Which one of the following local anesthetics is an ester of benzoic acid ?

RRB Staff Nurse Ahmedabad-2015

Pharmacology

Medium

Appeared in: RRB Staff Nurse Ahmedabad-2015

Explanation

Cocaine is a naturally occurring alkaloid derived from the coca plant.
Chemically, it is classified as an ester of benzoic acid, which distinguishes it from other ester-type anesthetics derived from PABA.
It functions as a local anesthetic by blocking sodium channels in nerve fibers, preventing pain signal transmission.
Uniquely among local anesthetics, it also blocks the reuptake of norepinephrine, causing significant vasoconstriction, which can be useful for reducing bleeding during surgery but also contributes to its cardiovascular risks.

Option A: Lidocaine is one of the most common local anesthetics, but it belongs to the amide class, not the ester class. Amide anesthetics are metabolized in the liver.
Option B: Although Procaine is an ester-type local anesthetic, it is a derivative of para-aminobenzoic acid (PABA), not benzoic acid. The metabolism of PABA esters is responsible for their higher potential for allergic reactions.
Option C: Ropivacaine is a modern local anesthetic belonging to the amide class. It is structurally similar to bupivacaine but is associated with a lower risk of cardiotoxicity.

Visual 1: Flowchart: Classification of Local Anesthetics. This visual should clearly branch into two main categories, Esters and Amides. The Esters branch should further divide into 'Benzoic Acid Esters' (showing Cocaine) and 'PABA Esters' (showing Procaine, Tetracaine). The Amides branch should list Lidocaine, Ropivacaine, etc.
Visual 2: Diagram: Chemical Structures of Ester vs. Amide Linkages. This diagram should compare the chemical backbone of an ester (like procaine) with an amide (like lidocaine), highlighting the ester bond (-COO-) and the amide bond (-NHCO-).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Chemical classification of local anesthetics (Esters vs. Amides) as background academic context rather than a clinical decision trigger.
The distinction between ester and amide anesthetics is critical for patient safety. A true allergic reaction to one class (e.g., esters) does not preclude the use of a drug from the other class (e.g., amides).
Nurses must be aware of how these drugs are metabolized. Ester metabolism in the plasma is rapid, while amide metabolism in the liver is slower. This has implications for patients with liver disease or pseudocholinesterase deficiency.
What if? If a patient has severe liver disease, an amide anesthetic like lidocaine would be cleared more slowly, increasing the risk of systemic toxicity. In such a case, an ester-type anesthetic (if no allergy exists) might be considered a safer choice as its metabolism is independent of liver function.

How to Approach the Question

Identify the key concepts in the question: 'local anesthetic' and 'ester of benzoic acid'. This signals a question about drug classification.
Recall the two primary classes of local anesthetics: esters and amides.
Use the mnemonic: Amide anesthetics generally have two 'i's in their name (e.g., lidocaine, ropivacaine), while esters have one (e.g., procaine, cocaine).
Apply the mnemonic to the options. Lidocaine and Ropivacaine are amides, so they can be eliminated.
You are left with two esters: Procaine and Cocaine. Recall or deduce the further sub-classification. Procaine is the classic example of a PABA ester. Therefore, Cocaine must be the ester of benzoic acid.

Concept Tested & Keywords

Concept Tested: Chemical classification of local anesthetics (Esters vs. Amides)
Stem keywords: local anesthetics, ester of benzoic acid
Lead-in keywords: Which one
Negative lead-in flag: false

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