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Oral Surgery > Chapter 11: Local anaesthetics history and pharmacology > Flashcards

Chapter 11: Local anaesthetics history and pharmacology Flashcards

1
Q

Definition of local anaesthetics

A

Loss of sensation in a circumscribed area of the body caused by a depression of excitation in nerve endings to an inhibition of the conduction process in peripheral nerves

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2
Q

What happened in the year 1884?

A

Koller: ophthalmologic meeting in Vienna: cocaine as LA

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3
Q

What happened in the year 1885?

A

Halsted injects cocaine into the mandibular nerve (through Six spine) and brachial plexus

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4
Q

Objective of local anaesthetics

A

Use of a substance that induces a transient and completely reversible state of anaesthesia

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5
Q

What happens when local anaesthetics are used for pain control?

A

They cease to provide a clinical effect when they are absorbed from the site of injection into the circulation

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6
Q

What is the prime factor of LA?

A

The redistribution of the LA from the nerve fibre into the cardiovascular system

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7
Q

What are the desirable properties of LA?

A
  • Not irritating to the tissue
  • To not cause any permanent alteration of nerve structure
  • Low systemic toxicity
  • Effective regardless of whether it is injected into tissue or applied to the mucous membrane
  • Time of onset of anaesthesia should always be as short as possible
  • The duration must be long enough to permit the completion of the procedure
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8
Q

Action of LA

A
  • LA prevent the generation and conduction of nerve impulses
  • Provoke a chemical roadblock between the source of impulse and the brain
  • The neutron is the structural unit of the nervous system
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9
Q

Physiology of the nerves

A
  • Nerves carry impulses
  • Impulses are irritated by the chemical, thermal, mechanical or electrical stimuli
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10
Q

What are the mode and site of action of LA?

A
  • Altering the basic resting potential of the nerve membrane
  • Altering the threshold potential
  • Decreasing the rate of depolarisation
  • Prolonging the rate of repolarisation
  • Primary effects of LA occur during the depolarisation phase
  • LA binds to specific receptors in the sodium channels
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11
Q

When do the primary effects of LA occur?

A

During the depolarisation phase

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12
Q

Do LA increase or decrease the depolarisation?

A

They decrease it

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13
Q

LA binds to specific receptors in the _____ channels

A

Sodium

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14
Q

pH of LA solutions is between _____

A

5-5.7

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15
Q

What happens when LA is injected into the tissue (regarding the pH)

A

The buffering capacity of the tissue fluids returns the pH at the site to a normal pH of 7.4

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16
Q

Most LA are secondary amines. True or False

A

False. Most LA are tertiary amines

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17
Q

Tissue pH value

A

7.4

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18
Q

LA are basic compounds poorly soluble in water. True or False

A

True

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19
Q

LA pKa value

A

From 7.5-10

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20
Q

LA combine with _____ to LA _____

A
  • acids
  • salts (hydrochloric salts dissolved in sterile water or saline solution)
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21
Q

When pKa is close to the pH of tissue, we have a more ____ onset because we have a high portion of ______ ______ that can cross the ionised membrane.

A
  • rapid
  • non-ionised base
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22
Q

What does the pKa affect?

A

The action

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23
Q

What does the lipid solubility affect?

A

The anaesthetic potency

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24
Q

What does protein binding affect?

A

The duration

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25
Q

What does the non-nervous tissue diffusion affect

A

The onset

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26
Q

What does the vasodilator activity affect

A

The anaesthetic potency and duration

27
Q

Classification of LA

A
  1. Esters:
    a. benzoic acid
    b. parminobenzoic acid
  2. Amides
28
Q

Ester LAs:

A
  1. Benzoic acid:
    - Butacaine
    - Cocaine
    - Ethyl amino-benzoate
    - Hexylcaine
    - Tetracaine
  2. Parminobenzoic acid:
    - Chloroprocaine
    - Procaine
    - Propoxycaine
29
Q

Amide LAs:

A
  • Articaine
  • Bupivacaine
  • Dibucaine
  • Etidocaine
  • Lidocaine
  • Mepivacaine
  • Prilocaine
  • Ropivacaine
30
Q

What LA is commonly used in dentistry? And why?

A

Bupivacaine, because of its duration

31
Q

What most differs the ester LAs from the amide LAs

A

Their structure

32
Q

What type of LAs is resistant to hydrolysis?

A

Amide LAs

33
Q

What type of LAs are aqueous solutions?

