CPT > Opioids > Flashcards

Opioids Flashcards

(37 cards)

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1
Q

Describe the pain signal transduction pathway

A
  1. Nociceptors stimulated
  2. Release of Substance P and Glutamate
  3. Afferent fibres stimulated (A-Delta and C fibres)
  4. Fibres decussate and ascend
  5. Synapse in thalamus
  6. Project to Sensory Cortex
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2
Q

Compare afferent C and A-Delta fibres

A

A-Delta fibres;
- Transmit sharp pain

C fibres;

  • Transmit dull pain
  • Unmyelinated (so need more stimulation to generate a response)
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3
Q

We can modulate pain via modulators in the PNS and CNS

State the modulators in the PNS and CNS

A

PNS: Substantia Gelatinosa

CNS: Peri-aqueductal grey

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4
Q

Describe the modulation of pain peripherally via the Substantia Gelatinosa

A
  • Normally A-Delta and C fibres detect pain and inhibit the Substantia Gelatinosa
  • Rubbing the site of pain sends impulses down A-Beta fibres, which stimulate the Substantia Gelatinosa
  • SG acts to inhibit ascending sensation of pain in dorsal horn
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5
Q

List 3 Endogenous Opioids that act to modulate pain

Opioid receptors are G Protein receptors. What are the 3 types of Opioid receptor?

A
  • Encephalins, Endorphins, Dynorphins
  • MOP (main one that is clinically relevant)
  • DOP
  • KOP
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6
Q

Where are MOP receptors found?

Describe what happens when an agonist binds to a MOP receptor

A
  • Mainly in Brainstem + Thalamus, but also in GI tract and Spinal cord
  • Agonist binds-> Decreases in cAMP-> K+ efflux
  • Leads to membrane hyperpolarisation
  • Decreased release of Substance P and GABA
  • Increased Dopamine release
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7
Q

What are 2 main mechanisms of Opioid tolerance (can start after 1 dose)

A
  • Phosphorylation and uncoupling

- cAMP production

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8
Q

Describe how Phosphorylation & Uncoupling can lead to Opioid tolerance

(Normally, agonist binds to receptor-> Decreased cAMP-> Decreased pain)

A
  • Intracellular phosphorylation occurs as Opioids bind
  • Causes changes in MOP receptors

Leading to;

  • Arrestins displacing the G Protein on the MOP receptors
  • Opioid binds less effectively to MOP receptor

Thus, diminished decrease in cAMP-> Diminished decrease in pain

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9
Q

Describe the mechanism of how cAMP production can lead to Opioid tolerance

(Normally, agonist binds to receptor-> Decreased cAMP-> Decreased pain)

A
  • As opioid is removed, cAMP inside cell starts to increase massively

Thus to get same level of pain reduction you either need to;

  • Decrease time between doses
  • Increase dose
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10
Q

How does cAMP production explain withdrawal symptoms

A

Increase in cAMP caused by opioid removal-> Neuronal excitability which is what causes withdrawal symptoms

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11
Q

Suggest 3 non-palliative uses of Opioids

A
  • SOB control
  • Cough
  • Diarrhoea
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12
Q

Strong Opioids (Morphine, Fentanyl) aren’t usually used for alleviating nerve pain (Diabetes, Shingles etc)

What kind of drugs do we use for this?
Suggest 3 groups of these drugs

A

Neuropathic drugs

  • Anticonvulsants
  • Tricyclics
  • Serotonin/ NA Reuptake Inhibitors
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13
Q

Name 2 Strong Agonists

A
  • Morphine

- Fentanyl

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15
Q

Describe the Absorption and Distribution of Morphine

A

A;

  • Oral, IV, IM, Rectal, Subcutaneous
  • Significant 1st pass effect so only 40% oral bioavailability

D;

  • Rapidly enters all tissues (including foetal)
  • Struggles to cross Blood-Brain Barrier
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16
Q

Describe the Metabolism and Elimination of Morphine

A

M;
- Glucororonidation in liver-> M6G (main therapeutic effect) and M3G (neuroexcitability effect)

E;
- Renally

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17
Q

Describe the Absorption and Distribution of Fentanyl

Study These Flashcards
A

A;

