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

The long path to NOAC

The discovery of anticoagulant drugs occurred at a time when the process of blood coagulation only had been roughly described and their mode of action was unknown. Nevertheless, heparin – which was discovered 100 years ago – and warfarin – which was developed in the 1920s – had taken off on a triumphal course which is unique in medical history. The synthesis of anticoagulants with targeted mode of action was only achieved at the end of the last century, e. g. the inhibitor of factor Xa fondaparinux or the recombinant production of the direct thrombin inhibitor hirudin, closely followed by the synthesis of the direct oral inhibitors of factor Xa and thrombin. These compounds had been clinically developed in the early 21st century and meanwhile, they have become available for several indications. Dabigatran is the only thrombin inhibitor and rivaroxaban, apixaban and edoxaban are the three factor Xa inhibitors which entered the market and have started replacing the conventional anticoagulants for treatment of venous thromboembolic complications and for prevention of stroke in patients with atrial fibrillation. They have several characteristics in common such as a reproducible bioavailability, much shorter halflives than vitamin K antagonists, low interaction with other drugs, fixed dosing regimens without the necessity for routine coagulation controls and a better risk-/benefit profile than conventional anticoagulants. However, there are differences between the various compounds with regard to metabolism, renal elimination and the various dosing regimens which definitely need to be considered when prescribed to various patient populations.

Rivaroxaban for thromboprophylaxis after total hip or knee arthroplasty: a meta-analysis with trial sequential analysis of randomized controlled trials

Venous thromboembolism (VTE) is the most widespread severe complication after total hip arthroplasty (THA) and total knee arthroplasty (TKA). We conducted this meta-analysis to further validate the benefits and harms of rivaroxaban use for thromboprophylaxis after THA or TKA. We thoroughly searched PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials. Trial sequential analysis (TSA) was applied to test the robustness of our findings and to obtain a more conservative estimation. Of 316 articles screened, nine studies were included. Compared with enoxaparin, rivaroxaban significantly reduced symptomatic VTE (P = 0.0001) and symptomatic deep vein thrombosis (DVT; P = 0.0001) but not symptomatic pulmonary embolism (P = 0.57). Furthermore, rivaroxaban was not associated with an increase in all-cause mortality, clinically relevant non-major bleeding and postoperative wound infection. However, the findings were accompanied by an increase in major bleeding (P = 0.02). The TSA demonstrated that the cumulative z-curve crossed the traditional boundary but not the trial sequential monitoring boundary and did not reach the required information size for major bleeding. Rivaroxaban was more beneficial than enoxaparin for preventing symptomatic DVT but increased the risk of major bleeding. According to the TSA results, more evidence is needed to verify the risk of major bleeding with rivaroxaban.

Risk of Gastrointestinal Bleeding with Rivaroxaban: A Comparative Study with Warfarin

Introduction. The risk of gastrointestinal (GI) bleeding with rivaroxaban has not been studied extensively. The aim of our study was to assess this risk in comparison to warfarin. Methods. We examined the medical records for patients who were started on rivaroxaban or warfarin from April 2011 to April 2013. Results. We identified 300 patients (147 on rivaroxaban versus 153 on warfarin). GI bleeding occurred in 4.8% patients with rivaroxaban when compared to 9.8% patients in warfarin group (p = 0.094). GI bleeding occurred in 8% with therapeutic doses of rivaroxaban (>10 mg/d) compared to 9.8% with warfarin (p = 0.65). Multivariate analysis showed that patients who were on rivaroxaban for ≤40 days had a higher incidence of GI bleeding than those who were on it for >40 days (OR = 2.8, p = 0.023). Concomitant use of dual antiplatelet agents was associated with increased risk of GI bleeding in the rivaroxaban group (OR = 7.4, p = 0.0378). Prior GI bleeding was also a risk factor for GI bleeding in rivaroxaban group (OR = 15.5). Conclusion. The incidence of GI bleeding was similar between rivaroxaban and warfarin. The risk factors for GI bleeding with rivaroxaban were the first 40 days of taking the drug, concomitant dual antiplatelet agents, and prior GI bleeding.

Evidence-Based Development and Rationale for Once-Daily Rivaroxaban Dosing Regimens Across Multiple Indications

Background:

Rivaroxaban, a direct factor Xa inhibitor, has been developed to meet clinical needs in a broad range of indications in adults: prevention of venous thromboembolism after elective hip or knee replacement surgery, treatment and secondary prevention of venous thromboembolism, prevention of stroke and systemic embolism in patients with nonvalvular atrial fibrillation having one or more risk factors, and in Europe, prevention of atherothrombotic events after an acute coronary syndrome in patients with elevated cardiac biomarkers. However, the precise dose and regimen vary with the indication, leading to this effort to provide clarity concerning the appropriate use of rivaroxaban. This article reviews the clinical development program for rivaroxaban and summarizes the evidence for each approved, indication-specific dose regimen.

