Anticoagulation: Where have we come from and where are we going? The evidence for and against novel anticoagulants

The incidence of stroke in patients with atrial fibrillation is greatly reduced by oral anticoagulation, with the full effect seen at international normalized ratio (INR) values of 2.0 or greater. The effect of the intensity of oral anticoagulation on the severity of atrial fibrillation-related stroke is not known but is central to the choice of the target INR. We studied incident ischemic strokes in a cohort of 13,559 patients with nonvalvular atrial fibrillation. Strokes were identified through hospitalization data bases and validated on the basis of medical records, which also provided information on the use of warfarin or aspirin, the INR at admission, and coexisting illnesses. The severity of stroke was graded according to a modified Rankin scale. Thirty-day mortality was ascertained from hospitalization and mortality files. Of 596 ischemic strokes, 32 percent occurred during warfarin therapy, 27 percent during aspirin therapy, and 42 percent during neither type of therapy. Among patients who were taking warfarin, an INR of less than 2.0 at admission, as compared with an INR of 2.0 or greater, independently increased the odds of a severe stroke in a proportional-odds logistic-regression model (odds ratio, 1.9; 95 percent confidence interval, 1.1 to 3.4) across three severity categories and the risk of death within 30 days (hazard ratio, 3.4; 95 percent confidence interval, 1.1 to 10.1). An INR of 1.5 to 1.9 at admission was associated with a mortality rate similar to that for an INR of less than 1.5 (18 percent and 15 percent, respectively). The 30-day mortality rate among patients who were taking aspirin at the time of the stroke was similar to that among patients who were taking warfarin and who had an INR of less than 2.0. Among patients with nonvalvular atrial fibrillation, anticoagulation that results in an INR of 2.0 or greater reduces not only the frequency of ischemic stroke but also its severity and the risk of death from stroke. Our findings provide further evidence against the use of lower INR target levels in patients with atrial fibrillation. Copyright 2003 Massachusetts Medical Society

Considerable variability exists in the use of pharmacological thromboprophylaxis among acutely ill medical patients, partly because clinically relevant end points have not been fully assessed in this population. We undertook an international, multicenter, randomized, double-blind, placebo-controlled trial using clinically important outcomes to assess the efficacy and safety of dalteparin in the prevention of venous thromboembolism in such patients. Patients (n=3706) were randomly assigned to receive either subcutaneous dalteparin 5000 IU daily or placebo for 14 days and were followed up for 90 days. The primary end point was venous thromboembolism, defined as the combination of symptomatic deep vein thrombosis, symptomatic pulmonary embolism, and asymptomatic proximal deep vein thrombosis detected by compression ultrasound at day 21 and sudden death by day 21. The incidence of venous thromboembolism was reduced from 4.96% (73 of 1473 patients) in the placebo group to 2.77% (42 of 1518 patients) in the dalteparin group, an absolute risk reduction of 2.19% or a relative risk reduction of 45% (relative risk, 0.55; 95% CI, 0.38 to 0.80; P=0.0015). The observed benefit was maintained at 90 days. The overall incidence of major bleeding was low but higher in the dalteparin group (9 patients; 0.49%) compared with the placebo group (3 patients; 0.16%). Dalteparin 5000 IU once daily halved the rate of venous thromboembolism with a low risk of bleeding.

Low-molecular-weight heparins such as enoxaparin are preferred for prevention of venous thromboembolism after major joint replacement. Apixaban, an orally active factor Xa inhibitor, might be as effective, have lower bleeding risk, and be easier to use than is enoxaparin. We assessed efficacy and safety of these drugs after elective total knee replacement. In ADVANCE-2, a multicentre, randomised, double-blind phase 3 study, patients undergoing elective unilateral or bilateral total knee replacement were randomly allocated through an interactive central telephone system to receive oral apixaban 2.5 mg twice daily (n=1528) or subcutaneous enoxaparin 40 mg once daily (1529). The randomisation schedule was generated by the Bristol-Myers Squibb randomisation centre and stratified by study site and by unilateral or bilateral surgery with a block size of four. Investigators, patients, statisticians, adjudicators, and steering committee were masked to allocation. Apixaban was started 12-24 h after wound closure and enoxaparin 12 h before surgery; both drugs were continued for 10-14 days, when bilateral ascending venography was scheduled. Primary outcome was the composite of asymptomatic and symptomatic deep vein thrombosis, non-fatal pulmonary embolism, and all-cause death during treatment. The statistical plan required non-inferiority of apixaban before testing for superiority; analysis was by intention to treat for non-inferiority testing. The study is registered at ClinicalTrials.gov, number NCT00452530. 1973 of 3057 patients allocated to treatment (1528 apixaban, 1529 enoxaparin) were eligible for primary efficacy analysis. The primary outcome was reported in 147 (15%) of 976 apixaban patients and 243 (24%) of 997 enoxaparin patients (relative risk 0.62 [95% CI 0.51-0.74]; p<0.0001; absolute risk reduction 9.3% [5.8-12.7]). Major or clinically relevant non-major bleeding occurred in 53 (4%) of 1501 patients receiving apixaban and 72 (5%) of 1508 treated with enoxaparin (p=0.09). Apixaban 2.5 mg twice daily, starting on the morning after total knee replacement, offers a convenient and more effective orally administered alternative to 40 mg per day enoxaparin, without increased bleeding. Bristol-Myers Squibb; Pfizer. Copyright 2010 Elsevier Ltd. All rights reserved.