Oral, direct Factor Xa inhibition with BAY 59-7939 for the prevention of venous thromboembolism after total hip replacement

Design, synthesis and discovery of 1-(2-(6-Chloro-3-methylsulfonyl)-naphthyl)-1H-pyrazole-5-carboxylamides as highly potent factor Xa inhibitors

Based upon the biphenyl 1-(2-naphthyl)-1H-pyrazole-5-carboxylamides reported in our previous communications, we designed and discovered 2-(6-chloro-3-methylsulfonyl)-naphthyl as an optimal factor Xa S1 binding element. Employing a key Diels-Alder reaction of 1,4-dihydro-2,3-benzoxathiin-3-oxide with maleic anhydride and a key Cu(I)-mediated methylsulfonylation, we prepared two biphenyl 1-(2-(6-chloro-3-methylsulfonyl)-naphthyl)-1H-pyrazole-5-carboxylamides as highly potent factor Xa inhibitors with K(i) values of 0.065 nM and 0.045 nM respectively, and demonstrated the synergistically enhanced binding interaction in the factor Xa S1 site.

Rivaroxaban: an oral direct factor Xa inhibitor for the prevention of thromboembolism

Rivaroxaban is a novel oral direct factor Xa inhibitor. It is currently awaiting approval from the US Food and Drug Administration as a prophylaxis for venous thromboembolism in total knee and hip replacements. Based on phase II and III trials, rivaroxaban has been shown to be as efficacious, if not more, as traditional antithrombotic therapy with similar safety profiles. The Regulation of Coagulation in Major Orthopedic Surgery Reducing the Risk of Deep Vein Thrombosis and Pulmonary Embolism (RECORD) phase III trials have shown rivaroxaban 10 mg once daily to be superior to the low molecular weight heparin, enoxaparin, when used for prophylaxis of venous thromboembolism in orthopedic surgeries. Rivaroxaban has been shown to have tolerable adverse effects and a low potential for drug-drug or drug-food interactions. It has the major advantages of once daily oral dosing and no required laboratory monitoring, giving it the potential to replace current antithrombotics in the market today.

Rivaroxaban for the prevention of venous thromboembolism following major orthopedic surgery: the RECORD trials

Patients undergoing total hip or knee arthroplasty face an increased risk for venous thromboembolism in the days and weeks following surgery. Hence, the routine application of prophylactic strategies is currently recommended. These include parenteral anticoagulants such as the low-molecular-weight heparins or fondaparinux and oral anticoagulants such as warfarin. New anticoagulant drugs are rapidly becoming available, including drugs that are administered orally, at fixed doses and without laboratory monitoring. Rivaroxaban is the first of a new class of anticoagulants: the selective, direct Factor Xa inhibitors. It has completed clinical evaluation in the setting of major orthopedic surgery and is now approved in many countries for the prevention of venous thromboembolism in patients undergoing total knee and hip arthroplasty. In this paper, we will review the trial data now supporting the clinical use of rivaroxaban and will discuss the potential role of this agent in daily clinical practice.

Rivaroxaban in Orthopedic Surgery — A Change of Paradigm?

Two selective, orally available anticoagulant agents, although with different targets in the coagulation cascade, have recently been approved in many countries on the indication of prophylaxis against venous thromboembolism (VTE) after major joint arthroplasty. This review discusses mainly the antifactor Xa drug, rivaroxaban, with a focus on the orthopedic trials. Pharmacokinetic characteristics and other clinical development programs with rivaroxaban are briefly reviewed. Although the aim of this article is not to review the direct thrombin inhibitor, dabigatran etexilate, some comparisons are made. For clinical results, these are obviously indirect and conclusions must be drawn with caution until head-to-head comparisons are performed. Whether the introduction of rivaroxaban is a change of paradigm will ultimately be decided in the eyes and mind of the beholder.

State-of-the-Art Review: Assessing the Safety Profiles of New Anticoagulants for Major Orthopedic Surgery Thromboprophylaxis

Background: The safety and efficacy of new anticoagulants are often initially tested for venous thromboembolism (VTE) prevention in patients undergoing major orthopedic surgery. Concern among surgeons about the risks for bleeding may result in suboptimal use of thrombophylaxis. Objective: To evaluate the definitions used to define bleeding outcomes in studies of new anticoagulants and to examine the influence the definition has on the perceived bleeding risk of thromboprophylaxis. Methods: The MedLine database was searched for phase III studies of new anticoagulants versus the standard comparator, enoxaparin, in patients undergoing major orthopedic surgery. Results: The definitions for major bleeding outcomes varied widely both across and within clinical trial programs of new anticoagulants. Studies which did not include surgical site bleeding in their definition for major bleeding showed lower major bleeding rates in comparison to those that did include this outcome. Other factors that influenced the rate of major bleeding included the timing of prophylaxis initiation in relation to surgery and the dose of anticoagulant therapy. The wide range of definitions used for major bleeding made it difficult to compare bleeding risk among studies of new anticoagulants. Conclusions: The definitions of bleeding events that clinical trials of thromboprophylaxis use in their assessment of new anticoagulants strongly influences each drug’s perceived safety profile and may underestimate bleeding risks. Clinical studies of new anticoagulants urgently need standardization of bleeding definitions to allow intertrial comparability and to ensure consistent reporting of clinically relevant outcomes.

