to permit rapid consideration for publication.
Possible Interactions Between Warfarin and 5-Fluorouracil
To the Edilor: Recently interactions between warfarin and antineoplastic agents have been reported ( 1 4 1 . To date, drug interaction with warfarin and S-fluorouracil has not yet been reported. We would like to report a case of possible interaction between warfarin and S-Fu.
A 75 year-old man with extensive adenocarcinoma of the colon (but no liver metastasis) was hospitalized for deep vein thrombosis of the left leg and was treated with heparin and warfarin. The warfarin dose ( 5 mg p.0. daily) was stable with the prothrombin time (PT) I I .3 sec (control 10 sec). The S-Fu. 1.200 mg in DSW 24 hr continuous infusion (42 mlihr) for S days, was started. On the 2nd day the PT began to rise, and the dose of warcarin was reduced to 2.5 mg p.0. daily. However, the PT was extremely prolonged and so warfarin was discontinued. S-Fu was continued, and the PT progressively rose despite discontinuation of the warfarin (Table I).
The patient did not have bleeding episodes. When he received 5-Fu alone, the PT was not prolonged, and when he received warfarin alone, the PTs were well controlled within the therapeutic range.
This case suggests a possible interaction between warfarin and S-Fu.