Question

The topical use of which of the following local anaesthetics is not recommended?

• A. Lignocaine
• B. Bupivacaine
• C. Cocaine
• D. Dibucaine

Hint:

Bupivacaine penetrates mucosa poorly and is unusually cardiotoxic if absorbed, so surface or topical use is avoided even though lignocaine, cocaine, and dibucaine are all used topically.

Answer 1

The Correct Option is B

Step 1: Note that all four drugs here are local anaesthetics.
Lignocaine, bupivacaine, cocaine, and dibucaine all block sodium channels in nerve fibres, but they differ in how well they cross mucous membranes and in how dangerous they are if absorbed in a large amount.

Step 2: Check which of these are actually used topically.
Lignocaine penetrates mucosa well and is a standard topical agent for the mouth, throat, and skin. Cocaine has natural vasoconstrictor activity along with anaesthetic action, which is why it is still used topically in some ENT and ophthalmic procedures on mucosa. Dibucaine is a potent amide anaesthetic used in topical creams and ointments.

Step 3: Focus on bupivacaine.
Bupivacaine penetrates mucous membranes poorly, so it gives an unreliable topical effect. More importantly, it carries a much higher risk of cardiotoxicity than lignocaine, because it binds cardiac sodium channels more avidly and dissociates from them more slowly, which can trigger serious ventricular arrhythmias if enough drug is absorbed.

Step 4: Put the two facts together.
Because bupivacaine both penetrates mucosa poorly and is unusually dangerous if it is absorbed systemically, its topical or surface use on mucous membranes is avoided in practice. It is reserved for infiltration and nerve block techniques where the dose and site are controlled.

Final Answer:
\[ \boxed{\text{Bupivacaine}} \]