Results:

Although initially investigated for twice-daily dosing, early observations, including the finding that the pharmacodynamic effects of rivaroxaban last longer than the elimination half-life, suggested that once-daily dosing might be attainable and effective. These observations were evaluated within the extensive phase II program, which, together with pharmacology studies, provides the evidence underpinning the selection of once-daily regimens for most, but not all, of the approved clinical indications for rivaroxaban.

Conclusion:

The evidence for each dosing regimen demonstrates that although pharmacology studies are of paramount importance, dose regimens must be subjected to careful empirical validation. Once-daily dosing was shown to be clinically appropriate for most rivaroxaban indications. Furthermore, a “one size fits all” approach to dosing frequency is unlikely to result in a regimen that yields optimal patient outcomes across different indications.

Oral direct factor Xa inhibitor versus enoxaparin for thromboprophylaxis after hip or knee arthroplasty: Systemic review, traditional meta-analysis, dose-response meta-analysis and network meta-analysis

OBJECTIVES

To analyze the efficacy and safety of direct factor Xa inhibitors for thromboprophylaxis after total hip or knee replacement. To delineate the dose response effect of direct factor Xa inhibitors. To compare the efficacy between any two direct factor Xa inhibitors.

DESIGN

Systemic review, traditional meta-analysis, dose-response meta-analysis and network meta-analysis.

DATA SOURCE

PubMed, EMBASE and Cochrane Library.

STUDY SELECTION

Randomized controlled trials of rivaroxaban, apixaban, betrixaban, darexaban and edoxaban were compared with enoxaparin for thromboprophylaxis after total hip or knee replacement. Two reviewers independently checked the quality of RCTs. Another two investigators independently extracted data. The primary efficacy outcomes (composite of deep venous thrombosis, non-fatal pulmonary embolism and death of all causes) and the primary bleeding outcomes (major bleeding and non-major but clinically relevant bleeding) were summarized for meta-analysis. Stata software was used for traditional meta-analysis and dose-response meta-analysis, and Winbugs software was used for network meta-analysis.

RESULTS

Twenty trials with 38,507 subjects in the intention-to-treat population were included. Compared with enoxaparin, the risk of total venous thromboembolism was lower with rivaroxaban (relative risk 0.70, 95% confidence interval 0.60 to 0.81), apixaban (0.62, 0.47 to 0.81), and edoxaban (0.62, 0.39 to 0.97) and similar to darexaban (0.96, 0.84 to 1.11) and betrixaban (1.28, 0.97 to 1.68). Compared with enoxaparin, the risk of major or clinically relevant non-major bleeding was higher with rivaroxaban (1.52, 1.14 to 2.02), lower with betrixaban (0.34, 0.14 to 0.84) and similar to apixaban (0.88, 0.73 to 1.05), darexaban (0.85, 0.66 to 1.09) or edoxaban (1.30, 0.72 to 2.33). The risk of major and clinically relevant non-major bleeding of rivaroxaban had a linear relationship with its treatment doses; the risk of total venous thromboembolism of betrixaban and darexaban had linear relationships with their respective treatment doses. There was no linear nor non-liner relationships between the effect of apixaban and its treatment dose. The ranking of total venous thromboembolism risk from low to high was: rivaroxaban, apixaban, edoxaban, enoxaparin, darexaban, and betrixaban. The ranking of major and clinically relevant non-major bleeding from low to high was: betrixaban, enoxaparin, darexaban, edoxaban, apixaban, and rivaroxaban.

CONCLUSIONS

Direct oral factor Xa inhibitors are more effective to prevent venous thromboembolism after total hip or knee replacement. Their anticoagulant effect was not necessarily compromised with a higher bleeding risk. Rivaroxaban, apixaban and edoxaban showed a better anticoagulant effect, as compared with enoxaparin. Rivaroxaban had a higher bleeding rate, while apixaban and edoxaban did not show significantly higher bleeding risks.

Timing the First Postoperative Dose of Anticoagulants: Lessons Learned From Clinical Trials

The non-vitamin K antagonist oral anticoagulants (NOACs), rivaroxaban, apixaban, and dabigatran, have been shown in phase 3 trials to be effective for thromboprophylaxis in patients undergoing elective hip or knee arthroplasty. Results from prior studies suggested that the safety of anticoagulants in such patients was improved if the first postoperative dose was delayed for at least 6 h after surgery. The timing of the first postoperative dose of the NOACs tested in phase 2 studies differed among the three NOACs: dabigatran was started 1 to 4 h postoperatively, whereas rivaroxaban and apixaban were started at least 6 and 12 h, postoperatively, respectively. Our review of the timing of initiation of thromboprophylaxis in randomized trials provides three related lessons. First, clinical trials performed before the NOACs were evaluated demonstrated that delaying the first dose of prophylactic anticoagulation until after major surgery is effective and safe. Second, the optimal timing of the first dose of prophylactic anticoagulation after surgery depends on the dose that is selected. Third, the results of the phase 3 trials with NOACs for thromboprophylaxis support the concept that acceptable efficacy and safety can be achieved when the appropriate first postoperative dose of anticoagulant is delayed for at least 6 h after surgery.

