The initial phase of oral anticoagulation with warfarin in outpatients with deep venous thrombosis

Patients with deep venous thrombosis (DVT) treated out of hospital usually start warfarin with the recommended 5 mg loading dose and have their International Normalized Ratio (INR) test performed every 2-3 days. Thus, achievement of the therapeutic range may be more difficult than for inpatients, possibly resulting in extended duration of low molecular weight heparin (LMWH) treatment. We retrospectively examined the charts of 55 DVT outpatients (mean age, 61.4 years; 30 males) to assess the actual duration of LMWH treatment and to identify predictors of a slow achievement of the INR range. Thirty patients (54.4%) reached the therapeutic INR range and stopped LMWH within 7 days, and 25 patients (45.6%) had to continue for an average of 10.5 days. The latter group was significantly younger than the former (57 and 65 years, respectively; P = 0.039). Patients younger than 60 years old had an odds ratio for an extended treatment of 4.92 (P = 0.0057). Algorithms with different loading doses of warfarin according to age should be proposed for outpatient treatment of DVT.