Slow induction of anticoagulation in out-patients not requiring heparin

• 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 (1)
  • this appears to avoid over-anticoagulation and bleeding associated with rapid loading

Notes:

• 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

Reference:

1. Guidelines on oral anticoagulation with warfarin, British Committee for Standards in Haematology (2011)
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.