Dosing of rivaroxaban by indication: getting the right dose for the patient

INTRODUCTION

Vitamin K antagonists were the only oral anticoagulants available for several decades, but they require frequent coagulation monitoring and dose adjustment. The direct oral anticoagulants rivaroxaban , dabigatran, apixaban, and, most recently, edoxaban have been approved for the management of specific thromboembolic indications.

AREAS COVERED

This review will provide a brief overview of the cell-based coagulation model, the main determinants of arterial and venous thrombosis, and the pharmacological rationale and clinical evidence for the different dosing regimens of rivaroxaban. Published articles indexed on PubMed and Medline covering arterial and venous thrombi pathophysiology, pharmacokinetics, and pharmacodynamics of rivaroxaban, and Phase II and Phase III clinical studies with rivaroxaban as well as real-world evidence were analyzed.

EXPERT OPINION

Education on pharmacokinetic/pharmacodynamic characteristics, as well as how to manage adverse events, is needed to increase physician knowledge and confidence in using direct oral anticoagulants, as specifically discussed for rivaroxaban in this article. The continued uptake of direct oral anticoagulants in clinical practice depends on understanding of the clinical evidence and reassurance provided by emerging real-world data.

Risk of gastrointestinal bleeding with dabigatran: a head-to-head comparative study with rivaroxaban

INTRODUCTION

The risk of gastrointestinal (GI) bleeding of dabigatran and rivaroxaban is relatively unexplored. The aim of our study was to compare this risk in both drugs.

METHODS

We examined the medical records of patients on either dabigatran or rivaroxaban from October 2010 to April 2013 in two hospitals.

RESULTS

A total of 374 patients (147 rivaroxaban vs. 227 dabigatran) were identified. GI bleeding occurred in 5.3% in the dabigatran when compared to 4.8% in the rivaroxaban group (p = 0.8215). Multivariate analysis showed that the odds of GI bleeding while on dabigatran for ≤40 days when compared to ≥40 days was 8.3 (p < 0.0001). In the rivaroxaban group, patients who were on the drug for ≤40 days had a higher incidence of bleeding when compared to those >40 days (OR = 2.8, p = 0.023). Concomitant use of antiplatelets (single or dual) or non-steroidal anti-inflammatory drugs was not associated with increased bleeding in the dabigatran group; however, the use of dual antiplatelet agents with rivaroxaban was associated with an increased risk of GI bleeding (OR = 7.4, p = 0.0378). Prior GI bleeding had a higher risk of bleeding in the rivaroxaban group (OR = 15.5, p = 0.0002).

CONCLUSION

Dabigatran was not associated with a higher incidence of GI bleeding. Both drugs had a higher bleeding risk in the first 40 days.

Rivaroxaban for the treatment and prevention of thromboembolic disease

Objectives

A number of direct oral anticoagulants are now available and offer alternative strategies for anticoagulation therapy. Rivaroxaban, a direct oral Factor Xa inhibitor, is approved for use across several thromboembolic indications. This article aims to provide an overview of the key pharmacological characteristics of rivaroxaban and the rationale and evidence for the use of different dose regimens across its licenced indications, and offer practical guidance to healthcare professionals on responsible use. References were sourced via PubMed searches using the search string (rivaroxaban AND (pharmacokinetics OR pharmacodynamics OR (clinical studies) OR (drug interaction)) NOT review NOT (children OR pediatrics OR paediatrics OR adolescent)).

Key findings

Rivaroxaban exhibits predictable pharmacokinetics and pharmacodynamics, and thus does not require routine coagulation monitoring, unlike vitamin K antagonists (e.g. warfarin). Rivaroxaban also has a lower potential for drug–drug and food–drug interactions compared with warfarin; however, co-administration with strong inhibitors of both cytochrome P450 3A4 and P-glycoprotein is not recommended. The data indicate that dose adjustment is not necessary for age, gender or body weight. The dosing regimens of rivaroxaban vary depending on the indication, and phase III studies have demonstrated a favourable benefit–risk profile of rivaroxaban compared with traditional standard of care.

Summary

Rivaroxaban may offer an anticoagulant option that could simplify and improve the management of patients with thromboembolic disorders.

Use of Thromboelastography (TEG) for Detection of New Oral Anticoagulants

CONTEXT

The clinical introduction of new oral anticoagulants (NOACs) has stimulated the development of tests to quantify the effects of these drugs and manage complications associated with their use. Until recently, the only treatment choices for the prevention of venous thromboembolism in orthopedic surgical patients, as well as for stroke and systemic embolism in patients with atrial fibrillation, were vitamin K antagonists, antiplatelet drugs, and unfractionated and low-molecular-weight heparins. With the approval of NOACs, treatment options and consequent diagnostic challenges have expanded.

