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ESA 5 - Pharmacology > Opioid Analgesics > Flashcards

Opioid Analgesics Flashcards

1
Q

Is pain objective or subjective?

A

Subjective

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2
Q

What are the two components of pain?

A
  • Physiological
  • Psychological
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3
Q

What is another name for the physiological perception of pain?

A

Nociception

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4
Q

Give two scenarios where the psychological aspect of pain becomes apparent

A
  • Phantom limb pain
  • Intractable pain
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5
Q

Which divisions of the nervous system do opioids affect?

A
  • CNS
  • PNS
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6
Q

What type of effect do opioids have on the CNS?

A

Psychoactive

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7
Q

What theory does the action of opioids in the PNS conform with?

A

The ‘gate theory’ of pain

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8
Q

To where in the CNS are pain signals initially transmitted to?

A

The substantia gelatinosa

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9
Q

Where is the substantia gelatinosa found?

A

The dorsal horn of the spinal cord

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10
Q

What can happen to pain signals within the substantia gelatinosa?

A

They can be modulated

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11
Q

What neurotransmitter is responsible for relaying pain signals within the substantia gelatinosa?

A

Substance P

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12
Q

How do opioids exert their effects at the spinal level?

A

Inhibit the release of Substance P from the nerve terminals in the substantia gelatinosa

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13
Q

What natural part of the pain pathway do opioids mimic to an extent?

A

Descending inhibitory nerves from the thalamus

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14
Q

What do the inhibitory descending nerves from the thalamus do?

A

Use inhibitory interneurones to block the release of Substance P within the substantia gelatinosa

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15
Q

How does rubbing an injury make it ‘better’?

A

Stimulation of mechanoreceptors that can have an inhibitory effect on pain transmission via the substantia gelatinosa

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16
Q

What are the 3 main types of endogenous opioid peptides?

A
  • Enkephalins
  • Endorphins
  • Dynorphins
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17
Q

What is the pre-cursor molecule for enkephalins?

A

Proenkephalin

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18
Q

What is the pre-cursor molecule for endorphins?

A

POMC

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19
Q

What else is POMC a pre-cursor for?

A
  • α-MSH
  • ACTH
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20
Q

What is the pre-cursor molecule for dynoprhins?

A

Prodynorphin

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21
Q

What are the two main types of enkephalins?

A
  • Met-enkephalin
  • Leu-enkephalin
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22
Q

What is the main type of endorphin?

A

β-endorphin

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23
Q

What are the three types of opioid receptors?

A
  • μ-opioid receptors
  • δ-opioid receptors
  • κ-opioid receptors
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24
Q

Where are μ-opioid receptors generally found?

A

Supraspinal i.e. in the brain

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25
Q

What effect does binding to μ-opioid receptors have?

A

Analgesia

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26
Q

Where are κ-opioid receptors mostly found?

A

Spinal cord

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27
Q

Where are δ-opioid receptors found?

A

They are widely distributed

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28
Q

What type of receptor are all opioid receptors?

A

GPCRs

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29
Q

Receptors at which location within the synapse are most important in pain control?

A

Presynaptic receptors

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30
Q

What effect does binding to μ-receptors have?

A

Opening of K⁺ channels and increased efflux of K⁺

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31
Q

What is the result of increased efflux of potassium?

A

Decreased excitability

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32
Q

What is the result of binding to κ-receptors?

A

Decreased influx of Ca²⁺ via channels

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33
Q

What is the result of binding to δ-receptors?

A

Decreased adenylate cyclase activity leading to decreased cAMP synthesis

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34
Q

Are the effects of the receptor sub-types limited to only one subtype?

A

No - each subtype can exert all of the effects i.e. cause increased efflux ok potassium, decrease calcium influx and decrease cAMP

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35
Q

What do all the effects of the opioid receptors have on the intracellular calcium?

A

Reduced entry of Ca²⁺

36
Q

What is the result of decreased entrance of calcium ions?

A

Less release of neurotransmitter (Substance P) vesicles into the synaptic cleft

37
Q

What receptor causes most of the opioid side-effects?

A

μ-receptors

38
Q

What side-effects does μ-receptor binding have?

A
  • Nausea
  • Vomiting
  • Constipation
  • Drowsiness
  • Miosis
39
Q

What are the two big problems of long-term opioid use?

A
  • Dependance
  • Tolerance
40
Q

What does dependence mean in terms of opioid use?

