Opioids Flashcards
What are the pharmacological effects of opioids?
- analgesia
- sedation
- bradycardia
- excitation
- respiratory depression
- nausea and vomiting
- decreased GI motility
- various urinary effects
- antitussive?
- minimal effect on inotrophy
- effects on the pupil, miosis (dogs), mydriasis (cats)
What opioid receptors are found in the brain and spinal cord?
- mu
- kappa
- delta
- NOP (nociception opioid peptide) receptor
Whatare the three families involved in the endogenous opioid system that has naturally occuring peptides?
- beta endorphin
- leucine (leu)- and methionine (met) - enkephalins
- dynorphins
What are neurotransmitters?
naturally occuring peptides
What is the endogenous ligand for the nociception opioid peptide?
nociceptin
What location is the delta receptir found?
brain and peropheral sensory neurones
What is the function of the delta receptor?
- analgesia
- antidepressant effects
-convulsive effects - physical dependence
- may modulate mu-opioid receptor-mediated respiratory depression
What is the location of the kappa receptor?
brain, spinal cord, peripheral sensory neurones
What are the functions of the kappa receptor?
- analgesia
- anticonvulsant effects
- depression
- dissociative/hallucinogenic effects
- diuresis
- miosis
- dysphoria
- neuroprotection
- sedation
- stress
What is the location of the mu receptor?
brain, spinal cord, periperal sensory neurones
What is the function of mu1 receptor?
analgesia and physical dependence
What is the function of the mu2 receptor?
respiratory depression, miosis, euphoria, reduced GI mortility, physical dependence
What is the function of the mu3 receptor?
possible vasodilation
What do full mu agonists do?
bind to and activate a receptor with the maximum response that an agonist can elicit at that receptor
What do partial agonists do?
bind to and activate a receptor but only have partial efficacy, even if they bind to all receptors
How will we know how the opioid will act?
- what receptors/receptor subtypes they have
- mechanism of action at these receptors (full or partialagonists, antagonitst)
- pharmacokinetics
- species differences
What are examples of a full mu agonist?
methadone and fentanyl
What are examples of partial agonists?
buprenorphine
What are examples of a mixed agonist-antagonist?
butorphanol
What are examples of antagonist?
naloxone
What is potency
how much you need to get an effect
What does efficacy meam?
how much effect you get
What can happen if you give pethidine IV?
allergic reaction
How can opioids be administered?
intramuscular, intravenous, subcutaneous, oral transmucosal/buccal, transdernal and epidural/spinal
What are the advantages of IV route?
rapid onset of action, reliable uptake, painless
What are the advantages of intramuscular route
reliable uptake
What are the advantages of subcutaneous route?
easy to perform
What are the advantages of oral transmucosal?
easy to perform
What are the advantages of transdermal route?
good for chronic use
What are the advantages of epidural/spinal route?
very effective analgesia for the right cases
What are the disadvantages of intravenous route?
need IV access
What are the disadvantages of intramuscular route?
painful- particularly large volumes
What are the disadvantages of subcutaneous route?
unreliable uptake
What are the disadvantages of oral transmucosal route?
only certain opioids (cat and buprenorphine)
What are the disadvantages of transdermal route?
no licensed products
What are the disadvantages epidural/spinal route?
no licensed opioids for this, technically difficult
What does the onset of action depend on?
- route of administration
- how quickly you see effect
- IV quicker than IM because need to get into blood stream
- peak effect when all drug is sitting on a receptor
- how quickly the drug is removed from the receptors
What drugs are ultra-short acting?
fentanyl, alfentanil, sufentanil, remifentanil
What are short acting opioids?
butorphanol, pethidine
What are medium-acting opioids?
methadone and morphine
What are longer acting opioids?
buprenorphine
What is the duration of action for fentanyl
20 minutes
When might you use fentanyl?
during high stimulus part of surgery in addition to other opioid analgesia
When might you use a short acting opioid?
pre-med or sedative combo, multimodal analgesia regimen
When would you use medium and longer acting opioids?
part of multimodal analgesia regimen, postoperative analgesia, painful patient
What can generally affect duration of action?
higher dose, duration of action increased
How can you increase duration of action?
- oral sustained release formulations
- IM or SC pellets, insoluble form, adding vasoconstrictor
- transdermal delivery systems
What are common misconceptions with opioids?
- cats become manic
- cannot be re-dosed within their expended duration of action
- respiraotyr depression can occur
- cannot be combined with other classes of analgesic drug
Why might a cat become manic due to opioid admin/
if given as pre-med. high dose or pain free cat
What are the useful clinical effects of opioids?
analgesia, sedation, cough suppression
Why do side effects occur?
due to potency
What is the antagonist for opioids?
naloxone
What are the two main side efeects we worry about with opioid administration?
respiratory depression and bradycardia
How can bradycardia be treated?
atropine or glycopyrrolate
What are some less worrysome side effects of opioids?
- sedation when not desired
- excitation
- gut stasis
- nausea and vomiting
What is the order of analgesia efficacy?
- fentanyl (most)
- methadone + morphine
- pethidine
- buprenorphine
- butorphanol (least)
What are the effects of administering fentanyl?
- some respiratory depression when given during anaesthesia
- induce bradycardia
- useful as CRI as short acting
What are the effects of giving methadone?
- reduced nausea + vomiting compared to morphine
- no concern for histamine release given IV
- minimal CVS and respiratory side effects
- NMDA receptor antagonist effects
What happens when pethidine is given?
- short acting
- large volume needed so painful IM
- histamine release of given IV
What happens when buprenorphine is given?
- good in cats
- not very effective suncut
- delayed onset of action
- painful on injectionand not palatable when given oral transmucosally
What happens when butorphanol is given?
- analgesia short lived, higher dosses needed
- may confound subsequent full mu-agonist
- good sedation
How should you plan perioperative analgesia?
- base off patients current and anticipated pain
- provide analgesia before it is needed
- pain score regularly
- consider other analgesics
