Sustained-release anesthetic compositions and methods of preparation thereof

Provided is an anesthetic composition for locally administering a local anesthetic agent to a subject in need thereof. The anesthetic composition has a lipid based complex prepared by hydrating a lipid cake containing a local anesthetic agent and a lipid mixture with an aqueous buffer solution at a pH higher than 5.5. Also provided is a method to prepare an anesthetic composition using a simpler and more robust for large-scale manufacture and for providing a high molar ratio of local anesthetic agent to phospholipid content as compared to the prior art. This anesthetic composition has a prolonged duration of efficacy adapted to drug delivery.