OBJECTIVE

To study the utility of thromboelastography (TEG) in monitoring and differentiating between 2 currently approved classes of NOACs, direct thrombin inhibitors (dabigatran) and factor Xa inhibitors (rivaroxaban and apixaban).

DESIGN

Blood samples from healthy volunteers were spiked with each NOAC in both the presence and absence of ecarin, and the effects on TEG were evaluated.

RESULTS

Both the kaolin test reaction time (R time) and the time to maximum rate of thrombus generation were prolonged versus control samples and demonstrated a dose response for apixaban (R time within the normal range) and dabigatran. The RapidTEG activated clotting time test allowed the creation of a dose-response curve for all 3 NOACs. In the presence of anti-Xa inhibitors, the ecarin test promoted significant shortening of kaolin R times to the hypercoagulable range, while in the presence of the direct thrombin inhibitor only small and dose-proportional R time shortening was observed.

CONCLUSIONS

The RapidTEG activated clotting time test and the kaolin test appear to be capable of detecting and monitoring NOACs. The ecarin test may be used to differentiate between Xa inhibitors and direct thrombin inhibitors. Therefore, TEG may be a valuable tool to investigate hemostasis and the effectiveness of reversal strategies for patients receiving NOACs.

Venous thromboembolism prophylaxis after total joint arthroplasty

Venous thromboembolism (VTE) prophylaxis after total joint arthroplasty is considered best practice. However, over the past 5 years, there has been considerable debate about the ideal prophylactic regimen or modality. The American Academy of Orthopaedic Surgeons and the American College of Chest Physicians published their most recent clinical practice guidelines about VTE prophylaxis in 2011 and 2012, respectively. In addition, the Surgical Care Improvement Project published their latest recommendations in 2014. In this review, commonly used VTE prophylaxis options and the latest clinical guidelines will be discussed.

A clinical and pharmacologic assessment of once-daily versus twice-daily dosing for rivaroxaban

Altering doses and regimens of a drug has consequences for the drug's pharmacokinetic and pharmacodynamic profile. Based on a half-life of 5-13 h, it is expected that the Factor Xa inhibitor rivaroxaban would be best suited to a twice-daily rather than a once-daily dose regimen. However, although rivaroxaban is used as a twice-daily regimen for the initial treatment of venous thromboembolism (VTE) and secondary prevention after acute coronary syndromes, the approved dosing is once-daily for prevention of VTE after orthopaedic surgery, long-term secondary prevention of VTE and stroke prevention in patients with non-valvular atrial fibrillation. Rivaroxaban dosing was based on the evaluation of the efficacy and safety of several rivaroxaban doses and regimens in phase II trials. A clear overall advantage of twice-daily dosing compared with once-daily dosing was not documented for indications for which once-daily dosing was subsequently selected. Once-daily dosing was therefore selected for these indications because it is expected to be associated with better compliance than twice-daily dosing, and potentially, with improved outcomes. These studies and data obtained with another Factor Xa inhibitor, edoxaban, in addition to previous experience with low molecular weight heparins, indicate that the clinical impact of once-daily versus twice-daily doses on outcome in terms of efficacy and safety cannot be reliably predicted from pharmacology data, e.g. elimination half-life, obtained during pre-clinical and early phase I clinical studies but rather should be ascertained empirically in phase II and III clinical trials.

A randomized direct comparison of the pharmacokinetics and pharmacodynamics of apixaban and rivaroxaban

Background

Currently, there are no direct comparisons of apixaban and rivaroxaban, two new oral direct factor Xa inhibitors approved for management of thromboembolic disorders.

Objective

Compare the pharmacokinetics and anti-factor Xa activity (AXA) of apixaban and rivaroxaban.

Methods

In this randomized, open-label, two-period, two-treatment crossover study, healthy subjects (N=14) received apixaban 2.5 mg twice daily (BID) and rivaroxaban 10 mg once daily (QD) for 4 days with a ≥4.5-day washout. Plasma samples were obtained for pharmacokinetic and AXA assessments; parameters were calculated using noncompartmental methods.

Results

Median time-to-maximum concentration was 2 hours for both compounds, and the mean half-life was 8.7 and 7.9 hours for apixaban and rivaroxaban, respectively. Daily exposure, the area under the curve (AUC_(0–24)), appeared similar for rivaroxaban (1,094 ng · h/mL) and apixaban (935 ng · h/mL), whereas mean peak-to-trough plasma concentration ratio was 3.6-fold greater for rivaroxaban (16.9) than apixaban (4.7). Coefficient of variation for exposure parameters (AUC_0–24, C_max, C_min) was 20%–24% for apixaban versus 29%–46% for rivaroxaban. Peak AXA, AXA AUC_(0–24), and AXA fluctuation were ~2.5-, 1.3-, and 3.5-fold higher for rivaroxaban than apixaban, respectively. Trough concentrations and AXA were lower for rivaroxaban (10 ng/mL and 0.17 IU/mL vs 17 ng/mL and 0.24 IU/mL for apixaban, respectively). Rivaroxaban exhibited a steeper concentration–AXA response (slope: 0.0172 IU/ng vs 0.0134 IU/ng for apixaban, P<0.0001).

