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AAPS PharmSciTech, Vol. 14, No. 2, June 2013 ( # 2013) DOI: 10.1208/s12249-013-9942-4 Research Article Photodegradation of Fleroxacin Injection: II. Kinetics and Toxicological Evaluation Wei Li,1 Jun Wang,2,3,4 and Yu-Zhu Hu3 Received 13 September 2012; accepted 22 February 2013; published online 6 March 2013 Abstract. Photodegradation kinetics of fleroxacin were investigated in different injections. Five commer- cial formulations were analyzed before and after irradiation by determining residual volumes of fleroxacin with high-pressure liquid chromatography (HPLC), and different decomposition functions and models were obtained. Concentration levels of fleroxacin in injections caused the differences in photodegradation kinetics instead of ingredients. Influences of different pH values and presence of NaCl on photodegradation of fleroxacin were observed. Low pH value decreased the efficacy of photolysis and enhanced photostability of fleroxacin injections. Tentative structure of a new degradation product afforded was proposed. An acute toxicity assay using the bioluminescent bacterium Q67 was performed for fleroxacin injections after exposure to light. The research proved that fleroxacin was more photolabile in dilute injection, and acute toxicity of dilute injection increased more rapidly than that of concentrated injection during irradiation. KEY WORDS: fleroxacin injection; kinetics; photodegradation; toxicity. INTRODUCTION injections and that concentration levels of fleroxacin caused