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Pharmacology of local anaesthetics Flashcards

1
Q

Define anaesthesia

A

Without feeling or sensation

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2
Q

Define local anaesthesia

A

Loss of feeling restricted to a particular region

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3
Q

When is local anaesthesia used?

A

To enable minor or major operative procedures to be carried out
To provide relief from prolonged severe pain

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4
Q

What can local anaesthesia be produced by?

A
  1. Local anaesthesia can be produced by:
  2. Cooling with ethyl chloride (block of neuronal conduction at 8-10°C)
  3. Pressure (used to reduce discomfort from injection in palatal tissue)
  4. Hypoxia
  5. Irreversible blockade (phenol ethanol, radiofrequency lesion)
  6. true local anesthetics
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5
Q

Give examples of irreversible blockers used as local anaesthetics

A

Phenol ethanol

Radiofrequency lesion

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6
Q

Describe true local anaesthetics

A

A substance applied to any nerve fibre in sufficient concentration will produce reversible blockade of axonal conduction without depolarisation

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7
Q

What is a local anaesthetic?

A

A local anaesthetic is a drug that causes reversible local anaesthesia and a loss of nociception (the neural processes of encoding and processing noxious stimuli)

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8
Q

Define nociception

A

The neural processes of encoding and processing noxious stimuli

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9
Q

How do local anaesthetics work?

A

They reversibly block impulse conduction along nerve axons and other excitable membranes that utilise sodium channels as the primary means of generating action potentials

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10
Q

What is the result of using local anaesthetics on specific nerve pathways?

A

Effects such as analgesia and paralysis can be achieved

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11
Q

Define analgesia

A

Loss of pain sensation

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12
Q

Loss of pain sensation

A

Loss of muscle power

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13
Q

Name some techniques local anaesthetics are used in?

A
  1. Topical application
  2. Subcutaneous injection
  3. Nerve block
  4. Epidural
  5. Intrathecal
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14
Q

Where is a topical anaesthetic applied?

A

Around the gums, cornea and skin prior to venipuncture

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15
Q

What is a Subcutaneous injection?

A

An infiltration anesthesia can be one or more injections

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16
Q

Where is a nerve block applied?

A

Around the nerve

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17
Q

Where is an epidural given?

A

Into the epidural space

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18
Q

Where is an intrathecal anesthetic given?

A

Into subarachnoid space

It is a form of spinal anesthesia

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19
Q

List some ideal properties of local anesthetic

A
  • stable in solution, (requires no additive)
  • non-irritating to tissues
  • no permanent damage to nerves
  • no systemic toxicity
  • no allergic response
  • potent
  • rapid onset of action
  • predictable duration of action
  • Must be a sensory not a motor block
  • Must have no active metabolites
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20
Q

On what day is the first recorded use of general anaesthetics?

A

October 16th 1846

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21
Q

What did Dr Karl koller notice?

A

That the end of his tongue went numb when he tasted cocaine

He then dropped some cocaine dissolved in water into his eye – noticed its tissue-numbing capabilities

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22
Q

What did Dr Koller demonstrate in 1884?

A

The potential for cocaine to be used as a local anaesthetic in eye surgery

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23
Q

What is Dr Kollers nick name?

A

Coca Koller

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24
Q

What replaced cocaine as a local anaesthetic and when?

A

In the 20th century, other agents such as lidocaine replaced cocaine as a local anaesthetic

