Local Anaesthetics

Question 1

How is differential block produced

Answer 1

Smaller diameter fibres affected first so pain and autonomic blocked, coarse touch and movement still work
Block is also use-dependent for Na channels

Question 2

Lidocaine use

Answer 2

Lidocaine used most, acts rapidly and when given with adrenaline (vasoconstrictor action) lasts 90 mins

Question 3

Local Anaesthetic MOA

Answer 3

Lipid-soluble form enters axon, gets protonated then binds to S6 subunit to block channel. Once enough channels blocked, action potential threshold can’t be reached.

Question 4

Local Anaesthetic SE

Answer 4

Hypersensitivity reactions, especially in atopic patients, and more often with esters of p-aminobenzoic acid
Local tissue injury
Drowsiness/numbness of tongue/blurred vision
Convulsions+ resp depression at high levels

Question 5

Topical application to mucosa drugs

Answer 5

Lidocaine
Benzocaine powder for burns
Lidocaine/prilocaine cream

Question 6

Injection into tissue

Answer 6

Lidocaine
Prilocaine
Given with vasoconstrictor to prolong local duration + reduce risk of systemic toxicity

Question 7

Prilocaine use

Answer 7

Prilocaine similar to lidocaine but metabolised more and less toxic at same dose

Question 8

Bupivacaine use

Answer 8

Bupivacaine has slow onset but lasts for a very long time, used in epidurals and spinal anaesthesia

Question 9

Benzocaine use

Answer 9

Benzocaine has low potency, used for surface anaesthesia

Question 10

Cocaine use

Answer 10

Cocaine used in surface anaesthesia where vasoconstrictor action wanted

Question 11

Tetracaine use

Answer 11

Tetracaine sometimes used to anaesthetise cornea but less toxic e.g. oxybuprocaine/proxymetacaine better as sting less