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.