  • IV, Epidural, Intrathecal, Nasal
  • 80 to 100% oral bioavailability

D;

  • Highly lipophilic AND protein bound (so to many tissues AND CNS)
  • Strongly crosses BBB
18
Q

Describe the Metabolism and Elimination of Fentanyl

Study These Flashcards
A

M;
- Hepatic via CYP 3A4

E;

  • Renally
  • Short half life of 6 mins
19
Q

Compare Fentanyl to Morphine

Study These Flashcards
A
  • 100x more potent
  • Higher affinity for MOP receptor
  • Less histamine release, sedation and constipation
20
Q

Suggest 2 uses and 3 side effects of Fentanyl

Study These Flashcards
A
  • Anaesthesia
  • Analgesia
  • Respiratory depression
  • Vomiting
  • Constipation
21
Q

State a Moderate Agonsist

22
Q

Describe the Absorption, Metabolism and Excretion of Codeine

Study These Flashcards
A

A;
- Oral, Subcutaneous

M;

  • Converted to Morphine via CYP 2D6 (Highly polymorphic)
  • Glucoronidation of Morphine

E;
- Renally

23
Q

Suggest a group of drugs that inhibits CYP 2D6, thus increasing plasma Codeine concentration

Study These Flashcards
A

Certain SSRIs (such as Fluoxetine)

24
Q

Compare Codeine to Morphine

List 2 actions and 2 side effects

Study These Flashcards
A
  • 10% of Morphine’s potency

Actions;

  • Cough depressant
  • Mild to moderate analgesia

Side effects;

  • Constipation
  • Respiratory depression (worse in children)
25
Q

Name a Mixed Agonist-Antagonist

Study These Flashcards
A

Buprenorphine

26
Describe the Absorption and Distribution of Buprenorphine
A; - Transdermal, Buccal, Sublingual D; - Very lipophilic so gets into a lot of tissues
27
Describe the Metabolism and Excretion of Buprenorphine
M; - Hepatic via CYP 3A4 - Glucoronidation E; - Biliary excretion more than renal (so safe in renal impairment) - Half life of 37 hours (given via patches usually)
28
Compare Buprenorphine to Morphine
- Higher affinity for MOP receptor, so not easily displaced by morphine (In case of OD) - Lower Efficacy, as a Partial Agonist - Antagonist at KOP receptors
29
List 2 actions and 4 side effects of Buprenorphine
- Moderate to severe analgesia - Opioid addiction treatment - Respiratory depression - Low BP - Nausea - Dizziness
30
Name an Antagonist Describe its onset of action How long does it action last?
Naloxone Rapid OoA Duration of action: 30-60 mins
31
Describe the Absorption and Distribution of Naloxone
A; - IV, IM, Oral, Nasal - Very low oral bioavailability (extensive 1st pass) D; - Very lipophilic (so gets into many tissues)
32
Describe the Metabolism and Excretion of Naloxone
M; - Glucoronidation in liver-> Naloxone-3-glucoronide E; - Renally
33
Compare Naloxone to Morphine and Buprenorphine
- Greatest affinity for MOP, least for KOP receptors | - Can displace Morphine, but not Buprenorphine from MOP
34
List 1 action and Side effect of Naloxone
- Competitive antagonism for opioids | - Short half life (so need to give as slow infusion)
35
What’s the most common cause of death in opioid OD What is the main treatment
Respiratory depression Naloxone
36
Suggest 8 groups of people who you should be cautious to prescribe long-term opioid use to
- Manual labourers/ drivers - Elderly - Bedbound - Asthmatics - Biliary tract obstruction (Buprenorphine) - Respiratory diseases - Renal impairment - Pregnancy
37
List 5 contraindications for Opioid use
- Hepatic failure - Acute respiratory destress - Comatose - Head injuries - Raised ICP
38
Morphine has a strong affinity for MOP receptors, completely activating them. 2 actions are Analgesia and Euphoria List 6 side effects
- Respiratory depression - Emesis - GI Tract (Constipation as it increases sphincter tone) - CVS - Miosis - Histamine release (caution in asthmatics)
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