Unit 5 - Opioids & Non-Opioid Analgesics Flashcards
what is transduction
pain reponse
Injured tissues release chemicals that activate peripheral nerves and/or cause immune cells to release proinflammatory compounds
chemical, mechanical, or thermal stimulus sensed by nociceptor and conve
nerve fibers that transmit “fast pain”
A-delta fibers
sharp, well-localized pain
nerve fibers that transmit “slow pain”
c fibers
dull, poorly localized pain
drugs that target transduction of pain
- NSAIDS
- LAs (infiltration at surgical site)
- steroids
- antihistamines
- opioids
how does inflammation contribute to pain transduction
- ↓ threshold to pain stimulus (allodynia)
- ↑ response to pain stimulus (hyperalgesia)
how is pain transmitted
Pain signal relayed through 3-neuron afferent pain pathway along spinothalamic
* 1st order neuron: periphery to dorsal horn (cell body in DRG)
* 2nd order: dorsal horn to thalamus (cell body in dorsal horn)
* 3rd order: thalamus to cerebral cortex (cell body in thalamus)
drugs that target pain transmission
LA for PNB
what is pain modulation
Pain signal modified (inhibited or augmented) as it advances to cerebral cortex
most important site of pain modulation
substantia gelatinosa in dorsal horn (Rexed lamina 2 & 3)
where does the descending inhibitory pain pathway begin
begins in periaqueductal gray & rostroventral medulla
projects to substantia gelatinosa
how is pain inhibited via the descending pain pathway
- Spinal neurons release GABA and glycine (inhibitor NTs)
- Descending pain pathway releases NE, serotonin, endorphins
how is pain modulation augmented
- central sensitization
- wind-up
drugs that target pain modulation
- neuraxial opioids
- NMDA antagonists
- a2 agonists
- AChE inhibitors
- SSRIs
- SNRIs
what is pain perception
Describes process of afferent pain signals in cerebral cortex & limbic system
drugs that target pain perception
general anesthetics, opioids, a2 agonists (sedation)
MOA of opioid receptors
- opioid binds to receptor
- GPCR activated (Gi)
- AC inhibited
- decreased intracellular cAMP
- Ca2+ conductance decreased
- K+ conductance increased
4 types of opioid receptors
mu, delta, kappa, ORL-1
where are opioid receptors located in the brain
periaqueductal gray, locus coeruleus, rostral ventral medulla
where are opioid receptors located in the spinal cord
primary afferent neurons in dorsal horn & interneurons
where are opioid receptors located in the periphery
sensory neurons and immune cells
precursors to endogenous opioids
- Pre-proopiomelanocortin = endorphins (mu receptor)
- Pre-enkephalin = enkephalins (delta receptor)
- Pre-dynorphin = dynorphins (kappa receptor)
endogenous ligand of mu opioid receptor
endorphin
endogenous ligand of delta opioid receptors
enkephalin
endogenous ligand of kappa opioid receptor
dynorphin
agonism of which opioid receptor can cause bradycardia
mu
CNS effects of mu agonism
- Sedation
- Euphoria
- Prolactin release
- Mild hypothermia
CNS effects of kappa agonism
- Sedation
- Dysphoria
- Hallucinations
- Delirium
how are pupils affected by opioid receptor agonism
Mu & kappa = miosis
GU effects of opioid receptors
- mu & delta = retention
- kappa = diuresis
GI effects of mu receptor agonism
N/V
↑ biliary pressure
↓ peristalsis
GI effects of mu receptor agonism
N/V
↑ biliary pressure
↓ peristalsis
which opioid receptors are assoc. with itching
mu, delta
which opioid receptor(s) is assoc. with antishivering effect
kappa
where is analgesia provided by mu receptors
- mu 1 = spinal and supraspinal
- mu 2 = spinal only
which mu receptor subtype is assoc. with respiratory depression, constipation, and physical dependence
mu-2
which mu receptor is assoc. with immune suppression
M3
effects of Mu-1 agonism
- Analgesia (supraspinal/spinal)
- Bradycardia
- Euphoria
- Low abuse potential
- Miosis
- Hypothermia
- Urinary retention
how do opioids affect CO2 response curve
shift to the right
decreased ventilatory response to CO2
dec. RR, increased Vt
how do opioids affect pupils
Stim of Edinger Westphal nucleus = PNS stim. of ciliary ganglion & CN 3 = pupil constriction
pts do not develop tolerance to this (miosis)
how do opioids affect pupils
Stim of Edinger Westphal nucleus = PNS stim. of ciliary ganglion & CN 3 = pupil constriction
pts do not develop tolerance to this (miosis)
how do opioids cause N/V
- CTZ stim (area postrema of medulla)
- Possible interaction with vestibular apparatus
respiratory effects of opioid overdose
centrally-mediated respiratory depression
* Net effect: ↓ Vm that can produce resp. acidosis
* ↑ PaCO2 = ↑ ICP if ventilation uncontrolled
how do opioids affect BP
- Minimal effect in healthy pts
- ↓ with morphine & meperidine likely r/t histamine release
- Dose-dependent vasodilation
opioids can cause myocardial depression if combined with:
N2O
how do opioids affect biliary pressure
increased (sphincter of oddi contraction)
GU effects of opioids
- Detrusor relaxation (contraction needed to pass urine into urethra)
- Urinary sphincter contraction
urinary retention
opioids assoc with histamine release
morphine, meperidine, codeine
immunologic effects of opioids
- Inhibition of cellular & humoral immune function
- Suppression of natural killer cell function
how do opioids affect thermoregulation
Resets hypothalamic temp set point = decreased core body temp
naturally-occuring phenanthrene derivative opioids
morphine
codeine
drugs that are morphine derivatives
hydromorphone, heroin, naloxone, naltrexone
opioids in phenylperidine class
fentanyl, sufentanil, remifentanil, alfentanil
opioid potency
sufentanil > fentanyl > remifentanil > alfentanil > hydromorphone > morphine > meperidine
10 mg morphine =
__ meperidine
__ hydromorphone
__ alfentanil
__ remifentanil
__ fentanyl
__ sufentanil
- 100 mg meperidine
- 1.4 mg hydromorphone
- 1000 mcg alfentanil
- 100 mcg remifentanil
- 100 mcg fentanyl
- 10 mcg sufentanil
2 factors that determine IV dose and relative ptoency of methadone
depends on patient’s daily opioid requirements & duration of therapy
what causes opioid dependence
occurs when a person taking a drug goes through withdrawal when discontinued
what causes opioid tolerance
occurs when patient requires higher dose to achieve given effect
what is opioid cross-tolerance
occurs when tolerance to 1 drug produces tolerance to another with similar effects
what is opioid addiction
a disease when a person can’t stop using a drug despite negative consequences
most likely causes of opioid tolerance and physical dependence
most likely d/t receptor desensitization, ↑ cAMP synthesis (Not d/t enzyme induction)
tolernace to nearly all side effects of opioids can be developed, except
mioisis, constipation
early s/s opioid withdrawal
diaphoresis, insomnia, restlessness
later s/s opioid withdrawal
abdominal cramping, N/V
onset, peak, and duration of withdrawal from fentanyl or meperidine
- onset = 2-6 hours
- peak = 6-12 hours
- duration = 4-5 days
which opioid agonists produce active metabolites
“M drugs”
morphine, meperidine (?hydromorphone)
metabolism of opioid agonists
All undergo hepatic biotransformation except remifentanil
onset, peak, & duration of morphine & heroin withdrawal
- onset = 6-18 hours
- peak = 36- 72 hours
- duration = 7-10 days