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Stage 3 Human Diseases > HD22&25 Local Anaesthetic > Flashcards

HD22&25 Local Anaesthetic Flashcards

1
Q

describe the ideal LA?

A
  • Specific and reversible action
  • Non-irritant
  • Produces no permanent damage
  • No systemic toxicity
  • Active topically and by injection
  • Rapid onset
  • Suitable duration of action
  • Chemically stable and sterilisable
  • Combinable with other agents
  • Non-allergic
  • Non-addictive
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2
Q

What would be the therapeutic ratio of the ideal LA?

A

High therapeutic ratio (difference in dose between the effect that would give you the dose you want and the dose that would cause toxic effects) = want it to be high

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3
Q

LA is not specific, what will affect transmission in any excitable tissue. What are the 3 excitable tissues

A
  • CNS
  • Cardiac
  • Motor
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4
Q

What are the uses of LA in dentistry (4)?

A
  • Operative pain management
  • Post-operative pain management - give LA while in GA so when wake aren’t in pain
  • Diagnosis – pulp sensibility tests (in the past), now used for atypical pain or to identify which tooth is causing the pain if a number are carious
  • Haemostasis – reduce bleeding during procedures
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5
Q

A chemical roadblock between the tooth and the brain

TRUE OR FALSE

A

true

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6
Q

Explain the theory of membrane expansion as the way LA works:

A

• The LA diffuses into cell membrane, cuasing it to expant. Therefore membrane is less permeable to Na and changes in polarisation do not occur.

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7
Q

what happens normally during membrane potential?

A

Sodium channel has 2 gates
• At rest – m gate closed/ h gate open
• Depolarisation – m gate opens which allows sodium to move inside cell + ve inside
• Repolarises – H gate closes which stops sodium moving into nerve cell membrane
• Potassium diffuses back out – electrochemical gradient shifts back (+ outside)
• Now in refractory period – cannot fire another impulse

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8
Q

What is the specific receptor theory of LA ?

A
  • Receptor on inside of H gate – LA attaches to receptor holding the gate closed
  • This holds it in the refractory period so that no more impulses can be fired
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9
Q

what are the 3 components of LA molecule?

A
  • Aromatic group (lipophilic)
  • Intermediate chain (ester or amide link)
  • Substituted amino terminal (hydrophilic)
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10
Q

What part of the LA molecule allows:

spatial separation of lipid and water-soluble components

A

Intermediate chain

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11
Q

What part of the LA molecule allows:
classification of LA into 2 major groups:
- Esters
- Amides

A

Intermediate chain

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12
Q

What 2 major groups can LA belong to (determined by Intermediate chain ):

A

Esters

- Amides

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13
Q

What 2 major groups can LA belong to (determined by Intermediate chain ):
2) Which are at greater risk of an allergic reaction?

A

Esters

  • Amides
    2) esters
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14
Q

Name the amide LAs:

A
  • Lidocaine
  • Prilocaine
  • Mepivacaine
  • Articaine
  • Bupivacaine
  • Levobupivacaine
  • Ropivacaine
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15
Q

Name the esters LAs:

which of these is a topical anaesthetic?

A
  • Benzocaine – topical anaesthetic
  • Amethocaine
  • Procaine
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16
Q

The binding site of LA is intracellular , what is the significance of this?
2) What is required for specific binding to any receptor by LA?

A

1) • Therefore LA needs to be lipophilic and uncharged to cross the cell membrane
2) • Specific binding to any receptor to achieve LA requires a charged molecule
• Therefore the LA needs to be in a charged form

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17
Q

• How can LA be uncharged (lipophilic) and charged at the same time?
2) What does this achieve?

A

• LAs are weak bases
• In solution the LA molecule will exist as both -
- Uncharged base
- Charged cation
2) - Lipid soluble to enter cells to work
- Charged form for specific binding once in cell

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18
Q

which is the more effective LA once injected, the one with a higher proportion of uncharged molecule or lower?

