A simple scheme to initiate oral anticoagulant treatment in outpatients with nonrheumatic atrial fibrillation

Atrial fibrillation (AF) is a common arrhythmia associated with an increased incidence of stroke, 1 Wolf P.A. Abbott R.D. Kannel W.B. Atrial fibrillation as an independent risk factor for stroke the Framingham study. Stroke. 1991; 22: 983-988 Crossref PubMed Scopus (5837) Google Scholar which is significantly reduced with oral anticoagulant treatment. 2 Laupacis A. Albers G.W. Dalen J.E. Dunn M.I. Jacobson A.K. Singer D.E. Antithrombotic therapy in atrial fibrillation. Chest. 1998; 114: 579S-589S Crossref PubMed Scopus (352) Google Scholar Diagnosis of AF is often made by means of ambulatory electrocardiography, with oral anticoagulant treatment initiated on an outpatient basis. The most popular protocol to initiate warfarin treatment considers prothrombin time-international normalized ratio (PT-INR) determinations every day for the first 4 days. 3 Fennerty A. Dolben J. Thomas P. Backhouse G. Bentley D.P. Campbell I.A. Routldge P.A. Flexible induction dose regimen for warfarin and prediction of maintenance dose. Br Med J. 1984; 288: 1268-1270 Crossref PubMed Scopus (155) Google Scholar This protocol was shown to be effective in a relatively young group of inpatients but not in older groups. 4 Cosh D.J. Moritz C.K. Ashman K.J. Dally R.J. Gallus A.S. Prospective evaluation of a flexible protocol for starting treatment with warfarin and predicting its mainteneance dose. Aust N Z J Med. 1989; 19: 191-197 Crossref PubMed Scopus (19) Google Scholar , 5 Cooper M.W. Hendra T.J. Prospective evaluation of a modified Fennerty regimen for anticoagulating elderly people. Age Ageing. 1998; 27: 655-656 Crossref PubMed Scopus (14) Google Scholar Moreover, the inconvenience of daily monitoring of treatment renders this scheme impractical for outpatients with AF. We have recently developed a scheme for early indication of warfarin maintenance dose on the basis of PT-INR at day 3 after 2 consecutive daily 10-mg doses of warfarin. 6 Pengo V. Zasso A. Barbero F, Biasiolo A, Rampazzo P, Brocco T. Initiation of warfarin treatment in out patients with nonrheumatic atrial fibrillation a scheme for early indication of maintenance dose. Clin Appl Thromb Hemost. 1998; 4: 274-276 Crossref Scopus (7) Google Scholar However, it was recently shown that a 5-mg loading dose produces less excess of anticoagulation, 7 Harrison L. Johnston M. Massicotte M.P. Crowther M. Moffat K. Hirsh J. Comparison of 5-mg and 10-mg loading doses in initiation of warfarin therapy. Ann Intern Med. 1997; 126: 133-136 Crossref PubMed Scopus (324) Google Scholar reinforcing the advice to initiate anticoagulation on an outpatient basis with an anticipated maintenance warfarin dose of 4 to 5 mg/day. 8 Hirsh J. Dalen J.E. Deykin D. Poller L. Bussey H. Oral anticoagulants Mechanism of action, clinical effectiveness and optimal therapeutic range. Chest. 1995; 108(suppl): 231S-240S Crossref Google Scholar Because excess anticoagulation and older age are associated with increased bleeding complications, 9 Palareti G. Leali N. Coccheri S. Poggi M. Manotti C. D'Angelo A. Pengo V. Erba N. Moia M. Ciavarella N. Devoto G. Berrettini M. Musolesi S. Bleeding complications of oral anticoagulant treatment an inception-cohort, prospective collaboratory study (ISCOAT). Lancet. 1996; 348: 423-428 Abstract Full Text Full Text PDF PubMed Scopus (1287) Google Scholar we decided to shift from the total 20-mg warfarin dose in 2 days (induction scheme) into a total of 20 mg of warfarin administered over 4 consecutive days. Similar to the induction scheme, we then established a correlation between the INR on the fifth day and the warfarin maintenance dose.