A

Ester LAs

34
Q

Systemic actions of LA

A
  • Intramuscular injection
  • Most of the systemic actions are related to their blood or plasma levels
  • CNS and CVS are especially susceptible to their action
35
Q

How long should the intramuscular injection take? And why?

A

5-10 minutes, to achieve peak blood level

36
Q

Side effects of LA in CNS

A

Side effects happen at higher levels:
- Anticonvulsant properties: in the initial phase of the drug concentration
- Preconvulsive signs and symptoms
- Convulsive phase: tonic-clinic convulsive episode

37
Q

There are no CNS side effect at lows levels of LA. True or False

A

True

38
Q

What are the pre convulsive signs and symptoms?

A

Numbness of the tongue
Slurred speech
Shivering
Tremors
Disorientation
Drowsiness
Visual disturbances

39
Q

Side effects of LA in CVS:

A
  • Vasodilators
  • Actions on myocardium: myocardial depression, decreased conduction rate and force of contraction
  • Hypotension
40
Q

Side effects of LA on the respiratory system at non-overdose levels

A

Relaxation over bronchial smooth muscle

41
Q

Side effects of LA on the respiratory system at overdose levels

A

May produce respiratory arrest

42
Q

Half-life of LA

A

Time to have a 50% reduction in blood level

43
Q

Metabolism of ester LAs

A

Hydrolysed in plasma by pseudocholinesterase enzyme (PABA)

44
Q

What ester LA is the most rapidly hydrolysed?

A

Chlorophrocaine

45
Q

What ester LA has the greatest potential toxicity?

A

Tetracaine

46
Q

Metabolism of amide LAs

A

Primary biotransformation in liver

47
Q

What amide LA undergoes metabolism in the liver and lungs?

A

Prilocaine

48
Q

What type of LA hardly appear in the urine as the parent compound?

A

Esters

49
Q

What type of LA appear in urine as the parent compound in a greater percentage

A

Amides

50
Q

A percentage of LA is excreted unchanged in urine. True or False

A

True

51
Q

Lidocaine properties

A
  • 2%
  • Without vasoconstrictor
  • Adrenaline 1:50 000
  • Adrenaline 1:100 000
  • Maximum dose 4.4 mg/kg
  • Onset of action: 2-3’
  • Topical action
  • Usual local anaesthetics 1:10 000, 0.1 mg/mL
52
Q

Mepivacaine properties

A
  • 3% without VC
  • 2% with adrenaline 1: 100 000
  • Maximum dose: 4.4 mg/kg (300 mg)
  • Onset 1-2’
53
Q

Articaine properties

A
  • 4% with adrenaline 1:100 000- 1:200 000
  • Maximum dose 7mg/kg (500 mg)
  • Onset of 2min
  • > Power and duration
  • Better bone diffusion
54
Q

Normal articaine carpules in a person weighing 60kg

A

5.8 with adrenaline 1:200 000 and adrenaline 1:100 000

55
Q

Normal mepivacaine carpules in a person weighing 60kg

A

7.3 with adrenaline

56
Q

Duration of prilocaine (3%) in pulp and soft tissues

A
  • 60-90 min in pulp
  • 120-240 min in soft tissues
57
Q

Duration of articaine in pulp and soft tissues with adrenaline 1:100 000

A
  • 75 min in pulp
  • 240 min in soft tissue
58
Q

Duration of articaine in pulp and soft tissues with adrenaline 1:200 000

A
  • 45 min in pulp
  • 180 min in pulp
59
Q

Duration of lidocaine (with adrenaline 1: 100 000) in pulp and soft tissues in an infiltration method

A
  • 60 min in pulp
  • 170 min in soft tissues
60
Q

Duration of lidocaine (with adrenaline 1: 100 000) in pulp and soft tissues in a nerve

A
  • 85 min in pulp
  • 190 min in soft tissues
61
Q

Prilocaine percentage

A

3%

62
Q

Vasoconstrictors sympathomimetics examples:

A
  • Epinephrine
  • Norepinephrine
  • Levonordefrin
  • Phynenylpephrin
63
Q

What are vasoconstrictors derived from?

A

Felypresi and omipresin

64
Q

Vasoconstrictors characteristics

A
  • Slow down LA absorption
  • Lower the LA dose necessary to block the nerve, lower toxicity
  • Lower peak doses of LA in blood up to 70% (lidocaine 2% + adrenaline 1:200 000)
  • Hemostatic in the injection area

Oral Surgery (5 decks)

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