Comparison of the 5-fluorouracil-warfarin and capecitabine-warfarin drug interactions.
OBJECTIVE
To compare the differences between the 5-fluorouracil-warfarin and capecitabine-warfarin drug interactions in patients receiving therapeutic doses of warfarin.


METHODS
Retrospective medical record review.


METHODS
Large academic Veterans Affairs health care system.


METHODS
Twenty-four patients who received concomitant therapeutic doses of warfarin and at least one dose of a fluoropyrimidine--5-fluorouracil or capecitabine--between January 2004 and May 2008.


RESULTS
The primary outcome was mean change in international normalized ratio (INR) from baseline to end of 90-day study period. Only patients who were taking warfarin before starting either fluoropyrimidine-based chemotherapy were included in the primary analysis. Of the 24 eligible patients, 15 (9 receiving 5-fluorouracil, 6 receiving capecitabine) were taking warfarin before receiving either fluoropyrimidine. No significant differences were noted in the average weekly warfarin dose or baseline INR between the 5-fluorouracil and capecitabine groups. The mean change in INR for patients taking warfarin before fluoropyrimidine use was 4.62 in the 5-fluorouracil group compared with 5.11 in the capecitabine group (p=0.87). The capecitabine group had a similar proportion of patients achieving an INR above 9 while taking warfarin compared with the 5-fluorouracil group (17% vs 22%). In those patients who required a warfarin dosage reduction, the dose was reduced by 38% and 41% in the 5-fluorouracil and capecitabine groups, respectively. No significant differences in bleeding events were reported within 90 days of concurrent use of either fluoropyrimidine with warfarin.


CONCLUSIONS
Our study suggests that in patients receiving concomitant warfarin and a fluoropyrimidine, no significant differences in INR elevation or bleeding events were noted with 5-fluorouracil compared with capecitabine.
School of Pharmacy, Texas Tech University Health Sciences Center, Dallas, Texas 75216, USA. sachin.shah@ttuhsc.edu
Sachin R
SR
Shah
Randall
R
Martin
Jonathan E
JE
Dowell
Sarah M Gressett
SM
Ussery
D000925:Anticoagulants / Q000494:pharmacology* / Q000627:therapeutic use; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology* / Q000627:therapeutic use; D000069287:Capecitabine; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D004347:Drug Interactions; D005260:Female; D005472:Fluorouracil / Q000031:analogs & derivatives* / Q000494:pharmacology* / Q000627:therapeutic use; D006470:Hemorrhage / Q000139:chemically induced; D006801:Humans; D019934:International Normalized Ratio / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014859:Warfarin / Q000009:adverse effects / Q000494:pharmacology* / Q000627:therapeutic use
D000925:Anticoagulants; D000964:Antimetabolites, Antineoplastic; D003841:Deoxycytidine; D014859:Warfarin; D000069287:Capecitabine; D005472:Fluorouracil