Analgesia Flashcards
why are opioids less commonly used for chronic pain management?
due to poor oral bioavailability
which class of analgesia is not often used for chronic pain management?
opioids
why are opioids a good choice as a perioperative drug?
They give good sedation and analgesia
What effect can opioids have at high doses?
excitation
what effect do opioids have on the heart?
bradycardia
what effect do opioids have on respiratory drive?
cause respiratory depression
what effects do opioids have on the GI system?
nausea and vomiting (premed), decreased GI motility
what effects do opioids have on the urinary system?
various urinary effects - bladder less sensitive to urge to urinate
which class of analgesic can have antitussive effects?
opioids
what effect do opioids have on inotropy?
minimal effect
what effects do opioids have on the eyes?
effects on the pupil - miosis in dogs (and most mammals), mydriasis in cats
what are the pharmacological effects of opioids in mammals?
analgesia
sedation
excitation
bradycardia
respiratory depression
nausea and vomiting, decreased GI motility
various urinary effects
antitussive
effects on pupil (miosis/mydriasis)
what type of system is the opioid system?
endogenous
what are the 3 families of naturally occurring opioid peptides (neurotransmitters)?
beta-endorphin
leucine and methionine - enkephalins
dynorphins
where are the opioid receptors mainly found?
in the brain and spinal cord
what are the 4 types of opioid receptor?
mu
kappa
delta
NOP (nociceptin opioid peptide) receptor
what are the subtypes of the delta opioid receptor?
delta 1 and 2
where are the delta opioid receptors found?
brain
peripheral sensory neurones
what is the function of the delta opioid receptors?
analgesia
antidepressant effects
convulsant effects
physical dependence
may modulate mu opioid receptor-mediated respiratory depression
what are the subtypes of the kappa opioid receptor?
k1, k2, k3
where are the kappa opioid receptors located?
brain
spinal cord
peripheral sensory neurones
what is the function of the kappa opioid receptors?
analgesia and sedation
anticonvulsant effects
depression
neuroprotection
dissociative/hallucinogenic effects
dysphoria
diuresis
miosis
stress
what are the subtypes of the mu opioid receptor?
mu 1, mu2, mu3
where are the mu opioid receptors located?
brain
spinal cord
peripheral sensory neurones
intestinal tract
what are the functions of the mu1 opioid receptors?
analgesia
physical dependence
what are the functions of the mu2 opioid receptors?
respiratory depression
miosis
euphoria
reduced GI motility
physical dependence
what are the functions of the mu3 opioid receptors?
possible vasodilation
where do opioid drugs act?
at the opioid receptors
what common opioid drugs are full agonists?
methadone and fentanyl
what common opioid is a partial agonist?
buprenophine
what common opioid is a mixed agonist-antagonist?
butorphanol
what is the antagonist for opioids?
naloxone
which opioids are associated with analgesia?
mu agonists
which opioids provide the most effective analgesia?
full mu agonists
why are full agonists effective analgesic agents?
they bind to and activate a receptor with the maximum response that an agonist can elicit at that receptor
why are partial agonists less effective than full agonists?
they bind to and activate a receptor but only have partial efficacy, even if they bind to all receptors
what is potency?
the amount of drug required to see a given effect
what is efficacy?
the relative ability of a drug-receptor complex to produce a maximum functional response
which is more potent out of methadone and buprenorphine?
buprenorphine
which is has better efficacy, methadone or buprenoprhine?
methadone
by which routes can opioids be administered?
