New oral anticoagulants: a view from the laboratory

Discovery of Milvexian, a High-Affinity, Orally Bioavailable Inhibitor of Factor XIa in Clinical Studies for Antithrombotic Therapy

Factor XIa (FXIa) is an enzyme in the coagulation cascade thought to amplify thrombin generation but has a limited role in hemostasis. From preclinical models and human genetics, an inhibitor of FXIa has the potential to be an antithrombotic agent with superior efficacy and safety. Reversible and irreversible inhibitors of FXIa have demonstrated excellent antithrombotic efficacy without increased bleeding time in animal models (Weitz, J. I., Chan, N. C. Arterioscler. Thromb. Vasc. Biol. 2019, 39 (1), 7-12). Herein, we report the discovery of a novel series of macrocyclic FXIa inhibitors containing a pyrazole P2' moiety. Optimization of the series for (pharmacokinetic) PK properties, free fraction, and solubility resulted in the identification of milvexian (BMS-986177/JNJ-70033093, 17, FXIa Ki = 0.11 nM) as a clinical candidate for the prevention and treatment of thromboembolic disorders, suitable for oral administration.

Effects of rivaroxaban and warfarin on the risk of gastrointestinal bleeding and intracranial hemorrhage in patients with atrial fibrillation: Systematic review and meta-analysis

To assess the risk of gastrointestinal bleeding and intracranial hemorrhage in patients with atrial fibrillation (AF) after the use of rivaroxaban or warfarin. To investigate the effects of rivaroxaban and warfarin on gastrointestinal and intracranial hemorrhage in patients with AF, we searched PubMed, Embase, and Medline from the establishment of databases up to 2020. We finally included 38 observational studies involving 1 312 609 patients for the assessment of intracranial hemorrhage, and 33 observational studies involving 1 332 956 patients for the assessment of gastrointestinal bleeding. The rates of intracranial hemorrhage were 0.55% in the rivaroxaban group versus 0.91% in the warfarin group (OR 0.59; 95% CI 0.53-0.66; p < .00001, I2 = 78%). The rates of gastrointestinal bleeding were 2.63% in patients with rivaroxaban versus 2.48% in those with warfarin (OR 1.06; 95% CI 0.96-1.17; p < .00001, I2 = 94%). Rivaroxaban could significantly reduce the risk of intracranial hemorrhage in patients with AF than warfarin, but the risk of gastrointestinal bleeding remained controversy due to no statistical significant difference. Notably, a subgroup analysis demonstrated that patients in rivaroxaban group with severe chronic renal diseases or undergoing hemodialysis exposed to less gastrointestinal hemorrhage risk than the group from warfarin.

First Report of Plant-Derived β-Sitosterol with Antithrombotic, in Vivo Anticoagulant, and Thrombus-Preventing Activities in a Mouse Model

Inhibitors of thrombin, a key enzyme in the blood coagulation cascade, are of great interest because of their selective specificity and effectiveness in anticoagulation therapy against cardiovascular disorders. The natural soybean phytosterol, β-sitosterol (BSS) demonstrated anticoagulant activity by dose-dependent inhibition of thrombin in an uncompetitive manner with a K_i value of 0.267 μM as well as by partial inhibition of thrombin-catalyzed platelet aggregation with a half-maximal inhibitory concentration (IC₅₀) value of 10.45 ± 2.88 μM against platelet-rich plasma and 9.2 ± 1.2 μM against washed platelets. An in silico study indicated binding of BSS to thrombin, which was experimentally verified by spectrofluorometric and isothermal calorimetric analyses. Under in vitro conditions, BSS demonstrated thrombolytic activity by activating plasminogen, albeit it is devoid of protease (fibrinogenolytic) activity. BSS was noncytotoxic to mammalian cells, nonhemolytic, demonstrated its in vivo anticoagulant activity when administered orally, and inhibited k-carrageen-induced thrombus formation in the tails of mice. Our results suggest that dietary supplementation of BSS may help to prevent thrombosis-associated cardiovascular disorders.

