title: Significant effect of capecitabine on the pharmacokinetics and pharmacodynamics of warfarin in patients with cancer.
abstract: OBJECTIVE
  Clinical cases of capecitabine and other fluorouracil-based chemotherapies potentiating the effects of coumarin derivatives have been reported. This study assessed the influence of capecitabine on the pharmacokinetics (PK) and pharmacodynamics (PD) of warfarin.
  
  
  METHODS
  Four patients with advanced/metastatic cancer completed the study, receiving a single oral dose of 20 mg warfarin before the start of standard capecitabine treatment (day 1), and again during the third cycle of capecitabine (day 61). PK parameters of warfarin and capecitabine and PD parameters of warfarin were assessed on days 1 and 61.
  
  
  RESULTS
  During capecitabine treatment, the area under the plasma concentration time curve from 0 to infinity (AUC(0-infinity)) of S-warfarin increased by 57% (90% CI, 32% to 88%) with a 51% prolongation of the elimination half-life (t(1/2); 90% CI, 32% to 74%). Exposure to R-warfarin was not significantly affected. Plasma concentrations of capecitabine and its metabolites were not influenced by warfarin. During capecitabine treatment, the effect of warfarin on the baseline corrected AUC of the International Normalized Ratio (INR) increased by 2.8 times (90% CI, 1.33 to 5.70), with the maximum observed INR value almost doubling. Because of the administration of vitamin K to some patients with elevated INRs, these figures are likely to underestimate the true PD effect. Mean baseline factor VII levels dropped while on capecitabine therapy, potentially contributing to the observed PD interaction, though this effect did not reach statistical significance.
  
  
  CONCLUSIONS
  There is a significant pharmacokinetic interaction between capecitabine and S-warfarin, resulting in exaggerated anticoagulant activity. Patients receiving warfarin anticoagulant therapy concomitantly with capecitabine should have their INR closely monitored and warfarin doses adjusted accordingly.
authors: Cancer Research UK Centre, Edinburgh, Scotland.
authors: Ross
authors: R
authors: Camidge
authors: Bruno
authors: B
authors: Reigner
authors: Jim
authors: J
authors: Cassidy
authors: Susan
authors: S
authors: Grange
authors: Markus
authors: M
authors: Abt
authors: Erhard
authors: E
authors: Weidekamm
authors: Duncan
authors: D
authors: Jodrell
mesh_terms: D000328:Adult; D000925:Anticoagulants / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology*; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D000069287:Capecitabine; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004357:Drug Synergism; D005167:Factor VII / Q000032:analysis; D005472:Fluorouracil / Q000031:analogs & derivatives; D006207:Half-Life; D006801:Humans; D008875:Middle Aged; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D011517:Prothrombin Time; D010837:Vitamin K 1 / Q000097:blood; D014859:Warfarin / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology*
chemical_list: D000925:Anticoagulants; D000964:Antimetabolites, Antineoplastic; D003841:Deoxycytidine; D014859:Warfarin; D000069287:Capecitabine; D010837:Vitamin K 1; D005167:Factor VII; D005472:Fluorouracil