Lecture 9: Opioid Analgesics Flashcards

1
Q

What is nociception

A

Sensory processing and transmission of noxious stimuli

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2
Q

What are the affective components of pain (2)

A

Sensation and tissue damage

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3
Q

Opioids are effective at addressing both ___and ___

A

Pain transmission and affective components (sensation and tissue damage)

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4
Q

Opioids are the most effective analgesics available for ___

A

Tx of systemic acute pain

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5
Q

What is the pain transmission pathway

A
  1. Spinal nerves
  2. Spinal cord in dorsal horn
  3. Release substance P and glutamate
  4. Spinal cord—>brain
  5. Descending pathway
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6
Q

What 3 ways do opioids block pain

A

Inhibit perception, transduction and modulate the spinal pathway

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7
Q

Where are Mu receptors found

A

Brain and in the spinal cord in dorsal horn

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8
Q

What does activation of mu receptors result in

A

Sedation, supraspinal and spinal analgesia, miosis, respiratory depression, euphoria, inhibition of ACh and dopamine release, decrease GI motility

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9
Q

Where are kappa receptors found

A

Cerebral cortex, spinal cord and other brain regions

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10
Q

What is the result of activating kappa receptors

A

Spinal and supraspinal analgesia, mild sedation, inhibition of vasopressin, miosis

Less respiratory depression than mu

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11
Q

Where are delta receptors located

A

Limbic system, cerebral cortex and spinal cord

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12
Q

What is the result of activating delta receptors

A

Spinal and supraspinal analgesia, inhibition of dopamine release and cardiovascular depression

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13
Q

What is the mechanism of action of opioids

A
  1. Act on Gi proteins
  2. Decrease cAMP
  3. Close VG Ca2+ channels
  4. Decrease NT release- ACh, glutamate, substance P, NE
  5. Open presynaptic K+ channels (mu) causing hyperpolarization
  6. Promote release of endogenous opioids that further inhibit pain transmission
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14
Q

What are the two overall effects of opioids

A
  1. Inhibition of pain transmission
  2. Simulation of descending inhibitory neurons
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15
Q

The primary use for opioids is ___

A

Analgesia

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16
Q

What are the endogenous opioids

A

Endorphins, enkephalins, dynorphins

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17
Q

Release of endorphins causes ___

A

Euphoria

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18
Q

Release of enkephalins causes ___

A

Decreases our sensation and reaction to pain

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19
Q

Drugs that stimulate __ receptors produce profound analgesia

A

U receptors

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20
Q

What is the mechanism in which opioids provide analgesia

A

They decrease the transmission of pain in the spinal cord and the sensation of pain in the cerebral cortex, increase release of encephalin from PAG further reducing pain transmission

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21
Q

Opioid receptors undergo ___ and ___ which may lead to decrease effect overtime/ tolerance

A

Desensitization and downregulation

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22
Q

What effects do opioids have on the CNS

A

At low doses: sedation
At high doses: excitement
Horses and cats: excitement
Dogs: sedation

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23
Q

Opioids may cause ___ in dogs

A

Dysphoria

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24
Q

Opioids may cause ___ and ___ in cats

A

Dysphoria and increased motor activity

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25
Q

What are the effects of opioids on the pupils

A

Miosis in most species
Mydriasis in cats and horses

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26
Q

What effects do mu receptor agonists have on respiratory system

A

They are respiratory depressants, increase arterial CO2 and decrease arterial O2 and pH

Result in panting in dogs and resetting hypothalamic temperature set point

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27
Q

What are the effects of opioids on the cardiovascular system

A

Bradycardia
Hypotension- vasodilation due to histamine release

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28
Q

What opioid is most likely to cause vasodilation from histamine release

A

Morphine

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29
Q

____ and ____ in cats from histamine may become dangerous

A

Pruritis and excoriation

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30
Q

What are the GI effects from opioids

A
  1. Stimulate CRTZ- vomiting
  2. Aspiration from vomiting
  3. Decrease GI-constipation and decrease gastric empty
  4. Anti-diarrhea
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31
Q

What receptors does morphine act on

A

Full mu receptor agonist
High doses stimulate kappa receptors

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32
Q

What species is morphine typically used in

A

Cats, dogs, and horses

33
Q

___can induce vomiting in dogs by stimulating CRTZ

A

Morphine

34
Q

How is morphine metabolized in cats vs dogs

A

Cats: sulfate conjugation
Dogs: glucoronidation

35
Q

What are the uses for morphine

A

Tx for acute pain in dogs, cats and horses

36
Q

What can morphine cause in horses and what would should be given with it

A

Excitement, give with xylazine, acepromazine, diazepam

37
Q

What are some adverse effects of morphine

A

Hyperexcitation, hypotension (d/t histamine), cerebral hemorrhage and edema (increase cerebral BF and ICP- don’t use with head injuries) , hyperthermia in dogs and rabbits, hyperthermia in cats, horses and ruminants

38
Q

What are the doses of morphine that produce excitation in dogs, cats and horses

A

Dogs: 20mg/kg
Cats: 5-10mg/kg
Horses: 0.66mg/kg

39
Q

What receptor does methadone act

A

Synthetic u agonist

40
Q

Methadone can be used as an alternative to ___in dogs and cats. Why?

