Opioids

Question 1

List the main pharmacological effects of opioids.

Answer 1

Analgesia
Sedation
Excitation
Bradycardia
Respiratory depression
Nausea/vomiting/decreased GI motility
Antitussive?
Urinary/pupillary effects

Question 2

Describe full agonists and give two examples.

Answer 2

Bind to and activate a receptor with the maximum response that an agonist can elicit at that receptor
Methadone and fentanyl

Question 3

Describe partial agonists and give an example.

Answer 3

Bind to and activate a receptor but only have partial efficacy, even if they bind to all receptors
Buprenorphine

Question 4

Give an example of a mixed agonist-antagonist.

Answer 4

Butorphanol

Question 5

Give an example of an antagonist.

Answer 5

Naloxone

Question 6

Which type of opioid is most associated with analgesia?

Answer 6

Mu agonists
Full mu agonists provide the most effective analgesia

Question 7

By what routes can be opioids be administered?

Answer 7

IM
IV
SC
OTM/buccal
Transdermal
Epidural/spinal

Question 8

Why are opioids not useful when administered orally?

Answer 8

Significant first pass metabolism resulting in poor oral bioavailability

Question 9

What are the (dis)advantages of IV opioids?

Answer 9

A = rapid onset of action, reliable uptake, painless (regardless of volume)

DA = Need IV access

Question 10

What are the (dis)advantages of IM opioids?

Answer 10

A = reliable uptake

DA = Painful (large volumes)

Question 11

What are the (dis)advantages of SC opioids?

Answer 11

A = easy to perform

DA = unreliable uptake

Question 12

What are the (dis)advantages of OTM opioids?

Answer 12

A = easy to perform

DA = Only certain opioids

Question 13

What are the (dis)advantages of transdermal opioids?

Answer 13

A = good for chronic use

DA = no licensed products

Question 14

What are the (dis)advantages of epidural/spinal opioids?

Answer 14

A = very effective analgesia (mostly intra-op)

DA = No licensed products, technically difficult

Question 15

List some ultra-short-acting (mins) opioids.

Answer 15

Fentanyl
Alfentanil, Sufentanil, Remifentanil

Question 16

List some short-acting (2hrs) opioids.

Answer 16

Butorphanol
Pethidine

Question 17

List some medium-acting (2-4hrs) opioids.

Answer 17

Methadone
Morphine

Question 18

List a longer-acting (6hrs) opioid.

Answer 18

Buprenorphine

Question 19

How can we increase duration of action of opioids?

Answer 19

Oral sustained release formulations
IM/SC - adding a vasoconstrictor
Transdermal delivery systems e.g. human fentanyl patches

Question 20

What are some common misconceptions surrounding opioids?

Answer 20

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

Question 21

Describe respiratory depression as a side effect of opioid admin.

Answer 21

Rarely clinically significant in awake animals
Most likely to be seen when administered during anaesthesia

Question 22

Describe bradycardia as a side effect of opioid admin.

Answer 22

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!

Question 23

List the opioids in order of analgesic efficacy.

Answer 23

MOST - fentanyl
Methadone + morphine
Pethidine
Buprenorphine
LEAST - butorphanol

Question 24

Describe fentanyl.

Answer 24

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

Question 25

Describe methadone.

Answer 25

Reduced nausea/vomiting compared to morphine No concern re histamine release given IV Minimal CVS and resp. side effects NMDA receptor antagonist effects

Question 26

Describe pethidine.

Answer 26

Short-acting limits post-op use Large volume = painful IM Histamine release if given IV Replaced in practice by methadone

Question 27

Describe buprenorphine.

Answer 27

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

Question 28

Describe butorphanol.

Answer 28

Analgesia short-lived, need high doses May confound subsequent full mu-agonist administration Sedation good Not subject to CD regulations

Question 29

Describe naloxone.

Answer 29

Specific antagonist so can be used to reverse effects of an opioid Analgesia will also be reversed! - provide alternative

Question 30

How can we select appropriate premedication opioids?

Answer 30

Sedation only = butorphanol Mild pain = buprenorphine Moderate pain = pethidine/methadone, buprenorphine Moderate to severe pain = methadone

Question 31

How can we select appropriate intra-op opioids?

Answer 31

Sedation = unnecessary Mild pain = unnecessary Moderate pain = methadone, fentanyl bolus/CRI Moderate to severe pain = methadone, fentanyl bolus/CRI, (epidural morphine)