New anticoagulants for atrial fibrillation

Although warfarin and other vitamin K antagonists have clearly the greatest efficacy among treatments commonly available in preventing stroke in atrial fibrillation, their use is associated with a substantial risk of major bleedings and are unpractical and difficult to use because of their narrow therapeutic window, their interaction with drugs and foods, and the need of frequent coagulation monitoring. Several new anticoagulants are now undergoing phase III clinical trials in atrial fibrillation with the aim of demonstrating noninferiority compared with vitamin K antagonists or superiority compared with aspirin in patients in whom vitamin K antagonists are contraindicated or not tolerated. These drugs fall in different pharmacological categories of oral direct thrombin inhibitors, parenteral long-lived indirect factor Xa inhibitors, and oral direct factor Xa inhibitors. Cardiologists need to be aware of the explosive pharmacological literature being accrued with these new drugs, as most of these will likely enter the clinical arena in the near future.

Cyanoguanidine-based lactam derivatives as a novel class of orally bioavailable factor Xa inhibitors

The N,N'-disubstituted cyanoguanidine is an excellent bioisostere of the thiourea and ketene aminal functional groups. We report the design and synthesis of a novel class of cyanoguanidine-based lactam derivatives as potent and orally active FXa inhibitors. The SAR studies led to the discovery of compound 4 (BMS-269223, K(i)=6.5nM, EC(2xPT)=32muM) as a selective, orally bioavailable FXa inhibitor with an excellent in vitro liability profile, favorable pharmacokinetics and pharmacodynamics in animal models. The X-ray crystal structure of 4 bound in FXa is presented and key ligand-protein interactions are discussed.

Rivaroxaban -- an oral, direct Factor Xa inhibitor: lessons from a broad clinical study programme

Anticoagulants are recommended for the prevention and treatment of venous thromboembolism (VTE), prevention of stroke in patients with atrial fibrillation (AF) and secondary prevention in patients with acute coronary syndrome (ACS). There is a clinical need for novel anticoagulants offering improvements over current standard of care, such as fixed oral dosing and no need for routine monitoring. Rivaroxaban, an oral, once-daily, direct Factor Xa inhibitor, has recently completed the RECORD phase III programme for the prevention of VTE in patients undergoing total hip or knee replacement (THR or TKR), an indication for which it is approved in Europe and Canada. It is being investigated in large-scale phase III studies for VTE treatment and prevention of stroke in patients with AF, and phase III studies will soon commence for secondary prevention in patients with ACS. Phase I studies demonstrated that no routine anticoagulation monitoring was required, while phase II studies suggested that fixed daily doses had a wide therapeutic window. The four RECORD studies consistently showed that rivaroxaban was significantly more effective than enoxaparin in the prevention of VTE after THR and TKR, with a similar safety profile. This review describes the development of this novel anticoagulant, from bench to bedside.

[Rivaroxaban: clinical pharmacology]

Rivaroxaban (Xarelto) is a new oral, direct and selective inhibitor of the factor Xa of the coagulation cascade. The main pharmacokinetic characteristics of rivaroxaban are a bioavailability of approximately 80-100%, a maximum concentration obtained in 2 to 4 hours, a terminal half-life of elimination of 7 to 11 hours, a renal elimination for 1/3 for the active hepatic metabolism from the cytochrome P450 (3A4) for the other 2/3. The main sources of variability are the renal and the liver function and potential interactions with some strong inhibitors or inducers of the CYP450 3A4. Phase II clinical studies have shown that this compound can be orally administrated, once or twice daily, without any biological monitoring and without any need for dose adjustment. There is a contra-indication in case of severe liver insufficiency and not recommended in case of severe renal impairment. Pharmacodynamically, Rivaroxaban is a direct and selective factor Xa inhibitor without any effect on the factor IIa and without any interaction on platelets. Four phases II with 2787 patients were carried out to for venous thromboembolic (VTE) prophylaxis after major orthopaedic surgery, showing that 10 mg once daily could be the optimal dose regimen to assess in phase III. Two phases II with 1446 patients were carried out for the treatment of VTE showing that 15 mg twice daily for 3 weeks and then 20 mg once daily could be the optimal dose regimen to evaluate in the following phases 3. No strong signal for a potential liver toxicity was shown during these 6 phases II.

Design, structure-activity relationships, X-ray crystal structure, and energetic contributions of a critical P1 pharmacophore: 3-chloroindole-7-yl-based factor Xa inhibitors

An indole-based P1 moiety was incorporated into a previously established factor Xa inhibitor series. The indole group was designed to hydrogen-bond with the carbonyl of Gly218, while its 3-methyl or 3-chloro substituent was intended to interact with Tyr228. These interactions were subsequently observed in the X-ray crystal structure of compound 18. SAR studies led to the identification of compound 20 as the most potent FXa inhibitor in this series (IC(50) = 2.4 nM, EC(2xPT) = 1.2 microM). An in-depth energetic analysis suggests that the increased binding energy of 3-chloroindole-versus 3-methylindole-containing compounds in this series is due primarily to (a) the more hydrophobic nature of chloro- versus methyl-containing compounds and (b) an increased interaction of 3-chloroindole versus 3-methylindole with Gly218 backbone. The stronger hydrophobicity of chloro- versus methyl-substituted aromatics may partly explain the general preference for chloro- versus methyl-substituted P1 groups in FXa, which extends beyond the current series.

