Opioids Flashcards
List the main pharmacological effects of opioids.
Analgesia
Sedation
Excitation
Bradycardia
Respiratory depression
Nausea/vomiting/decreased GI motility
Antitussive?
Urinary/pupillary effects
Describe full agonists and give two examples.
Bind to and activate a receptor with the maximum response that an agonist can elicit at that receptor
Methadone and fentanyl
Describe partial agonists and give an example.
Bind to and activate a receptor but only have partial efficacy, even if they bind to all receptors
Buprenorphine
Give an example of a mixed agonist-antagonist.
Butorphanol
Give an example of an antagonist.
Naloxone
Which type of opioid is most associated with analgesia?
Mu agonists
Full mu agonists provide the most effective analgesia
By what routes can be opioids be administered?
IM
IV
SC
OTM/buccal
Transdermal
Epidural/spinal
Why are opioids not useful when administered orally?
Significant first pass metabolism resulting in poor oral bioavailability
What are the (dis)advantages of IV opioids?
A = rapid onset of action, reliable uptake, painless (regardless of volume)
DA = Need IV access
What are the (dis)advantages of IM opioids?
A = reliable uptake
DA = Painful (large volumes)
What are the (dis)advantages of SC opioids?
A = easy to perform
DA = unreliable uptake
What are the (dis)advantages of OTM opioids?
A = easy to perform
DA = Only certain opioids
What are the (dis)advantages of transdermal opioids?
A = good for chronic use
DA = no licensed products
What are the (dis)advantages of epidural/spinal opioids?
A = very effective analgesia (mostly intra-op)
DA = No licensed products, technically difficult
List some ultra-short-acting (mins) opioids.
Fentanyl
Alfentanil, Sufentanil, Remifentanil
List some short-acting (2hrs) opioids.
Butorphanol
Pethidine
List some medium-acting (2-4hrs) opioids.
Methadone
Morphine
List a longer-acting (6hrs) opioid.
Buprenorphine
How can we increase duration of action of opioids?
Oral sustained release formulations
IM/SC - adding a vasoconstrictor
Transdermal delivery systems e.g. human fentanyl patches
What are some common misconceptions surrounding opioids?
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
Describe respiratory depression as a side effect of opioid admin.
Rarely clinically significant in awake animals
Most likely to be seen when administered during anaesthesia
Describe bradycardia as a side effect of opioid admin.
Vagally mediated, can be treated with anticholinergics e.g. atropine/glycopyrrolate
Low doses of anticholinergics might promote worsening of bradycardia - give more!
High doses promote tachycardia - wait!
List the opioids in order of analgesic efficacy.
MOST - fentanyl
Methadone + morphine
Pethidine
Buprenorphine
LEAST - butorphanol
Describe fentanyl.
Some resp. depression when given during anaesthesia (dose dependent)
Likely to induce a bradycardia
Most useful as CRI due to short-acting
Boluses can be useful to minimise nociception to acute noxious stimuli during surgery
Describe methadone.
Reduced nausea/vomiting compared to morphine
No concern re histamine release given IV
Minimal CVS and resp. side effects
NMDA receptor antagonist effects
Describe pethidine.
Short-acting limits post-op use
Large volume = painful IM
Histamine release if given IV
Replaced in practice by methadone
Describe buprenorphine.
Multi-dose preparation has preservative (pain on injection/not palatable OTM)
Good evidence to support use in cats
May not be effective SC
? Delayed onset of action (analgesia + sedation)
Schedule 3 opioid but to be treated like a schedule 2
Describe butorphanol.
Analgesia short-lived, need high doses
May confound subsequent full mu-agonist administration
Sedation good
Not subject to CD regulations
Describe naloxone.
Specific antagonist so can be used to reverse effects of an opioid
Analgesia will also be reversed! - provide alternative
How can we select appropriate premedication opioids?
Sedation only = butorphanol
Mild pain = buprenorphine
Moderate pain = pethidine/methadone, buprenorphine
Moderate to severe pain = methadone
How can we select appropriate intra-op opioids?
Sedation = unnecessary
Mild pain = unnecessary
Moderate pain = methadone, fentanyl bolus/CRI
Moderate to severe pain = methadone, fentanyl bolus/CRI, (epidural morphine)
