From the Guidelines
The answer is (a) tetracaine. Tetracaine is an aminoester local anesthetic, which means its chemical structure contains an ester linkage between an aromatic group and an intermediate chain that connects to an amine group, as seen in the table comparing local anesthetic agents 1. This ester bond is the key characteristic that distinguishes aminoesters from aminoamides. The other options - lidocaine, bupivacaine, mepivacaine, and etidocaine - are all aminoamide local anesthetics, which contain an amide linkage instead of an ester. Some key points about these local anesthetics include:
- Maximum doses with and without epinephrine
- Duration of action
- Potential for systemic toxicity, such as seizures or methemoglobinemia, especially with topical application to mucosal surfaces 1. The distinction is important clinically because aminoesters are metabolized by plasma cholinesterases, making them shorter-acting and more likely to cause allergic reactions compared to aminoamides, which are metabolized in the liver. Tetracaine is commonly used in topical anesthetic preparations for procedures involving mucous membranes or the eye, and its use requires careful consideration of the maximum allowable safe dosage to avoid toxicity 1.
From the Research
Aminoester Classification
- The aminoester classification of local anesthetic agents includes procaine, chloroprocaine, and tetracaine 2.
- Tetracaine is specifically mentioned as an aminoester local anesthetic agent in the study 2, 3.
- Based on the provided evidence, tetracaine (a) is the correct answer as it is classified as an aminoester.