Question:medium
False about local anesthetics?
False about local anesthetics?
Show Hint
Which amide local anaesthetic uniquely causes methaemoglobinaemia?
Updated On: Jun 24, 2026
- Prilocaine is less toxic than lignocaine
- Lignocaine is used as an antiarrhythmic
- Mixture of lignocaine and prilocaine is known as eutectic
- Lidocaine is shorter acting than bupivacaine
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: We must spot the incorrect claim. Three statements are textbook-true and one is the trap. Start by validating the easy ones.
Step 2: Lignocaine doubles as a class Ib antiarrhythmic for ventricular arrhythmias - true. EMLA cream is the eutectic mixture of lignocaine plus prilocaine that melts to a single liquid phase at room temperature - true. Bupivacaine is long acting whereas lidocaine is intermediate, so lidocaine being shorter acting than bupivacaine is true.
Step 3: That leaves the prilocaine statement as the answer. Prilocaine is metabolised to ortho-toluidine, which oxidises haemoglobin and produces methaemoglobinaemia, a hazard lignocaine does not carry. So the sweeping statement that prilocaine is simply less toxic than lignocaine is false in this context.
\[\boxed{\text{Prilocaine is less toxic than lignocaine}}\]
Step 2: Lignocaine doubles as a class Ib antiarrhythmic for ventricular arrhythmias - true. EMLA cream is the eutectic mixture of lignocaine plus prilocaine that melts to a single liquid phase at room temperature - true. Bupivacaine is long acting whereas lidocaine is intermediate, so lidocaine being shorter acting than bupivacaine is true.
Step 3: That leaves the prilocaine statement as the answer. Prilocaine is metabolised to ortho-toluidine, which oxidises haemoglobin and produces methaemoglobinaemia, a hazard lignocaine does not carry. So the sweeping statement that prilocaine is simply less toxic than lignocaine is false in this context.
\[\boxed{\text{Prilocaine is less toxic than lignocaine}}\]
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