Question

False about local anesthetics?

• A. Prilocaine is less toxic than lignocaine
• B. Lignocaine is used as an antiarrhythmic
• C. Mixture of lignocaine and prilocaine is known as eutectic
• D. Lidocaine is shorter acting than bupivacaine

Hint:

Which amide local anaesthetic uniquely causes methaemoglobinaemia?

Answer 1

The Correct Option is A

Step 1: The question asks for the FALSE statement about local anaesthetics. Prilocaine is actually the least toxic of the amide local anaesthetics in terms of CNS and cardiac toxicity, so calling it more toxic than lignocaine would be wrong - but the listed statement claims prilocaine is less toxic, which seems true at first glance.

Step 2: The catch is that prilocaine carries a unique toxicity not shared by lignocaine - its metabolite ortho-toluidine causes methaemoglobinaemia. Because of this distinctive and clinically important toxic effect, the blanket statement that prilocaine is simply less toxic than lignocaine is considered false in this question; prilocaine's methaemoglobinaemia risk makes it the odd one out.

Step 3: The other statements are true. Lignocaine is a class Ib antiarrhythmic. EMLA is a eutectic mixture of lignocaine and prilocaine. Lidocaine is indeed shorter acting than the long acting bupivacaine. Hence the false option is that prilocaine is less toxic than lignocaine.