A
  • The quicker the LA enters the cell the more effective it is and the quicker it acts
  • Therefore, LA with a high proportion of uncharged molecules after injection are most effective
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19
Q

what is ionisation?

A

ratio of charged to uncharged

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20
Q

what governs ionisation?

A
  • pH – can be controlled usually

* pKa (dissociation constant) – set within each LA (cannot change)

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21
Q

what is the affect on LA uptake when the pH around the neurone is low?
2) what tissues have a lower pH?

A

• Lower pH - less uncharged molecules present (difficult to cross membrane as not uncharged)
2)infected tissues

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22
Q

what affect does pKa have on the onset of action of LA?
2) list the pKa of these from high to low:
lidocaine
bupivacaine
procaine
articaine

A

1) the lower the pKa the better
2) procaine -9.1
bupivacaine- 8.1
articaine- 7.8
lidocaine- 7.9

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23
Q

For more ionisation does pH need to be high or low?

2) for pKa ?

A

1) high

2) low

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24
Q

What chemico-physical properties influence the onset of LA?

A
  • Ionisation (pH and pKa) - onset

* Partition coefficient - onset

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25
Q

What chemico-physical properties influence the duration of action of LA?

A
  • Protein binding – duration of action

* Vasodilator ability – duration of action

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26
Q

what does the partition coefficient measure?

2) what does a higher partition coefficient mean?
3) what does this means in terms of LA with a high partition coefficient in the body?

A

measures lipid solubility
2) more lipid soluble
3) • Therefore crosses nerve sheath quicker
• Therefore higher partition coefficient the faster the onset of action

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27
Q

why is lidocaine the gold standard?

A

its partition coefficient is 3 while for procaine it is 0.6

28
Q

Proteins bind to drugs. bound portion acts as what and has what role?

A

• Bound portion acts as a reservoir from which free drug can be released to replace what has been used/metabolised

29
Q

Give half-lifes:
lidocaine 64%
bupivacaine 96%

A

lidocaine- half life 90 mins

bupivacaine- half life 160 mins

30
Q

Give protein binding percentages:
lidocaine- half life 90 mins
bupivacaine- half life 160 mins

A

lidocaine 64%

bupivacaine 96%

31
Q

Most LAs are vasodilators, what is the exception?

2) what is the significance of this?

A

cocaine

2) vasoconstrictor added to conteract this

32
Q

What is inside an LA cartridge?

A
  • Anaesthetic agent
  • Vasoconstrictor
  • Reducing agent (only present if vasoconstrictor is – prevents it breaking down)
  • Ringer’s solution – forms bulk of cartridge, which all this shit dissolves in
  • Preservative
33
Q

what are the benefits of vasoconstrictor in LA?

A
  • More profound anaesthesia
  • Longer lasting anaesthesia – prevents dilation of vessels which would wash it away
  • Better haemostasis
34
Q

what vasoconstrictors are used in the UK?

A

Vasoconstrictors used in the UK
• Adrenaline (epinephrine) – a catecholamine
• Felypressin (octapressin) – a synthetic peptide

35
Q

what can adrenaline affect?

A
  • Blood vessels
  • Heart
  • Lungs
  • Metabolism
  • Wound healing
36
Q

where are the following receptors found:

1) Alpha adrenoreceptors:
2) Beta adrenoreceptors:

A
  • Skin and mucous membrane

2) - Skeletal muscle and liver

37
Q

what is the vascular affect of adrenaline acting on beta adrenoreceptors?

A
  • Vasodilation
  • Reduced diastolic BP
  • Fainting with high doses
38
Q

what is the vascular affect of adrenaline acting on

alpha adrenoreceptors:?

A

vasoconstriction

39
Q

what is the metabolic affect of adrenaline acting on

1) alpha
2) beta adrenoreceptors?

A
  • Alpha adrenoreceptor inhibition of insulin release → increase blood glucose
  • Beta adrenoreceptor activation of sodium-potassium pump → potassium pumped intracellular → decrease plasma potassium (hypokalaemia)
40
Q

1) what are the direct cardiac effects of adrenaline?

