Pharmacology of local anaesthetics

Question 1

Define anaesthesia

Answer 1

Without feeling or sensation

Question 2

Define local anaesthesia

Answer 2

Loss of feeling restricted to a particular region

Question 3

When is local anaesthesia used?

Answer 3

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

Question 4

What can local anaesthesia be produced by?

Answer 4

Local anaesthesia can be produced by:

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

Question 5

Give examples of irreversible blockers used as local anaesthetics

Answer 5

Phenol ethanol

Radiofrequency lesion

Question 6

Describe true local anaesthetics

Answer 6

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

Question 7

What is a local anaesthetic?

Answer 7

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)

Question 8

Define nociception

Answer 8

The neural processes of encoding and processing noxious stimuli

Question 9

How do local anaesthetics work?

Answer 9

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

Question 10

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

Answer 10

Effects such as analgesia and paralysis can be achieved

Question 11

Define analgesia

Answer 11

Loss of pain sensation

Question 12

paralysis

Answer 12

Loss of muscle power

Question 13

Name some techniques local anaesthetics are used in?

Answer 13

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

Question 14

Where is a topical anaesthetic applied?

Answer 14

Around the gums, cornea and skin prior to venipuncture

Question 15

What is a Subcutaneous injection?

Answer 15

An infiltration anesthesia can be one or more injections

Question 16

Where is a nerve block applied?

Answer 16

Around the nerve

Question 17

Where is an epidural given?

Answer 17

Into the epidural space

Question 18

Where is an intrathecal anesthetic given?

Answer 18

Into subarachnoid space

It is a form of spinal anesthesia

Question 19

List some ideal properties of local anesthetic

Answer 19

• 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

Question 20

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

Answer 20

October 16th 1846

Question 21

What did Dr Karl koller notice?

Answer 21

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

Question 22

What did Dr Koller demonstrate in 1884?

Answer 22

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

Question 23

What is Dr Kollers nick name?

Answer 23

Coca Koller

Question 24

What replaced cocaine as a local anaesthetic and when?

Answer 24

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

Question 25

What is the aromatic terminal of LA’s described as and why?

Answer 25

Lipophilic as is contains no positive or negative charges

Question 26

Define lipophilic

Answer 26

Lipid soluble

Question 27

Why is the aromatic terminal essential for LA’s?

Answer 27

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

Question 28

What is the amino terminal in local anaesthetics described as?

Answer 28

Water soluble or hydrophilic

Question 29

Why is solubility in water essential for LA’s?

Answer 29

1. To allow for the dissolution in a solvent to permit injection
2. To allow penetration through interstitial fluid allowing administration

Question 30

How does the amide structure of articaine differ from other local anaesthetics?

Answer 30

The amide structure is similar but the molecular structure differs through the presence of a thiophene ring instead of a benzene ring

Question 31

Name some ester linked agents

Answer 31

Cocaine

Procaine

Question 32

Describe what cocaine does and when it was used?

Answer 32

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

Question 33

What are the major disadvantages of cocaine?

Answer 33

Cocaine is an intense vasoconstrictor and has a potential to cause cardiovascular toxicity

Question 34

Describe what procaine does and when it was used?

Answer 34

First used in 1905 as a nerve blocker
Has low potent and last for a short duration
Not used much now

Question 35

Name the type of procaine given as an epidural during childbirth

Answer 35

2-chloroprocaine

Question 36

Name some amide linked agents

Answer 36

1. Lidocaine
2. Prilocaine
3. Mepivacaine
4. Bupivacaine
5. Ropivacaine
6. Articaine

Question 37

What does lidocaine do?

Answer 37

It is used as a vasodilator
It reduces cardiac excitability
Affects the central nervous system in large doses