Chapter 10 - Local Anesthetics

Abstract

Local anesthetics block the generation and propagation of impulses in nerves. They achieve this primarily via blocking the influx of sodium ions through voltage-gated sodium channels. There are two chemical classes in clinical use: amino esters and amino amides. Differences in chemical structure can lead to a range of variances in clinical features, including potency, speed of onset, and duration of action. Local anesthetics have broad clinical uses such as topical and mucosal application, infiltration, a wide range of peripheral and plexus blocks, and spinal and epidural administration. They can also be administered systemically for both acute and chronic pain. With adherence to safe practice patterns and dosing guidelines, local anesthetics generally have a very good margin of safety. Nevertheless, they can produce a range of complications. When administered in large doses or by inadvertent injection into a vein or artery, local anesthetics produce systemic toxicities, notably cardiac depression and conduction disturbances, seizures, and central nervous system depression. Local anesthetics can produce local toxicity to nerves. The risk of neurotoxicity varies in part with local concentration and duration of exposure, but is also influenced by a range of clinical variables that increase nerve vulnerability. There is an unmet need for new formulations that can provide longer duration of analgesia, more sensory selectivity, and better local and systemic safety. Local anesthetics have an increasing role in programs to enhance and improve postoperative recovery.