Rivaroxaban and apixaban induce clotting factor Xa fibrinolytic activity

Essentials Activated clotting factor X (FXa) acquires fibrinolytic cofactor function after cleavage by plasmin. FXa-mediated plasma fibrinolysis is enabled by active site modification blocking a second cleavage. FXa-directed oral anticoagulants (DOACs) alter FXa cleavage by plasmin. DOACs enhance FX-dependent fibrinolysis and plasmin generation by tissue plasminogen activator.

BACKGROUND

When bound to an anionic phospholipid-containing membrane, activated clotting factor X (FXa) is sequentially cleaved by plasmin from the intact form, FXaα, to FXaβ and then to Xa33/13. Tissue-type plasminogen activator (t-PA) produces plasmin and is the initiator of fibrinolysis. Both FXaβ and Xa33/13 enhance t-PA-mediated plasminogen activation. Although stable in experiments using purified proteins, Xa33/13 rapidly loses t-PA cofactor function in plasma. Bypassing this inhibition, covalent modification of the FXaα active site prevents Xa33/13 formation by plasmin, and the persistent FXaβ enhances plasma fibrinolysis. As the direct oral anticoagulants (DOACs) rivaroxaban and apixaban bind to the FXa active site, we hypothesized that they similarly modulate FXa fibrinolytic function.

METHODS

DOAC effects on fibrinolysis and the t-PA cofactor function of FXa were studied in patient plasma, normal pooled plasma and purified protein experiments by the use of light scattering, chromogenic assays, and immunoblots.

RESULTS

The plasma of patients taking rivaroxaban showed enhanced fibrinolysis correlating with FXaβ. In normal pooled plasma, the addition of rivaroxaban or apixaban also shortened fibrinolysis times. This was related to the cleavage product, FXaβ, which increased plasmin production by t-PA. It was confirmed that these results were not caused by DOACs affecting activated FXIII-mediated fibrin crosslinking, clot ultrastructure and thrombin-activatable fibrinolysis inhibitor activation in plasma.

CONCLUSION

The current study suggests a previously unknown effect of DOACs on FXa in addition to their well-documented anticoagulant role. By enabling the t-PA cofactor function of FXaβ in plasma, DOACs also enhance fibrinolysis. This effect may broaden their therapeutic indications.

A comparison of apixaban and dabigatran etexilate for thromboprophylaxis following hip and knee replacement surgery

INTRODUCTION

Patients who have undergone hip or knee replacement surgery are exposed to a high risk of developing a post-operative venous thromboembolus and so have a need for an effective, medication-based, thrombosis prophylaxis. New orally active anticoagulants have been available for a few years now. These specific substances directly block either thrombin (e.g., dabigatran etexilate) or Factor Xa (e.g., apixaban). It is not clear whether there are any efficacy differences between these two substances because there have never been any head-to-head studies carried out.

MATERIALS AND METHODS

We have carried out a study comparing two new orally active anticoagulants dabigatran etexilate (Pradaxa^®) and apixaban (Eliquis^®) that were each given to two groups of 200 patients respectively, who had undergone elective hip or knee arthroplasty (100 each). Each patient was assessed for pre- and post-operative hemoglobin concentrations, post-operative blood loss, the number of transfused erythrocyte concentrates, the duration of wound secretion, clinical thromboembolic complications (deep vein thrombosis, pulmonary embolism, myocardial infarct), as well as gastrointestinal, intracranial or wound-related bleeding complications.

RESULTS

Dabigatran etexilate treatment led to a significant increase in the duration of wound secretion in both arthroplasty groups when compared to apixaban: wound secretion lasted 1.2 days longer on average in the dabigatran etexilate group than in the apixaban group (4.1 ± 2.1 vs. 2.9 ± 1.8 days). There were no significant differences observed between the two anticoagulant groups when comparing pre- and post-operative Hb values, post-operative blood loss and the other clinical parameters.

CONCLUSIONS

Thus, it appears that the direct thrombin inhibitor, dabigatran etexilate, is associated with a longer period of wound secretion following the implantation of hip and knee endoprostheses than that associated with the Factor Xa inhibitor, apixaban.

