(PM3B) Pain & Analgesia Flashcards

1
Q

What are the components of pain?

A

(1) Sensory
(2) Emotional

Hence why it is subjective

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2
Q

What are some different methods to rate pain?

A

(1) Numeric rating scale
- 1-10
- functional scale

(2) Visual analogue scale
- No pain to worst possible pain

(3) Verbal Pain Intensity Scale
- for young/ disabled patients
- no pain to unimaginable/ unspeakable pain
- also a 1-10 scale

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3
Q

What do the different numbers (1-5) of a functional pain scale correspond to?

A

0 = no pain

1 = tolerable + pain does not prevent activities

2 = tolerable + pain prevents some activities

3 = Intolerable + pain does not prevent use of phone/ TV/ reading

4 = Intolerable + pain prevents use of phone/ TV/ reading

5 = Intolerable + pain prevents verbal communication

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4
Q

What is the purpose of acute pain?

A

Protective mechanism

e.g. thermal burns

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5
Q

What are the types of pain?

A

(1) Nociceptive pain

(2) Neuropathic pain

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6
Q

What type of pain is caused by a tissue injury?

A

Nociceptive pain

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7
Q

How long does acute nociceptive pain last?

A

<3-6 months

Desirable

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8
Q

How long does chronic nociceptive pain last?

A

> 6 months

Undesirable

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9
Q

What is allodynia?

A

Pain after stimulation

Not normally painful

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10
Q

What is hyperalgesia?

A

Increased pain from a stimulus that normally causes pain

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11
Q

What is neuropathic pain?

A

Nerve injury

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12
Q

What are some conditions that are associated with neuropathic pain?

A

(1) Diabetic neuropathy
(2) Phantom limb pain
(3) Cancer pain
(4) Chemotherapy-induced peripheral neuropathy
(5) Postherapeutic neuralgia

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13
Q

How may neuropathic pain be described?

A

(1) Severe
(2) Sharp
(3) Burning
(4) Cold
(5) Numb
(6) Tingling
(7) Weakness

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14
Q

What is the pain pathway?

A

(1) Detection of pain in the periphery
(2) Transmission of pain signals from periphery to spinal cord
(3) Reception of signal by higher central brain centres

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15
Q

Describe the role of local neuronal circuits and descending inhibitory pathways from higher brain centres.

A

Signals are amplified or inhibited

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16
Q

Describe the myelination state of non-nociceptive Aß.

A

Myelinated

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17
Q

Describe the myelination state of nociceptive C.

A

Unmyelinated

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18
Q

What sensation do non-nociceptive Aß fibres produce?

A

Touch + pressure

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19
Q

What sensation do nociceptive C fibres produce?

A

Dull + burning pain

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20
Q

What sensation do nociceptive A-delta produce?

A

Sharp pain

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21
Q

What is the gate control theory of pain?

A

Melzack + Wall’s theory

Inhibitory interneurons in spinal cord control incoming sensory information before it’s transmitted to the brain

(1) Activation of C/ A-∂ fibres open gate (increased pain)
- direct excitation of gate OR inhibition of SG interneurons

(2) SG interneurons inhibit
- close the gate
- reduce pain

(3) Activation of Aß fibres close gate by excitation of Sg interneurons

(4) Descending inhibitory pathways from CNS close gate
- inhibit the gate OR direct activation of SG interneurons

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22
Q

What are some inflammatory mediators of peripheral pain?

A

(1) Bradykinin
(2) Substance P
(3) ATP
(4) Protons

(5) Prostaglandins
- particularly PGE2 + PGF2

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23
Q

What is the role of bradykinin as an inflammatory mediator of peripheral pain?

A

Activates B2 receptors in nociceptive neurones + B1 receptors via a metabolite

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24
Q

What is the role of substance P as an inflammatory mediator of peripheral pain?

A

Activates NKA (neurokinin) receptors in nociceptive neurones

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25
Q

What is the role of ATP as an inflammatory mediator of peripheral pain?

A

Activates P2X3 receptors

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26
Q

What is the role of protons (H+) as an inflammatory mediator of peripheral pain?