New compounds in the management of venous thromboembolism after orthopedic surgery: focus on rivaroxaban

Rivaroxaban (Xarelto) is a member of a new class of oral, direct (antithrombin-independent) factor Xa inhibitors, which restrict thrombin generation both in vitro and in vivo. After oral administration the absorption is near 100%, the bioavailability is near 80%, and the elimination half-life is 5-9 hours with mixed excretion via the renal and fecal/biliary routes. The pharmacokinetics of rivaroxaban are predictable and consistent with a rapid onset of antithrombotic action within 2 hours after administration. Phase II clinical studies have been carried out in patients undergoing total hip arthroplasty (THA) or total knee arthroplasty (TKA) and a dose of 10 mg once daily for thromboprophylaxis was selected for further clinical development. The results of the phase III studies showed a significantly better antithrombotic efficacy of rivaroxaban compared with enoxaparin both in the short term (10-14 days) in TKA patients and long term (35 +/- 4 days) in THA patients with a comparable safety. Symptomatic thromboembolic events were also significantly reduced with rivaroxaban. Liver enzyme elevation was seen in patients treated with rivaroxaban, but there was no indication of an increased risk of liver toxicity compared with enoxaparin. In conclusion, rivaroxaban is a potent and safe new compound for antithrombotic prophylaxis in orthopedic surgery.

New anticoagulants

PURPOSE OF REVIEW

Although current anticoagulants such as unfractionated and low-molecular-weight heparins and the vitamin K antagonists are effective for the prevention and treatment of thrombosis, they have several limitations. The vitamin K antagonists, the only approved oral anticoagulants, have a narrow therapeutic window, thereby requiring regular laboratory monitoring of the international normalized ratio and intermittent adjustments in dose. New anticoagulants have been developed that selectively inhibit thrombin or factor Xa, and have predictable dose-response relationships.

RECENT FINDINGS

Fondaparinux is a synthetic pentasaccharide, which binds to antithrombin, thereby indirectly inhibiting factor Xa. Fondaparinux demonstrated efficacy compared with low-molecular-weight heparin in randomized clinical trials and is approved for the prevention and treatment of venous thromboembolism. A number of oral direct factor Xa inhibitors and oral direct thrombin inhibitors are in advanced phases of clinical development for the prevention and treatment of thrombosis. The current status of these anticoagulants will be reviewed along with the challenges faced in designing pivotal clinical trials of these agents in comparison to existing anticoagulants.

SUMMARY

Selective inhibitors of specific coagulation factors have the potential to be more effective, safer, and easier to use than existing anticoagulants. Approval of one or more of these agents will lead to an improved drug armamentarium for the prevention and treatment of thrombosis.

Differences in urinary prothrombin fragment 1 + 2 levels after total hip replacement in relation to venous thromboembolism and bleeding events

BACKGROUND

Prothrombin fragment 1 + 2 is excreted in urine (uF1 + 2) as a result of thrombin generation and, therefore, may be a useful marker of coagulation status.

OBJECTIVES

To assess uF1 + 2 levels after total hip replacement (THR) in patients with venous thromboembolism (VTE) and bleeding events.

PATIENTS/METHODS

This study was conducted in parallel with a prospective, dose-finding study evaluating the efficacy and safety of different doses of rivaroxaban (Xarelto, Bayer HealthCare AG, Wuppertal, Germany) for thromboprophylaxis, relative to enoxaparin. Deep vein thrombosis was diagnosed by mandatory venography performed 5-9 days after THR, or earlier if symptomatic. Symptomatic pulmonary embolism was diagnosed by objective testing. Bleeding complications were registered and stratified into major bleeding, clinically relevant, non-major bleeding, and minor bleeding, using predefined criteria.

RESULTS

Eighty-four patients had a VTE and 57 patients had a bleeding event (n = 722). Significantly higher median uF1 + 2 levels were observed in the VTE group on day 3 after THR (P = 0.03), compared with control. Median uF1 + 2 levels were lower in the bleeding group on day 3 after THR (P = 0.005) and on the day of venography (P = 0.36), compared with control. Comparisons between the VTE and bleeding groups showed significantly lower median uF1 + 2 levels in the bleeding group on day 3 after THR and on the day of venography (P < 0.0001 and P = 0.006, respectively).

CONCLUSIONS

Measurement of uF1 + 2 could provide a simple clinical test to evaluate non-invasively the intensity of coagulation activation after THR. However, further studies are required to confirm these encouraging preliminary results.

Dose-escalation study of the pharmacokinetics and pharmacodynamics of rivaroxaban in healthy elderly subjects

OBJECTIVE

The aim of this study was to investigate the pharmacokinetics and pharmacodynamics of rivaroxaban--a novel, oral, direct Factor Xa (FXa) inhibitor--in healthy elderly subjects.

RESEARCH DESIGN AND METHODS

In this single-centre, single-blind, placebo-controlled, parallel-group, dose-escalation study, 48 subjects (aged 60-76 years) were randomized to receive a single oral dose of 30, 40 or 50 mg of rivaroxaban or placebo.

