Which of the following local anaesthetics is most likely to produce an allergic reaction –
**Core Concept**
Local anaesthetics can cause allergic reactions, but the likelihood varies among different agents. This is due to the presence of para-aminobenzoic acid (PABA) or its ester derivatives in some local anaesthetics, which are more likely to trigger an allergic response.
**Why the Correct Answer is Right**
The local anaesthetic most likely to produce an allergic reaction is benzocaine, an ester-type local anaesthetic. This is because benzocaine contains a PABA-like structure, which is a common allergen. When benzocaine is metabolized, it breaks down into para-aminobenzoic acid (PABA), a known allergen that can trigger an immune response. This is in contrast to amide-type local anaesthetics like lidocaine, which are less likely to cause allergic reactions.
**Why Each Wrong Option is Incorrect**
**Option A:** Lidocaine is an amide-type local anaesthetic and is less likely to cause allergic reactions.
**Option B:** Prilocaine is also an amide-type local anaesthetic and is not commonly associated with allergic reactions.
**Option C:** Procaine is an ester-type local anaesthetic, but it is less commonly used and less likely to cause allergic reactions compared to benzocaine.
**Clinical Pearl / High-Yield Fact**
When considering local anaesthetics, it's essential to remember that ester-type local anaesthetics like benzocaine are more likely to cause allergic reactions due to their PABA-like structure.
**Correct Answer:** A. Benzocaine