Persistent phototransformation products of vardenafil (Levitra®) and sildenafil (Viagra®)

Abstract

As pharmaceutically active compounds (PhACs) are increasingly detected in the aquatic environment, the importance of investigating their transformation products–products of naturally occurring hydrolysis, biodegradation, and solar-mediated photochemical reactions – for persistence and ecotoxicity remains an important part of assessing the pharmaceutical’s environmental impact and fate. In this study, the solar phototransformation of vardenafil (active ingredient in Levitra®) and sildenafil (Viagra®), two structurally similar compounds used to treat erectile dysfunction, was studied, with special attention to potentially persistent phototransformation (PT) products. PT products for vardenafil are identified here for the first time. Dilute solutions were prepared in buffered (pH=7.4) aqueous solutions, both with and without Suwanee River humic acid (SRHA) and fulvic acid (SRFA), and exposed to simulated sunlight. The PT products were identified via Liquid Chromatography–Electrospray Ionization–Mass Spectrometry (LC–ESI–MS) and confirmed by MS/MS. Both SRHA and SRFA were observed to lead to more extensive degradation of VRD while having minimal effect on SLD. At least two PT products, SLD-392 and VRD-392, were observed to be notably persistent, indicating their potential impact in the aquatic environment and highlighting the need for investigations of transformation products in natural water samples.