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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
What is meant by intrinsic activity of opioids?
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
What is the mechanism of action of codeine?
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
What is codeine metabolised to in the liver?
Morphine and norcodeine
28
How are morphine and norcodeine excreted?
Renally
29
How much of a dose of codeine is excreted in the urine in 24 hours?
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
What is the half-life of codeine?
3-4 hours
31
What liver enzyme converts codeine to morphine?
CYP2D6
32
What percentage of the population has a deficiency in CYP2D6, thus preventing conversion of codeine to morphine?
Approx 7%
33
What is the maximum daily dose of codeine that can be taken?
240mg
34
What is the mechanism of action of tramadol?
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
What hourly interval would you consider prescribing codeine at if you were giving it PRN or regularly?
6 hourly
36
What dose would you prescribe of dihydrocodeine?
30 mg every 4-6 hours
37
What is the mechanism of action of dihydrocodeine?
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
How is dihydrocodeine excreted?
Renally
39
When should you be careful when prescribing weak opiods?
* **Elderly** - can cause delerium * **Renal impairment** - can cause accumulation and toxicity
40
What is the potency of codeine vs morphine?
1/10th of the dose of morphine e.g. 10 mg morphine = 100 mg codeine
41
What is the potency of dihydrocodeine vs morphine?
1/10th potency of morphine e.g. 10 mg morphine = 100mg dihydrocodeine
42
What is the potency of tramadol vs morphine?
1/10th to 1/6th potency of morphine
43
How is tramadol excreted?
Almost entirely by the kidneys
44
What is the half-life of tramadol?
6 hrs
45
What dose of tramadol would you prescribed someone in acute pain?
50-100 mg
46
How often would you prescribe a dose of tramadol?
4-6 hourly
47
What should be the maximum daily dose of tramadol?
400 mg/24 hours
48
What are side effects associated with tramadol?
* **Arrythmias** * **Confusion** * **N+V** * **Hallucinations** * **Euphoric mood** * **Urinary Retention** * **Headache** * **Dizziness**

Anaesthetics (17 decks)

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