Non-major bleeding with apixaban versus warfarin in patients with atrial fibrillation

Objective

We describe the incidence, location and management of non-major bleeding, and assess the association between non-major bleeding and clinical outcomes in patients with atrial fibrillation (AF) receiving anticoagulation therapy enrolled in Apixaban for Reduction in Stroke and other Thromboembolic Events in Atrial Fibrillation (ARISTOTLE).

Methods

We included patients who received ≥1 dose of study drug (n=18 140). Non-major bleeding was defined as the first bleeding event considered to be clinically relevant non-major (CRNM) or minor bleeding, and not preceded by a major bleeding event.

Results

Non-major bleeding was three times more common than major bleeding (12.1% vs 3.8%). Like major bleeding, non-major bleeding was less frequent with apixaban (6.4 per 100 patient-years) than warfarin (9.4 per 100 patient-years) (adjusted HR 0.69, 95% CI 0.63 to 0.75). The most frequent sites of non-major bleeding were haematuria (16.4%), epistaxis (14.8%), gastrointestinal (13.3%), haematoma (11.5%) and bruising/ecchymosis (10.1%). Medical or surgical intervention was similar among patients with non-major bleeding on warfarin versus apixaban (24.7% vs 24.5%). A change in antithrombotic therapy (58.6% vs 50.0%) and permanent study drug discontinuation (5.1% (61) vs 3.6% (30), p=0.10) was numerically higher with warfarin than apixaban. CRNM bleeding was independently associated with an increased risk of overall death (adjusted HR 1.70, 95% CI 1.32 to 2.18) and subsequent major bleeding (adjusted HR 2.18, 95% CI 1.56 to 3.04).

Conclusions

In ARISTOTLE, non-major bleeding was common and substantially less frequent with apixaban than with warfarin. CRNM bleeding was independently associated with a higher risk of death and subsequent major bleeding. Our results highlight the importance of any severity of bleeding in patients with AF treated with anticoagulation therapy and suggest that non-major bleeding, including minor bleeding, might not be minor.

Trial registration number

NCT00412984; post-results.

Gastrointestinal Bleeding in Patients With Atrial Fibrillation Treated With Rivaroxaban or Warfarin: ROCKET AF Trial

BACKGROUND

Gastrointestinal (GI) bleeding is a common complication of oral anticoagulation.

OBJECTIVES

This study evaluated GI bleeding in patients who received at least 1 dose of the study drug in the on-treatment arm of the ROCKET AF (Rivaroxaban Once-daily Oral Direct Factor Xa Inhibition Compared with Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation) trial.

METHODS

The primary outcome was adjudicated GI bleeding reported from first to last drug dose + 2 days. Multivariable modeling was performed with pre-specified candidate predictors.

RESULTS

Of 14,236 patients, 684 experienced GI bleeding during follow-up. These patients were older (median age 75 years vs. 73 years) and less often female. GI bleeding events occurred in the upper GI tract (48%), lower GI tract (23%), and rectum (29%) without differences between treatment arms. There was a significantly higher rate of major or nonmajor clinical GI bleeding in rivaroxaban- versus warfarin-treated patients (3.61 events/100 patient-years vs. 2.60 events/100 patient-years; hazard ratio: 1.42; 95% confidence interval: 1.22 to 1.66). Severe GI bleeding rates were similar between treatment arms (0.47 events/100 patient-years vs. 0.41 events/100 patient-years; p = 0.39; 0.01 events/100 patient-years vs. 0.04 events/100 patient-years; p = 0.15, respectively), and fatal GI bleeding events were rare (0.01 events/100 patient-years vs. 0.04 events/100 patient-years; 1 fatal events vs. 5 fatal events total). Independent clinical factors most strongly associated with GI bleeding were baseline anemia, history of GI bleeding, and long-term aspirin use.

CONCLUSIONS

In the ROCKET AF trial, rivaroxaban increased GI bleeding compared with warfarin. The absolute fatality rate from GI bleeding was low and similar in both treatment arms. Our results further illustrate the need for minimizing modifiable risk factors for GI bleeding in patients on oral anticoagulation.