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25
What is the aromatic terminal of LA’s described as and why?
Lipophilic as is contains no positive or negative charges
26
Define lipophilic
Lipid soluble
27
Why is the aromatic terminal essential for LA’s?
In order for them to penetrate fatty tissues such as the lipid sheath of nerves in order to gain access to the nerve cell membranes to reach its site of action
28
What is the amino terminal in local anaesthetics described as?
Water soluble or hydrophilic
29
Why is solubility in water essential for LA’s?
1. To allow for the dissolution in a solvent to permit injection 2. To allow penetration through interstitial fluid allowing administration
30
How does the amide structure of articaine differ from other local anaesthetics?
The amide structure is similar but the molecular structure differs through the presence of a thiophene ring instead of a benzene ring
31
Name some ester linked agents
Cocaine | Procaine
32
Describe what cocaine does and when it was used?
It was first used in 1884, It is a good penetrator It is not used as much now as it is a drug of abuse, It blocks sodium re uptake
33
What are the major disadvantages of cocaine?
Cocaine is an intense vasoconstrictor and has a potential to cause cardiovascular toxicity
34
Describe what procaine does and when it was used?
First used in 1905 as a nerve blocker Has low potent and last for a short duration Not used much now
35
Name the type of procaine given as an epidural during childbirth
2-chloroprocaine
36
Name some amide linked agents
1. Lidocaine 2. Prilocaine 3. Mepivacaine 4. Bupivacaine 5. Ropivacaine 6. Articaine
37
What does lidocaine do?
It is used as a vasodilator It reduces cardiac excitability Affects the central nervous system in large doses
38
Name the most commonly used amid linked LA used in dent?
Articaine
39
Name the ketone type agent we use as an LA
Dyclonine
40
What is dyclonine used as?
A liquid topical anaesthetic agent
41
Heat properties does dyclonine have
Has bactericidal and fungicidal properties
42
What is the pKa of most LAs and what does this mean?
Between 8.0 -9.0 | This means at pH 7.4about 5 - 20% of the LA will be in the non ionised form
43
What does a pKa value indicate?
It is the acid dissociation constant | It indicates the pH at which the ionised and non ionised forms of the substance are at equal concentrations
44
Why must a high concentration of LA be administered?
As only a small fraction of LA molecules will reach the target site
45
Name some of the major determinant of how well the LA will penetrate the tissues
1. Site of administration 2. the lipid solubility of the drug 3. The pKa of the drug 4. Pathophysiological factors eg inflammation
46
What are sodium channels?
They are integral membrane proteins that form ion channels | These channels allow sodium ions to pass through the cells plasma membrane
47
What is the trigger for voltage gated sodium channels to open?
Voltage change
48
How do local anaesthetic drugs affect sodium channels?
They inhibit the influx of Na+ ions through ththe voltage gated sodium Channels This means an action potential cannot be generated so conduction inhibited
49
What is an action potential?
It is a self regenerating wave of electrochemical activity that allow excitable cells to carry a signal over a distance
50
When are sodium channels closed?
When the channel is fully polarised
51
What happens as you increase the concentration of LA to thte nerve fibre?
1. Threshold for excitation increases 2. Impulse conduction slows 3. Rate of the rise of the action potential declines 4. Actionable potential amplitude decreases 5. Ability to generate action potential is abolished
52
What is the sensitivity to inhibition by LAs a function of?
Nerve diameter | Myelination
53
Describe post ganglion is autonomic nerves
They have a small diameter and are unmyelinated
54
State the order of sensitivity to LA inhibition
Autonomic > warmth > pain> touch > pressure
55
Do sodium channels in the rested state or activated state have a higher affinity to LA?
Channels in the activated state
56
Which LA blocks only the sodium ion channels in their resting state?
Benzocaine
57
What is acidosis?
An increased acidity of the blood plasma
58
When does acidosis occur?
When arterial p( falls below 7.35
59
When does alkalosis occur?
When arterial pH is over 7.45
60
What does acidosis do?
It can partly reduce the action of LA
61
Why does acidosis reduce the action of LA?
Because most of the anaesthetic is ionised and therefore can not cross the cell membrane to reach the cytoplasmic facing site of action on the sodium channel
62
Local anaesthetic in which form can cross the cell membrane?
Only the non ionised for of LA can cross the cell membrane to reach the cytoplasmic facing site of action on the sodium channel
63
Describe characteristic of neurones that are more sensitive to blockage by LA
1. Short axons 2. Nerves which are not in their resting state 3. Small myelinated nerves 4. motor nerves are usually blocked first in large mixed nerves
64
What happens to the level of inhibition when there are long intervals between nerve impulses?
The level of inhibition of each impulse will be the same (tonic blockade)
65
What happens to the level of inhibition when there are short intervals between nerve impulses?
The level of inhibition increases with each impulse (phasic blockade)
66
Administration of LA at which side has the fastest absorption rate?
Intravenous
67
Administration of LA at which side has the slowest absorption rate?
Subcutaneous infiltration
68
List the sites we can administer LA from fastest to slowest absorption rate
1. Intravenous 2. Mucous membrane 3. Intercostal block 4. Causal block 5. Epidural block 6. Brachial plexus block 7. Peripheral nerve block 8. Subcutaneous infiltration
69
What us hypersensitivity a result of?
Anaphylactic reaction (allergic reaction) to LA
70
Hypersensitivity is associated with which toe of LA?
Esters and very rarely with amides
71
How can LA toxicity affect the CNS?
Initial effects are excitatory with involuntary muscle activity Later effect is depressant which may lead to unconsciousness
72
How can LA toxicity affect the Heart?
Possible feduction in cardiac output may lead to circulatory collapse (Rare)
73
What is a toxic effect of prilocaine and articaine?
Methaemoglobinaemia
74
What are some of the symptoms of Methaemoglobinaemia?
1. Cyanosis 2. Lethargy 3. Respiratory distress which doesn’t respond to oxygen
75
What is the treatment for Methaemoglobinaemia?
Administer methylene blue intravenously 1-2mg/kg
76
Is Methaemoglobinaemia a concern in the dental practice?
No because we use small amounts of LA
77
What do vasoconstrictors do?
They restrict the diffusion of the LA away from the site of injection and thus allows the LA to stat at rhs site for longer producing a longer duration of action
78
Wh6 are LAs frequently given with vasoconstrictors?
To: 1. prolong action 2. reduce plasma levels (less risk of CNS effects?) 3. ‘greater anaesthesia’ or reduced dose 4. reduced operative haemorrhage
79
Which vasoconstrictors is usually used?
epinephrine (adrenaline) 1:200,000, or norepinephrine (noradrenaline) 1:100,000
80
When are vasoconstrictors not administered with LA?
when injected into extremities (fingers & toes) since, with a more limited circulation, there is a risk of tissue hypoxia

APM- pharmacology (3 decks)

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