RESULTS

Rivaroxaban was absorbed rapidly, reaching peak plasma concentration (C(max)) 4 h after dosing in all groups. Bioavailability, in terms of the area under the plasma concentration-time curve (AUC) and C(max), increased slightly (less than dose proportionally) after administration of rivaroxaban 40 mg compared with 30 mg, but was not increased further with rivaroxaban 50 mg. Rivaroxaban pharmacodynamic effects (inhibition of FXa activity and prolongation of prothrombin time, activated partial thromboplastin time and HepTest) all showed a similar pattern, with maximum inhibition of FXa activity increasing from 68% after rivaroxaban 30 mg to 75% after 40 mg and no further increase with the 50 mg dose. Most adverse events were mild; observed rates were less than placebo for the 30 and 40 mg dose groups, and similar to placebo for 50 mg. No differences were found between male and female subjects. Effects of rivaroxaban doses above 50 mg were not investigated in this study.

CONCLUSIONS

Each single dose of rivaroxaban was well tolerated, with predictable pharmacokinetics and pharmacodynamics at doses up to 40 mg, and provided effective anticoagulation in healthy elderly subjects. Adverse events were somewhat elevated in the 50 mg group, but given the small sample size, no specific conclusions can be drawn about this dosing level.

The top 4 advances in antithrombotic care in the last year

Important clinical data with a significant impact on the clinical management of venous thromboembolism (VTE) were presented at The International Society of Thrombosis and Haemostasis (ISTH) meeting, held in Geneva, Switzerland in July of 2007. In addition, 2 new guidelines for the management of patients with acute coronary syndromes (ACS) were published in 2007, and will have a significant impact on daily practice. Finally, the approval of new practice-changing, paradigm-shifting oral anticoagulants is on the horizon. This article will review the top 4 advances in antithrombotic care and discuss their impact on the clinical management of VTE.

New antithrombotic drugs: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This chapter focuses on new antithrombotic drugs that are in phase II or III clinical testing. Development of these new agents was prompted by limitations of existing antiplatelet, anticoagulant, or fibrinolytic drugs. Addressing these unmet needs, this chapter (1) outlines the rationale for development of new antithrombotic agents, (2) describes the new antiplatelet, anticoagulant, and fibrinolytic drugs, and (3) provides clinical perspectives on the opportunities and challenges faced by these novel agents.

Extended duration rivaroxaban versus short-term enoxaparin for the prevention of venous thromboembolism after total hip arthroplasty: a double-blind, randomised controlled trial

BACKGROUND

The risk of venous thromboembolism is high after total hip arthroplasty and could persist after hospital discharge. Our aim was to compare the use of rivaroxaban for extended thromboprophylaxis with short-term thromboprophylaxis with enoxaparin.

METHODS

2509 patients scheduled to undergo elective total hip arthroplasty were randomly assigned, stratified according to centre, with a computer-generated randomisation code, to receive oral rivaroxaban 10 mg once daily for 31-39 days (with placebo injection for 10-14 days; n=1252), or enoxaparin 40 mg once daily subcutaneously for 10-14 days (with placebo tablet for 31-39 days; n=1257). The primary efficacy outcome was the composite of deep-vein thrombosis (symptomatic or asymptomatic detected by mandatory, bilateral venography), non-fatal pulmonary embolism, and all-cause mortality up to day 30-42. Analyses were done in the modified intention-to-treat population, which consisted of all patients who had received at least one dose of study medication, had undergone planned surgery, and had adequate assessment of thromboembolism. This study is registered at ClinicalTrials.gov, number NCT00332020.

FINDINGS

The modified intention-to-treat population for the analysis of the primary efficacy outcome consisted of 864 patients in the rivaroxaban group and 869 in the enoxaparin group. The primary outcome occurred in 17 (2.0%) patients in the rivaroxaban group, compared with 81 (9.3%) in the enoxaparin group (absolute risk reduction 7.3%, 95% CI 5.2-9.4; p<0.0001). The incidence of any on-treatment bleeding was much the same in both groups (81 [6.6%] events in 1228 patients in the rivaroxaban safety population vs 68 [5.5%] of 1229 patients in the enoxaparin safety population; p=0.25).

INTERPRETATION

Extended thromboprophylaxis with rivaroxaban was significantly more effective than short-term enoxaparin plus placebo for the prevention of venous thromboembolism, including symptomatic events, in patients undergoing total hip arthroplasty.

Short- and long-term efficacy of aspirin and clopidogrel for thromboprophylaxis for mechanical heart valves: an in vivo study in swine

OBJECTIVE

In the interest of exploring alternatives to warfarin, we tested the hypothesis that clopidogrel combined with aspirin is effective for thromboprophylaxis of mechanical valves using a swine model.

METHODS

Adult swine underwent heterotopic implantation of a modified bileaflet mechanical valved conduit bypassing the ligated, native descending thoracic aorta. Animals were randomized to no anticoagulation (n = 7), 175 U/kg dalteparin administered subcutaneously twice daily (n = 9), 325 mg of aspirin (n = 6), 75 mg of clopidogrel (n = 6), or 325 mg of aspirin and 75 mg of clopidogrel daily (n = 6) and survived for 30 days. Additionally, 11 animals were randomized to no anticoagulation (n = 5) or 325 mg of oral aspirin and 75 mg of clopidogrel daily (n = 6) and survived for 150 days.