Comparison of the Novel Oral Anticoagulants Apixaban, Dabigatran, Edoxaban, and Rivaroxaban in the Initial and Long-Term Treatment and Prevention of Venous Thromboembolism: Systematic Review and Network Meta-Analysis

Background

Anticoagulation with low molecular weight heparin and vitamin K antagonists is the current standard of care (SOC) for venous thromboembolism (VTE) treatment and prevention. Although novel oral anti-coagulants (NOACs) have been compared with SOC in this indication, no head-to-head randomised controlled trials (RCTs) have directly compared NOACs. A systematic review and network meta-analysis (NMA) were conducted to compare the efficacy and safety of NOACs for the initial and long-term treatment of VTE.

Methods

Electronic databases (accessed July 2014) were systematically searched to identify RCTs evaluating apixaban, dabigatran, edoxaban, and rivaroxaban versus SOC. Eligible patients included adults with an objectively confirmed deep vein thrombosis (DVT), pulmonary embolism (PE) or both. A fixed-effect Bayesian NMA was conducted for outcomes of interest, and results were presented as relative risks (RR) and 95% credible intervals (Crl).

Results

Six Phase III RCTs met criteria for inclusion: apixaban (one RCT; n = 5,395); rivaroxaban (two RCTs; n = 3,423/4,832); dabigatran (two RCTs; n = 2,539/2,568); edoxaban (one RCT; n = 8,240). There were no statistically significant differences between the NOACs with regard to the risk of ‘VTE and VTE-related death. Apixaban treatment was associated with the most favourable safety profile of the NOACs, showing a statistically significantly reduced risk of ‘major or clinically relevant non-major (CRNM) bleed’ compared with rivaroxaban (0.47 [0.36, 0.61]), dabigatran (0.69 [0.51, 0.94]), and edoxaban (0.54 [0.41, 0.69]). Dabigatran was also associated with a significantly lower risk of ‘major or CRNM bleed’ compared with rivaroxaban (0.68 [0.53, 0.87]) and edoxaban (0.77 [0.60, 0.99]).

Conclusions

Indirect comparisons showed statistically similar reductions in the risk of ‘VTE or VTE-related death for all NOACs. In contrast, reductions in ‘major or CRNM bleed’ for initial/long-term treatment were significantly better with apixaban compared with all other NOACs, and with dabigatran compared with rivaroxaban and edoxaban. Results from the current analysis indicate that the NOACs offer clinical benefit over conventional therapy while highlighting relative differences in their bleeding profile.

Recanalization Therapies in Acute Ischemic Stroke Patients

Background—

We explored the safety of intravenous thrombolysis (IVT) or intra-arterial treatment (IAT) in patients with ischemic stroke on non-vitamin K antagonist oral anticoagulants (NOACs, last intake <48 hours) in comparison with patients (1) taking vitamin K antagonists (VKAs) or (2) without previous anticoagulation (no-OAC).

Methods and Results—

This is a multicenter cohort pilot study. Primary outcome measures were (1) occurrence of intracranial hemorrhage (ICH) in 3 categories: any ICH (ICH any ), symptomatic ICH according to the criteria of the European Cooperative Acute Stroke Study II (ECASS-II) (sICH ECASS-II ) and the National Institute of Neurological Disorders and Stroke (NINDS) thrombolysis trial (sICH NINDS ); and (2) death (at 3 months). Cohorts were compared by using propensity score matching. Our NOAC cohort comprised 78 patients treated with IVT/IAT and the comparison groups of 441 VKA patients and 8938 no-OAC patients. The median time from last NOAC intake to IVT/IAT was 13 hours (interquartile range, 8–22 hours). In VKA patients, median pre-IVT/IAT international normalized ratio was 1.3 (interquartile range, 1.1–1.6). ICH any was observed in 18.4% NOAC patients versus 26.8% in VKA patients and 17.4% in no-OAC patients. sICH ECASS-II and sICH NINDS occurred in 2.6%/3.9% NOAC patients, in comparison with 6.5%/9.3% of VKA patients and 5.0%/7.2% of no-OAC patients, respectively. At 3 months, 23.0% of NOAC patients in comparison with 26.9% of VKA patients and 13.9% of no-OAC patients had died. Propensity score matching revealed no statistically significant differences.