A

Activate acid-sensing ion channels (ASICs)

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27
Q

What is the role of prostaglandins as an inflammatory mediator of peripheral pain?

A

PGE2 + PGF2

Greatly increase responses to bradykinin and 5-HT

Increase sensitisation

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28
Q

What are prostanoids?

A

Prostaglandins + thromboxane

Produced from precursors in cell membrane

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29
Q

What are some important neurotransmitters in hyperalgesia?

A

(1) Glutamate
- acts at AMPA to mediate acute pain
- acts at NMDA receptors (delayed)

(2) Substance P
- acts at NK1 receptors
- enhances NMDA action (hypersensitivity)

(3) Nitric oxide
- enhances further transmission of pain signal

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30
Q

What factor limits non-opioids?

A

Ceiling effect

Dose above which there is no further pharmacological action

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31
Q

What is the mechanism of action of opiates?

A

Increase descending inhibitory pathways

Decrease neuropeptide release

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32
Q

What is acetylsalicylic acid?

A

Aspirin

33
Q

Which analgesic is most appropriate for dysmenorrhoea?

A

Aspirin

34
Q

Give some examples of indoles.

A

(1) Diclofenac

(2) Indomethacin

35
Q

Give some examples of propionic acid derivatives.

A

(1) Ibuprofen
(2) Naproxen
(3) Ketoprofen

36
Q

What is etoricoxib licensed for?

A

(1) Ankylosing spondylitis
(2) Osteoarthritis
(3) Rheumatoid arthritis
(4) Acute gout

37
Q

What is celecoxib licensed for?

A

(1) Ankylosing spondylitis
(2) Osteoarthritis
(3) Rheumatoid arthritis

38
Q

Why were rofecoxib and valdecoxib withdrawn?

A

Cardiovascular side effects

39
Q

Why was lumiracoxib withdrawn?

A

Hepatotoxicity problems

40
Q

What is nefopam?

A

Non-opioid

For persistent pain if NSAIDs or opioids are not suitable

Causes little-no respiratory depression

Can have sympathomimetic + antimuscarinic side effects

41
Q

What is paracetamol?

A

Non-opioid

Reduces the production of prostaglandins in CNS

42
Q

For which type of pain are NSAIDs and opioids most effective?

A

Nociceptive pain

43
Q

How is neuropathic pain most commonly treated?

A

(1) Anti-epileptics

(2) Tricyclic antidepressants

44
Q

What are some anti-epileptics used to treat neuropathic pain?

A

(1) Sodium channel blockers
- Carbamazepine
- Phenytoin

(2) via effects on Calcium channels
- gabapentin
- pregabalin

45
Q

What are some tricyclic antidepressants used to treat neuropathic pain?

A

(1) Duloxetine (SSRI/ SNRI)

(2) Imipramine/ amitriptyline
- for diabetic neuropathy

46
Q

Name some less commonly used drugs to treat neuropathic pain.

A

(1) Ketamine
- binds to NMDA receptor

(2) Lidocaine/ bupivacaine
- blocks sodium channels

(3) Ziconotide
- new generation calcium channel blockers
- administered intrathecally

(4) Cannabinoid agonists
- e.g. sativex
- for multiple sclerosis

(5) Botulinum toxin
- reduces muscular hyperactivity

47
Q

What are opioids?

A

Highly effective analgesic

Act spinally + supraspinally

Produce analgesia in mild-moderate pain

48
Q

Is morphine an agonist/ antagonist?

A

Agonist

49
Q

Is naloxone an agonist/ antagonist?

A

Antagonist

50
Q

Is methadone an agonist/ antagonist?

A

Agonist

51
Q

Is pethidine an agonist/ antagonist?

A

Agonist

52
Q

What are the different opioid receptors?

A

(1) M-receptor
(2) ∂-receptor
(3) k-receptor
(4) ORL1-receptor

53
Q

Which drugs bind to the ORL1-receptor?

A

None

Endogenous opioid peptide (nociceptin) only

54
Q

To which opioid receptor does morphine bind?

A

M-receptor

55
Q

To which opioid receptor does fentanyl bind?

