Polymorphism of a Novel Sodium Ion Channel Blocker

2‐{[4‐(4‐Fluorophenoxy)phenyl]‐methylene}‐hydrazinecarboxamide, a member of the semicarbazone family which has shown potential therapeutic use as anticonvulsants, has been found to exist in two polymorphic forms denoted A and B. In addition to reporting aspects of the physical characterization of both forms, the crystal structure of polymorph A has been determined directly from powder X‐ray diffraction data using the Genetic Algorithm technique for structure solution, followed by Rietveld refinement. This structure is compared with that of polymorph B, which was determined previously from single crystal X‐ray diffraction data. Knowledge of the crystal structures of the two polymorphs provides the opportunity for establishing structure‐property relationships. This work further emphasizes the scope and utility of ab initio structure solution from powder X‐ray diffraction data in the pharmaceuticals field. © 2003 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2017-2026, 2003