Local anaesthetics

Question 1

Local anaesthetic

Answer 1

Local anaesthetics produce a transient and reversible loss of sensation (analgesia) in a circumscribed region of the body without loss of consciousness.
Normally, the process is completely reversible

Question 2

General structure of local anaesthetic

Answer 2

Aromatic ring (lipophilic)
 Intermediate linkage
 Terminal amine (hydrophilic)

Question 3

How do local anaesthetics work?

Answer 3

1. Local anaesthetic (in its unionised form) passes though membrane.
2. Local anaesthetic (in its ionised form) binds to sodium channels from intracellular part.
3. This blocks the initiation and propagation of the action potential.

Question 4

What is importance of high potency for local anaesthetics?

Answer 4

Potency = lipid soluble

High lipid soluble = able to use lower concentrations and prevent toxicity.

Question 5

Local anaesthetics onset

Answer 5

5 mins

Question 6

Duration of action of local anaesthetics

Answer 6

1-1.5 h

Question 7

Esters clearance

Answer 7

Hydrolysed via plasma cholinesterase

Question 8

Amides clearance

Answer 8

Metabolism via hepatic enzymes

Question 9

Excretion of local anaesthetics

Answer 9

Kidneys

Small amounts of esters in urine as hydrolysed in plasma

Question 10

Dialysis patients and local anaesthetics excretion

Answer 10

Dialysis patients may not be able to excrete the unchanged portion of amide and esters so can lead to toxicity