Local Anaesthetics

Question 1

Where is Lidocaine metabolised and excreted

Answer 1

• Hepatic metabolism
• Protein bound
• Renally excreted

Question 2

How can lidocaine toxicity be treated?

Answer 2

IV 20% lipid emulsion

Question 3

Drugs which interact with lidocaine

Answer 3

Beta blockers
ciprofloxacin
phenytoin

Question 4

Features of lidocaine toxicity

Answer 4

• Initial CNS over activity (blocks inhibiting pathways)
• then CNS depression as lidocaine (blocks both inhibitory and activating pathways)
• Cardiac arrhythmias

Question 5

Mechanism of action of bupivicaine

Answer 5

• binds to the intracellular portion of sodium channels
• blocks sodium influx => prevents depolarization

Question 6

Lignocaine has a longer duration of action than bupivicaine. TRUE/FALSE

Answer 6

FALSE

• Bupivicaine has much longer duration of action than lignocaine
• used for topical wound infiltration at the end of surgical procedures

Question 7

Why is bupivicaine contra-indicated in regional blockage?

Answer 7

cardiotoxic
=> C/I in case the tourniquet fails.

Levobupivicaine = less cardiotoxic

Question 8

What is the usual choice of local anaesthetic for IV regional anaesthesia?

Answer 8

Prilocaine
- far less cardiotoxic

Question 9

In what types of tissue do local aneasthetics have reduced effect?

Answer 9

The dissociation of anaesthetic shifts in tissues that are acidic

e.g. abscess
=> reduced efficacy

Question 10

Why is adrenaline often added to local anaethetic?

Answer 10

• prolongs the duration of action at the site of injection
• permits usage of higher doses

Question 11

The use of adrenaline in local anaesthetic is contra-indicated in patients taking what drugs?

Answer 11

MAO inhibitors
tricyclic antidepressants