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Part 3 – PM3B > (PM3B) Local Anaesthetics > Flashcards

(PM3B) Local Anaesthetics Flashcards

1
Q

What is the resting membrane potential of a cell?

A

-70mV

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2
Q

What is the depolarised membrane potential following the overshoot?

A

+50mV

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3
Q

How long does an action potential take to generate and be reset?

A

5msec

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4
Q

What are the stages of action potential generation?

A

(1) Stimulating current (at -70mV)
(2) Depolarisation
(3) Overshoot (to +50mV)
(4) Repolarisation
(5) Hyperpolarising afterpotential

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5
Q

Which major currents determine an action potential?

A

(1) Sodium current
- moves inwards
- depolarising current

(2) Potassium current
- moves outward
- hyperpolarising current

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6
Q

Which sodium channel opens following activation?

A

m-gate (depolarisation)

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7
Q

Which sodium channel opens following inactivation?

A

h-gate

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8
Q

Which potassium channel opens following activation?

A

n-gate

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9
Q

What is TTX?

A

Tetrodotoxin

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10
Q

Which voltage-gated sodium channels are considered tetrodotoxin (TTX) sensitive?

A

(1) rNav1.1
(2) rNav1.2
(3) rNav1.3

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11
Q

Which voltage-gated sodium channels are considered tetrodotoxin (TTX) non-selective?

A

(1) rNav1.7
(2) rNav1.4
(3) rNav1.6

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12
Q

Which voltage-gated sodium channels are considered tetrodotoxin (TTX) resistant?

A

(1) rNav1.5
(2) rNav1.8
(3) rNav1.9

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13
Q

What are the main structures in cocaine, lidocaine, bupivacaine etc?

A

(1) Aromatic region
(2) Ester/ amide bond
(3) Basic amine

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14
Q

Why are cocaine, procaine, and tetracaine considered to be short-acting?

A

Have an ester bond

Esters metabolised by plasma esterases

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15
Q

Why are lidocaine and bupivacaine considered to be long-acting?

A

Have an amide bond

Metabolised by liver

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16
Q

What are the pathways utilised by local anaesthetics?

A

(1) Hydrophobic
(2) Hydrophilic

Depends on ionisation state of local anaesthetic

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17
Q

What is the hydrophilic pathway, in terms of local anaesthetics?

A

Major mode of local anaesthetic action

~90%

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18
Q

What is the hydrophobic pathway, in terms of local anaesthetics?

A

Secondary mode of local anaesthetic action

~10%

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19
Q

Describe the physicochemical properties of local anaesthetics.

A

Weak bases (pKa ~8-9)

Largely ionised at neutral pH

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20
Q

What ionisation of local anaesthetics is required to act?

A

Must cross membrane in unionised form

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21
Q

What is use-dependence?

A

More a channel is open the greater the drug block

Increased access to drug binding site

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22
Q

How is local anaesthetic action characterised?

A

(1) Duration of action/ degree of tissue penetration
(2) Use-dependent block of sodium channels

(3) Preferential block of small diameter nerve fibres
- nociceptive C and A-delta fibres are blocked more readily than Aß fibres

(4) Preferential block of inactivated state of sodium channels
- Local anaesthetics have a higher affinity for inactivated state

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23
Q

Describe the onset of action of cocaine.

A

Medium

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24
Q

Describe the onset of action of procaine.

A

Medium

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25
Q

Describe the onset of action of lidocaine

A

Rapid

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26
Q

Describe the onset of action of tetracaine.

A

Very slow

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27
Q

Describe the onset of action of bupivacaine.

A

Slow

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28
Q

Describe the onset of action of prilocaine.

A

Medium

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29
Q

Describe the onset of action of articaine.

A

Rapid

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30
Q

Describe the duration of action of cocaine.

A

Medium

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31
Q

Describe the duration of action of procaine.

A

Short

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32
Q

Describe the duration of action of lidocaine.

A

Medium

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33
Q

Describe the duration of action of tetracaine.

34
Q

Describe the duration of action of prilocaine.

35
Q

Describe the duration of action of articaine.

36
Q

Describe the tissue penetration of cocaine.

37
Q

Describe the tissue penetration of procaine.

38
Q

Describe the tissue penetration of lidocaine.

39
Q

Describe the tissue penetration of tetracaine.

40
Q

Describe the tissue penetration of bupivacaine.

41
Q

Describe the tissue penetration of prilocaine.

42
Q

Describe the tissue penetration of articaine.

43
Q

What are the main undesirable effects of cocaine?

A

CV + CNS effects

Due to block of amine uptake

44
Q

What are the main undesirable effects of lidocaine?

A

Same as cocaine

Less tendency to cause CNS effects

45
Q

What are the main undesirable effects of procaine?

A

Same as cocaine

Less tendency to cause CNS effects

46
Q

What are the main undesirable effects of tetracaine?

