title: Does heart failure exacerbation increase response to warfarin? A critical review of the literature.
abstract: BACKGROUND
  Numerous factors, such as other drugs, diet, and age, are well documented as altering response to warfarin. Less attention has been focused on the effect of disease states on the response to oral anticoagulants. Decompensated heart failure is reported to increase response to warfarin, but documentation is limited.
  
  
  OBJECTIVE
  The purpose of this review is to critically examine the evidence of a possible effect of heart failure exacerbations on response to warfarin.
  
  
  METHODS
  A literature search was completed of the last 60 years using several databases, including PubMed, MEDLINE, EMBASE, and SCOPUS. Key terms in our search included 'warfarin' AND 'heart failure' and 'heart failure exacerbation' (or 'decompensated heart failure') AND 'effect on warfarin'. When relevant citations were found, the references cited by those authors were checked.
  
  
  RESULTS
  Several reports from 1946-1989 suggested that decompensated heart failure increases response to oral anticoagulants. Unfortunately, these early reports have important limitations. More recent reports, since the widespread use of the international normalized ratio (INR), also suggest that heart failure exacerbations are associated with increased response to warfarin. Patient populations are small in these reports.
  
  
  CONCLUSIONS
  Heart failure exacerbations may be associated with an increased response to warfarin and other vitamin K antagonists, but many reports are inadequate, and it appears that not all patients are susceptible to this effect. More frequent monitoring of INR in patients with decompensated heart failure is warranted. It is prudent to initiate warfarin at lower doses in patients with a history of heart failure and to monitor INR every 1-2 weeks during times of instability in ambulatory patients, and daily INRs in hospitalized patients. Given the large number of variables that impact on warfarin dose requirement, it is difficult to clearly establish the effect of decompensated heart failure on response to warfarin. Further studies must take all of these variables into account.
authors.affiliation: College of Pharmacy, University of Tennessee Health Science Center; Methodist University Hospital, Memphis, TN 38163, USA. tself@utmem.edu
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Self
authors.forename: Anne B
authors.initials: AB
authors.lastname: Reaves
authors.forename: Carrie S
authors.initials: CS
authors.lastname: Oliphant
authors.forename: Chris
authors.initials: C
authors.lastname: Sands
mesh_terms: D000925:Anticoagulants / Q000627:therapeutic use*; D006333:Heart Failure / Q000503:physiopathology*; D006801:Humans; D019934:International Normalized Ratio; D014859:Warfarin / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D014859:Warfarin