Tetracaine is the Amino Ester Local Anesthetic
The correct answer is B. Tetracaine. Tetracaine is classified as an amino ester local anesthetic, while lidocaine, bupivacaine, and mepivacaine are all amino amide local anesthetics 1.
Classification of Local Anesthetics
Local anesthetics are divided into two major chemical classes based on their molecular structure:
Amino Esters:
- Contain an ester linkage between the aromatic portion and the intermediate chain
- Examples include:
- Tetracaine
- Procaine
- Chloroprocaine
Amino Amides:
- Contain an amide linkage between the aromatic portion and the intermediate chain
- Examples include:
- Lidocaine
- Mepivacaine
- Bupivacaine
- Ropivacaine
Key Differences Between Amino Esters and Amino Amides
Metabolism
- Amino Esters: Metabolized by plasma cholinesterases (hydrolyzed in the blood) 2
- Amino Amides: Metabolized primarily in the liver 2
Allergic Potential
- Amino Esters: Higher potential for allergic reactions
- Amino Amides: Lower incidence of allergic reactions 3
Stability
- Amino Esters: Less stable in solution
- Amino Amides: More stable in solution
Evidence from Guidelines
Multiple pediatric anesthesia and sedation guidelines clearly categorize tetracaine as an ester local anesthetic. The American Academy of Pediatrics guidelines for monitoring and management of pediatric patients during sedation specifically list tetracaine under the "Esters" category in their local anesthetic classification tables 1.
In these guidelines, lidocaine, mepivacaine, and bupivacaine are consistently categorized under "Amides" 1.
Clinical Implications
Understanding the classification of local anesthetics is important because:
- Patients with allergies to one amino ester may have cross-reactivity with other amino esters but typically not with amino amides
- Metabolism pathways differ, affecting duration of action and potential for toxicity
- Dosing and safety profiles vary between classes
Therefore, tetracaine (option B) is the only amino ester among the given options.