Multisite mucous membrane bleeding due to a possible interaction between warfarin and 5-fluorouracil.

A 59-year-old man being treated for colon cancer experienced epistaxis, hematemesis, hematuria, and hematochezia. Laboratory evaluation revealed a greatly prolonged prothrombin time. It is possible that the bleeding was due to an interaction between 5-fluorouracil and warfarin. The former may inhibit the synthesis of cytochrome P-4502C9, leading to impaired metabolism of the latter.