A

If opiods are removed the patient sufferes from withdrawal symptoms

41
Q

What does tolerance mean with respect to opiate use?

A

A higher dose is needed to achieve the same effect

42
Q

What is the danger of opiates tolerance?

A

Users need a higher dose to the point where it risks respiratory depression and death

43
Q

The risk of respiratory depression has what consequence on opiate prescribing?

A

Monitoring is required

44
Q

What effect can opiates have on the CVS?

A

Can cause hypotension

45
Q

What side-effect can be caused by κ-receptor binding?

A

Dysphoria

46
Q

What are the type of opioid receptor binding drugs?

A
  • Agonists
  • Partial agonists
  • Agonist/antagonist
  • Antagonist
47
Q

Give an opioid receptor agonist

A

Morphine (the gold standard)

48
Q

Give an opioid receptor partial agonist

A

Buprenorphine

49
Q

Give an opioid receptor agonist/antagonist

A

Nalbuphine

50
Q

How do opioid receptor agonist/antagonists work?

A

They exert an agonistic effect at one receptor sub-type and cause an antagonistic action at another

51
Q

Give an opioid receptor antagonist

A

Naloxone

52
Q

What can naloxone be used for?

A

Reversal of opioid induced respiratory depression

53
Q

What is the half-life of morphine?

A

~4 hours

54
Q

What is the oral bioavailability of morphine?

A

25%

55
Q

What is the half-life of diamorphine (heroin)?

A

5 minutes

56
Q

What is the half-life of methadone?

A

~24 hours

57
Q

What is the oral bioavailability of methadone?

A

90%

58
Q

What is another opioid with a good oral bioavailability?

A

Codeine

59
Q

Does morphine enter Phase 1 metabolism?

A

No - it already has hydroxyl groups so enters straight into Phase 2 metabolism

60
Q

To what metabolites is morphine metabolised to?

A
  • Morphine-6-glucuronide
  • Morphine-3-glucuronide
61
Q

Why does morphine have a ‘slightly extended half-life’?

A

Morphine-6-glucuronide is still an active molecule

62
Q

How are morphine metabolites excreted?

A

In the urine

63
Q

What is the result of urinary excretion of morphine metabolites?

A

Urine can be screened for opioid use

64
Q

Despite its short half-life of 5 minutes, why is heroin the opiate of choice for substance misusers?

A

Becuase its structure allows for rapid entry across the blood-brain barrier where it is the metabolised to morphine after which it has the usual ~4 hour half life

65
Q

What are the clinical uses of opioids?

A
  • Analgesia
  • Anaesthesia
66
Q

What sort of pain are opioids used to treat?

A

Moderate to severe pain (particularly pain with a visceral origin)

67
Q

What are the indications for morphine?

A
  • Analgesia (particularly terminal illness)
  • Diarrhoea
68
Q

What are the indications for diamorphine?

A

Analgesia (in terminal illness only due to its tendency to cause dependence)

69
Q

What are the indications for methadone?

A

Maintenance in opiod dependence

70
Q

What are the indications of tramadol?

A

Analgesia

71
Q

What are the extra-opioid effects of tramadol?

A

5-HT and NA re-uptake inhibition (minor anti-depressant side-effects)

72
Q

What type of drug is morphine?

A

A pro-drug

73
Q

What is codeine metabolised to?

A

Morphine

74
Q

What converts codeine to morphine?

A

CYP2D6

75
Q

What is the clinical significance of CYP2D6?

A

It has significant genetic polymorphism meaning some people cannot metabolise codeine to morphine and so receive no benefits

76
Q

What is codeine used for?

A

Mild analgesia

77
Q

What is the route of administration of morphine?

A

Oral

78
Q

What is the indication of fentanyl?

A

Anaesthesia

79
Q

Why does fentanyl work as an anaesthetic agent?

A

It has up to 100x the potency of morphine

80
Q

What is the indication for pethidine?

A

Analgesia in labour

81
Q

What is the route of administration of pethidine?

A

IM

82
Q

What is the dangerous side-effect of pethidine?

A

It is metabolised to not pethidine which can cause convulsions

83
Q

What are the indications for naloxone?

A
  • Opioid toxicity
  • Respiratory depression
  • Treatment of dependence
84
Q

What are the medico-legal implications of opioid prescribing?

A

May are controlled drugs e.g. morphine, diamorphine and pethidine

85
Q
A

ESA 5 - Pharmacology (28 decks)

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