Conclusion

Apixaban 2.5 mg BID demonstrated less intersubject variability in exposure, lower AXA AUC, and higher trough and smaller peak-to-trough fluctuations in plasma concentration and AXA, suggesting more constant anticoagulation compared with rivaroxaban 10 mg QD. However, the clinical impact of these differences on the relative efficacy and safety of apixaban and rivaroxaban remains to be determined.

Rivaroxaban vs. low molecular weight heparin for the prevention of venous thromboembolism after hip or knee arthroplasty: a cohort study

BACKGROUND

Rivaroxaban is increasingly used to prevent venous thromboembolism after hip or knee arthroplasty. Studies evaluating the effectiveness of rivaroxaban compared to low molecular weight heparin after orthopedic surgery in routine practice are scarce.

PATIENTS AND METHODS

We conducted a retrospective cohort study in 121 hospitals in Ontario, Canada, between 2002 and 2012. We included patients aged 66 years or older (median age 73 years) who received an outpatient prescription for subcutaneous low molecular weight heparin (n = 11 471) or oral rivaroxaban (n = 12 850) on hospital discharge after a total knee or hip arthroplasty. The two coprimary outcomes assessed within 30 days of the prescription date were emergency department visit or hospitalization with venous thromboembolism (either deep vein thrombosis or pulmonary embolism; primary efficacy outcome) and a hospitalization with non-traumatic major hemorrhage (primary safety outcome).

RESULTS

Rivaroxaban use increased over the study period. Compared to low molecular weight heparin, rivaroxaban was associated with a lower 30-day risk of hospitalization with venous thromboembolism (0.47% vs. 0.81%; relative risk 0.58; 95% confidence interval 0.42-0.81; P = 0.001) with no significant difference in hospitalizations for major bleeding (0.18% vs. 0.20%; relative risk 0.89; 95% confidence interval 0.50-1.59; P = 0.700).

CONCLUSIONS

In routine practice, anticoagulant prophylaxis with rivaroxaban compared to low molecular weight heparin after hospital discharge from total hip or knee arthroplasty is associated with a lower risk of symptomatic venous thromboembolism with no difference in the risk of bleeding.

Clinical use of rivaroxaban: pharmacokinetic and pharmacodynamic rationale for dosing regimens in different indications

Target-specific oral anticoagulants have become increasingly available as alternatives to traditional agents for the management of a number of thromboembolic disorders. To date, the direct Factor Xa inhibitor rivaroxaban is the most widely approved of the new agents. The dosing of rivaroxaban varies and adheres to specific schedules in each of the clinical settings in which it has been investigated. These regimens were devised based on the results of phase II dose-finding studies and/or pharmacokinetic modeling, and were demonstrated to be successful in randomized, phase III studies. In most cases, the pharmacodynamic profile of rivaroxaban permits once-daily dosing. A once-daily dose is indicated for the prevention of venous thromboembolism (VTE) in patients undergoing hip or knee replacement surgery, the long-term prevention of stroke in patients with non-valvular atrial fibrillation, and the long-term secondary prevention of recurrent VTE. Twice-daily dosing is required in the acute phase of treatment in patients with VTE and in the combination of rivaroxaban with standard single or dual antiplatelet therapy for secondary prevention after acute coronary syndrome events. This article reviews the empirical and clinical rationale supporting the dose regimens of rivaroxaban in each clinical setting.

New oral pharmacotherapeutic agents for venous thromboprophylaxis after total hip arthroplasty

Patients undergoing total hip arthroplasty (THA) are at high risk for developing venous thromboembolism and, therefore, require short term prophylaxis with antithrombotic agents. Recently, target specific oral anticoagulants (TSOA) including the direct thrombin inhibitor, dabigatran, and the factor Xa inhibitors rivaroxaban, apixaban, and edoxaban have been approved for THA thrombopropylaxis in various countries. The TSOAs provide a rapid acting, oral alternative to parenteral agents including low-molecular weight heparins (LMWH) and fondaparinux; and compared to warfarin, they do not require routine laboratory monitoring and possess much fewer drug-drug interactions. Based on phase III clinical studies, TSOAs have established themselves as an effective and safe option for thromboprophylaxis after THA compared to LMWH, particularly enoxaparin, but require additional evaluation in specific populations such as the renally impaired or elderly. The ability to monitor and reverse these TSOAs in the case of bleeding complications or suspected sub- or supra-therapeutic anticoagulation is of importance, but remains investigational. This review will focus on the drug-specific characteristics, efficacy, safety, and economic impact of the TSOAs for thromboprophylaxis following THA, as well as the aspects of therapeutic monitoring and anticoagulation reversal in the event of bleeding complications or a need for urgent reversal.

