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Gwen - Anaesthetics > Opiods - Weak > Flashcards

Opiods - Weak Flashcards

1
Q

What are indications for weak opiod use?

A

Mild-to-moderate pain

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2
Q

What are examples of weak opiods?

A
  • Tramadol
  • Codeine
  • Dihydrocodeine
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3
Q

How are weak opiods metabolised?

A

In the liver:

  • Codeine -> small amounts of morphine
  • Dihydrocodeine -> dihydromorphine
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4
Q

What is the mechanism of action of weak opiods?

A

Act against mu receptors in the CNS. Activation of these G protein-coupled receptors has several effects that, overall, reduce neuronal excitability and pain transmission.

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5
Q

How do opioids cause respiratory depression?

A

In the medulla, they blunt the response to hypoxia and hypercapnoea, reducing respiratory drive and breathlessness.

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6
Q

How do opioids reduce sympathetic activity?

A

By relieving pain, breathlessness and associated anxiety, opioids reduce sympathetic nervous system (fight or flight) activity

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7
Q

What are the main opioid receptors?

A
  • Mu receptors
  • Delta Receptors
  • Kappa receptors
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8
Q

What type of membrane protein are opioid receptors?

A

G-protein coupled transmembrane receptors

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9
Q

How does binding of opioids to opioid receptors dull pain?

A

Causes reduction of synaptic transmission

  • Closing of presynaptic Ca2+ channels → hyperpolarization → reduced release of acetylcholine, noradrenaline, serotonin, glutamate, nitric oxide, and substance P (presynaptic inhibition)
  • Opening of postsynaptic K+ channels → hyperpolarization (postsynaptic inhibition)
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10
Q

What are the two main mechanisms by which opioids relieve pain?

A
  • Raise pain threshold
  • Change in pain perception
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11
Q

Why do 10% of caucasian individuals find codeine and dihydrocodeine largely ineffective?

A

Possess a less active form of metabolising enzyme P450 2D6

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12
Q

What is the mechanism of action of tramadol?

A

A synthetic analogue of codeine - best classified as a ‘moderate’ strength opioid. Once made active, acts against:

  • µ-receptor agonists
  • Serotonergic pathways
  • Adrenergic pathways

Due to Sertonergic and Adrenergic activity, acts as serotonin and norad reuptake inhibitors - contributes to effect

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13
Q

What are the therapeutic effects of opioids which act against mu receptors?

A
  • Analgesia
  • Slowed GI transit
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14
Q

What are side effects of mu receptor agonism?

A
  • Respiratory depression with subsequent rise in CO2 (and possibly ICP)
  • Vasodilation
  • Constipation
  • Miosis
  • Bradycardia
  • Strong addiction
  • Euphoria
  • Urinary retention/constipation
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15
Q

What are therapeutic effects of delta receptor agonism?

A

Analgesia

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16
Q

What are the side effects of delta receptor agonism?

A
  • Respiratory depression
  • Tolerance
  • Addiction
17
Q

What are therapeutic effects of kappa receptor agonism?

A
  • Analgesia
  • Sedation
  • Slowed gastrointestinal transit
18
Q

What are side effects of kappa receptor agonism?

A
  • Dysphoria
  • Sedation
  • Constipation
19
Q

What are common side effects of weak opioids?

A
  • Nausea
  • Constipation
  • Dizziness
  • Drowsiness
  • Resp depression
  • Neuro depression
20
Q

When must you be cautious when prescribing opioids?

A
  • Significant respiratory disease
  • Renal impairment
  • Liver impairment
  • Elderly
  • Epilepsy
21
Q

What interactions are important to be aware of when using opioids?

A
  • Other sedating drugs - benzos, antipsychotics, TCAs
  • SSRIs - lower seizure threshold
22
Q

What should you always consider prescribing in someone with regular opioid administration?

A

Stimulant laxative

23
Q

For weak opioid use, when would you review for effect?

A

1-2 hours after administration

24
Q

What is meant by receptor affinity in terms of opioids?

A

Certain opioids have a stronger receptor affinity than comparatively stronger opioids - the weaker opioid inhibits the stronger opioid competitively, which has no effect

25
Q

What is meant by intrinsic activity of opioids?

A

Substances that bind to a receptor but have no intrinsic activity can antagonise the effect of the agonists, if the receptor affinity of the antagonist is higher

26
Q

Management of morphine toxicity

A

Naloxone

Gwen - Anaesthetics (16 decks)

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