Conclusions—

IVT/IAT in selected patients with ischemic stroke under NOAC treatment has a safety profile similar to both IVT/IAT in patients on subtherapeutic VKA treatment or in those without previous anticoagulation. However, further prospective studies are needed, including the impact of specific coagulation tests.

Current and emerging strategies in the management of venous thromboembolism: benefit-risk assessment of dabigatran

Venous thromboembolism (VTE) is a disease state that carries significant morbidity and mortality, and is a known cause of preventable death in hospitalized and orthopedic surgical patients. There are many identifiable risk factors for VTE, yet up to half of VTE incident cases have no identifiable risk factor and carry a high likelihood of recurrence, which may warrant extended therapy. For many years, parenteral unfractionated heparin, low-molecular weight heparin, fondaparinux, and oral vitamin K antagonists (VKAs) have been the standard of care in VTE management. However, limitations in current drug therapy options have led to suboptimal treatment, so there has been a need for rapid-onset, fixed-dosing novel oral anticoagulants in both VTE treatment and prophylaxis. Oral VKAs have historically been challenging to use in clinical practice, with their narrow therapeutic range, unpredictable dose responsiveness, and many drug-drug and drug-food interactions. As such, there has also been a need for novel anticoagulant therapies with fewer limitations, which has recently been met. Dabigatran etexilate is a fixed-dose oral direct thrombin inhibitor available for use in acute and extended treatment of VTE, as well as prophylaxis in high-risk orthopedic surgical patients. In this review, the risks and overall benefits of dabigatran in VTE management are addressed, with special emphasis on clinical trial data and their application to general clinical practice and special patient populations. Current and emerging therapies in the management of VTE and monitoring of dabigatran anticoagulant-effect reversal are also discussed.

Ecotin: Exploring a feasible antithrombotic profile

Ecotin is an Escherichia coli-derived protein that can inhibit serine proteases. It has been suggested that this protein (ecotin-WT) and some of its variants could be used to develop a prototype to treat thrombosis. In this work, the effect of ecotin-WT and a variant of this protein harboring two mutations (Met84Arg and Met85Arg, ecotin-RR) were analyzed to determine their ability to prevent thrombus formation using in vivo models. Ecotins were analyzed in vitro using the coagulation tests. An in vivo venous thrombosis rat model and a pulmonary thromboembolism mouse model were used to investigate the antithrombotic activity. The bleeding time in rats using a tail-transection model was evaluated as a possible side effect caused by the administration of these proteins. Ecotin-RR was more effective in inhibiting thrombin than ecotin-WT. Both ecotins presented similar mechanisms of anticoagulation activity and were able to decrease thrombus formation. In contrast, only ecotin-RR increased survival rates in the in vivo pulmonary thromboembolism model, reinforcing the antithrombotic activity of ecotin-RR. Ecotin-WT and more so ecotin-RR showed potent antithrombotic effects, not associated with bleeding. The presented results indicate that ecotin-WT and ecotin-RR may be new scaffolds that could be used to develop anticoagulation molecules.

Inhibition of Factor XI activity as a promising antithrombotic strategy

Prevention and treatment of thromboembolic disorders with minimal bleeding risk remains a significant unmet medical need. Studies in Factor XI (FXI)-deficient humans and experimental animal models suggest that targeting FXI in humans provides antithrombotic benefits with reduced bleeding liability compared with current standard of care. In this review, we describe an exciting era in the discovery and development of antithrombotic agents as multiple therapeutic modalities for FXI(a) inhibition progress through preclinical and clinical development.

Heterocyclic core analogs of a direct thrombin inhibitor

Thrombin is a serine protease that plays a key role in blood clotting. Pyrrolidine 1 is a potent thrombin inhibitor discovered at Merck several years ago. Seven analogs (2-8) of 1 in which the pyrrolidine core was replaced with various heterocycles were prepared and evaluated for activity against thrombin, clotting factors VIIa, IXa, Xa, and XIIa, and trypsin. The thiomorpholine analog 6 was the most active, essentially matching the thrombin inhibitory activity of 1 with slightly improved selectivity over trypsin.

