Organic solvents, such as N-methyl-2-pyrrolidone, are foreign to the human body and can cause unwanted side effects both acutely and chronically. [0005] U.S. Pat. No. 5,543,158 discloses nanoparticles or microparticles formed from a water-insoluble block copolymer consisting essentially of poly(alkylene glycol) and poly(lactic acid).