A

M-receptor

56
Q

To which opioid receptor does buprenorphine bind?

A

k-receptor

57
Q

Which endogenous opioid peptides bind to the opioid M-receptor?

A

(1) ß-endorphin

(2) enkephalin

58
Q

Which endogenous opioid peptides bind to the opioid ∂-receptor?

A

(1) Met-enkephalin

(2) Leu-enkephalin

59
Q

Which endogenous opioid peptides bind to the opioid k-receptor?

A

(1) dynorphin A

(2) dynorphin B

60
Q

Describe the supra-spinal action of opioid-induced analgesia.

A

(1) Opioid action at µ (∂ + k) receptors
(2) Enhances descending inhibitory pathway in brain
(3) Involves noradrenaline + serotonin (5-HT) release
(4) via GABA inhibition

61
Q

Describe the spinal action of opioid-induced analgesia.

A

(1) Activation of pre-synaptic receptors
- µ > ∂

(2) Reduces transmitter release

62
Q

Where do opioid agonists act?

A

All at µ receptors

Except pentazocine
- k agonist

63
Q

What is morphine?

A

Gold-standard to which all opioids are compared

Metabolised to potent analgesic morphine-6-glucuronide

IV or PO as morphine sulphate tablets (MST)

64
Q

What do fentanyl, alfentanil, sufentanil, and remifentanil have in common?

A

Opioid agonists

Very potent

Short-duration

Often as a transdermal patch

65
Q

What is oxycodone?

A

Opioid agonist

Primarily used for control of pain in palliative care

66
Q

What is pethidine?

A

Opioid agonist

Used during labour
- due to lack of effect on uterine contraction

67
Q

What is codeine?

A

Opioid agonist

Low efficacy + orally effective

Not addictive

Causes constipation with long-term use

68
Q

What is dihydrocodeine?

A

Opioid agonist

Similar efficacy to codeine

Can cause more nausea + vomiting

69
Q

What is diamorphine (heroin)?

A

Opioid agonist

Metabolised to morphine

High lipid solubility
- leads to rapid action

Higher efficacy

70
Q

What do tramadol and tapentadol have in common?

A

Opioid agonist

Weak opioids

Inhibitors of noradrenaline uptake/ transport system

71
Q

What is buprenorphine?

A

Partial opioid agonist

Long duration

Can be given sublingually

72
Q

What are some common side effects of opioid agonist use?

A

(1) Euphoria
(2) Respiratory depression
(3) Cough suppression
(4) Nausea
(5) Constipation

73
Q

What is euphoria, with relation to opioid use?

A

Common side effect of opioid agonist use

Action on reward pathway
- increases dopamine release

k-agonists (pentazocine) causes dysphoria

  • nightmares
  • hallucinations
74
Q

What is respiratory depression, with relation to opioid use?

A

Common side effect of opioid agonist use

Reduced sensitivity of respiratory centre

Most common cause of death from overdose

Treated with naloxone

75
Q

What is cough suppression, with relation to opioid use?

A

Common side effect of opioid agonist use

Anti-tussive effect

Can be therapeutically useful

76
Q

What is nausea, with relation to opioid use?

A

Common side effect of opioid agonist use

Activation of chemoreceptor trigger zone
- in turn activates vomiting centre

Treated with anti-emetics

77
Q

What is constipation, with relation to opioid use?

A

Common side effect of opioid agonist use

Due to maintained contraction of smooth muscle

78
Q

What is the neuropathic pain ladder?

A

(1) TCA/ SNRI/ voltage-gated calcium channel subunit ligand
- TCA = amitryptyline
- SNRI = duloxetine
- voltage-gated calcium channel ligand = pregabalin/ gabapentin

(2) Consider tramadol or capsaicin cream
- or add SNRI if not already used in first line

79
Q

What is the nociceptive (analgesic) pain ladder?

A

(1) Non-opioid/ NSAID
(2) Weak opioid for mild-moderate pain (e.g. codeine) + non-opioid + adjuvant
(3) Strong opioid for moderate-severe pain (e.g. morphine) + non-opioid + adjuvant