Factors associated with major bleeding events: insights from the ROCKET AF trial (rivaroxaban once-daily oral direct factor Xa inhibition compared with vitamin K antagonism for prevention of stroke and embolism trial in atrial fibrillation)

OBJECTIVES

This study sought to report additional safety results from the ROCKET AF (Rivaroxaban Once-daily oral Direct Factor Xa Inhibition Compared with Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation).

BACKGROUND

The ROCKET AF trial demonstrated similar risks of stroke/systemic embolism and major/nonmajor clinically relevant bleeding (principal safety endpoint) with rivaroxaban and warfarin.

METHODS

The risk of the principal safety and component bleeding endpoints with rivaroxaban versus warfarin were compared, and factors associated with major bleeding were examined in a multivariable model.

RESULTS

The principal safety endpoint was similar in the rivaroxaban and warfarin groups (14.9 vs. 14.5 events/100 patient-years; hazard ratio: 1.03; 95% confidence interval: 0.96 to 1.11). Major bleeding risk increased with age, but there were no differences between treatments in each age category (<65, 65 to 74, ≥75 years; pinteraction = 0.59). Compared with those without (n = 13,455), patients with a major bleed (n = 781) were more likely to be older, current/prior smokers, have prior gastrointestinal (GI) bleeding, mild anemia, and a lower calculated creatinine clearance and less likely to be female or have a prior stroke/transient ischemic attack. Increasing age, baseline diastolic blood pressure (DBP) ≥90 mm Hg, history of chronic obstructive pulmonary disease or GI bleeding, prior acetylsalicylic acid use, and anemia were independently associated with major bleeding risk; female sex and DBP <90 mm Hg were associated with a decreased risk.

CONCLUSIONS

Rivaroxaban and warfarin had similar risk for major/nonmajor clinically relevant bleeding. Age, sex, DBP, prior GI bleeding, prior acetylsalicylic acid use, and anemia were associated with the risk of major bleeding. (An Efficacy and Safety Study of Rivaroxaban With Warfarin for the Prevention of Stroke and Non-Central Nervous System Systemic Embolism in Patients With Non-Valvular Atrial Fibrillation: NCT00403767).

Rivaroxaban for the treatment of acute coronary syndromes

INTRODUCTION

Recurrent ischemic events after an acute coronary syndrome (ACS) are frequent, despite current antiplatelet therapies and revascularization. Warfarin reduces recurrent ischemia but increases bleeding. Warfarin is difficult to administer with the proportion of time achieving therapeutic international normalized ratios varying within and among individuals. The newer oral anticoagulants have predictable dose-effect relationships and no monitoring is required.

AREAS COVERED

The pharmacology of rivaroxaban , evidence for the use of rivaroxaban in ACS, and the management of bleeding complications are covered in this article.

EXPERT OPINION

Arterial thrombosis is traditionally thought to be more platelet mediated than clotting factor mediated. Nonetheless, in the acute therapy for ACS, anticoagulation is a cornerstone treatment and there is persistent thrombin generation. Research has focused on finding a "sweet spot" of anticoagulation with high anti-ischemic and low bleeding effects. It follows that with chronic therapy post-ACS, there could also be a "sweet-spot" of anticoagulation. This may depend on the intrinsic vascular disease burden, the intervention delivered (stenting or bypass surgery), and background antiplatelet therapy. Rivaroxaban, a new oral factor Xa inhibitor, in a low-dose regimen-reduced ischemic events including mortality across a broad ACS population in the ATLAS-ACS trial with increased bleeding but without increasing fatal bleeding. Rivaroxaban is an attractive new treatment option for ACS.

Antithrombotic therapy for stroke prevention in non-valvular atrial fibrillation

The world faces an epidemic of atrial fibrillation and atrial fibrillation-related stroke. An individual's risk of atrial fibrillation-related stroke can be estimated with the CHADS(2) or CHA(2)DS(2)VASc scores, and reduced by two-thirds with effective anticoagulation. Vitamin K antagonists, such as warfarin, are underused and often poorly managed. The direct thrombin inhibitor dabigatran etexilate and factor Xa inhibitors rivaroxaban and apixaban are new oral anticoagulants that are at least as efficacious and safe as warfarin. Their advantages are predictable anticoagulant effects, low propensity for drug interactions, and lower rates of intracranial haemorrhage than with warfarin. A disadvantage is the continuing need to develop and validate rapidly effective antidotes for major bleeding and standardised tests that accurately measure plasma concentrations and anticoagulant effects, together with the disadvantage of possible higher rates of gastrointestinal haemorrhage and greater expense than with warfarin. The new oral anticoagulants should increase the number of patients with atrial fibrillation at risk of stroke who are optimally anticoagulated, and reduce the burden of atrial fibrillation-related stroke.

