Pain Flashcards
What is pain?
An unpleasant sensory or emotional experience associated with actual or potential tissue damage.
What is nociceptive pain?
Pain that arises from actual or threatened damage to non-neural tissue due to the activation of nociceptors.
What are examples of nociceptive pain?
Muscle sprain, strain Dental pain Cuts, burns Inset stings Post-operative
What is neuropathic pain?
Pain caused by a lesion or disease of the somatosensory nervous system.
What are conditions associated with neuropathic pain?
Multiple sclerosis Stroke Traumatic brain injury Cancer Surgery
What is acute pain and what causes it?
Pain that lasts up to 12 weeks, usually due to tissue injury thus patients typically recover.
What is chronic pain and what causes it?
Pain that exceeds 12 weeks, usually due to changes in neural connections and sensitivity.
Paracetamol MOA?
Unknown, potential inhibition of COX
Paracetamol ADR?
Few at therapeutic doses, overdose may cause fatal liver toxicity
NSAIDs MOA?
Reduce prostaglandin synthesis by inhibiting COX, resulting in analgesic, anti-inflammatory and anti-pyretic effects.
What is the difference between COX1 and COX2 selectivity?
COX-2 inhibition results in reduction of inflammation, pain and fever.
What are some COX2 selective NSAIDs?
Diclofenac, Celecoxib
NSAIDs ADR?
- GI: Potential GI upset (take with food)
- CV: May increase risk of heart failure hospitalization
- Renal: renal failure due to decreasing renal blood flow
What are the benefits vs risks of COX2 NSAIDs?
These have greater specificity for inflammation, pain and fever, less GI upset but may increase risk of CV events.
What are weak opioids?
Codeine
Tramadol
Dihydrocodeine
What are strong opioids?
Morphine Oxycodone Methadone Fentanyl Pethidine
Opioids MOA?
Binds to opiate receptors (delta kappa mu) in the CNS, inhibiting ascending pain pathways.
What are opioids indicated for?
Short-term acute nociceptive pain.
Opioids ADR?
Sedation, dizziness Respiratory depression Nausea Constipation Addiction
What is tolerance?
The need for increasing doses to achieve the same effect
What is physical dependence?
Physical symptoms of withdrawal if the next dose is not received
What is addiction?
Chronic relapsing disorder characterised by compulsive drug seeking and continued use despite harmful consequences.
What is hyperalgesia?
Increased sensitivity to pain with prolonged use.
What drugs are recommended for nociceptive pain?
Paracetamol
NSAIDs
Opioids
What drugs are recommended for neuropathic pain?
Tricyclic antidepressants
Gabapentinoids
Anticonvulsants
What questions should be asked for a patient with acute pain when taking history?
Severity of pain 0-10? Where is the pain, is it radiating? When did the pain start? What makes the pain stop? What makes the pain worse?
What is the WHO analgesic ladder?
- Paracetamol/NSAID
- Weak opioid
- Strong opioid
Start at a higher step and then work down, continuing adjunct treatments.
What are types of chronic pain?
Chronic neuropathic pain (diabetic neuropathy)
Arthritic pain
Chronic intermittent pain (recurrent headaches)
What are the goals of chronic pain treatment?
- Empower patient to lead role in pain management
- Focus on improving function and disability
- Encourage patient to remain active and stay positive
What are the types of neuropathic pain?
Sensory
Motor
Autonomic
What are types of sensory pain?
- Allodynia: pain experienced from stimulus that does not usually cause pain
- Hyperalgesia: exaggerated pain response to normal stimulus
- Dysaesthesia: unpleasant sensation
- Hypesthesia: decreased sensitivity to stimulation
- Loss of proprioception: inability to control movement
What is motor and autonomic pain?
Weakness, absent reflexes
Changes in skin colour due to vasodilation
What is the S-LANSS pain score?
A way to measure a patient’s pain. Score >12 suggests predominantly neuropathic pain.
What is the first line choice for neuropathic pain?
Tricyclic antidepressants (amitriptyline, nortriptyline)
TCAs MOA?
Increases synaptic concentration of serotonin by inhibition of their reuptake by the presynaptic neuronal membrane pump.
How should TCAs be dose?
Start low, go slow to avoid ADR
Reduce dose gradually before stopping to prevent antidepressant discontinuation syndrome.
Gabapentinoids MOA?
While gabapentinoids are structurally similar to GABA, they do not act on GABA receptors, and instead act on a variety of receptors through the brain to bring about pain relief effects.
Pharmacokinetic considerations of gabapentinoids?
Pregabalin has more predictable pharmacokinetics
Gabapentin ADR?
Sedation
Mood disorders
Respiratory depression
Potential for abuse
What is central sensitisation?
Persistent state of high reactivity to pain and touch.
What are the three types of opioid receptors?
Mu
Kappa
Delta
What is the structure of an opioid receptors?
G-protein coupled receptor
7 transmembrane domains
Variation is in extracellular loops
What do mu receptor agonists do?
Produce analgesic effects, respiratory depression, euphoria, release of hormones
What is a mu receptor agonist?
MORphine
What is the structure of morphine?
5-ring system 2 hydroxyl groups Ether linkage between C4 and C5 Basic and tertiary amine 5 chiral centres.
How is codeine different from morphine?
Methylated at the 3-position
- increases ability of drug to cross BBB
- lower analgesic potency
- lower addiction potential
How is oxycodone different from morphine?
Methylated at the 3-position
Hydroxylated at the 14-position
- increases affinity for MOR receptor
Reduced double bond at C7/8 and oxidation at 6
- increases flexibility
What is the structure of tramadol?
Codeine but with B,D,E rings removed
Two chiral centers in cyclohexane ring therefore 4 possible stereoisomers
- R enantiomer responsible for serotonin uptake
- S enantiomer responsible for norepinephrine uptake
What is the structure of fentanyl?
Alkyl chains which provide high lipophilicity.
High potency, rapid onset, short duration of action.
What is the structure of methadone?
Racemate of R and S enantiomers
Long acting mu-receptor agonist
Metabolites are responsible for long duration of action
What is nalaxone?
Opioid receptor blocker, used for opioid overdose (Narcan)
