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Pharmacology I > 12. Pharmacology of pain: Opoid receptor agonists > Flashcards

12. Pharmacology of pain: Opoid receptor agonists Flashcards

1
Q

Nociception

A

Mechanism:

  • Peripheral stimuli → CNS
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2
Q

Polymodal nociceptors (PMN)

A

Main peripheral sense neurons that respond to noxious stimuli

  • Sensitised to prostaglandins
  • Release glutamate (fast transmitter) & various peptides
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3
Q

Nociceptive fibres terminate in…

A

Superficial layers of the dorsal horn

  • Forming synaptic connections with transmission neurons running to the thalamus
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4
Q

Transmission of nociceptive fibres to the dorsal horn is subjected to…

A

Modulatory influences constituting “Gate control” mechanism

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5
Q

Descending pathways from the midbrain & brainstem exert…

A

Strong inhibitory effect on dorsal horn transmission

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6
Q

Opidoids cause analgesia by…

A
  • By activating the descending pathways
  • By inhibiting transmission in the dorsal horn
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7
Q

Opioids mimic actions of…

A

Endogenous opioids (Endorhpin & encephalin)

  • Peptides produced in nervous & endocrine systems
  • Stimulate opioid receptors
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8
Q

List the opioid receptors

A
  • μ (mu)
  • κ (kappa)
  • δ (delta)
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9
Q

All opioid receptors function by…

A

Exerting inhibitory modulation of synaptic transmission in both CNS & peripheral nerve cells

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10
Q

Indications of opioid agonist use

A
  • Premedication before general anaesthesia
  • Neuroleptanalgesia
  • Combination in balance anaesthesia
  • Analgesia
  • Diarrhoea
  • Antitussive (cough prevention)
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11
Q

Side effects of opioid agonist use

A
  • Respiratory depression
  • Bradycardia
  • Vasodilation, hypotension
  • Vomiting
  • Constipation
  • Urinary retention
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12
Q

List some opioid agonists

A
  • Morphine
  • Butorphanol
  • Buprenorphine
  • Fentanyl
  • Tramadol
  • Methadone
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13
Q

Morphine

A
  • Agonist, Schedule 2
  • Analgesic
  • Depression of respiratory, vasomotor & cough centres
  • Stimulation of chemoreceptor trigger zone & vomiting centre
  • Myosis (constriction of pupil)
  • Inhibition of peristaltic movements
  • Good somatic & visceral analgesia
  • Treatment of diarrhoea, cough suppression
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14
Q

Butorphanol

A
  • Synthetic mixed agonist
  • Similar to morphine
  • Slow onset, relatively long duration (3-4hr)
  • Used alone or in combination with α2 agonists

Dog/cat: Analgesic, premedication, ↓non-productive cough

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15
Q

Buprenorphine

A
  • Semisynthetic mixed agonist
  • More potent than morphine with less side effects
  • Onset 15 minutes after IV
  • Long duration (12hr)
  • Not to be used in bone surgery
  • Slight sedation
  • Primary drug for pancreatitis
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16
Q

Fentanyl

A
  • Synthetic agonist, Schedule 2
  • Somatic analgesia
  • Respiratory depression, bradycardia
  • Few minutes duration
  • Transdermal patches
    • Peak action at 24 hours
    • Used for 3 days
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17
Q

Give the safer derivatives of fentanyl

A
  • Remifentanyl (short action/quick elimination)
  • Alfentanyl
  • Sufentanyl

Soon to replace fentanyl - Safer

18
Q

What is used for morphine/fentanyl overdose? Why?

A

Buprenorphines

  • Higher affinity to μ receptors that morphine/fentanyl
19
Q

Morphine:

  • Receptor binding
  • µ
  • κ
  • Analgesia
A
  • Receptor binding = Full agonist
  • µ = +++
  • κ = +
  • Analgesia = +++
20
Q

Methadone:

  • Receptor binding
  • µ
  • κ
  • Analgesia
A
  • Receptor binding = Full agonist
  • µ = +++
  • κ =
  • Analgesia = +++
21
Q

Fentanyl:

  • Receptor binding
  • µ
  • κ
  • Analgesia
A
  • Receptor binding = Full agonist
  • µ = +++
  • κ = ++
  • Analgesia = ++++
22
Q

Tramadol:

  • Receptor binding
  • µ
  • κ
  • Analgesia
A
  • Receptor binding = Full agonist
  • µ = +
  • κ =
  • Analgesia ++
23
Q

Butorphanol:

  • Receptor binding
  • µ
  • κ
  • Analgesia
A
  • Receptor binding = Agonist-antagonist
  • µ = -
  • κ = ++
  • Analgesia = +
24
Q

Buprenorphine:

  • Receptor binding
  • µ
  • κ
  • Analgesia
A
  • Receptor binding = Partial agonist
  • µ = ++
  • κ =
  • Analgesia = ++
25
Q

Naloxone:

  • Receptor binding
  • µ
  • κ
  • Analgesia
A
  • Receptor binding = Antagonist
  • µ = ATG
  • κ = ATG
  • Analgesia = -
26
Q

Morphine:

  • Duration of action
  • Dose
A
  • Duration of action = 2-6hr
  • Dose = 0.1-0.8 IV. IM. IC.
    • PO:
      • Dog = 4-10mg
      • Cat = 2-4 mg
27
Q

Fentanyl:

  • Duration of action
  • Dose
A
  • Duration of action = 15-30 min
  • Dose =
    • 0.002-0.005 IV bolus​
    • 5-40µg/kg/h​
28
Q

Sufentanyl:

  • Duration of action
  • Dose
A
  • Duration of action = 10-20 min
  • Dose =
    • 0.003-0.005 IV bolus​
    • 3µg/kg/h​
29
Q

Tramadol:

  • Duration of action
  • Dose
A
  • Duration of action = 6-8hr (retard 8-12)
  • Dose =
    • 2-4 IV. IM
    • 3-10 PO
30
Q

Butorphanol:

  • Duration of action
  • Dose
A
  • Duration of action = 1-3hr (4)
  • Dose = 0.2-0.4
31
Q

Naloxon:

  • Duration of action
  • Dose
A
  • Duration of action = 30 min
  • Dose = 0.01-0.04
32
Q

Buprenorphine:

  • Duration of action
  • Dose
A
  • Duration of action = 4-8hr
  • Dose = 0.01-0.02
33
Q

Because fentanyl is lipophilic…

A

It can be used on skin as a transdermal patch

34
Q

Morphine: Speed of onset

A
  • IV = 15 minutes
  • IM = 30 minutes
  • SC = 45 minutes

Fentanyl has a 2-3 minute onset, so is therefore preferred.

35
Q

Degradation of morphine in the body

A

Morphine → Morphine-glucuronide (active form)

via liver activation

36
Q

Because tramadol is more active in cats than dogs…

A

A lower dose should be given

37
Q

Use of acepromazine (ACP)

A

Used before surgery to prevent vomiting

38
Q

Why are opioids used for cardiovascular patients?

A

Opioids don’t cause hypotension

Cats are very resistant

39
Q

Preferred drug for pancreatitis

A

Buprenorphine

40
Q

Tramadol

A
  • Broad therapeutic index
  • High PO bioavailability
  • Good antitussive
41
Q

Methadone

A

Synthetic agonist

Pharmacology I (19 decks)

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