Omeprazole is one of the world-wide most consumed
pharmaceuticals for treatment of
gastric diseases. As opposed to other frequently used
pharmaceuticals,
omeprazole is scarcely detected in urban
wastewaters and environmental waters. This was corroborated in a previous research, where parent
omeprazole was not detected while four transformation products (TPs), mainly resulting from hydrolysis, were found in effluent
wastewaters and surface waters. However, the low abundance of
omeprazole TPs in the water samples together with the fact that
omeprazole suffers an extensive metabolism, with a wide range of excretion rates (between 0.01 and 30%), suggests that human urinary metabolites should be investigated in the water environment. In this work, the results obtained in excretion tests after administration of a 40 mg
omeprazole dose in three healthy volunteers are reported. Analysis by liquid chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry (LC-QTOF MS) reported low concentrations of
omeprazole in urine. Up to twenty-four
omeprazole metabolites (OMs) were detected and tentatively elucidated. The most relevant OM was an
omeprazole isomer, which obviously presented the same exact mass (m/z 346.1225), but also shared a major common fragment at m/z 198.0589. Subsequent analyses of surface water and effluent
wastewater samples by both LC-QTOF MS and LC-MS/MS with triple quadrupole revealed that this metabolite (named as OM10) was the compound most frequently detected in water samples, followed by OM14a and OM14b. Up to our knowledge, OM10 had not been used before as urinary
biomarker of
omeprazole in waters. On the contrary, parent
omeprazole was never detected in any of the water samples. After this research, it seems clear that monitoring the presence of
omeprazole in the aquatic environment should be focused on the OMs suggested in this article instead of the parent compound.