Pain Flashcards
What is Nociception? (pain process)
Transduction
Transmission
Perception
Modulation
Types of noxious stimuli
Mechanical: incision, tumor mass
Thermal: burn, frostbite
Chemical: toxin, chemotherapy
Transduction
conversion of a mechanical, thermal, or chemical stimulus to a neuronal action potential
Starts in the periphery in response to noxious stimuli; where primary nociceptive fibers (afferents) are activated
Which causes the nociceptors cause the release of serotonin, bradykinin, histamine, substance P, and prostaglandins
Opioid receptor sites can be found in the CNS, peripheral nerves, and GI tract
Naturally occurring morphine-like substances :
Endorphins
Enkephalins
Transmission
Second step of nociception
Where the stimuli move from the peripheral nervous system, to the spinal cord through the dorsal root ganglion, into the ascending tract to the brain
Types of Nociceptive fibers:
A – delta (δ) fibers:
Thinly myelinated, large in diameter, and fast-conducting fibers
Transmit sharp, localized (somatosensory) pain that is sensitive to mechanical and thermal stimuli
C-fibers:
Unmyelinated, small in diameter, and slow-conducting fibers
Transmit dull, aching (visceral) pain that is diffuse
Mu (μ): Primarily pain receptors (most common)
Analgesia, respiratory depression, euphoria,
decreased GI activity, sedation, and physical dependence
Kappa (k):
Some analgesia, sedation, decreased GI motility
Dysphoria
Somatic Pain
Well-localized
Sharp, aching, throbbing, gnawing
Activation of nociceptors resulting from cutaneous, musculoskeletal, and deep tissues
Examples: Bone pain, soft tissue injury
Visceral
Poorly localized
Deep, aching, cramping, pressure, referred
Activation of nociceptors resulting from stretching, distention, or inflammation
Examples: bowel obstruction, biliary colic
Full Opioid Agonists
Bind to opioid receptors resulting in activation
Activation of mu receptors leads to analgesia (pain reliever) as well as respiratory depression, euphoria, and sedation
Activation of the kappa receptors leads to analgesia as well as sedation and decreased GI motility
Medications:
Morphine, Fentanyl, Codeine, Oxycodone, Hydromorphone, Meperidine, and methadone
Common side effects: respiratory depression, constipation, orthostatic hypotension, and urinary retention
High risk of dependence; are controlled substances
Morphine
Is the GOLD standard
Affect central and peripheral receptors
Not the drug for everyone (can be allergic)
Major side effects: analgesia, drowsiness, mental clouding, respiratory depression, constipation, urinary retention, nausea and vomiting, hypotension, pruritis
Has active metabolites, such as M6-G, which can accumulate
Multiple routes of administration and formulations
Hydromorphone (Dilaudid)
Pharmacologic effects essentially identical to Morphine
Often confused with morphine (stronger than Morphine)
Most potent than Morphine, but not more effective
No active metabolites
Both drugs are available in short-acting forms
No extended-release form hydromorphone – available
Oxymorphone extended-release available in 4 dose sizes
Food and drink can affect absorption of extended-release formulation
Hydromorphone (Dilaudid)
Pharmacologic effects essentially identical to Morphine
Often confused with morphine (stronger than Morphine)
Most potent than Morphine, but not more effective
No active metabolites
Both drugs are available in short-acting forms
No extended-release form hydromorphone – available
Oxymorphone extended-release available in 4 dose sizes
Food and drink can affect absorption of extended-release formulation
Codeine, Hydrocodone, and Oxycodone (take for mild pain)
Codeine
About 10% is metabolized to morphine by CYP 2D6 pathway
About 10% of Caucasians are poor metabolizers
25% Ethiopians are rapid metabolizers
Constipation a major side effect
Effectiveness basically the same of ASA or acetaminophen
Hydrocodone
Has a better side effect profile than Codeine
Not available as a single entity
Oxycodone
Available in short-acting (tablets and liquid) and extended-release formulations
Meperidine (Demerol)
Proven to be not as effective as originally thought
Rapid onset but with short duration of action
Active metabolites- 2-4 hours
No evidence that efficacy enhanced by Vistaril or Phenergan
Does not have a lesser effect on the sphincter of Oddi
300 mg PO = 10 mg of IV morphine
Now limited to use in short procedures or to treat rigors
NOT used for long term
Tramadol (Ultram)
-Weak mu opioid agonist
-Blocks reuptake of norepinephrine and serotonin
Is not a controlled substance
Analgesic ceiling
Has active metabolites
Side effects: nausea, dizziness, confusion, seizures, dry mouth
Tramadol (Ultram)
-Weak mu opioid agonist
-Blocks reuptake of norepinephrine and serotonin
Is not a controlled substance
Analgesic ceiling
Has active metabolites
Side effects: nausea, dizziness, confusion, seizures, dry mouth
Methadone
Mu-opioid receptor agonist
Used to help patients withdrawal from opioid abuse
Decreases cravings and euphoric effects of opioids
Long half life (15-30 hours), it duration of action of analgesia is up to 12 hours
Blocks NMDA receptor —decrease CNS pain threshold
Lipophilic -Stays in the fat for a long time
High protein bonding
Numerous side effects
Can cause Q-T prolongation
? Decreases spread of HIV
Helps with people with long term pain.
Opioid Agonists-Antagonists
Bind to more than one opioid receptor site, but block other receptors
Antagonize mu receptors and agonists to kappa receptors
Medications: Nalbuphine and Buprenorphine
(Not first line, not common)
Cause many of the same side effects
Sedation
Respiratory distress
Constipation
May have more psychotic reactions
Relief of pain in labor and delivery
Careful in COPD
Those experiencing MI or with severe CAD (cardiac stimulation).
Do not give Pentazocine to cardiac patients
Hepatic and Renal disease
Buprenorphine (Buprenex)
Partial mu agonists, but in high doses acts as an antagonist
Can be injectable, IV and sublingual, nasal spray
Available since the 1980’s for parenteral use
Used in place of methadone to treat opioid addiction
Long duration of effect (2-3 days)
Subutex – sublingual
Subuxone – with naloxone (Schedule III)
High risk for abuse
Nalbuphine (Nubain)
A mixed agonist –antagonists
Kappa receptor agonist
Mu receptor antagonist
Used in women experiencing labor when epidural anesthesia not an option
Also used in anesthesia
Short acting and lower risk of respiratory distress in both mother and baby
Opioid Antagonists
Used to reverse opioid when levels are too high
Drugs:
Naloxone (Narcan, Evzio)
Naltrexone (Revia)
Work by reversing the effects of opioids
Respiratory distress
Hemodynamic instability
Over sedation
Those with opioid addiction will experience withdrawal
Can be given IV, IM, SQ, or as a nasal spray
Benozdiazepines
Often prescribed by treatment of pain
Evidence shows they don’t work
Concomitant use with opioids increase risk of sedation and respiratory depression
Highly addictive
Medications: Alprazolam, Diazepam, Clonazepam, Lorazepam
Act as an antagonist of opioids
May help with withdrawal symptoms
Increase risk of overdose at high doses
