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Opioid Agonists/antagonists Flashcards

1
Q

Opioid receptor

A

Serpentine molecule embedded in cell membrane
- 1 terminal ending exposed to extracellular envi
- other terminus is intracellular

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2
Q

Types of opioid receptors

A

Mu, Kappa, Delta, Sigma

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3
Q

Presynaptic function of opioid receptors

A

Inhibits neurotransmitter release (ACh, Dopamine, norepinephrine, substance P, GABA)

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4
Q

postsynaptic function of opioid receptors

A

Decreases neuronal excitability through hyperpolarization of cell membranes

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5
Q

Mu receptor subtypes

A

Analgesia (supraspinal & spinal)
Euphoria, ventilatory depression, bradycardia, urinary retention, physical dependence

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6
Q

Kappa subtype receptors

A

Analgesia (supraspinal & spinal)
Dysphoria, sedation, miosis

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7
Q

Delta subtypes receptors

A

Analgesia (supraspinal & spinal)
Ventilatory depression, urinary retention, modulation of Mu activity

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8
Q

Tissues for receptor distribution

A

Brain
Spinal cord
GIT
UIT
Synovium
Leukocytes
Uterus

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9
Q

Pure opioid agonist binding affinity

A

Produces dose-dependent increase in effect until max stimulation of receptor achieved
Effect increases as dose (or plasma concentration) increases until it plateaus at max effect

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10
Q

Partial opioid agonist binding affinity

A

Binding at given receptors causes an effect that is less pronounced than that of a pure agonist
Produces dose-dependent increase in effect, but plateaus at max effect less than max effect of full agonist

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11
Q

Opioid agonist-antagonist binding affinity

A

Causes stimulators effect at one receptor but blocks effect or causes less pronounced effect at another
Effects of these drugs depends on previous opioid exposure

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12
Q

Opioid antagonist affinity

A

Binds to receptor with high affinity & produces no effect
- reverses receptor mediated effects of agonists by inhibiting binding of agonist & displacing previously bound agonist due to greater receptor affinity of antagonist (competitive binding)

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13
Q

Full agonist classifications

A

Morphine, hydromorphone , methadone, oxymorphone, fentanyl

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14
Q

Partial agonist classifications

A

Buprenophine

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15
Q

Agonist-antagonist classifications

A

Butorphanol

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16
Q

Antagonist classifications

A

Naloxone, nalmefene, naltrexone

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17
Q

Different potency

A

Ex fentanyl and morphine have different potency meaning one will act quicker with less drug

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18
Q

Different efficacy

A

Ex morphine and buprenophine
Drugs given at same amount will have greater or less effect than the other

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19
Q

PD absorption considerations

A

Lipophilic /absorption rate
Bioavailability via SQ & IM
Low oral bioavailability
Transdermal absorption - fentanyl bypasses GIT and skips first pass hepatic effects
Transmucosal absorption - buprenorphine by passes first pass metabolism, variable absorption

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20
Q

PD considerations - distribution

A

Morphine is hydrophilic
P-glycoprotein efflux pumps limit CNS effects
- limit BBB crossing
- ex loperamide ->reduced central effects

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21
Q

PD considerations - mutations

A

Homozygous mutation in MDR1 gene
- BC, Aussie, GS, shetlands, sheepdogs, whippets
- significant central effects
- morphine, methadone, fentanyl, buprenophine, oxycodone

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22
Q

PD considerations - metabolism & elimination

A

Metabolized through hepatic microsomal enzyme
Morphine - phase III glucuronidation to morphine-3-glucuronide (EXCEPTION, poor glucur, rapidly metabolizes morphine through sulfate conjugate
Elim through biliary or renal
^ elim time in geriatric
Remifentanil met is via plasma esterase

23
Q

Which of the following best describes the opioid & classification?
Buprenophine - full Mu agonist
Methadone - partial Mu agonist
Fentanyl - Mu antagonist & K agonist
Oxymorphone - full Mu agonist

A

Oxymorphone - full mu agonist

24
Q

CNS effects - analgesia

A

Inhibition of presynaptic NT release & post hyperpolarization of neuronal membranes = v excitability = v transmission within spinal cord
^^regulation of supraspinal descending antinociception pathways
- epidural = saturate spinal opioid receptors = effects on C-fibers & A-delta fiber nociceptors

