ANALGESIA Flashcards
circulating beta-endorphin is derived predominantly from the __________ where it is released
pituitary
circulating proenkephalins are derived from the ___________ and exocrine glands of the stomach and intestine
adrenal medulla
what is the precursor molecule for beta-endorphin?
proopiomelanocortin (POMC)
which type of analgesics modulate initial signal transduction for pain?
NSAIDs
which type of drugs blocks signal conduction in nociceptive fibers?
Na+ channel blockers (local anesthetics)
how do opioids antidepressants, NSAIDs and alpha-adrenergic agonists all modulate transmission of pain?
modulate transmission of pain sensation in the spinal cord by decreasing the signal relayed from peripheral to central pain pathways
activating a peripheral nerve leads to influx of what two cations which results in depolarization of the polarized nerve membrane and generation of an action potential?
influx of sodium & Calcium
sensitizing agents act via what two intracellular signaling systems can modulate both the extent of originating ion influx and the sensitivity of the voltage-gated sodium channels to increase the likelihood of propagation and conduction of the pain impulses?
G-proteins coupled receptor either activates Phospholipase C to increase Ca2+ release from intracellular stores and activates protein kinase C, OR increases cAMP, activates protein kinase A and phosphorylates sodium channels
What effect do Norepinephrine (acting via alpha-2 receptors), GABA (acting via GABAb receptors) and endogenous opiates, endorphin and encephalin have on the pre synaptic terminal in the spinal cord?
Norepinephrine, GABA, endogenous opiates, endorphin and encephalin all inhibit calcium entry to teh pre-synaptic terminal
what effect do norepinephrine, GABA, endogenous opiates, endorphin and encephalin have on the post-synaptic membrane in the spinal cord?
activate potassium channels, leading to an increase in K+ conductance and hyperpolarization of the cell
(reduces the likelihood of the depolarization and the onward transmission of the pain signal is interrupted)
what effect does activating mu opiate receptors have on the presynaptic terminal?
decreases calcium influx
what effect does activating mu opiate receptors have on the post-synaptic membrane?
increases potassium efflux
how do NMDA receptors cause sustained or intense activation of central transmission?
activating NMDA receptors leads to postsynaptic calcium influx (Ca2+ influx activates signal transduction ascades that can enhance both short-term and long term excitability of the synapse)
what are the two drugs that block NMDA receptors?
ketamine
dextromethorphan
how can ketamine and dextromethorphan be used to prevent surgery-induced sensitization?
preemptive block of NMDA receptors
what are some of the adverse effects of ketamine?
hallucinations, amnesia, CV pressor, increased ICP
what are some of the adverse effects of dextromethorphan?
dizziness, confusion, fatigue
what is allodynia?
normally innocuous stimuli are now painful
what is hyperalgesia?
high intensity stimuli perceived as more painful
what are some of the extra-neuronal inflammatory components?
bradykinin, protons, histamine, PGE2, Nerve growth factor (NGF)
how do the extra-neuronal inflammatory components (bradykinin, protons, histamine, PGE2, NGF) cause increased pain perception?
G-protein coupled effects
reduced activation threshold
increased current conducted
what are the intra-neuronal mechanisms that increased the pain perception?
Substance P & CGRP (released from termini of primary afferents)
how do the intra-neuronal molecules like substance P & CGRP increase pain perception?
stimulates inflammatory cells to release histamine and TNF-alpha, recruits granulocytes to the site of inflammation
what is neuropathic pain?
pain arising from transection of mechanical damage to the nerve axon
explain how neuropathic pain lead to the continued perception of injury
loss of neurotrophic support alters gene expression in the injured nerve fiber
-inflammatory cytokines alter gene expression in both injured and adjacent uninjured nerve fibers (changes in gene expression lead to altered sensitivity and activity of nociceptive fibers)
what Na+ channel blocking drug is used to treat trigeminal neuralgia?
CARBAMAZEPINE
The rewiring of the peripheral and central pain pathways following nerve damage involves changes in expression of what ion channel?
Na+
what are the adverse effects of opioids?