RESULTS

At 30 days, we observed 216 +/- 270 mg of thrombus for the no anticoagulation group, 53 +/- 91 mg for the dalteparin group, 33 +/- 23 mg for the aspirin group, 25 +/- 10 mg for the clopidogrel group, and 17 +/- 9 mg for the combined aspirin and clopidogrel group, respectively (P < .01 for clopidogrel and aspirin vs no anticoagulation). At 150 days, we observed 223 +/- 200 mg of thrombus for the no anticoagulation group and 4 +/- 4 mg for the aspirin and clopidogrel group (P = .02). Mean platelet deposition on the valve was 4.1 x 10(9) +/- 3.6 x 10(9) for the no anticoagulation and 6.81 x 10(7) +/- 1.4 x 10(8) for the combined aspirin and clopidogrel groups, respectively (P = .03). No major hemorrhagic events were observed.

CONCLUSIONS

Effective short- and long-term thromboprophylaxis of mechanical valves can be achieved by using dual-antiplatelet therapy in this porcine model. Prospective human trials should be conducted with combination aspirin and clopidogrel as an alternative to warfarin in patients with bileaflet mechanical aortic valves.

Rivaroxaban versus enoxaparin for thromboprophylaxis after hip arthroplasty

BACKGROUND

This phase 3 trial compared the efficacy and safety of rivaroxaban, an oral direct inhibitor of factor Xa, with those of enoxaparin for extended thromboprophylaxis in patients undergoing total hip arthroplasty.

METHODS

In this randomized, double-blind study, we assigned 4541 patients to receive either 10 mg of oral rivaroxaban once daily, beginning after surgery, or 40 mg of enoxaparin subcutaneously once daily, beginning the evening before surgery, plus a placebo tablet or injection. The primary efficacy outcome was the composite of deep-vein thrombosis (either symptomatic or detected by bilateral venography if the patient was asymptomatic), nonfatal pulmonary embolism, or death from any cause at 36 days (range, 30 to 42). The main secondary efficacy outcome was major venous thromboembolism (proximal deep-vein thrombosis, nonfatal pulmonary embolism, or death from venous thromboembolism). The primary safety outcome was major bleeding.

RESULTS

A total of 3153 patients were included in the superiority analysis (after 1388 exclusions), and 4433 were included in the safety analysis (after 108 exclusions). The primary efficacy outcome occurred in 18 of 1595 patients (1.1%) in the rivaroxaban group and in 58 of 1558 patients (3.7%) in the enoxaparin group (absolute risk reduction, 2.6%; 95% confidence interval [CI], 1.5 to 3.7; P<0.001). Major venous thromboembolism occurred in 4 of 1686 patients (0.2%) in the rivaroxaban group and in 33 of 1678 patients (2.0%) in the enoxaparin group (absolute risk reduction, 1.7%; 95% CI, 1.0 to 2.5; P<0.001). Major bleeding occurred in 6 of 2209 patients (0.3%) in the rivaroxaban group and in 2 of 2224 patients (0.1%) in the enoxaparin group (P=0.18).

CONCLUSIONS

A once-daily, 10-mg oral dose of rivaroxaban was significantly more effective for extended thromboprophylaxis than a once-daily, 40-mg subcutaneous dose of enoxaparin in patients undergoing elective total hip arthroplasty. The two drugs had similar safety profiles. (ClinicalTrials.gov number, NCT00329628.)

Rivaroxaban versus enoxaparin for thromboprophylaxis after total knee arthroplasty

BACKGROUND

We investigated the efficacy of rivaroxaban, an orally active direct factor Xa inhibitor, in preventing venous thrombosis after total knee arthroplasty.

METHODS

In this randomized, double-blind trial, 2531 patients who were to undergo total knee arthroplasty received either oral rivaroxaban, 10 mg once daily, beginning 6 to 8 hours after surgery, or subcutaneous enoxaparin, 40 mg once daily, beginning 12 hours before surgery. The primary efficacy outcome was the composite of any deep-vein thrombosis, nonfatal pulmonary embolism, or death from any cause within 13 to 17 days after surgery. Secondary efficacy outcomes included major venous thromboembolism (i.e., proximal deep-vein thrombosis, nonfatal pulmonary embolism, or death related to venous thromboembolism) and symptomatic venous thromboembolism. The primary safety outcome was major bleeding.

RESULTS

The primary efficacy outcome occurred in 79 of 824 patients (9.6%) who received rivaroxaban and in 166 of 878 (18.9%) who received enoxaparin (absolute risk reduction, 9.2%; 95% confidence interval [CI], 5.9 to 12.4; P<0.001). Major venous thromboembolism occurred in 9 of 908 patients (1.0%) given rivaroxaban and 24 of 925 (2.6%) given enoxaparin (absolute risk reduction, 1.6%; 95% CI, 0.4 to 2.8; P=0.01). Symptomatic events occurred less frequently with rivaroxaban than with enoxaparin (P=0.005). Major bleeding occurred in 0.6% of patients in the rivaroxaban group and 0.5% of patients in the enoxaparin group. The incidence of drug-related adverse events, mainly gastrointestinal, was 12.0% in the rivaroxaban group and 13.0% in the enoxaparin group.

CONCLUSIONS

Rivaroxaban was superior to enoxaparin for thromboprophylaxis after total knee arthroplasty, with similar rates of bleeding. (ClinicalTrials.gov number, NCT00361894.)

Pharmacotherapy of atrial fibrillation: an old option with new possibilities

BACKGROUND

Atrial fibrillation is the most common sustained arrhythmia observed worldwide. Despite modern ablative treatment options, pharmacotherapy remains the first-line therapy in patients with atrial fibrillation.

OBJECTIVE

Based on recently published guidelines for the management of atrial fibrillation, the present paper reviews the current and emerging concepts of pharmacotherapy in atrial fibrillation.