25
Which opioid is more hydrophilic ?
Morphine
26
CNS effects - sedation
Dose-dependent sedation, more profound sedation w phenothiazines and alpha-2s
27
CNS effects - excitation
High does or rapid IV= excitation (^ plasma concentration quickly achieved) Cats & horses can exhibit Dysphoric /excitatory behavior lasting few hours
28
CNS effects - dysphoria & euphoria
Vocalizing, thrashing, ataxia, hypersensitivity
29
CNS effects - thermoregulation
Hypo response: dogs, rabbits, birds (more profound w phenothiazines/inhalants) Hyper response: cats, horses, rum, pigs Cats: hydromorphone, morphine, buprenophine, butorphanol, up to 5 hours post extubation
30
Respiratory effects
Direct depression from brainstem (Mediated by supraspinal Mu2 opioid receptors) Decreased responsiveness to ^ CO2 Dose dependent resp depression (Consider ICP, lung disease) Antitussives effects Panting Opioids cross placenta = resp depression of neo
31
Cardiovascular effects - Bradycardia
Opioid induced medullary vagal stim 2nd degree atrioventricular block Anti-muscarinics block/reverse this effect Caution in young patients -minimal effects of myocardial contractility, C output, arterial blood pressure (at clinical doses)
32
Peristaltic effects
Propulsion contractions decreased - constipation, ileum, concerning in horses & rum Non-propulsive contractions increased - occasionally causing defecation - dogs>cats
33
Endocrine effects
Histamine release - morphine, meperidine Nausea & vomiting - direct stim of CTZ, IV
34
Urinary effects
Mu effect - increases ADH & natriuretic peptide, v urine production Kappa effect - decreases ADH, diuresis
35
Immune system effects
Morphine, fentanyl, codeine, methadone = Immunosuppression
36
Ocular effects
Dogs, rabbits, rats = miosis Cats, horses, rum = mydriasis
37
Potential for substance abuse
Regulated substance Tolerance & physical dependence Opioid induced hyperalgesia Gene expression affecting opioid metabolism
38
Process of selection opioids
Degree of pain Duration of pain/procedure Sedation requirement Adverse effects Specific species requirements/limits Available routes of admin Cost
39
Morphine Analgesia, sedation, peak onset, side effects, routes
Analgesia - severe pain sedation - excellent sedation peak onset - 15-30 minutes, duration 3-4 hrs side effects - histamine release, mania in cats/horses, vomiting, renal disease may impair clearance routes - SQ, IM, IV, epidural
40
Hydromorphone Analgesia, sedation, peak onset, side effects, routes
Analgesia - severe pain sedation - good sedation peak onset - 15 min, dur 4-6 hours side effects - vomiting if IM, less histamine release, panting in dogs, hyperthermia in cats routes - SQ, IM, IV
41
Methadone Analgesia, sedation, peak onset, side effects, routes
Analgesia - severe sedation - good peak onset - 15, dur 4-6hr side effects - no histamine release, no vomit, panting in dogs routes - SQ, IM, IV
42
Fentanyl Analgesia, sedation, peak onset, side effects, routes
Analgesia - severe sedation - good peak onset - 6-8 minutes, duration 30-60 minutes side effects - no histamine, no vomiting, bradycardia, chest rigidity (v compliance) routes - IM, IV, transdermal
43
Buprenorphine Analgesia, sedation, peak onset, side effects, routes
Analgesia - mild to moderate sedation - minimal peak onset - 45-90 minutes, dur 6-8 hrs side effects - high affinity for receptor, plateau effect, not effectively reversed w antagonist routes - PO, Transmucosal, IM, IV
44
Butorphanol Analgesia, sedation, peak onset, side effects, routes
Analgesia - mild sedation - good peak onset - 10-15 minutes, dur 1-2 hrs side effects - high affinity for receptor, plateau effect, can reverser effect of pure Mu agonists routes - SQ, IM, IV
45
Which of the following opioids should be avoided in a dog diagnosed w cutaneous & visceral mast cell tumors? Buprenorphine Methadone Morphine Oxymorphone
Morphine Because of histamine release
46
Reasons and effects of reversing effects with antagonists
Opioid overdose or excessively sedated or obtunded from opioids ^ alertness, responsiveness, coordination, ^awareness of pain
47
Naloxone
Prototypical Mu antagonist Onset: 2-5 min 0.01-0.04 mg/kg IV -> lasts 20-40 min Opioid effects could reoccur
48
Nalmefene, naltrexone
4x as potent as Naloxone Onset: 2-5 min Duration: 1-2 hours
49
Methlynaltrexone
Quaternary derivative of naltrexone Controls GIT side effects of opioids (ileus) without effecting centrally mediated analgesia
50
Considerations for clinical use
Systemic use Regional or local admin Parenteral sustained release Injectable subcutaneous
51
Which is the best option in a cat that needs an abdominal explore, but also presented w hepatic and renal dysfunction? Buprenorphine Remifentanil Methadone
Remifentanil - metabolized by plasma esterases
52
Oral opioids
Tramadol, codeine, hydrocodone
53
Tramadol with dogs & horses
Metabolized by O-desmethyltramadol (M1) via P450 enzymes which determines the strength of analgesia Dogs & horses produce less M1 = weak analgesia Cats produce substantial M1 = effective analgesia

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