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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
  • Blunt response to hypoxia and hypercapnia
  • General CNS depression
  • Reduced tone in muscles maintaining airway patency
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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)
  • Constipation
  • Miosis
  • Bradycardia
  • Strong addiction
  • Euphoria
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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
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17
Q

What are therapeutic effects of kappa receptor agonism?

A
  • Analgesia
  • Sedation
  • Slowed gastrointestinal transit
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18
Q

What are side effects of kappa receptor agonism?

A
  • Dysphoria
  • Sedation
  • Constipation
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19
Q

What are common side effects of weak opioids?

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

What is the mechanism of action of codeine?

A

Centrally acting weak analgesic - exerts effects on mu receptors, although has low affinity, and its analgesic effect is due to its conversion to morphine

27
Q

What is codeine metabolised to in the liver?

A

Morphine and norcodeine

28
Q

How are morphine and norcodeine excreted?

A

Renally

29
Q

How much of a dose of codeine is excreted in the urine in 24 hours?

A

Approx 86% - 70% of the dose is excreted as free codeine, 10% as free and conjugated morphine and a further 10% as free or conjugated norcodeine

30
Q

What is the half-life of codeine?

A

3-4 hours

31
Q

What liver enzyme converts codeine to morphine?

A

CYP2D6

32
Q

What percentage of the population has a deficiency in CYP2D6, thus preventing conversion of codeine to morphine?

A

Approx 7%

33
Q

What is the maximum daily dose of codeine that can be taken?

A

240mg

34
Q

What is the mechanism of action of tramadol?

A

Centrally acting opioid analgesic. It is a non selective pure agonist at μ-, δ- and κ-opioid receptors with a higher affinity for the μ-receptor. Other mechanisms which may contribute to its analgesic effect are inhibition of neuronal reuptake of noradrenaline and enhancement of serotonin release.

35
Q

What hourly interval would you consider prescribing codeine at if you were giving it PRN or regularly?

A

6 hourly

36
Q

What dose would you prescribe of dihydrocodeine?

A

30 mg every 4-6 hours

37
Q

What is the mechanism of action of dihydrocodeine?

A

Metabolized in the liver by CYP 2D6 into an active metabolite, dihydromorphine, and by CYP 3A4 into secondary primary metabolite, nordihydrocodeine. A third primary metabolite is dihydrocodeine-6-glucuronide. Dihydromorphine is metabolite with a high affinity for mu opioid receptors

38
Q

How is dihydrocodeine excreted?

A

Renally

39
Q

When should you be careful when prescribing weak opiods?

A
  • Elderly - can cause delerium
  • Renal impairment - can cause accumulation and toxicity
40
Q

What is the potency of codeine vs morphine?

A

1/10th of the dose of morphine e.g. 10 mg morphine = 100 mg codeine

41
Q

What is the potency of dihydrocodeine vs morphine?

A

1/10th potency of morphine e.g. 10 mg morphine = 100mg dihydrocodeine

42
Q

What is the potency of tramadol vs morphine?

A

1/10th to 1/6th potency of morphine

43
Q

How is tramadol excreted?

A

Almost entirely by the kidneys

44
Q

What is the half-life of tramadol?

A

6 hrs

45
Q

What dose of tramadol would you prescribed someone in acute pain?

A

50-100 mg

46
Q

How often would you prescribe a dose of tramadol?

A

4-6 hourly

47
Q

What should be the maximum daily dose of tramadol?

A

400 mg/24 hours

48
Q

What are side effects associated with tramadol?

A
  • Arrythmias
  • Confusion
  • N+V
  • Hallucinations
  • Euphoric mood
  • Urinary Retention
  • Headache
  • Dizziness

Anaesthetics (17 decks)

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