Local Anaesthetics: SAR and Techniques

Introduction

• Definition — Local anaesthetics (LAs) reversibly block the generation and conduction of nerve impulses in a restricted area, causing loss of sensation (especially pain) without structural nerve damage and without loss of consciousness.
• Universality — Act on any part of the neurone and every fibre type; on a nerve trunk they produce sensory + motor + autonomic block over the supplied area. At clinical concentrations the effect is fully reversible.
• Vs analgesics — Provide complete loss of all sensory modalities (not mere analgesia); drug is delivered directly to the nerve, and the systemic circulation only terminates the effect.
• Historical anchor — Cocaine was the first LA — introduced by Carl Koller (1884) for corneal anaesthesia; procaine (Einhorn, 1905) was the prototype synthetic ester. Lidocaine (1948) became the prototype amide and the most versatile agent.