Simple and rapid assay for effect of the new oral anticoagulant (NOAC) rivaroxaban: preliminary results support further tests with all NOACs

Background

New oral anticoagulant (NOAC) drugs are known to influence the results of some routine hemostasis tests. Further data are needed to enable routine assessment of the effects of NOAC on clotting parameters in some special circumstances.

Methods

Following administration of rivaroxaban to patients, at the likely peak and trough activity times, we assessed the effects on prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), and clotting time using Russell’s viper venom, and in the presence of phospholipids and calcium reagent available as DVVreagent® and DVVconfirm®. The data were used to determine an adequate NOAC plasma level based on anticoagulant activities expressed as a ratio (patients/normal, R-C).

Results

DVVconfirm as R-C could be rapidly performed, and the results were reasonably sensitive for rivaroxaban and probably for other FX inhibitors. This assay is not influenced by lupus anticoagulant and heparin, does not require purified NOAC as control, and will measure whole-plasma clotting activity.

Conclusions

We propose a cut-off R-C value of 4.52 ± 0.33 for safety, but clinical studies are needed to establish whether this cut-off is useful for identifying patients at increased risk of hemorrhage or exhibiting low anticoagulation effect. It also seems possible that normal R-C could indicate an absence of anticoagulant activity when rivaroxaban is discontinued due to episodes of uncontrolled bleeding during anticoagulation or for emergency surgery.

New oral anticoagulants: are coagulation units still required?

Chronic antithrombotic therapy involves the use of anticoagulants, antiplatelets given either as monotherapy or in combination for the prevention of thrombotic complications. The most feared and sometimes fatal complication with this therapy is bleeding. It should be considered a "golden rule" that a drug or combination of drugs that maximizes efficiency (decreased thromboembolic risk) will probably be less safe (increased risk of bleeding), and this holds true either for single therapy or during combined therapy. The chances of bleeding indicated by risk tables can be useful but show only a snapshot, and the biological, social, environmental, and drug changes and therapeutic adherence also determine changes in the risk of thrombosis and bleeding. Bleeding is an eventuality that occurs in places of "locus minoris resistentiae," and the results of careful phase 3 studies thus cannot be completely predictive of outcomes when a medication is introduced on the pharmaceutical market. With the use of warfarin, the International Normalized Ratio (INR) that has been established to indicate adequately balanced therapy is between 2.0 and 3.0. With the new oral anticoagulants, the pharmaceutical companies emphasize that it is not necessary to monitor anticoagulant effects. In studies with different doses of new oral anticoagulants, however, incidence of clinically significant bleeding complications have been directly related to the doses. Therefore, therapeutic excesses can condition bleeding risk and therapeutic limitation can increase thrombotic risk, especially when short-acting drugs such as the new oral anticoagulants are used. Hence, it is imperative to establish an appropriate method for monitoring new oral anticoagulants, setting levels of safety and effectiveness through periodic dosage and monitoring of their anticoagulant effects. Therefore, we still recommend the use of anticoagulation units for monitoring during treatment with the new oral anticoagulants.

Anticoagulation for prosthetic valves

Implantation of prosthetic valve requires consideration for anticoagulation. The current guideline recommends warfarin on all mechanical valves. Dabigatran is the new generation anticoagulation medication which is taken orally and does not require frequent monitoring. This drug is approved for treatment for atrial fibrillation and venous thromboembolism, but the latest large trial showed that this drug increases adverse events when used for mechanical valve anticoagulation. On-X valve is the new generation mechanical valve which is considered to require less anticoagulation due to its flow dynamics. The latest study showed that lower anticoagulation level lowers the incidence of bleeding, while the risk of thromboembolism and thrombosis remained the same. Anticoagulation poses dilemma in cases such as pregnancy and major bleeding event. During pregnancy, warfarin can be continued throughout pregnancy and switched to heparin derivative during 6-12 weeks and >36 weeks of gestation. Warfarin can be safely started after 1-2 weeks of discontinuation following major bleeding episode.

An adaptive-design dose-ranging study of PD 0348292, an oral factor Xa inhibitor, for thromboprophylaxis after total knee replacement surgery

BACKGROUND

PD 0348292 is an oral, selective, direct and reversible factor Xa inhibitor. This was an adaptive dose-ranging study evaluating a 100-fold PD 0348292 dose range in subjects undergoing total knee replacement (TKR).

OBJECTIVE

To assess the efficacy and safety of a dose range of PD 0348292 relative to enoxaparin for the prevention of venous thromboembolism (VTE).