A

Morphine- reduce vomiting, nausea and defecation

41
Q

What is methadone used for

A

Pre-anesthetic or analgesia in dogs or cats

42
Q

Does methadone have a long or short half life and duration of action

A

Long

43
Q

What are some adverse effects of methadone

A

Sedation, respiratory depression

44
Q

What receptors do oxymorphone and hydromorphone act on

A

U agonists

45
Q

Hydromorphone and oxymorphone have less___than morphine

A

Vasodilation/histamine release

46
Q

What are some side effects of oxymorphone, hydromorphone

A

Panting in dogs, bradycardia, sedation, and hyperthermia in cats

47
Q

What is oxymorphone, hydromorphone used for

A
  1. Analgesia in dogs, cats and horses
  2. Preanesthetic administration
  3. Neurleptanalgesia
  4. Anesthesia in swine combined with ketamine and xylazine
48
Q

Hydromorphone combined with ___can decrease vomiting and panting in dogs

A

Acepromazine

49
Q

Hydrocodone is converted to hydromorphone and can be used as a __in dogs

A

Antitussive

50
Q

What receptor does fentanyl act on

A

U agonist

51
Q

What are some uses for fentanyl

A
  1. Anesthetic induction regimen
  2. Control intra-op and post-op pain
  3. Chronic pain
52
Q

What are some adverse effects of fentanyl

A
  1. Auditory stimuli may evoke motor response
  2. Panting, defecating, flatulence
  3. Bradycardia and hypersalivation
53
Q

What are the benefits of fentanyl patch

A

Provide long lasting pain relief for up to 4 days

54
Q

What receptor does alfentanil act on

A

U receptor agonist

55
Q

What is alfentanil used for

A
  1. Analgesic and sedative
  2. Adjunctive for anesthesia particularly in cats
56
Q

What receptor does sufentanil act on

A

U receptor agonist (more potent than fentanyl)

57
Q

What is sufentanil used for

A

Adjunctive anesthesia, epidural analgesia, post-op analgesic

58
Q

What are some adverse effects of sufentanil

A

Sedation, respiratory depression, bradycardia

59
Q

What is carfentanil used for

A

Labeled for IM to immobilize large/wild animals

60
Q

What are some adverse effects of carfentanil

A
  1. Disruption of body temperature- hyper/hyporthermia that can be fatal in field
  2. Respiratory and CNS depression
61
Q

What is the reversal agent for carfentanil

A

Naltrexone

62
Q

What receptors does tramadol act on

A
  1. Weak u receptor agonist
  2. Inhibits reuptake of serotonin and NE
  3. Stimulates alpha2 receptors via NE
63
Q

What is tramadol used for

A

Analgesia, antitussive

64
Q

What are some adverse effects of tramadol

A

Seizures if given with other antidepressants/ fluoxetine

65
Q

What receptors does buprenorphine act on

A

Partial agonist on u receptors and antagonist on k receptors

66
Q

Buprenorphine is resistant to antagonism by what reversal

A

Naloxone

67
Q

What is buprenorphine used for

A

Pre-op and post-op analgesia in small animals and analgesia in horses

68
Q

What are some adverse effects of buprenorphine

A

Respiratory depression, excitement, mydriasis in cats, sedation

69
Q

What receptors does butorphanol act on

A

K receptor agonist, partial agonist or antagonist for u receptors

70
Q

Butorphanol can be used as a reversal for what receptor and what does it reverse and what is maintained

A

Reverse effects of u agonist- sedation, respiratory depression while maintaining analgesia from k effect

71
Q

What is butorphanol labeled for

A
  1. Antitussive in dogs from chronic upper respiratory infections
  2. Analgesia in cats
  3. Visceral pain in horses with colic
  4. Analagesia and chemical restraint in cattle combined with ketamine
  5. Mild to moderate pain
  6. Anti-emetic for chemo patients
72
Q

What are some adverse effects of butorphanol

A
  1. Head bobbing in horses, ataxia, sedation or excitement
  2. P-gp metabolism so decrease does 25% in heterozygous MRD1 mutations and 50% in homozygous
73
Q

What receptors does nalbuphine act on

A

K receptor agonist, u receptor antagonist

74
Q

What are the uses for nalbuphine

A
  1. IM to control mild to moderate pain or pre surgery protocol
  2. Topical administration for pain from corneal ulcers
75
Q

What receptors does Naloxone act on

A

High affinity u receptor antagonist, low affinity for k

76
Q

What are the uses for Naloxone

A

Reverse opioid induced sedation, respiratory depression, dysphoria

77
Q

What are some adverse effects of Naloxone

A
  1. Reversal of analgesia
  2. Nausea, vomiting, hypotension, tachycardia
78
Q

What receptors does naltrexone act on

A

U receptor antagonist

79
Q

What is naltrexone used for

A
  1. Reverse opioid induced immobilization of large animals
  2. Oral administration to tx behavioral problems in dogs