Introduction
The local anaesthetic agents fall into two chemical groups, depending on the chemical linkage present:
Question: How does this structural difference influence the pharmacokinetics of these agents?
Fig 1 Amide linkage in the structure of lidocaine
Fig 2 Ester linkage in the structure of amethocaine.
Answer: Ester linkages are more readily broken down, because esterases are present in a variety of tissues as well as in the bloodstream. Amide bonds are broken by amidases, which are found in the liver. Therefore, ester local anaesthetics have a shorter duration of action than amide local anaesthetics and are less commonly used for local blocks. In addition, amides are more highly protein-bound, which also increases their relative duration of action.