Week 6 Flashcards
(47 cards)
Choice of medication
Based on underlying pain mechanisms
* Acute pain: regulated by the opioidergic system
* Persistent pain: associated with a neuropathic component where central sensitisation requires:
– a reduced role of opioids
– an increased contribution of adjuvant/other types of medications
Adjuvant Agents
- Used as supplements to make analgesics more effective,
or - As distinct primary therapy in certain painful conditions.
- May reduce opioid side effects by reducing the dosage used to obtain acceptable pain control.
- May also control symptoms and reduce analgesic requirements.
*Amitriptyline (Tryptanol)
*Carbemazepine (Tegretol)
*Pregabalin (Lyrica)
*Gabapentin (Neurontin)
*Diazepam (Valium)
*Dexamethasone
*Imipramine (Tofranil)
*Phenytoin (Dilantin)
Paracetamol
- Effective analgesic for Mild‐moderate pain
- Oral, IV, PR
- Soft tissue and musculoskeletal origin
Also: - Supplementation of opioids when managing moderate
to severe pain with opioid sparing effect
Evidence for effects on various central mechanisms: - prostaglandin production
- serotonergic, opioid, nitric oxide (NO) & cannabinoid
pathways - probable combination of interrelated pathways
Non‐Steroidal Anti‐Inflammatory Drugs (NSAIDs)
Mild‐to‐moderate pain
* Muscular‐skeletal inflammation and tissue injury e.g.
* Muscular aches
* Tissue sprains
* Osteoarthritis
* Rheumatoid arthritis
* Low back pain
* Headache
NSAIDs non selective
- Ibuprofen (Nurofen - oral)
- Naproxen (Naprosyn - oral)
- Diclofenac (Voltaren - oral)
- Indomethacin (Indocid -
oral/PR) - Ketorolac (Toradol - IM / IV)
NSAIDs cox-2 specific
- Celecoxib
(Celebrex – Oral)
NSAIDs long acting
- Meloxicam (Mobic - Oral)
- Preferential but not Cox 2
Opioids
- Moderate to severe pain: acute or persistent
- Act as agonists at receptor sites in the brain,
spinal cord and other sites outside of the CNS
3 Primary receptors: - mu (μ), delta (δ) and kappa (Ќ)
- Analgesia is mediated mainly via the μ receptor
Opioids types
Morphine: most commonly used, various routes
* Fentanyl: rapid action; strong; various routes
* Oxycodone: oral; used as a step down agent from IV opioids
* Hydromorphone: 5 x potent as morphine; various routes
* Methadone: oral, long action; for persistent pain
* Pethidine: less used, offers no advantage over other opioids
* Codeine: oral with other drugs e.g. paracetamol
* Buprenorphine: SL, IM, SC, TD; long action
Tramadol
- Synthetic, weak mu opioid receptor agonist
- Enhances noradrenergic (40%) and serotonergic (20%)
inhibition - Reduced incidence of respiratory depression
- Lower abuse potential
- Less constipating
- Oral/parenteral
Ketamine
- NMDA antagonist (N‐methyl‐D‐aspartate)
- Dissociative anaesthetic agent
- Ketamine treatment effective for relief of
postoperative pain - For acute and persistent pain
- Often used with an opioid for improved analgesia
& opioid sparing
Cannabis
- Cannabinoid and endocannabinoid systems: special
receptor molecules embedded in the brain and neural
pathways. - The receptors influence the flow of chemical signals to
the brain. - Cannabinoids bind with the endocannabinoid
receptors, suppress signals such as pain, nausea and
depression, boost signals of appetite and euphoria.
Anticonvulsants
Example: Gabapentin or Pregabalin
- Modulates neurotransmitter release by binding to voltage
gated Ca++ channels
- Closes pre-synaptic Ca++ channels
- Diminishes excessive neuronal activity and neurotransmitter
release
- Used for neuropathic pain, post-heretic neuralgia, diabetic
neuropathy, fibromyalgia
Antidepressants
Can exert their analgesic action without any effects on mood
in patients with persistent pain
Lower dose and shorter delay to achieve optimal analgesic
action than required for antidepressant action
Central blockade of serotonin and noradrenaline reuptake
process.
Category includes: tricyclic antidepressants (TCAs),
selective serotonin reuptake inhibitors (SSRI) and serotoninnorepinephrine reuptake inhibitors (SNRIs).
MORNRI: Tapentadol
Mu-opioid receptor agonist (MOR)/noradrenaline
reuptake inhibition(NRI) (MOR-NRI)
Both mechanisms contribute to the analgesic activity
to produce analgesia in a synergistic manner
Relatively moderate activity at the two target sites is
sufficient to produce strong analgesic effects.
Used for both nociceptive and neuropathic pain
Local anaesthetic
Lignocaine
Relieves pain by acting directly on damaged pain fibers under the patch
Reduces aberrant firing of sodium channels.
Lignocaine patches are generally safe and lack systemic side effects.
Effective in PHN, post-stroke pain and complex regional pain syndrome (CRPS)
Capsaicin
Capsaicin is an alkylamide found in capsicum
Selectively stimulates primary afferent C fibers.
These C fibers express TRV1, capsaicin receptors that
nonselectively gate cations, including Na+ & Ca++ which
depolarize axons.
Primary mechanism is depletion of substance P:
neuropeptide involved in the transmission of pain signals
Pain relief is not instantaneous: cumulative depletion of
substance P over a period of weeks brings full effect
Balanced analgesia
- Class of medication used should be determined by
the pathology of the pain and effect of Tx - The medication is optimised with dosage and timing:
–Pre‐emptive
–Regular analgesics
–Break through analgesics - Note: treat side‐effects promptly
WHO: Pharma treatment strategy
Underlying cause of pain should be treated whenever
possible
Individualised therapy
Use a systematic approach
- a two or three step strategy
Oral administration in most patients with persistent
medical illness
Regular administration of analgesics (“by the clock”)
combined with a rescue strategy for breakthrough and
intermittent pain
Monitor and evaluate for therapeutic and adverse
effects
Need to prevent/limit unwanted effects
WHO guidelines
non‐pharmacological
non‐opioid medicines
opioid analgesics
co‐analgesics and
adjuvant medicines
rescue doses
routes of administration
efficacy
safety (including risks)
cost effectiveness
limitations
benefits
side effects and their
prevention
Administration modalities
- Oral
- Rectal
- Intermittent IM or SC injection
- Transdermal
- SC infusion
- IV infusion
- Patient Controlled Analgesia (PCA)
- Epidural
- Intrathecal
- Other regional technique
Acute pain
Various modalities
* Patient‐controlled analgesia
* Epidural and intrathecal analgesia
* Other regional analgesic procedures
* Continuous infusions of opioids, local anaesthetics,
ketamine and other drugs
* Limited trajectory: healing process
* An individually tailored approach
Predominantly nociceptive pain:
* Paracetamol/NSAIDs
* Opioids
* Adjuvant drugs
* Non‐pharmacological & psychological intervention
The following groups may have special needs that require particular
attention:
* Children
* Pregnant patients
* Elderly patients
* Aboriginal and cultural groups
* non‐English speaking people
* Patients with cognitive behavioural and/or sensory impairments
Management Plan: Three phases
- Assessment
– History and physical examination +/‐ further investigations - Management
–Discuss pain management options
–Provide information, assurance and advice encouraging
return to normal activity - Review
–Reassess and revise
Consider patient co‐morbidities
- Age
- Renal or liver impairment
- Opioid tolerance
- Substance abuse
- Respiratory compromise
- Insulin dependent diabetes
- Cardiac Disease