Sedation Resp. depression N/V increased ICP Constipation Urinary Retention Itching around nose, urticaria postural hypotension behavioral restlessness
opioids act mainly as an agonist on what receptor?
mu-receptor agonist
what are the adverse effects of acetaminophen?
hepatic toxicity and liver failure at high doses, hypersensitivity
what are the main adverse effects of NSAIDs?
GI irritation, platelet inhibition, renal insufficiency or failure, cardiovascular hypersensitivity
what is the MOA of the gabapentinoids?
inhibition of voltage gated Ca2+ channels
how are the gabapentinoids (gabapentin, pregabalin) administered?
PO
what are the main adverse effects of the gabapentinoids?
sedation, peripheral edema, GI, decrease dose for renal insufficiency
what is the MOA for clonidine and dexmedetomidine?
alpha-2 receptor agonist
what are the adverse effects of clonidine?
sedation, hypotension, bradycardia
what are the functions of the Mu opioid receptor (OP-3)?
supraspinal & spinal analgesia; sedation; decrease respiration; decrease GI transit; modulation of hormone & NT release
what are the functions of the delta opioid (OP-1) receptors?
supraspinal & spinal analgesia; modulation of hormone and NT release
what are the functions of the kappa opioid (OP-2) receptors?
supraspinal & spinal analgesia; psychotomimetic effects; decrease GI transit
Name the opioid receptor type: endorphins> enkephalins> dynorphins
mu opioid receptor (OP-3)
name the opioid receptors type: enkephalins > endorphins & dynorphins
delta opioid receptors (OP-1)
name the opioid receptor type: dynorphins»_space; endorphins & enkephalins
kappa opioid receptor (OP-2)
what are the american pain society and the american academy of pain medicine’s five MAIN recommendations?
- Try other treatments first
- assess the risk for abuse
- Keep expectations realistic
- Start w/ a short term trial
- Weight individuals potential harm / benefit ratio
for the opioids that are considered full agonist, which receptor do they mostly act on?
OP-3
which 4 full agonist (at the mu receptor) opioids have a low oral:IV potency ratio?
morphine
hydromorphone
oxymorphone
fentanyl
which full agonist at the mu receptor opioid drug has a high oral:IV potency ratio?
methadone
Name the 7 opioids that are considered full agonists at the mu receptor?
Morphine hydromorphone oxymorphone methadone meperidine fentanyl
which drug is the only full agonist opioid that also has some activity on kappa receptors?
morphine
name the 7 opioids that are only partial agonists at the mu receptor
codeine hydrocodone oxycodone pentazocine nalbuphine buprenorphine butorphanol
which two opioids that are partial agonists at the mu receptor are only available in IV form?
Nalbuphine
Butorphanol
which opioid is often given as a patch to provide 48-72 hours of relatively stable drug delivery?
fentanyl
what is the benefit to the peripheral analgesia devise (PCA)?
the dose rate and max delivery/hr dose is set by te nurse or physician and the controls locked to prevent tampering
why does oral morphine have a low bioavailability?
it has a high first pass metabolism
which organ serves as the main reservoir for opiate distribution because it has greater relative bulk?
skeletal muscle
what can happen with frequent high dose administration or continuous infusion of highly lipophilic & slowly metabolized opioids (e.g. fentanyl)?
can lead to accumulation (depot storage site, can release drug slowly, once dosing is terminated)
opiates would really like to accumulate in what kind of tissue, but is limited by the poor blood supply to this tissue?
adipose tissue
explain how enkephalin signaling can persist, yet morphine has a loss of drug activity?
Enkephalin has a relative balance b/w desensitization and resensitization.
Morphine has a slow persistent desensitization and little recycling, favoring loss of drug activity
which adverse effects of opioids have a minimal chance of tolerizing?
miosis
constipation
convulsions
which adverse effects of opioids have a high chance of tolerizing?
Analgesia euphoria, dysphoria mental clouding sedation resp. depression antidiuresis N/V Cough Suppression
what is the most common and persistent side effect from opioids?
CONSTIPATION
what is the prophylactic treatment for opioid-induced constipation?
stool softener & laxatives (also increased consumption of fluids and dietary fiber)
what class of drugs may be useful to treat refractory constipation due to opioid agonists?
opioid antagonists (avoid in the presence of bowel obstruction)