METHODS

A MEDLINE search was conducted using the keyword 'atrial fibrillation' and 'drug therapy'. The reviewed literature included clinical trials and published reviews as well as clinical guidelines.

RESULTS

The mainstay of atrial fibrillation therapy is the prevention of thromboembolic events. With growing knowledge of the pathophysiology of atrial fibrillation new drug targets have been identified that promise improved outcomes in atrial fibrillation management and this will allow individual drug treatment in the near future.

Randomized, double-blind, crossover study to investigate the effect of rivaroxaban on QT-interval prolongation

BACKGROUND

Rivaroxaban (BAY 59-7939) is a novel, oral, direct Factor Xa inhibitor in advanced clinical development for the prevention and treatment of thromboembolic disorders. Unwanted pro-arrhythmic effects are a common reason for drugs failing to gain regulatory approval; these properties can be detected by assessing the effect of the drug on the QT interval.

OBJECTIVE

This study was performed, in accordance with International Conference on Harmonisation (ICH) E14 guidance, to assess whether rivaroxaban prolongs the QT interval.

STUDY DESIGN

This was a prospective, randomized, double-blind, double-dummy, four-way crossover study.

SETTING

The study was conducted at a clinical pharmacology research unit.

SUBJECTS

Healthy male and female subjects (n = 54) aged > or =50 years were enrolled and remained in the study unit for 3 days for each treatment. Of these, 50 patients were eligible for the QT analysis.

INTERVENTION

Subjects received single oral doses of rivaroxaban 45 mg or 15 mg, moxifloxacin 400 mg (positive control), or placebo.

OUTCOME MEASURES

Multiple ECGs were taken at frequent intervals after drug administration, and the QT interval was measured manually under blinded conditions at a central laboratory. The Fridericia correction formula (QTcF) was used to correct the QT interval for heart rate. The primary outcome was the effect of rivaroxaban or moxifloxacin on the placebo-subtracted QTcF 3 hours after administration. The frequency of outlying QTcF values and the tolerability of the treatments were also assessed.

RESULTS

All treatments were well tolerated and had no effect on heart rate. Moxifloxacin established the required assay sensitivity; placebo-subtracted QTcF 3 hours after moxifloxacin administration was prolonged by 9.77 ms (95% CI 7.39, 12.15). Placebo-subtracted QTcF values 3 hours after rivaroxaban administration were -0.91 ms (95% CI -3.33, 1.52) and -1.83 ms (95% CI -4.19, 0.54) with rivaroxaban 45 mg and 15 mg, respectively. QTcF was not prolonged with rivaroxaban at any time, and the frequency of outlying results with rivaroxaban and placebo was similar.

CONCLUSION

This thorough QT study, which was performed in accordance with ICH E14 guidelines, shows that rivaroxaban does not prolong the QTc interval. Therefore, the potential of rivaroxaban for the prevention and treatment of thromboembolic disorders, including chronic cardiovascular disorders, can be investigated in appropriate clinical studies without the need for intensive monitoring of the QTc interval.

SR123781A: a new once-daily synthetic oligosaccharide anticoagulant for thromboprophylaxis after total hip replacement surgery: the DRIVE (Dose Ranging Study in Elective Total Hip Replacement Surgery) study

OBJECTIVES

This study assessed the dose response of SR123781A for the prevention of venous thromboembolism (VTE) in patients undergoing total hip replacement (THR) surgery.

BACKGROUND

Despite VTE preventive measures, residual VTE complications still occur after THR. SR123781A, a synthetic oligosaccharide with a mixed profile of anti-factor Xa and IIa activities, could be an alternative to current treatments.

METHODS

In this double-blind study, 1,023 patients undergoing THR were randomly assigned to 1 of 5 daily doses of SR123781A or to a calibrator arm of enoxaparin 40 mg. Treatment was continued for 10 days or until bilateral venography was performed after a minimum of 5 days.

RESULTS

A significant dose-response effect for VTE was observed for SR123781A (p < 0.0001). The VTE rates were 21.2%, 17.7%, 13.5%, 7.0%, and 4.4% in the 0.25-, 0.5-, 1.0-, 2.0-, and 4.0-mg dose groups of SR123781A, respectively, and 8.7% in the enoxaparin group. Doses of 2.0 and 4.0 mg of SR123781A reduced the risk of VTE by 67% and 79%, respectively, compared with the 0.25-mg dose group. Major bleeding was observed in 1.2%, 0.6%, 0.6%, 0.6%, and 5.8% of the patients in the 0.25-, 0.5-, 1.0-, 2.0-, and 4.0-mg dose groups of SR123781A, respectively, and in 0.6% of patients in the enoxaparin group. The dose-response effect for major bleeding was significant (p = 0.0037).

CONCLUSIONS

The model based on these dose-finding study results suggests that SR123781A doses ranging from 1.5 to 2.5 mg show a reasonable risk-to-benefit ratio for VTE prevention after major orthopedic surgery.