METHODS

Extensive dose-response modeling and trial simulations were used to select the PD 0348292 dose range for the Phase 2 study. Subjects were randomized to a blinded PD 0348292 dose (0.1 mg qd to 10 mg qd) or open-label enoxaparin (30 mg bid) for 6-14 days after TKR surgery. Efficacy was assessed by mandatory bilateral venography. Results were analyzed using a dose-response modeling approach.

RESULTS

Observed VTE frequency ranged from 1.4-37.1% across PD 0348292 doses and was 18.1% for enoxaparin. The PD 0348292 dose-response relationship for VTE was statistically significant (P < 0.0001). The dose of PD 0348292 equivalent to enoxaparin 30 mg bid for VTE prevention was estimated to be 1.16 mg (95% CI = 0.56 mg, 2.41 mg) qd. Total bleeding ranged from 4.9% to 13.8% across PD 0348292 doses and was 6.3% with enoxaparin. The dose-response relationship for total bleeding was not statistically significant (P = 0.2464). Overall, PD 0348292 and enoxaparin were well tolerated.

CONCLUSION

Characterization of the dose-response relationship for VTE and bleeding using an adaptive Phase 2 study design provided a strong quantitative basis for Phase 3 dose selection.

New oral therapies for the prevention and treatment of venous thromboembolism

PURPOSE

Data comparing traditional and novel anticoagulants are reviewed, and the potential use of new oral agents for the prevention and treatment of venous thromboembolism (VTE) is assessed.

SUMMARY

Practical challenges in using traditional anticoagulants are well established and have led to the search for new oral agents. Apixaban, rivaroxaban, and dabigatran etexilate are new oral anticoagulants that may offer simpler, more effective, and safer treatment and prevention of VTE, which may increase adherence to such therapy, improve outcomes, and decrease overall health care costs. Their immediate onset of anticoagulant effect, ease of oral administration, and lack of needed regular anticoagulation monitoring are of interest in the medical and pharmacy communities. However, in the treatment and prevention of VTE, more data will be needed to determine their ultimate place in therapy. This review is intended to provide pharmacists with an objective overview of practical considerations that can help them understand the clinical data to facilitate their selection of anticoagulants.

CONCLUSION

Apixaban, rivaroxaban, and dabigatran etexilate are new oral agents for the prevention and treatment of VTE.

The new oral anticoagulants in atrial fibrillation: once daily or twice daily?

The new anticoagulants (NOACs) tested for prevention or treatment of venous thromboembolism (VTE), stroke prevention in atrial fibrillation (AF), and acute coronary syndromes (ACS) differ in bioavailability, metabolism, route of excretion and interaction with other drugs, but have remarkably similar pharmacokinetics, with very similar half lives. However the choice of dosing regimens in different clinical conditions has been different for the various NOACs, and has been established on the basis of widely different considerations, including the clinical setting (venous versus arterial thrombosis), the indications (prophylaxis versus treatment), the likelihood of concomitant antiplatelet drugs, and marketing opportunities; these latter were based on the knowledge that patients' compliance is generally better with once daily than with twice daily dosing. Current prevailing wisdom is that peak plasma drug concentrations are important determinants of bleeding: since a fractioning of the total daily dose into a twice daily regimen reduces peak plasma drug concentrations compared with once daily dosing, this should maximize safety. However, recent pharmacokinetic analyses of a phase II study with edoxaban in AF found that bleeding, with the same daily dosing, was less frequent with once daily dosing than with twice daily dosing, and correlated - better than other pharmacokinetic parameters - through drug concentrations. Higher rates of bleeding have been also reported with the twice daily versus once daily dosing of darexaban in a phase II study in ACS. These results may lead to a rethinking on the pathophysiology of bleeding in the setting of anticoagulation.

New oral anticoagulants increase risk for gastrointestinal bleeding: a systematic review and meta-analysis

BACKGROUND & AIMS

A new generation of oral anticoagulants (nOAC), which includes thrombin and factor Xa inhibitors, has been shown to be effective, but little is known about whether these drugs increase patients' risk for gastrointestinal bleeding (GIB). Patients who require OAC therapy frequently have significant comorbidities and may also take aspirin and/or thienopyridines. We performed a systematic review and meta-analysis of the risk of GIB and clinically relevant bleeding in patients taking nOAC.

METHODS

We queried MEDLINE, EMbase, and the Cochrane library (through July 2012) without language restrictions. We analyzed data from 43 randomized controlled trials (151,578 patients) that compared nOAC (regardless of indication) with standard care for risk of bleeding (19 trials on GIB). Odds ratios (ORs) were estimated using a random-effects model. Heterogeneity was assessed with the Cochran Q test and the Higgins I(2) test.

