What is the difference between ester and amide local anesthetics?

The correct answer indicates that esters are metabolized by plasma cholinesterase. This is an important distinction between esters and amides, as it influences their pharmacokinetics, including the duration of action.

Esters, such as procaine and benzocaine, undergo hydrolysis primarily by plasma cholinesterase, an enzyme abundant in the plasma. This rapid breakdown leads to a shorter duration of action for many ester anesthetics since they are quickly metabolized and eliminated from the systemic circulation.

In contrast, amide local anesthetics, such as lidocaine and bupivacaine, are predominantly metabolized in the liver by hepatic enzymes. This generally results in a longer duration of action for most amide anesthetics compared to esters, since their metabolism is less rapid compared to the hydrolysis seen with esters.

Understanding the metabolic pathways of these two classes provides insight into their clinical uses, the onset and duration of anesthesia, and potential side effects associated with their respective metabolites.