Structural characterization of anhydrous naloxone‐ and naltrexone hydrochloride by high resolution laboratory X‐ray powder diffraction and thermal analysis

The crystal structures of the analgesic compounds anhydrous naloxone and naltrexone hydrochloride were determined ab initio from high resolution laboratory X‐ray powder diffraction data. Both compounds crystallize in the orthorhombic space group P212121 with lattice parameters of a = 14.6588(10) Å, b = 17.4363(9) Å, c = 7.96200(22) Å, and V = 2035.06(23) Å3 for naloxone hydrochloride and a = 15.4560(5) Å, b = 14.9809(4) Å, c = 7.84121(18) Å, and V = 1815.58(11) Å3 for naltrexone hydrochloride. The crystal structure of anhydrous naloxone hydrochloride forms one‐dimensional chains through hydrogen bonds. In the crystal structure of anhydrous naltrexone hydrochloride, two‐dimensional sheets are formed by hydrogen bonds. The dehydration processes of naloxone hydrochloride dehydrate and naltrexone hydrochloride tetrahydrate was analyzed by DTA, DSC, TG, and MG. © 2007 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 3316-3323, 2007