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CPT > Opioids > Flashcards

Opioids Flashcards

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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

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

A

M;
- Hepatic via CYP 3A4

E;

  • Renally
  • Short half life of 6 mins
19
Q

Compare Fentanyl to Morphine

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

A
  • Anaesthesia
  • Analgesia
  • Respiratory depression
  • Vomiting
  • Constipation
21
Q

State a Moderate Agonsist

A

Codeine

22
Q

Describe the Absorption, Metabolism and Excretion of Codeine

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

A

Certain SSRIs (such as Fluoxetine)

24
Q

Compare Codeine to Morphine

List 2 actions and 2 side effects

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

A

Buprenorphine

26
Q

Describe the Absorption and Distribution of Buprenorphine

A

A;
- Transdermal, Buccal, Sublingual

D;
- Very lipophilic so gets into a lot of tissues

27
Q

Describe the Metabolism and Excretion of Buprenorphine

A

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
Q

Compare Buprenorphine to Morphine

A
  • 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
Q

List 2 actions and 4 side effects of Buprenorphine

A
  • Moderate to severe analgesia
  • Opioid addiction treatment
  • Respiratory depression
  • Low BP
  • Nausea
  • Dizziness
30
Q

Name an Antagonist

Describe its onset of action

How long does it action last?

A

Naloxone

Rapid OoA
Duration of action: 30-60 mins

31
Q

Describe the Absorption and Distribution of Naloxone

A

A;

  • IV, IM, Oral, Nasal
  • Very low oral bioavailability (extensive 1st pass)

D;
- Very lipophilic (so gets into many tissues)

32
Q

Describe the Metabolism and Excretion of Naloxone

A

M;
- Glucoronidation in liver-> Naloxone-3-glucoronide

E;
- Renally

33
Q

Compare Naloxone to Morphine and Buprenorphine

A
  • Greatest affinity for MOP, least for KOP receptors

- Can displace Morphine, but not Buprenorphine from MOP

34
Q

List 1 action and Side effect of Naloxone

A
  • Competitive antagonism for opioids

- Short half life (so need to give as slow infusion)

35
Q

What’s the most common cause of death in opioid OD

What is the main treatment

A

Respiratory depression

Naloxone

36
Q

Suggest 8 groups of people who you should be cautious to prescribe long-term opioid use to

A
  • Manual labourers/ drivers
  • Elderly
  • Bedbound
  • Asthmatics
  • Biliary tract obstruction (Buprenorphine)
  • Respiratory diseases
  • Renal impairment
  • Pregnancy
37
Q

List 5 contraindications for Opioid use

A
  • Hepatic failure
  • Acute respiratory destress
  • Comatose
  • Head injuries
  • Raised ICP
38
Q

Morphine has a strong affinity for MOP receptors, completely activating them.

2 actions are Analgesia and Euphoria

List 6 side effects

A
  • Respiratory depression
  • Emesis
  • GI Tract (Constipation as it increases sphincter tone)
  • CVS
  • Miosis
  • Histamine release (caution in asthmatics)

CPT (19 decks)

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