Local anaesthetics

Question 1

Define a local anaesthetic

Answer 1

Local anaesthetics reversibly block nerve conduction when applied to a restricted area of the body (to allow for a procedure) without loss of consciousness

Question 2

Why are local anaesthetics necessary?

Answer 2

To block pain from nociceptors
Pain not perceived
However still detected by sensory receptors

Question 3

What mechanism is stopped to prevent perception of pain?

Answer 3

Action potentials

Particularly voltage-gated Na+ channels

Question 4

What suffix suggests a local anaesthetic?

Answer 4

-aine

Question 5

When was the first synthetic local anaesthetic produced?

Answer 5

1905

Question 6

Name chemical structures that are common in local anaesthetics

Answer 6

Benzene ring
Amine group
Physical separation of these two structures

Question 7

Describe the common structure of a local anaesthetic

Answer 7

Aromatic ring - linkage - basic amine group

Question 8

What is the purpose of the linkage group?

Answer 8

Either an amide or ester

Allows for metabolism, makes them reversible

Question 9

How might a local anaesthetic with an ester linkage differ to one with an amide linkage?

Answer 9

Esters are metabolised very quickly in the body
The effect will be short-lasting
Amides have a much longer lasting effect as they are metabolised slower

Question 10

What is the purpose of the aromatic ring?

Answer 10

Aromatic rings make a molecule lipophilic

Allows the molecule to cross the cell membrane

Question 11

What is the purpose of the amine group

Answer 11

To allow the molecule to go between charged and uncharged state

Question 12

What pH is a local anaesthetic?

Answer 12

Weak base

Question 13

What is the ionisation state of a local anaesthetic?

Answer 13

Determined by pH

Question 14

What happens at the cell membrane?

Answer 14

Unionised version crosses the cell membrane

Ionised form blocks voltage gated channel from the inside

Question 15

What form of voltage gated channels can the local anaesthetic block?

Answer 15

It can block open channels

“Use-dependent block”

Question 16

If local anaesthetic blocks open channels, what is the relationship between pain and blocking?

Answer 16

Increase in pain
= increase in open channels
= increase in blocked channels

Question 17

Name some factors that affect the effectiveness of local anaesthetic

Answer 17

Tissue pH

Question 18

What could cause a change in tissue pH?

Answer 18

Infection

Bacteria produce acid

Question 19

Which neurones are targeted by local anaesthetic?

Answer 19

All of them

No specificity

Question 20

Which neurones are more sensitive to local anaesthetic?

Answer 20

Sensory neurones are more sensitive than motor neurones

Question 21

Name routes of administration of local anaesthetic

Answer 21

Topical anaesthesia
Infiltration anaesthesia
Nerve block anaesthesia
Epidural anaesthesia
Spinal anaesthesia

Question 22

What are some unwanted effects of local anaesthetic?

Answer 22

Non-specific: hypersensitivity

Specific: high doses, injected into vessels

Question 23

What could happen if local anaesthetic reached the CNS?

Answer 23

Tremor
Convulsions
Respiratory and cardiac failure (brain stem)

Question 24

What could happen if local anaesthetic reached the cardiovascular system?

Answer 24

Cardiac muscle contractility decreases
Blood vessels dilate
Blood pressure decreases

Question 25

What drugs are administered at the same time as local anaesthetics?

Answer 25

Vasoconstrictors

Question 26

Why are vasoconstrictors administered?

Answer 26

Reduces movement and unwanted effects

Increases duration of action

Question 27

Name the properties of good local anaesthetic

Answer 27

Reversible
Block nerve conduction in nociceptive neurones
Effective for the time of the procedure
Low toxicity