Trifluridine is an analogue of the nucleoside thymidine, and is used as a chemotherapeutic agent against metastatic colorectal cancer. It is rapidly degraded by thymidine phosphorylase, so it has been combined with tipiracil, which is a thymidine phosphorylase inhibitor. It is combined in a ratio of approx 1:0.5 in the product Lonsurf. Lonsurf is prescription only

Answer: P1S1S3

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