Tipiracil is a thymidine phosphorylase (TPase) inhibitor. IC50 & Target: thymidine phosphorylase^[1] In Vitro: Tipiracil is an inhibitor of thymidine phosphorylase. Tipiracil increases trifluridine exposure by inhibiting its metabolism by thymidine phosphorylase. The combination of Trifluridine and Tipiracil is a new oral treatment for metastatic colorectal cancer^[2]. Tipiracil prevents degradation of FTD through a first-pass effect as a thymidine phosphorylase inhibitor^[3].