Coumarin (1,2-benzopyrone) is a natural compound whose metabolism in humans was established in the 1970s. However, a new metabolite was recently identified in human plasma, indicating that the metabolism of coumarin has not been completely elucidated. To complement the knowledge of its metabolism, a rapid and sensitive method using UPLC-QTOF-MS was developed. A total of 12 metabolites was identified using MetaboLynxTM software, including eight metabolites not previously reported in human urine. The identified biotransformation included hydroxylation, glucuronidation, sulfation, methylation, and conjugation with N-acetylcysteine. The present work demonstrates that the metabolism study of coumarin was incomplete, possibly due to limitations of old techniques. The identification of eight inedited metabolites of such a simple molecule suggests that the information regarding the metabolism of other drugs may also be incomplete, and therefore, new investigations are necessary.
