Abstract: The present disclosure provides for methods of producing analgesia in a subject. In some cases, methods produce analgesia in a subject undergoing arthroscopic subacromial decompression surgery. The present disclosure also relates to improved sustained release drug delivery systems. In some cases, a composition comprises an active pharmaceutical agent; at least one of sucrose acetate isobutyrate and a polyorthoester; an organic solvent; and 2,6-dimethylaniline, wherein the 2,6-dimethylaniline is present at a level less than 500 ppm. In some cases, a composition comprises bupivacaine N-oxide at a level less than 1 wt %, based on weight of the composition. In some cases, a composition comprises metal present at a level less than 5 ppm. Dosage forms and methods are also provided.