IV
orally
subcut
IM
oral transmucosal (buccal)
why is pethidine not administered IV?
can induce allergic reactions
what route of opioid administration is less efficacious in cats?
subcut buprenorphine
why do opioids have poor oral bioavailability?
very significant first pass metabolism
what are the advantages of administering opioids IV?
rapid onset of action
reliable uptake
painless - drug volume unimportant
what are the disadvantages of administering opioids IV?
need IV access
what is the advantage of administering opioids IM?
reliable uptake
what is the disadvantage of administering opioids IM?
painful, particularly if administering large volumes
what is the advantage of administering opioids SC?
easy to perform
what is the disadvantage of administering opioids SC?
unreliable uptake
what is the advantage of administering opioids OTM?
easy to perform
what is the disadvantage of administering opioids OTM?
only certain opioids (cats and buprenorphine)
what is the advantage of administering opioids transdermally?
good for chronic use
what is the disadvantage of administering opioids transdermally?
no licensed products
what is the advantage of administering opioids epidural/spinal?
very effective analgesia for the right cases (mostly intraoperative)
what is the disadvantage of administering opioids eipdural/spinal?
no licensed opioids for this
technically difficult
what does the onset of action of a drug depend on?
route of administration
what is the peak effect of a drug?
the time it takes for a drug to reach the maximum concentration after administration of a drug that needs to be absorbed
which opioids are ultra-short-acting?
fentanyl (mins)
unlicensed - alfentanil, sufentanil, remifentanil
which opioids are short-acting (2hrs)
butorphanol
pethidine
which opioids are medium-acting (2-4hrs)
methadone and morphine
which opioids are longer-acting (6hrs)
buprenorphine
what has the main effect on duration of action of an opioid?
dose given
what are the 4 most common misconceptions surrounding opioid administration to animals?
opioids cause mania in cats
opioids cannot be re-dosed within their expected ‘duration of action’
respiratory depression can occur
opioids cannot be combined with other classes of analgesic drug
why is ‘opioids cause mania in cats’ a misconception?
only occurs at really high doses and generally in pain-free cats e.g. overdosing at pre-med
why is ‘opioids always cause respiratory depression’ a misconception?
it is a significant issue in humans but with vet patients it is mostly an issue with patients who are anaesthetised where there is airway control and we can ventilate if necessary
which other drug cannot be given with opioids?
tramadol (and other opioids)
which opioid is a partial mu agonist?
buprenorphine
which opioid is a kappa agonist?
butorphanol
what do side effects of opioids mostly relate to?
potency - those with greatest analgesic efficacy have the greatest likelihood of side effects
when are side effects of opioids less likely to be seen?
when the animal is in pain
how do opioids cause bradycardia and how can this be treated?
vagally mediated
can be treated with anticholinergics (atropine, glycopyrrolate)
what can occur with low IV doses of anticholinergics to treat bradycardia?
might promote a worsening of the bradycardia
what can occur with high IV doses of anticholinergics to treat bradycardia?
tachycardia
how should you manage accumulation of opioids in the body?
decrease frequency of dosing
why can management of gut stasis with opioid use be tricky?
pain causes reduced gut motility but so do opioids
list the common opioid drugs in order of analgesic efficacy (least to most)
butorphanol
buprenorphine
pethidine
methadone and morphine
fentanyl
when might morphine be a better choice clinically than methadone?
if a CRI is needed
what are the effects of fentanyl?
dose-dependent respiratory depression
bradycardia
useful for CRI as very short-acting
what are the advantages of methadone compared to some other opioids?
equi-or more efficacious analgesia and reduced nausea/vomiting compared to morphine
minimal CVS and respiratory side effects
why is pethidine rarely used in practice?
short acting - limits post-operative use
large volume - painful IM
histamine release if given IV
methadone is just better lol
why is buprenorphine painful on injection and not palatable to cats?
multi-dose preparation has preservative
which schedule 3 opioid should be kept in a locked cupboard?
buprenorphine
does butorphanol have good analgesic efficacy?
no - if any it is short lived, likely to require higher doses than given clinically
does butorphanol give good sedation?
yes
why is butorphanol attractive to practitioners?
not subject to controlled drugs regulations
what must be considered when using naloxone?
analgesic effect of opioid will also be reversed - need to provide alternative
what is the advantage of using intra-operative local analgesia?
spares inhalational agent in CVS unstable patients
what dosing interval should be used for methadone if being administered repeatedly over several days?
12-18 hours to prevent accumulation
which opioids are used for CRI?
morphine, fentanyl if morphine inadequate