Test 1: 5 opioids Flashcards
classes of opioid receptors
μ
κ
δ
effects of μ opioid receptor
analgesia
bradycardia
↓breathing
↓GI motlility
vomiting
↓urine production
effects of kappa opioid receptors
analgesia
↑urine production
effects of delta opioid receptor
analgesia
↓breathing
where are opioid receptors
brain, spinal cord, periphery
where are the opioid sites in the brain
- Rostral ventromedial medulla (RVM)
- Midbrain Periaqueductal gray (PAG)
what will opioids do in the brain
- Enhances descending inhibition
- Decreases descending facilitation
- Influences nociceptive processing (perception)
where are opioid receptors in the spinal cord
dorsal horn of the spinal cord
how does opioids work in the spinal cord
- Reduce the release of excitatory neurotransmitters
- Reduce the excitability of neurons that carry pain signals
where are opioid receptors in the periphery
nerve endings
how does opioids work in the periphery
- Inhibit afferent nociceptive transmission
- Upregulated with inflammation
why use κ agonist
will be μ antagonist
will wake up patient
butorphanol
efficacy vs potency
efficacy: how well the drug works: The maximum response achievable from an applied or dosed agent
potency: how much drug you need: Measurement of drug activity in terms of the amount required to produce an effect of given intensity
Measurement of drug activity in terms of the amount required to produce an effect of given intensity
potency
Comparisons are made to morphine
- “How much drug you need”
The maximum response achievable from an applied or dosed agent
efficacy
how well the drug works
The extent or fraction to which a drug binds to receptors at any given concentration
affinity
“How strong is the binding with receptor”
what are some ways to give an opioid
- IV – 100% bioavailability, IM/SC – well absorbed
- Oral – variable bioavailability, 1st pass effect, formulation/species dependent
- Oral Transmucosal – pH of the mouth x pKa of the drug
- Transdermal – lipophilic with low molecular weight, but VERY variable absorption
- Epidural – lipophilicity affects onset and duration
- Longer action with low lipid solubility = morphine
- Spinal/ Subarachnoid – lower dose than epidural
- Topical – cornea – peripheral μ opioid receptors
- Intraarticular – opioid receptors upregulated in inflamed joints
how are opioids metabolized
in the liver
CYP450 and/or glucuronidation
(opioids can last longer in cats= no glucuronidation)
except Remifentanil- metabolized by plasma esterase
which opioid is broken down by plasma esterases
Remifentanil
can be used in liver failure patients
how does opioids cause sedation
species dependent (Dogs > cats/ horses)
- Increase effects of other sedatives (phenothiazines, alpha-2)
can cause excitement in cats at high doses, and cause excitement in horses without pain
what happens to horse if you give opioids without pain
will cause excitement
other than sedation, what will opioids do to the brain
Reduce cerebral metabolic rate
maintain cerebral blood flow and intracranial pressure
can cause vomiting and stop cough
dogs ↓temp
cats, ruminants and pigs ↑temp
opioids will do what to thermoregulation
Species-specific effects
Dogs – Hypothermia
* Reset thermoregulatory point in hypothalamus = pant at normal body temperature
Cats, ruminants, pigs - Hyperthermia
what will opioids do to respiratory center
dose dependent depressent
direct effect in the respiratory center
Decreased responsiveness of chemoreceptors to CO2 and hypoxia
humans and primates can stop breathing and die with overdose
effects of opioids on the heart
Minimal effects in cardiac output, rhythm, and arterial blood pressure
some bradycardia can occur
IV meperidine and morphine can cause
histamine release
vasodilation and hypotension
opioids will do what to GI tract
decrease motility
- Mediated by μ and δ receptors in the myenteric plexus
- Predispose to ileus and constipation
- Colic in horses and tympany in ruminants
effects of opioids on urinary tract
may cause urinary retention
* Decrease detrusor contractility
* Decreased sensation of urge
Special caution for epidural administration
woody chest is caused by
rare muscle rigidity with full opioid agonists
what will opioids do to pupil size
- Mydriasis – cats, horses, ruminants
- Miosis – dogs, rabbits, rats
what are some opioid antagonists
Naloxone
- Naltrexone
- Methylnaltrexone
- Diprenorphine
— is a partial μ agonist
Buprenorphine
opioid
— are agonist- antagonist
Butorphanol
Nalbuphine
— can cause histamine releases after fast IV administration
IV meperidine and morphine
what opioid is used for epidural analgesia
morphine
Crosses BBB slower than synthetics opioids
* Persists in epidural space for 12 – 24h
hydromorphone has a — duration
short 2-4 hr
morphine lasts 4-8 hrs
hydro 10 x more potent
— can cause panting in dogs and hyperthermia in cats
hydromorphone
10 x more potent then morphine
shorter duration (2-4 hrs)
methadone
Opioid agonist + NMDA antagonist – good for chronic / neuropathic pain
no vomiting!
potency, onset and duration similar to morphine
— is an opioid used for chronic/ neuropathic pain
methadone
Opioid agonist + NMDA antagonist
No vomiting
NMDA is a glutamate receptor= excitatory
meperidine
- Route: IM, SC
- Duration: 1-4h
- No vomiting and less bradycardia
- Market histamine release
- Analgesia (0.1) not profound as morphine – short procedures / mild pain
— is Highly lipid-soluble, short-acting synthetic opioid with 30 min duration
fentanyl
can be given as CRI or transdermal patches
100 x more potent then morphine
what opioid is not metabolized by the liver
Remifentanil
Analog of fentanyl
200 x more potent then morphine
— are high potency opioids used in large wildlife mammals
Carfentanil and Etorphine (M99)
Etorphine (3000x )
Carfentanil (10000x)
Butorphanol
Agonist at κ receptor and antagonist at μ receptor
short duration 1 hr
Can be used to partially antagonize full opioid drugs
Mild sedation – better if combined with other sedatives
Commonly used in horses and birds
— is an agonist at κ receptor and antagonist at μ receptor that is used in horses and birds
butorphanol
Minimal analgesia
Short duration – 1h
Mild sedation – better if combined with other sedatives
— can be given tranmucosally in cats due to their high pH
buprenorphine
Partial μ agonist
short onset and long duration (6-12 hrs)
— is a Partial μ agonist and the duration is —
buprenorphine
1hr onset, 6-12 hr duration
can be given IV, IM or SC
transmucosal in cats
— will reverse opioids
nalaxone: duration 30-60 mins, may need to redose
naltrexone: long lasting for reversal of high potency opioids
what is MAC reduction?
minimum alveolar concentration
will reduce the amount of inhalant required to maintain the anesthetic plan
opioids will cause a MAC reduction
why use opioids with anesthesia
- Sedation in premed – reduce patient stress
- Analgesia
- MAC Reduction-reduce amount of inhalant needed, improve cardiovascular stability