Potent anticoagulants are associated with a higher all-cause mortality rate after hip and knee arthroplasty

Anticoagulation for thromboprophylaxis after THA and TKA has not been confirmed to diminish all-cause mortality. We determined whether the incidence of all-cause mortality and pulmonary embolism in patients undergoing total joint arthroplasty differs with currently used thromboprophylaxis protocols. We reviewed articles published from 1998 to 2007 that included 6-week or 3-month incidence of all-cause mortality and symptomatic, nonfatal pulmonary embolism. Twenty studies included reported 15,839 patients receiving low-molecular-weight heparin, ximelagatran, fondaparinux, or rivaroxaban (Group A); 7193 receiving regional anesthesia, pneumatic compression, and aspirin (Group B); and 5006 receiving warfarin (Group C). All-cause mortality was higher in Group A than in Group B (0.41% versus 0.19%) and the incidence of clinical nonfatal pulmonary embolus was higher in Group A than in Group B (0.60% versus 0.35%). The incidences of all-cause mortality and nonfatal pulmonary embolism in Group C were similar to those in Group A (0.4 and 0.52, respectively). Clinical pulmonary embolus occurs despite the use of anticoagulants. Group A anticoagulants were associated with the highest all-cause mortality of the three modalities studied.

New issues in oral anticoagulants

Polymorphisms in CYP2C9, a critical cytochrome P-450 enzyme in the metabolism of warfarin, alters its clearance and affects dosing. CYP*1 has higher activity than either the *2 or *3 variants, and patients with the *2 or *3 variants require a lower dose. VKORC1 is the enzyme inhibited by warfarin, and its levels are affected by several polymorphisms that can be divided into high or low level haplotypes, and patients with high level haplotypes require higher warfarin doses. The use of algorithms for dosing that incorporate pharmacogenomic information perform better than those using clinical data alone. Considerable effort is ongoing to develop new oral anticoagulants as alternatives to warfarin, and three agents are in advanced development. Dabigatran is an oral direct thrombin inhibitor that has been compared with enoxaparin for prevention of VTE following hip or knee replacement. Based on non-inferiority results in European trials, it has now been approved for marketing in Europe. Phase III trials with a new oral Xa inhibitor, rivaroxaban, have been completed in hip or knee replacement, and rivaroxaban was superior to enoxaparin in prevention of VTE with no increase in bleeding complications. Phase III studies with apixaban, another oral Xa inhibitor, are in progress. These agents are also being evaluated in large studies for prevention of stroke in atrial fibrillation and for VTE treatment.

Emergence of new oral antithrombotics: a critical appraisal of their clinical potential

In Western countries, venous thromboembolism (VTE) is a widespread and serious disorder, with hospital admission rates that appear to be increasing. Current anticoagulant therapies available for the prevention and treatment of VTE have several drawbacks that make them either difficult to manage effectively, due to a need for careful monitoring to control coagulation, or, in the case of parenterally administered agents, inconvenient for long-term use. To address some of these issues, new anticoagulants are in clinical development that can be orally administered and directly target specific factors in the coagulation cascade. This article reviews the rationale behind development of these novel agents and provides a critical appraisal of their clinical potential. In addition, the impact that the introduction of such agents into clinical practice would have is discussed from the patient perspective.

Amino(methyl) pyrrolidines as novel scaffolds for factor Xa inhibitors

The design and synthesis of a novel class of amino(methyl) pyrrolidine-based sulfonamides as potent and selective FXa inhibitors is reported. The amino(methyl) pyrrolidine scaffolds were designed based on the proposed bioisosterism to the piperazine core in known FXa inhibitors. The SAR study led to compound 15 as the most potent FXa inhibitor in this series, with an IC(50) of 5.5 nM and PT EC(2x) of 1.7 microM. The proposed binding models show that the pyrrolidine cores are in van der Waals contact with the enzyme surface, and the flexibility of amino(methyl) pyrrolidines allows the two nitrogen atoms to anchor both the P1 and P4 groups to fit similarly in the S1 and S4 pockets.

New oral Xa and IIa inhibitors: updates on clinical trial results

Heparins and VKAs have been the cornerstones of anticoagulation therapy for several decades and these agents have become most important drugs in the primary and secondary prevention of venous and arterial thromboembolic disease. Although effective, their use has been hampered by numerous limitations. In the search for new agents matching the 'ideal' anticoagulant profile, a number of different steps in the coagulation cascade have been targeted, including direct thrombin inhibition, and direct inhibition of Factor Xa. There are currently a host of promising new agents at various stages of development and clinical evaluation. With potential benefits including predictable efficacy, rapid onset of action, ability to bind clot-bound coagulation factors and no requirement for therapeutic monitoring, these new agents are set to improve the management of thromboembolic disorders.

Discovery of 1-(4-methoxyphenyl)-7-oxo-6-(4-(2-oxopiperidin-1-yl)phenyl)-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-c]pyridine-3-carboxamide (apixaban, BMS-562247), a highly potent, selective, efficacious, and orally bioavailable inhibitor of blood coagulation factor Xa

Efforts to identify a suitable follow-on compound to razaxaban (compound 4) focused on modification of the carboxamido linker to eliminate potential in vivo hydrolysis to a primary aniline. Cyclization of the carboxamido linker to the novel bicyclic tetrahydropyrazolopyridinone scaffold retained the potent fXa binding activity. Exceptional potency of the series prompted an investigation of the neutral P1 moieties that resulted in the identification of the p-methoxyphenyl P1, which retained factor Xa binding affinity and good oral bioavailability. Further optimization of the C-3 pyrazole position and replacement of the terminal P4 ring with a neutral heterocycle culminated in the discovery of 1-(4-methoxyphenyl)-7-oxo-6-(4-(2-oxopiperidin-1-yl)phenyl)-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-c]pyridine-3-carboxamide (apixaban, compound 40). Compound 40 exhibits a high degree of fXa potency, selectivity, and efficacy and has an improved pharmacokinetic profile relative to 4.