2) what are the indirect cardiac effects of adrenaline?

A 
1) Direct effect
•	Activation of beta-adrenoreceptors
•	Increases rate and force of contraction
•	Increases cardiac output
2) Secondary to metabolic changes
41
Q

what are the pulmonary effects of adrenaline? what receptors are involved?

A
  • Stimulation beta-adrenoreceptors
  • Bronchiolar relaxation
  • Theoretical in LA doses
42
Q

what vasoconstrictor is involved in wound healing?

A
  • Decreased oxygen tension in tissues

* Increased fibrinolysis – decreased stability of blood clots

43
Q

Why is it so important to aspirate?

A
  • 1:80 000 = 12.5g/mL
  • 2.2mL contains 27.5g
  • 0.00825micrograms in blood system naturally occurs in BV therefore MUST aspirate
44
Q

What does felypression cause?

2) How is it not as good as adrenaline?
3) why is it given?

A
  • Coronary artery vasoconstriction
  • Oxytocic action on uterus
    2) poorer control of haemorrhage of adrenaline
    3) given if can’t tolerate adrenaline
45
Q

what is the number of micrograms of these in 2.2mL:

1) adrenaline
2) felypressin

A

1) 27.5

2) 1.2

46
Q

rate LA ends up in blood stream depends on:

A

 Vasodilatory ability

 Protein binding capacity – higher it is, slower enters bloodstream

47
Q

• Once in circulation LA partially bound to _____1_____and __2___
• Unbound portion free to enter any ____3___
Not inhibited by barriers to ___4___, therefore will cross ___5___ and ___6__

A

1) plasma proteins
2) proteins
3) liver
4) diffusion
5) BBB
6) placenta

48
Q

highly perfused organs will receive higher levels of LA… including:

A

brain, liver , kidneys

49
Q

metabolism of esters in blood is rapid , what enzyme metabolises this?

A

pseudocholinesterase

50
Q

what reaction occurs to esters in liver?

A

hydrolysis

51
Q

Are the metabolites of esters active?

A

no

52
Q

What is the major metabolite of ester vasoconstrictors?

A

para-aminobenzoic acid (PABA)

53
Q

People who lack psuedocholinesterase, what are they at risk of?

A

• 1 in 2800 lack pseudocholinesterase – sux apnoea (muscle relaxant) and risk of ester overdose

54
Q

What is sux apnoea

A

permanently paralysed as body cannot metabolise drug, as don’t have the enzyme

55
Q

What are ester allergies usually allergic to?

A

para-aminobenzoic acid (PABA)

56
Q

Compare the metabolism of amides to esters?

A

• More complex than esters, therefore longer half life

57
Q

what is the primmary site of metabolism of amides?

A

liver

58
Q

What reactions (and order) for metabolism of amides?

A 
o	Dealkylation
o	Hydrolysis
o	Hydroxylation
o	Further dealkylation
o	Conjugation
59
Q

What properties can metabolites possess?

A

• Metabolites can possess LA and sedative properties

60
Q

prilocaineis partly metabolised where?

A

lung

61
Q

articaine undergoes hydrolysis where and by what enzyme?

A

• Articaine also undergoes hydrolysis in plasma by pseudocholinesterase (liver and blood)

62
Q

Where is lidocaine excreted?

A
  • Via kidney

* <3% excreted unchanged in urine

63
Q

How long does it take adrenaline to appear in plasma/ systemic circulation?

A

• Appears in systemic circulation rapidly – peak plasma levels couple of mins after intra oral injection

64
Q

What enzyme is involved in the methylation of adrenaline?

2) where is transported for deamination?
3) what is it conjugated with?
4) wat is it excreted in?
5) What % is excreted unchanged in urine?

A

1) COMT
2) deamination
3) sulphate
4) urine
5) 1%

65
Q

What enzymes are involved in adrenaline excretion?

A

COMT
MAO
ADH

Stage 3 Human Diseases (10 decks)

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