Investigation of Drug Interaction Between Warfarin and UFT or S-1

Fluoropyrimidines (FU) in combination with warfarin (WF) are reported to increase prothrombin time-international normalized ratio (PT-INR) and bleeding. In the present study, we investigated retrospectively the timing of expression of blood coagulation abnormality in 11 patients treated with WF and UFT or S-1 concomitantly in Okayama University Hospital and Ako City Hospital. In 11 patients, 6 were UFT in combination with WF (UFT group), 5 were S-1 in combination with WF (S-1 group). In all patients, PT-INR was significantly increased after combination with UFT or S-1. The PT-INR elevated rate of the S-1 group was 214.5% and its rate of the UFT group was 178.2%. The PT-INR elevated rate was higher in the S-1 group than in the UFT group. The PT-INR was increased 2.8 times after four months in the UFT group. These results suggest that the careful monitoring of PT-INR elevation and bleeding is necessary in patients receiving UFT in combination with WF as well as S-1 in combination with WF.