Effects of the oral, direct factor xa inhibitor rivaroxaban on platelet-induced thrombin generation and prothrombinase activity

Rivaroxaban (BAY 59-7939) is an oral, direct factor Xa inhibitor in advanced development. This study was undertaken to investigate its effects on thrombin generation. In this placebo-controlled, randomized, crossover study, 12 healthy subjects received rivaroxaban (single 5- or 30-mg dose) or placebo. Thrombin generation was investigated by measuring the endogenous thrombin potential and prothrombinase-induced clotting time. Maximal effect of rivaroxaban was observed 2 hours after drug administration: prothrombinase-induced clotting time was prolonged 1.8 and 2.3 times baseline after rivaroxaban 5 and 30 mg, respectively. Collagen-induced endogenous thrombin potential was reduced by approximately 80% and approximately 90% compared with baseline after rivaroxaban 5 and 30 mg, respectively, and tissue factor-induced endogenous thrombin potential was reduced by approximately 40% (5 mg) and approximately 65% (30 mg), respectively. Thrombin generation remained inhibited for 24 hours. There was a close correlation between plasma concentration of rivaroxaban and prolongation of prothrombinase-induced clotting time and reduction in endogenous thrombin potential. Rivaroxaban strongly inhibits platelet-induced thrombin generation, after activation of either platelets or the coagulation pathway, even in the presence of minimal factor Xa inhibition in plasma.

Anithrombotic prevention in vascular disease: bases for a new strategy in antithrombotic therapy

A tendency toward bleeding often undercuts the beneficial preventive effect of higher doses of a single antithrombotic drug or combined antithrombotic therapy. Although high doses of antithrombotic drugs may be necessary for optimal prevention, such therapy can also elicit more frequent bleeding. Although major bleeding could be a reversible event is likely to lead clinicians to discontinue antithrombotic therapy which in turn could increase the risk of myocardial infarction, stroke, and cardiovascular death. Thus, to prevent thrombotic events without frequent bleeding complications, the preferred approach might be to use anti-inflammatory drugs in addition to the first-line antithrombotic drugs to reduce inflammation and thrombin formation in atheroma. Although some preliminary data have been already published, to confirm the potential benefit of anti-inflammatory drugs in acute coronary syndromes large prospective double-bind randomized trials are necessary.

Enantiopure five-membered cyclicdiamine derivatives as potent and selective inhibitors of factor Xa. Improving in vitro metabolic stability via core modifications

We previously reported a series of enantiopure cis-(1R,2S)-cyclopentyldiamine derivatives as potent and selective inhibitors of Factor Xa (FXa). Herein, we describe our approach to improve the metabolic stability of this series via core modifications. Multiple resulting series of compounds demonstrated similarly high FXa potency and improved metabolic stability in human liver microsomes compared with the cyclopentyldiamide 1. (3R,4S)-Pyrrolidinyldiamide 31 was the best overall compound with human FXa K(i) of 0.50 nM, PT EC(2x) of 2.1 microM in human plasma, bioavailability of 25% and t(1/2)of 2.7h in dogs. Further biochemical characterization of compound 31 is also presented.

Treatment of Proximal Deep-Vein Thrombosis With the Oral Direct Factor Xa Inhibitor Rivaroxaban (BAY 59-7939)

Background— An effective and safe oral anticoagulant that needs no monitoring for dose adjustment is urgently needed for the treatment of diseases that require long-term anticoagulation. Rivaroxaban (BAY 59-7939) is an oral direct factor Xa inhibitor currently under clinical development.

Methods and Results— This randomized, parallel-group phase II trial in patients with proximal deep-vein thrombosis explored the efficacy and safety of rivaroxaban 10, 20, or 30 mg BID or 40 mg once daily compared with enoxaparin 1 mg/kg BID followed by vitamin K antagonist. Each treatment was administered for 12 weeks. The primary efficacy end point was an improvement in thrombotic burden at day 21 (assessed by quantitative compression ultrasonography; ≥4-point improvement in thrombus score) without recurrent symptomatic venous thromboembolism or venous thromboembolism-related death. The primary safety end point was major bleeding during 12 weeks of treatment. Outcomes were adjudicated centrally without knowledge of treatment allocation. The primary efficacy end point was achieved in 53 (53.0%) of 100, 58 (59.2%) of 98, 62 (56.9%) of 109, and 49 (43.8%) of 112 patients receiving rivaroxaban 10, 20, or 30 mg BID or 40 mg once daily, respectively, compared with 50 (45.9%) of 109 patients treated with enoxaparin/vitamin K antagonist. There was no significant trend in the dose-response relationship between rivaroxaban BID and the primary efficacy end point ( P =0.67). Major bleeding was observed in 1.7%, 1.7%, 3.3%, and 1.7% of patients receiving rivaroxaban 10, 20, or 30 mg BID or 40 mg once daily, respectively. There were no major bleeding events with enoxaparin/vitamin K antagonist.

Conclusions— Results of this proof-of-concept and dose-finding study support phase III evaluation of the orally active direct factor Xa inhibitor rivaroxaban, because efficacy and safety were apparent in the treatment of proximal deep-vein thrombosis across a 3-fold range of fixed daily dosing.