Oral direct factor Xa inhibitors

Vitamin K antagonists, such as warfarin, have been the mainstay of oral anticoagulation for many decades. Although effective, warfarin has numerous limitations, including a variable dose requirement from patient to patient because of differences in dietary vitamin K intake, common genetic polymorphisms, and multiple drug interactions that affect its pharmacodynamics and metabolism. Consequently, warfarin requires frequent monitoring to ensure that a therapeutic anticoagulant effect has been achieved because excessive anticoagulation can lead to bleeding, and because insufficient anticoagulation can result in thrombosis. Such monitoring is burdensome for patients and physicians and is costly for the health care system. These limitations have prompted the development of new oral anticoagulants that target either factor Xa or thrombin. Although the path to the development of these drugs has been long, the new drugs are at least as effective and safe as warfarin, but they streamline clinical care because they can be administered in fixed doses without routine coagulation monitoring. This article focuses on rivaroxaban, apixaban, and edoxaban, the oral factor Xa inhibitors in the most advanced stages of development. After 20 years of discovery research, these agents are already licensed for several indications. Thus, the long path to finding replacements for warfarin has finally reached fruition. Therefore, development of the oral factor Xa inhibitors represents a translational science success story.

Efficacy and safety of novel oral anticoagulants for treatment of acute venous thromboembolism: direct and adjusted indirect meta-analysis of randomised controlled trials

OBJECTIVE

To critically review the effectiveness of the novel oral anticoagulants (rivaroxaban, dabigatran, ximelagatran, and apixaban) in the treatment of acute venous thromboembolism.

DESIGN

Systematic review and random effects meta-analysis. Data were extracted independently by two investigators. An adjusted indirect comparison was performed to compare between novel oral anticoagulants.

DATA SOURCES

Medline, Embase, and Cochrane Library (from inception to April 2012). Hand searching of relevant scientific works and contact with experts.

STUDY SELECTION

Randomised controlled trials of novel oral anticoagulants compared with vitamin K antagonists for acute venous thromboembolism. Selected outcomes were recurrent events, major bleeding, and all cause mortality.

RESULTS

Nine studies met our inclusion criteria, involving 16,701 patients evaluated for efficacy and 16,611 for safety. Data were stratified according to different novel oral anticoagulants. For recurrent acute venous thromboembolism, there were no significant differences in events rates between any of the anticoagulants and conventional treatment (rivaroxaban (four studies): relative risk 0.85, 95% confidence interval 0.55 to 1.31; dabigatran (two studies): 1.09, 0.76 to 1.57; ximelagatran (two studies): 1.06, 0.62 to 1.80; and apixaban (one study): 0.98, 0.20 to 4.79). Rivaroxaban reduced the risk of major bleeding compared with conventional treatment (0.57, 0.39 to 0.84), whereas other novel oral anticoagulants did not (0.76 (0.49 to 1.18) for dabigatran; 0.54 (0.28 to 1.03) for ximelagatran; 2.95 (0.12 to 71.82) for apixaban). For all cause mortality there were no significant differences between the novel oral anticoagulants and conventional treatment (0.96 (0.72 to 1.27) for rivaroxaban; 1.00 (0.67 to 1.50) for dabigatran; 0.67 (0.42 to 1.08) for ximelagatran; 6.89 (0.36 to 132.06) for apixaban). The adjusted indirect comparison between rivaroxaban and dabigatran did not show superiority of either drug over the others for major bleeding (0.75, 0.41 to 1.34) or the other endpoints.

CONCLUSIONS

Compared with vitamin K antagonists, the novel oral anticoagulants had a similar risk of recurrence of acute venous thromboembolism and all cause mortality, though rivaroxaban was associated with a reduced risk of bleeding.