Abstract: Objective To establish a model for assessment of photosensitizing agents in vitrO.Methods Hislidine photooxidation method was employed.Histidine was irradiated wilh UVA in the presence of pipemidic acid and norfloxacin.Then the remaining histidine was assessed Pauly reaction.Results Histidine concenlration in pipemidic acid solution and norfloxacin solution decrdased after UVA irradiation The photodegradation rate of histidine increased with the increase of UVA dosage and drug concenlration.Conclusion Both pipemidie acid and norfloxacin cause photoxidation of histidine.

Key words: Photosensitizing agents, Photooxidation histidine