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MD2 - Pharmacology > Opioid Analgesics > Flashcards

Opioid Analgesics Flashcards

1
Q

What type of receptors are opioid receptors. How do they function?

A

Opioid receptors are inhibitory G-protein coupled receptors.

Opioid agonists bind to receptor and cause inhibition of neurotransmitter release.

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2
Q

What are the three major classes of opioid receptors

A
  • Mu
  • Kappa
  • Delta
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3
Q

What effects do µ opioid receptors mediate? (5)

A
  • Analgesia
  • Euphoria
  • Respiratory depression
  • Bradycardia
  • Reduced gut motility
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4
Q

Describe the locations of opioid receptors and their role in the effects seen with opioid use.

A

CNS

Brain

  • Brain stem = analgesia
  • Limbic system = abuse, addiction
  • Cortex

Dorsal horn of spinal cord

  • Presynaptic = analgesia
  • Postsynaptic

PNS

  • Nociceptive fibres expressed after injury
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5
Q

Which receptor does morphine act on?

A

µ-receptor agonist.

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6
Q

How are opioids dosed?

A

Titrated to effect - minimise life-threatening adverse effects such as respiratory depression.

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7
Q

Describe the metabolism/excretion and mechanism of action of morphine

A

Metabolised in the liver to morphine-3-gluconoride and morphine-6-gluconoride.

Morphine-6-gluconoride is the active compound, producing analgesic effect.

Metabolites are renally excreted.

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8
Q

What are the indications and contraindications to morphine use?

A

Indications:

  • Moderate to severe acute pain
  • Palliative care
  • Pre-operative analgesic

Contraindications:

  • Hepatic / Renal failure
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9
Q

Compare codeine to morphine

A

Codeine is a pro-drug:

  • Demethylated to morphine
  • CYP2D6 enzyme

Codeine is 10x LESS potent than morphine.

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10
Q

Describe the two types of genetics defects to be wary of when administering codeine?

A
  1. Approx 10% of patients lack the enzyme to convert codeine.
  2. Small % of people are ‘rapid metabolisers’ and can incur adverse effects at normal doses.
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11
Q

Indications of codeine use:

A
  • Mild to moderate acute pain
  • Antitussive (cough suppressant)
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12
Q

Compare the bioavailability of morphine and codeine

A

Morphine has a low bioavailability of 35% - mostly used IV.

Codeine has good bioavailability.

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13
Q

Side effects of opioid use, regardless of strength

A
  • Nausea and vomiting
  • Constipation
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14
Q

Name the synthetic µ-opioid receptor agonist

A

Oxycodone.

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15
Q

What level of pain is oxycodone good for?

A

Moderate to severe pain relief.

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16
Q

WHat are teh three types of oral preparations of oxycodone?

A
  1. Immediate release oxycodone (Oxynorm)
  2. Controlled release oxycodone (Oxycontin)
  3. Controlled release oxycodone with naloxone (Targin)

Addition of naloxone (opioid antagonist) = reduced opioid induced constipation and protects from abuse.

17
Q

What is tramadol?

A

An atypical centrally acting analgesic.

18
Q

Mechanism of action of tramadol?

A

Metabolised in the liver to active metabolite

  • Agonist to µ-opioid receptor
  • Serotonin reuptake inhibitor
  • Noradrenaline reuptake inhibitor
19
Q

Effects of tramadol, compared to morphine.

A

In equi-analgesic doses to morphine, tramadol has:

  • Less respiratory depression
  • Less constipation

Serotonergic effects:

  • Nausea, vomiting, confusion
  • Interaction with other serotonergic drugs (SSRIs, TCAs)
20
Q

Contraindication to using tramadol?

A

Due to its interaction with other serotonergic drugs, it lowers seizure threshold

  • AVOID in epilepsy.
21
Q

Uses for tramadol:

A

Useful in avoiding adverse effects of opioids:

  • Respiratory depression
  • Tolerance and dependence
  • Constipation

Can be used in neuropathic pain treatment.

22
Q

Uses for methadone?

A

Good in neuropathic pain - NMDA antagonist effect.

Major use is opioid replacement in addiction.

23
Q

Why are opioids not ideal for chronic pain relief?

A

Development of tolerance - all opioid antagonists.

  • Around 2 weeks with morphine
24
Q

Describe how opioid withdrawal can occur, and what are the symptoms?

A

Occurs with:

  • Abrupt discontinuation
  • Administration of antagonist

Symptoms of withdrawal:

  • Nausea, vomiting, diarrhoea
  • Anorexia
  • Sweating, shivering, anxiety

MD2 - Pharmacology (4 decks)

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