Question

In ophthalmology, a patient is allergic to amino-ester local anaesthetics. Which agent can be safely used instead?

• A. Cocaine
• B. Procaine
• C. Prilocaine
• D. Bupivacaine

Hint:

Switch from ester to amide; amides carry two letter i in their name.

Answer 1

The Correct Option is C

Step 1: Local anaesthetics are divided into two chemical classes - amino-esters and amino-amides. A patient allergic to one class can usually tolerate an agent from the other class, because the allergenic breakdown product (para-aminobenzoic acid, PABA) is produced only by esters.

Step 2: Amino-esters include cocaine, procaine, tetracaine (amethocaine), benzocaine and chloroprocaine. These are hydrolysed by plasma pseudocholinesterase to PABA, which is the main trigger for hypersensitivity reactions.

Step 3: Amino-amides include lidocaine, prilocaine, bupivacaine, mepivacaine and ropivacaine. They are metabolised in the liver and do not form PABA, so they are the safe choice when a patient is allergic to esters.

Step 4: Among the options, cocaine, procaine and tetracaine are all esters and must be avoided. Prilocaine is an amide and is therefore a correct safe alternative. Bupivacaine is also an amide and equally acceptable, but prilocaine is selected as the single best answer here.