Abstract: A method of lyophilizing an oxazaphosphorin and a preparation produced thereby including dissolving an oxazaphosphorin in water, adding an amino acid to a molar ratio of between 1 to 10 amino acid to 1 oxazaphosphorin to produce a mixture and lyophilizing said mixture to remove said water, is disclosed.

Abstract: A process employing a supercritical fluid anti-solvent for sizing prednisolone acetate is disclosed. The process optionally incorporates sterilization filters. Average particle sizes of about 1 .mu.m or less (number average) and narrow particle size ranges are obtainable. The process comprises the steps of (a) forming a solution by dissolving prednisolone acetate in acetone such that the concentration of prednisolone acetate is approximately 80% or less of its solubility in acetone; and (b) transporting the solution formed in step (a) through an orifice having a diameter of 50-100 .mu.m into a mixer/expander containing compressed CO.sub.2, wherein the compressed CO.sub.2 is at a temperature from about 40.degree. to 80.degree. C. and has a density less than the density of the solution by at least 0.3 g/cc, to expand the solution so that the acetone dissolves in the CO.sub.2 and the prednisolone acetate precipitates.