Why are esters not used more frequently for local anesthesia?

• A. Allergenic risks, low effectiveness
• B. Short shelf life
• C. High cost
• D. Slow onset

Answer: (A)

Esters are not used more often for local anesthesia mainly because they carry a higher risk of allergic or hypersensitivity reactions. When esters are metabolized in the blood, they form para-aminobenzoic acid (PABA) derivatives, which can trigger immune responses in susceptible individuals. This allergy risk makes clinicians prefer amide-type local anesthetics. In addition, esters are rapidly hydrolyzed by plasma cholinesterases, leading to a shorter and more variable duration of anesthesia, reducing predictability for procedures. These factors together explain why esters are less frequently chosen. Shelf life, cost, or slow onset are not as consistently limiting as the allergy risk and shorter duration.