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4 Clinical Pharmacology and Intro to Prescribing > 16 Opioids > Flashcards

16 Opioids Flashcards

1
Q

Differentiate between nociception and pain.

A

Nociception= non concious neural traffic due to trauma or potential trauma to tissue

Pain= complex, unpleasant awarness of sensation modified by experience, expectation, immediate context and culture

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2
Q

How do we feel pain? (explain the pathway)

A
  1. Nociceptors stimulated
    1. Release Substance P and Glutamate
  2. Afferent nerve stimulated
    1. A delta fibres= sharp pain
    2. C fibres= dull pain
  3. Fibres decussate then ascend
  4. Synapse in thalamus
  5. Project to post central gyrus
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3
Q

We can modulate pain peripherally and centrally. Where can the modulators be found?

A

Peripherally: substantia gelatinosa

Centrally: peri aqueductal grey

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4
Q

How do we modulate pain peripherally?

A

Substantia gelatinosa

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5
Q

How do we modulate pain centrally?

A
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6
Q

Name 3 endogenous opioids.

A

Enkephalins

Dynorphins

B-endorphins

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7
Q

What receptors do the endogenous opioids act on? (3) Where are each of these receptor types found and what actions do they have?

A
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8
Q

Outline the WHO analgesic ladder:

A
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9
Q

What drug types might be give to treat neuropathic pain?

A

Anticonvulsants

Tricyclics

Serotonin/Noradrenaline reuptake inhibitors

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10
Q

In general, how to opioids work?

A

Exploit endogenous opioid receptors

Main effect= via μ- receptors

Aim to modulate pain

(Also indicated in: - cough, diarrhoea, palliation)

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11
Q

There are many different drugs in the opioid class. Give an example of a:

Strong agonist

Moderate agonist

Mixed agonist/antagonist

Antagonist

A

Strong agonist

  • Morphine
  • Fentanyl

Moderate agonist

  • Codeine

Mixed agonist/antagonist

  • Buprenorphine

Antagonist

  • Naloxone
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12
Q

How is morphine administered? Why does it sometimes need to be administered IV rather than orally?

A

Orally

IV

Intramuscular

Sub cut

PR

Gut absorption erratic and only has 40% oral availability due to first pass metabolism

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13
Q

Can morphine enter the foetal tissue?

A

Yes- can enter all tissues including foetal BUT not very good at crossing blood brain barrier compared to other opioids

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14
Q

Where is morphine metabolised and excreted?

A

Metabolised: liver

Excreted: renally

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15
Q

What action does morphine have? How does it work?

A

Strong affinity for μ-receptors, minimal for K and δ.

Complete activation of μ

Actions:

  • Analgesia
  • Euphoria
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16
Q

Give 6 side effects of morphine:

A
17
Q

How is fentanyl abdministered? What’s its bioavailability like?

A

Fentanyl

Administered:

  • IV
  • Epidural
  • Intrathecal (into CSF)
  • Nasal

Bioavailability:

  • 80-100%
18
Q

How well does Fentanyl cross the blood brain barrier? How is fentanyl metabolised and excreted?

A

Well- highly lipohilic, highly protein bound

Metabolism: Hepatic - CYP3A4

Elimination: Renally excreted (half-life= 6 mins)

19
Q

What actions does fentanyl have?

A

Actions of fentanyl:

  • Analgesia
  • Anaesthetic
20
Q

How does fentanyl compare to morphine (in terms of affinity for μ-receptors and side effects)

A

Affinity:

Higher affinity for μ-receptors

Side effects:

Less:

  • Histamine release
  • Sedation
  • Constipation
21
Q

What side effects might a patient get from taking fentanyl? (3)

A
  1. Respiratory depression
  2. Constipation
  3. Vomiting
22
Q

How is codeine administered?

A
  • PO (Per Os)
  • Sub cutaneous
23
Q

How does codeine work? Why might its effects be different within the population? How is it eliminated?

A

Codeine–> Morphine via CYP2D6

Varying CYP2D6 in population

CYP2D6 inhibited by Fluoxetine (SSRI)

Eliminated: same way as morphine

Glucoronidation of morphine and renal excretion

24
Q

What actions does codeine have? How does it differ from morphine in terms of potency?

A

Codeine= 1/10th potency compared to morphine

Actions:

  • Mild-moderate analgesia
  • Cough depressant
25
Q

What are the 2 main side effects of codeine?

A
  1. Constipation (give patient laxatives- esp elderly)
  2. Respiratory depression= worse in children
26
Q

How is Buprenorphine administered?

A

Transdermal (patch), buccal, sublingual

= very lipophilic

27
Q

How is Buprenorphine metabolised and excreted?

A

Metabolised:

Hepatic- CYP3A4

Glucoronidation

Elimination:

Biliary > Renal

SAFE in renal impairment

half life= 37 hrs

28
Q

What actions does Buprenorphine have and how does it exert its effects?

A

Buprenorphine

Actions:

  • Moderate-severe pain
  • Opioid addiction treatment

Mechanism:

  • High affinity for μ-receptor, antagonist at K receptors
  • Lower E(max) than morphine (as= partial agonist)
  • Long duration of action
29
Q

Give some of the side effects of Buprenorphine.

A
  • Respiratory depression
  • Low BP
  • Nausea
  • Dizziness
30
Q

How can Naloxone be administered? What’s its bioavailability like?

A

Administration:

  • IV
  • IM
  • Intransal
  • PO

–> Needs to be given as slow infusion

allow heroin/morphine to metabolise

Bioavailability:

  • = very low- extensive FIRST PASS EFFECT
  • –> rapid onset of action
    • (duration of action= 30-60mins)
31
Q

How is naloxone metabolised and excreted?

A

Hepatic–> naloxone-3-glucuronide

Renally excreted

32
Q

What is naloxone used for?

A

Used for opioid overdose (reversal agent)

Will dislodge anything at μ receptors (except buprenorphine)

33
Q

What are the 2 main mechanisms that cause opioid tolerance?

A
  1. Phosphorylation and uncoupling
    1. Repeated exposure
    2. Intracellular phosphorylation
      1. Reduced sensitivity of opioid receptor or
      2. Arrestin proteins bind to receptor instead of g-protein
  2. cAMP production
    1. Opioid given= reduces intracellular cAMP
    2. Opioid withdrawn- cell flooded with cAMP
    3. ‘Rebound effect’
      1. Explains withdrawal symptoms- increase neuronal excitability
34
Q

Who would you need to make special considerations for when prescribing opioids? (8)

A
35
Q

Give some contraindications for opioids.

A
36
Q

What does PRN mean? (with relation to prescribing)

A

= pro re nata

= AS NEEDED

37
Q

Opioids are strictly controlled drugs (under misuse of drugs legislation). What information should you make sure to record if prescribing opioids to a patient?

A
38
Q

With opioids- start low and titrate up.

Useful info - most common prescriptions:

A

4 Clinical Pharmacology and Intro to Prescribing (27 decks)

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