slow induction of anticoagulation in out-patients not requiring heparin

Last reviewed 01/2018

  • for outpatients who do not require rapid anticoagulation a slow-loading regimen is safe and achieves therapeutic anticoagulation in the majority of patients within 3–4 weeks
    • this appears to avoid over-anticoagulation and bleeding associated with rapid loading


  • various slow induction regimes have been used. For example:
      • outpatients requiring anticoagulation for atrial fibrillation
        • 200 patients were started on 3 mg of warfarin daily for 1 week and subsequent doses determined by weekly INR measurement (2)
        • by day 15, 86% of patients had an INR greater than 2 and 58% had reached a stable maintenance dose by day 22 and 85% by day 29
          • day 8 INR was predictive of maintenance dose
          • 11 patients had an INR greater than 4 and no patient suffered a thrombotic or bleeding complication in the first month
      • an alternative outpatient regimen in which patients received 2 mg warfarin daily for 2 weeks was able to predict the maintenance dose from the 2-week INR
        • only one patient (total 107) had an INR greater than 3·0 in the first 2 weeks and five had INRs greater than 4 at some time after week 2 (3)
        • more than 50% of INRs were between 2·0 and 3·0 after week 2


  1. Baglin TP et al. British Committee for Standards in Haematology - Guidelines on oral anticoagulation (warfarin): third edition - 2005 update British Journal of Haematology 2006; 132 (3): 277–285.
  2. Janes S et al. Safe introduction of warfarin for thrombotic prophylaxis in atrial fibrillation requiring only a weekly INR. Clinical and Laboratory Haematology 2004; 26:43–47
  3. Oates A et al. A new regimen for starting warfarin therapy in out-patients. British Journal of Clinical Pharmacology 1998; 46: 157–161.