Nifuroxazide Photodecomposition: Identification of the (Z)-isomer by 1H-NMR Study

 The objective of this work was to identify the transformation product of nifuroxazide which appeared during stability studies of the drug in hard-capsules using high-performance liquid chromatography. The impurity appears on exposure to light, and test samples contained 21.5% of the impurity after two hours of exposure to light at room temperature. Mass spectrometry, infrared and nuclear magnetic resonance spectroscopy indicated the occurrence of a geometric isomer of nifuroxazide. In general, ¹H-¹H NOE difference experiments after irradiation were in agreement with a photochemical Z/E isomerisation of nifuroxazide following exposure to ambient light. Correspondence: Dr. M. J. Galmier, Faculté de Pharmacie, Place Henri Dunant, B.P. 38, F-63001 Clermont-Ferrand Cédex, France. e-mail: galmier@inserm484.u-clermont1.fr Received August 8, 2002; accepted November 9, 2002