A

Same as cocaine

Less tendency to cause CNS effects

47
Q

What are the main undesirable effects of bupivacaine?

A

Same as cocaine

Less tendency to cause CNS effects

Greater tendency to cause cardiotoxicity

48
Q

What are the main undesirable effects of prilocaine.

A

No vasodilator activity

49
Q

What are the main undesirable effects of articaine?

A

Same as cocaine

Less tendency to cause CNS effects

50
Q

What are the main undesirable effects of articaine?

A

Same as cocaine

Less tendency to cause CNS effects

51
Q

Describe the duration of action of articaine.

52
Q

Describe the tissue penetration of cocaine.

53
Q

Describe the tissue penetration of procaine.

54
Q

Describe the tissue penetration of lidocaine.

55
Q

Describe the tissue penetration of tetracaine.

56
Q

Describe the tissue penetration of bupivacaine.

57
Q

Describe the tissue penetration of prilocaine.

58
Q

Describe the tissue penetration of articaine.

59
Q

What are the main undesirable effects of cocaine?

A

CV + CNS effects

Due to block of amine uptake

60
Q

What are the main undesirable effects of lidocaine?

A

Same as cocaine

Less tendency to cause CNS effects

61
Q

What are the main undesirable effects of procaine?

A

Same as cocaine

Less tendency to cause CNS effects

62
Q

What are the main undesirable effects of tetracaine?

A

Same as cocaine

Less tendency to cause CNS effects

63
Q

What are the main undesirable effects of bupivacaine?

A

Same as cocaine

Less tendency to cause CNS effects

Greater tendency to cause cardiotoxicity

64
Q

What is IV regional anaesthesia?

A

Injected into limb

Local anaesthesia diffuses rapidly to desired site of action

Systemic toxicity prevented by a cuff

65
Q

Why may inflamed tissue be resistant to local anaesthesia action? Why?

A

Inflamed tissue becomes acidic

Local anaesthesia action is pH dependent (pKa ~8-9)

  • more acidic = more ionised
  • meaning less local anaesthesia entry
  • less block
66
Q

When is cocaine used therapeutically?

A

Rarely

Upper respiratory tract

67
Q

When is procaine used therapeutically?

A

No longer used

First synthetic agent

68
Q

When is lidocaine used therapeutically?

A

Widely used for local anaesthesia + ventricular dysrhythmias

69
Q

When is tetracaine used therapeutically?

A

Spinal + corneal anaesthesia

70
Q

When is bupivacaine used therapeutically?

A

Widely used due to long duration of action

Levobupivacaine used more commonly (racemate)

  • causes less cardiotoxicity
  • causes less CNS depression
71
Q

When is prilocaine used therapeutically?

A

Widely used

NOT in obstetric analgesia
- risk of methaemoglobinaemia

72
Q

What is articaine used therapeutically?

73
Q

What are some potential routes of local anaesthesia?

A

(1) Surface anaesthesia
(2) Infiltration anaesthesia
(3) Nerve block anaesthesia
(4) Spinal anaesthesia
(5) Epidural anaesthesia
(6) IV regional anaesthesia

74
Q

What is surface anaesthesia?

A

Applied directly to mucous membrane

Solution/ spray/ lozenge/ cream

e. g.
- lidocaine to mouth
- tetracaine to cornea
- lidocaine/ prilocaine cream to skin

75
Q

What is infiltration anaesthesia?

A

Injected directly into tissue

Anaesthetises nerve ending

e.g. lidocaine/ prilocaine for wound stitching + minor surgery

Danger of systemic toxicity
- use vasoconstrictors concomitantly

76
Q

What is nerve block anaesthesia?

A

Injected CLOSE TO nerve trunk

Anaesthetises whole area of nerve distribution

e.g. bupivacaine block of mandibular nerve in dental surgery

Can be used to relieve neuropathic pain

77
Q

What is spinal anaesthesia?

A

Injected into subarachnoid space (intrathecal)

Between 2nd + 5th vertebrae

e.g. bupivacaine/ levobupivacaine/ ropivacaine

Used in Caesarean section/ rectal surgery

Long duration of action

78
Q

What is epidural anaesthesia?

A

Injected directly into epidural space

e.g. bupivacaine in obstetrics

79
Q

Why may inflamed tissue be resistant to local anaesthesia action? Why?

A

Inflamed tissue becomes acidic

Local anaesthesia action is pH dependent (pKa ~8-9)

  • more acidic = more ionised
  • meaning less local anaesthesia entry
  • less block
80
Q

(1) Will local anaesthesia have more action on a rapidly conducting nerve or a slower conducting nerve?
(2) Why?

A

(1) Rapidly conducting nerve

(2) Local anaesthesia is use-dependent
- higher frequency = more opening
- leads to more local anaesthesia entry
- means greater depth of block
- also promotes inactivity, where local anaesthesia have greater affinity

Part 3 – PM3B (32 decks)

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