The antiviral drug zanamivir counteracts the influenza A and B viruses by preventing the infection of further healthy cells. In pandemic cases, large amounts will be administered and will therefore enter the wastewater. For this reason the potential of a photocatalytic wastewater treatment process aiming at the degradation of zanamivir was explored using aqueous solutions of zanamivir and the primary transformation product guanidine, which were irradiated with UV light under various conditions in the presence of TiO2 as a photocatalyst. By studying the transformation behavior of these substances it can be demonstrated that using TiO2 as a photocatalyst can accelerate the transformation of zanamivir. Simultaneously, however, this leads to a decrease of photon efficiency due to turbidity. Based on these findings, an optimization of the amount of TiO2 suspended in aqueous zanamivir solutions during irradiation and a first rough cost estimate were carried out. Further results show that guanidine cannot be transformed using UV radiation and TiO2 as a photocatalyst. (C) 2015 Elsevier B.V. All rights reserved.