Lecture 2 Flashcards
Types of pain
Nociceptive
Neuropathic/functional
Nociceptive pain
Caused by damage to body tissue, secondary to noxious stimuli
Neuropathic/functional pain
Disengaged from noxious stimuli or healing; Described in terms of chronic pain, result of nerve damage or abnormal operation of nervous system
Postherpetic neuralgia - pain type?
Neuropathic/functional pain
Diabetic neuropathy - type of pain?
Neuropathic/functional
Neuropathic pain
Result of nerve damage
Pain regulated by -
Excitatory & inhibitory neurotransmitters in response to stimuli
Perception of pain - 3 systems?
- Afferent pathways
- CNS
- Efferent pathways
Afferent pathway
send signals to spinal cord
CNS system involvement in pain pathway
discriminate & localize pain, arouse & alert (fight/flight), motivational factors
Efferent pathway
Modulate pain sensation
Pathophysiology - 4 stages of pain
- Stimulation
- Transmission
- Perception
- Modulation
Pain - Stimulation pathophysiology
Involves stimulation of free nerve endings - nociceptors
Pain - Transmission pathophysiology
Afferent fibers synapse into various layers of the spinal cords dorsal horn - pain impulses transmitted to brain stem — thalamus via ascending pathways — then finally to CNS
Ascending transmission pathway
Peripheral pain receptors to spinal cord to medulla to brain stem to midbrain to cortex
Pain - perception pathophysiology
The point at which pain becomes a conscious experience
Pain - modulation
Initiation of the anti-nociceptive system
Endogenous opiate system in CNS releases “endorphins”
Location of pain modulation
Descending system - inhibits pain transmission at dorsal horn
Neuropathic pain
Rewiring of pain circuits - anatomically and biochemically
The goal of managing pain
Reduce peripheral sensation (the cause) and decrease central stimulation
Pain severity vs. therapy measurement
Numerical assessment unless cognitive deficit or children - use face scale
Mild pain scale
1-3
Mild pain treatment
APAP, aspirin, NSAID, COX-2 inhibitors
Moderate pain scale
4-7
Moderate pain treatment
NSAID, opioid + APAP, tramadol
Severe pain scale
8-10
Severe pain treatment
Opioids
Reason for combination therapy (opioid + another Rx)
- Take advantage of the synergistic effect on pain
2. To limit the dose
Benefits of non-opioids
Availability, additive therapy when combined with opioids, inexpensive, low abuse
Only true “pain killers”
NSAIDs - decreasing inflammation (large cause of pain)
Disadvantages of non-opioids
Effects are “capped”, not effective at a certain pain level, side effects - can be toxic, limited parenteral availability
APAP
Tylenol
Tylenol - MOA
Believed to inhibit synthesis of prostaglandins in CNS; work peripherally to block pain impulse generation
Tylenol Dose
325-650 mg Q4H or 1000 mg q6h
Maximum dose of Tylenol/day
4 grams/day
Maximum Tylenol dose for liver impairment/alcoholism
2grams/day
Dosage forms of Tylenol
PO, PR, IV ($$$)
Tylenol black box warning
Hepatotoxicity and failure with excessive doses (>4g/day)
COX
Enzyme - cycle-oxygenase
COX binds to
Arachidonic acid
Arachidonic acid
Inflammatory mediator released in setting of tissue injury
COX-1 and COX-2
Isoenzymes
COX-1 pathway
Generates cytoprotective prostaglandins and thromboxane
COX-1 pathway location
GI, kidney, lung
COX-1 pathway effects
Platelet aggregation, vasoconstriction
COX-2 pathway
Inflammatory prostaglandins and prostacyclin
COX-2 effects
Inflammation, pain, antiplatelet, vasodilation
What pathway is blocked from NSAIDs?
COX-1 and COX-2
Salicylates
Aspirin
Aspirin MOA
Irreversibly binds to COX-1 and COX-2 enzymes
Aspirin properties
Analgesia, anti-inflammatory, antipyretic, antiplatelet
Aspirin - harmful
Antiplatelet - irreversible. Prevents synthesis of thromboxane A
Thromboxane A
Vasoconstrictor & inducer of platelet aggregation
Aspirin onset
15-20 min
Aspirin peak
1-3 hours
Aspirin duration
3-6 hours
Aspirin half life
3 hours
Aspirin elimination
Urine and liver
Aspirin adverse events
GI irritation and bleeding (ulcers), dizziness, deafness, tinnitus (salicylism) with high doses, Reye’s syndrome
Reye’s syndrome
Liver disorder and encephalopathy - occurs in children with viral infections
Aspirin - unique adverse effect
Asthamtics - increase risk of bronchospasm, urticaria, angioedema
Aspirin contraindication
Active peptic ulcer, history of GI bleed, hypersensitivity to aspirin or NSAID
Aspirin safety
Avoid use with recent surgery
NSAIDs general properties
Same as aspirin: analgesic, anti-inflammatory, antipyretic, antiplatelet (reversible)
Different property in general NSAID vs. aspirin
General NSAID: antiplatelet (reversible)
Ibuprofen maximum dosage/day
2400 mg
Indomethacin max dose/day
200 mg
Ketorolac max dose/day
120 mg
Naproxen max dose/day
600 mg
Common NSAIDs
Ibuprofen, indomethacin, ketorolac, naproxen
NSAID adverse effects - cardio
Fluid retention, hypertension, edema
NSAID - adverse effects - GI
Irritation, ulcers, bleeding, perforation
NSAIDs adverse effects - respiratory
Bronchospasm
NSAIDs adverse effects - skin
Rash
NSAIDs adverse effects - renal
Insufficiency or failure