Ultra‐Long‐Duration Local Anesthesia Produced by Injection of Lecithin‐Coated Tetracaine Microcrystals

This study was designed to determine if microencapsulated tetracaine would provide a longer duration of local anesthesia than nonmicroencapsulated (neat) tetracaine. Local anesthesia was determined by monitoring the response of the rat to tail clamping after the installation of a subcutaneous ring block. Ten percent microencapsulated tetracaine was found to provide local anesthesia of the tail for a 43‐hour duration. Ten percent tetracaine solution was toxic. One percent tetracaine solution provided a tail block lasting 8 hours. Lecithin membranes without drug provided no block. This study demonstrates that lecithin‐coated tetracaine microcrystals produce a local anesthetic effect that is ultra‐long in duration, reversible, and not systemically toxic. 1994 American College of Clinical Pharmacology