12. Pharmacology of pain: Opoid receptor agonists Flashcards
(41 cards)
1
Q
Nociception
A
Mechanism:
- Peripheral stimuli → CNS
2
Q
Polymodal nociceptors (PMN)
A
Main peripheral sense neurons that respond to noxious stimuli
- Sensitised to prostaglandins
- Release glutamate (fast transmitter) & various peptides
3
Q
Nociceptive fibres terminate in…
A
Superficial layers of the dorsal horn
- Forming synaptic connections with transmission neurons running to the thalamus
4
Q
Transmission of nociceptive fibres to the dorsal horn is subjected to…
A
Modulatory influences constituting “Gate control” mechanism
5
Q
Descending pathways from the midbrain & brainstem exert…
A
Strong inhibitory effect on dorsal horn transmission
6
Q
Opidoids cause analgesia by…
A
- By activating the descending pathways
- By inhibiting transmission in the dorsal horn
7
Q
Opioids mimic actions of…
A
Endogenous opioids (Endorhpin & encephalin)
- Peptides produced in nervous & endocrine systems
- Stimulate opioid receptors
8
Q
List the opioid receptors
A
- μ (mu)
- κ (kappa)
- δ (delta)
9
Q
All opioid receptors function by…
A
Exerting inhibitory modulation of synaptic transmission in both CNS & peripheral nerve cells
10
Q
Indications of opioid agonist use
A
- Premedication before general anaesthesia
- Neuroleptanalgesia
- Combination in balance anaesthesia
- Analgesia
- Diarrhoea
- Antitussive (cough prevention)
11
Q
Side effects of opioid agonist use
A
- Respiratory depression
- Bradycardia
- Vasodilation, hypotension
- Vomiting
- Constipation
- Urinary retention
12
Q
List some opioid agonists
A
- Morphine
- Butorphanol
- Buprenorphine
- Fentanyl
- Tramadol
- Methadone
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
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
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
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
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
Naloxone:
* Receptor binding
* µ
* κ
* Analgesia
* Receptor binding = Antagonist
* µ = ATG
* κ = ATG
* Analgesia = -
26
Morphine:
* Duration of action
* Dose
* Duration of action = **2-6hr**
* Dose = **0.1-0.8 IV. IM. IC.**
* **PO:**
* **Dog = 4-10mg**
* **Cat = 2-4 mg**
27
Fentanyl:
* Duration of action
* Dose
* Duration of action = **15-30 min**
* Dose =
* **0.002-0.005 IV bolus******
* **5-40µg/kg/h**
28
Sufentanyl:
* Duration of action
* Dose
* Duration of action = **10-20 min**
* Dose =
* **0.003-0.005 IV bolus******
* **3µg/kg/h**
29
Tramadol:
* Duration of action
* Dose
* Duration of action = **6-8hr (retard 8-12)**
* Dose =
* **2-4 IV. IM**
* **3-10 PO**
30
Butorphanol:
* Duration of action
* Dose
* Duration of action = **1-3hr (4)**
* Dose = **0.2-0.4**
31
Naloxon:
* Duration of action
* Dose
* Duration of action = **30 min**
* Dose = **0.01-0.04**
32
Buprenorphine:
* Duration of action
* Dose
* Duration of action = **4-8hr**
* Dose = **0.01-0.02**
33
Because fentanyl is lipophilic...
It can be used on skin as a transdermal patch
34
Morphine: Speed of onset
* IV = 15 minutes
* IM = 30 minutes
* SC = 45 minutes
## Footnote
*Fentanyl has a 2-3 minute onset, so is therefore preferred.*
35
Degradation of morphine in the body
Morphine → Morphine-glucuronide *(active form)*
## Footnote
*via liver activation*
36
Because tramadol is more active in cats than dogs...
A lower dose should be given
37
Use of acepromazine (ACP)
**Used before surgery to prevent vomiting**
38
Why are opioids used for cardiovascular patients?
Opioids don't cause hypotension
## Footnote
*Cats are very resistant*
39
Preferred drug for pancreatitis
Buprenorphine
40
Tramadol
* Broad therapeutic index
* High PO bioavailability
* Good antitussive
41
Methadone
Synthetic agonist
