acid in the stomach and reduce risk of bleeding.
How can you prevent NSAID problems?
Prescribe lower risk NSAIDs
Start at lowest dose
Don’t combine NSAIDs
Avoid in pt with previous reactions to aspirin or other NSAIDs
Avoid concomitant treatment in those taking low dose aspirin
Give examples of weak opioids
Codeine phosphate, dihydrocodeine
What do opioids do?
Act on the CNS to alter the perception of pain, but have no anti-inflammatory properties
When are opioids used?
For moderate to severe pain (but ineffective in dental pain)
What are some adverse effects of weak opioids?
Can be unpleasant eg nausea, constipation
Variable metabolism amongst different people
Ultra-rapid metabolisers will convert more to morphine and vice versa
What are the problems with combination agents?
Reduction of scope to titration individual components
Increased risk of side effects with low dose combinations without significant additional relief of pain
Increased danger from overdose
Examples of combination drugs?
Co-codamol - codeine phosphate and paracetamol
Co-dydramol - dihydrocodeine and paracetamol
Co-codaprin - codeine phosphate and aspirin
What happens in a paracetamol overdose - what is the mechanism of toxicity?
NAPQI = toxic intermediate accumulation as can’t be conjugated with glutathione
Mechanisms of NAPQI-induced hepatic injury include - glutathione depletion, direct oxidising and arylating effects
When you overwhelm the usual metabolic pathway, you create N-acetyl-p-benzoquinoneimine, which is a toxic substance causing liver and renal damage
What is tramadol?
Opioid analgesic and enhanced 5HT and adrenergic pathways
Indicated for moderate to severe pain
Side effects = N&V, drowsiness, respiratory depression, hypotension
Give examples of strong opioid agents
Morphine
Fentanyl
Oxycodone
Pethidine
What do strong opioids do?
Act on Mu and Kappa receptors in the CNS
Analgesic, euphoria, sedative effects
When are strong opioids used?
For severe post-operative pain
Repeat use can be associated with dependent, can become tolerant
When should you avoid strong opioids?
Respiratory depression, hypotension and liver impairment
Adverse effect of strong opioids?
Metabolised to norpethidine - which can accumulate in renal impairment
Can stimulate the CNS and cause seizures
Examples of adjuvant agents
Used at a lower dose than their usual indications
Tricyclic antidepressants - eg amitriptyline, dosulepin
Anti epileptic agents - eg pregabalin, gabapentin, carbamezapine
Anxiolytics - eg diazepam
When is gabapentin usually used?
For trigeminal neuralgia, not much in epilepsy
When is carbamezapine use?
Epilepsy
Widely used in facial pain clinics and complex TMD
What anxiolytics are used for things other than their intended indication?
Benzodiazepines (eg diazepam) can be used in conscious sedation and muscle relaxation
Used in lower doses than those given for hypnotic use
Useful in trismus from muscle relaxation etc
What might you use to treat chronic oral and facial pain?
Eg persistent idiopathic facial pain or Temporomandibular dysfunction
Prolonged use of analgesics/adjuvant agent treatment
Specialist referral and psychological support
What painful acute problems can affect the mucosa and how to treat?
Acute herpetic gingivostomatitis, aphthous ulceration, erythema multiforme
Maybe better treated topically
Eg benzydamine hydrochloride oral rinse or spray
When is opioid dependence an issue?
Generally irrelevant in terminal care or acute pain
Relevant if addicts try to persuade you to prescribe (self-inflicted injury, refuses surgical intervention, allergies to simple analgesia)
What should you be cautious of with analgesics and liver disease?
Risk of bleeding increased - NSAIDs
Caution with paracetamol (regular, high dose)
Opioids may be slowly metabolised and precipitate encephalopathy in liver failure
What should you be cautious of with analgesics and kidney (renal) disease?
NSAIDs may further increase renal impairment
Elimination of some drugs decreased - lower doses required
What should you take into consideration with analgesics and children?
Choice of analgesic based on suitability for the condition and the child
Usually NSAIDs/paracetamol suitable
Prescribe by weight or age banding
Dosing errors are common
DO NOT prescribe aspirin to children <16yrs - risk of Reye’s syndrome
Codeine phosphate only for severe pain in >12yrs. BE VERY AWARE as children respond differently due to variable metabolism.
Sugar-free medicines should be provided where possible
