Uses and actions of local anaesthetics

Question 1

Definition of local anaesthetics

Answer 1

Reversibly block nerve conduction when applied to a local area of the body to enable a procedure to be carried out without loss of consciousness

Question 2

All local anaesthetics end with the suffix …..

Answer 2

• caine

e. g. lidocaine

Question 3

How to local anaesthetics work?

Answer 3

They block sodium channels and so block pain signals from sensory receptors reaching the brain

Question 4

What are the 3 chemical components of local anaesthetics? How do they contribute to function?

Answer 4

Aromatic ring - lipid soluble so can pass through cell membrane
Amide or ester linkage - allow breakdown to produce metabolites, ester is faster
Basic amine group - proton acceptors, ionisation is determined by pH

Question 5

What part of local anaesthetics are people usually allergic to?

Answer 5

The metabolites

Question 6

Give 4 examples of LA’s, their linkage and their duration of action

Answer 6

Procaine/Cocaine: ester –> short (30mins)
Lidocaine: amine –> medium (1-2hrs)
Prilocaine: amine –> medium (3hrs)
Bupivacaine –> long (4hrs)

Question 7

Which is the main factor that affecting the effectiveness of local anaesthetics?

Answer 7

tissue pH

e.g. infection causes decrease in pH, more of the ionised form, less absorption

Question 8

Explain what is meant by use-dependent block in regards to the action of local anaesthetics

Answer 8

If more pain is generated, more action potentials, more sodium channels open, greater action of LA

Question 9

Describe the relationship between axon diameter and local anaeasthetic action

Answer 9

Smaller diameter axons are more sensitive

Less LA is needed

Question 10

What are the 6 routes of administration for LA’s

Answer 10

topical
IV - biers block (blocks pain in extremities 
infiltration
spinal 
epidural
nerve block

Question 11

What are 4 unwanted effects of LA’s?

Answer 11

Non-specific - allergy
Specific - high dose, wrong place
Effects CNS - tremor, seizures
CV effects - decreases contractility, dilates blood vessels

Question 12

What other drugs are commonly adminstersted with LA’s?

Answer 12

Vasoconstrictors to prolong duration of action

Question 13

4 properties of good local anaesthetics

Answer 13

reversible
block nerve conduction in nociceptive neurones
effective for time of procedure
low toxicity