Photodegradation of Moxifloxacin Hydrochloride Solutions under Visible Light Irradiation: Identification of Products and the Effect of pH on their Formation.

The photodegradation study is essential for the phototoxicity assessment of fluoroquinolones. Various LC-MS techniques and ultraviolet (UV) lamp irradiation conditions have been used for the identification of their photodegradation products. In this study, visible light (400-760 nm) lamp irradiation was selected for the photodegradation of moxifloxacin (MOXI) hydrochloride solutions. Two photodegradation products were identified by LC-MS/MS at first, but one product could not be speculated from the mass spectrum and any known degradation mechanisms. To obtain an adequate amount for the structure elucidation, this unknown product was isolated by recrystallization and semi-preparative HPLC. Then, its structure was further identified by 1H-NMR, 13C-NMR, and 2D-NMR. Based on spectral data, this new photodegradation product was unambiguously named as 7-[3-(3-aminopropyl)-1H-pyrrol-1-yl]-1-cyclopropyl-6-fluoro-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid, which was formed through the open of hexahydroxy N-containing heterocycle and the formation of two alkene bonds in pyrrole ring. The effects of solution pH value on the formation of photodegradation products were compared. Their production was minimum at pH 5.0 and maximum at pH 7.0. Because MOXI hydrochloride has been used extensively in clinical practice and visible light is the most possible light source that pharmaceutical products are exposed to, our study is important for the quality control of MOXI liquid preparations.