Patent ID: 8193355

Claim:
A process for preparing risedronate sodium hemipentahydrate represented by formula 1, which consists of the steps of: adding 2-(3-pyridyl)-1-hydroxyethane-1,1-bisphosphonic acid (risedronic acid) represented by formula 3: and an inorganic base to purified water and dissolving the mixture at a temperature of 50 to 80° C., provided that no solvent other than the purified water is added to the mixture; cooling the solution to a temperature of 5 to 30° C. for crystallization; and filtering and vacuum drying to obtain a crystallized product, wherein the risedronate sodium hemipentahydrate product is crystalline having X-ray powder diffraction pattern as presented in FIG. 1 , thermogravimetry analysis (TGA) as presented in FIG. 2 , and contains water in a range from 11.9% to 13.9% by weight.