RESULTS

The overall OR for GIB among patients taking nOAC was 1.45 (95% confidence interval [CI], 1.07-1.97), but there was substantial heterogeneity among studies (I2, 61%). Subgroup analyses showed that the OR for atrial fibrillation was 1.21 (95% CI, 0.91-1.61), for thromboprophylaxis after orthopedic surgery the OR was 0.78 (95% CI, 0.31-1.96), for treatment of venous thrombosis the OR was 1.59 (95% CI, 1.03-2.44), and for acute coronary syndrome the OR was 5.21 (95% CI, 2.58-10.53). Among the drugs studied, the OR for apixaban was 1.23 (95% CI, 0.56-2.73), the OR for dabigatran was 1.58 (95% CI, 1.29-1.93), the OR for edoxaban was 0.31 (95% CI, 0.01-7.69), and the OR for rivaroxaban was 1.48 (95% CI, 1.21-1.82). The overall OR for clinically relevant bleeding in patients taking nOAC was 1.16 (95% CI, 1.00-1.34), with similar trends among subgroups.

CONCLUSIONS

Studies on treatment of venous thrombosis or acute coronary syndrome have shown that patients treated with nOAC have an increased risk of GIB, compared with those who receive standard care. Better reporting of GIB events in future trials could allow stratification of patients for therapy with gastroprotective agents.

Rivaroxaban and other novel oral anticoagulants: pharmacokinetics in healthy subjects, specific patient populations and relevance of coagulation monitoring

Unlike traditional anticoagulants, the more recently developed agents rivaroxaban, dabigatran and apixaban target specific factors in the coagulation cascade to attenuate thrombosis. Rivaroxaban and apixaban directly inhibit Factor Xa, whereas dabigatran directly inhibits thrombin. All three drugs exhibit predictable pharmacokinetic and pharmacodynamic characteristics that allow for fixed oral doses in a variety of settings. The population pharmacokinetics of rivaroxaban, and also dabigatran, have been evaluated in a series of models using patient data from phase II and III clinical studies. These models point towards a consistent pharmacokinetic and pharmacodynamic profile, even when extreme demographic factors are taken into account, meaning that doses rarely need to be adjusted. The exception is in certain patients with renal impairment, for whom pharmacokinetic modelling provided the rationale for reduced doses as part of some regimens. Although not routinely required, the ability to measure plasma concentrations of these agents could be advantageous in emergency situations, such as overdose. Specific pharmacokinetic and pharmacodynamic characteristics must be taken into account when selecting an appropriate assay for monitoring. The anti-Factor Xa chromogenic assays now available are likely to provide the most appropriate means of determining plasma concentrations of rivaroxaban and apixaban, and specific assays for dabigatran are in development.

NEW ANTICOAGULANTS AS THROMBOPROPHYLAXIS AFTER TOTAL HIP OR KNEE REPLACEMENT

Objectives: Due to a high risk of thromboembolism in patients undergoing major orthopedic surgery, it has become standard practice to give thromboprophylactic treatment. We assessed the relative efficacy and cost-effectiveness of two new oral anticoagulants, rivaroxaban and dabigatran, relative to subcutaneous enoxaparin for the prevention of thromboembolism after total hip replacement (THR) and total knee replacement surgery (TKR).

Methods: We conducted a systematic review of the literature to assess efficacy and safety, and evaluated quality of documentation using GRADE. Cost-effectiveness was assessed by developing a decision model. The model combined two modules; a decision tree for the short-term prophylaxis and a Markov model for the long-term complications and survival gain.

Results: For rivaroxaban compared with enoxaparin, we found statistically significant decreases in deep vein thrombosis, but also a trend toward increased risk of major bleeding. For mortality and pulmonary embolism there were no statistically significant differences between the treatments. We did not find statistically significant differences between dabigatran and enoxaparin for our efficacy and safety outcomes. Assuming a willingness to pay of EUR62,500 per QALY, rivaroxaban following THR had a probability of 38 percent, and enoxaparin following TKR had a probability of 34 percent of being cost-effective. Clinical efficacy had the greatest impact on decision uncertainty.

Conclusions: Dabigatran and rivaroxaban are comparable with enoxaparin following THR and TKR regarding the efficacy and safety outcomes. However, there is great uncertainty regarding which strategy is the most cost-effective. More research on clinical efficacy of rivaroxaban and dabigatran is likely to change our results.

Rivaroxaban: a novel oral anticoagulant for the prevention and treatment of several thrombosis-mediated conditions

The development of rivaroxaban (XARELTO®) is an important new medical advance in the field of oral anticoagulation. Thrombosis-mediated conditions constitute a major burden for patients, healthcare systems, and society. For more than 60 years, the prevention and treatment of these conditions have been dominated by oral vitamin K antagonists (such as warfarin) and the injectable heparins. Thrombosis can lead to several conditions, including deep vein thrombosis, pulmonary embolism, myocardial infarction, stroke, and/or death. Prevention and treatment of thrombosis with an effective, convenient-to-use oral anticoagulant with a favorable safety profile is critical, especially in an aging society in which the risk of thrombosis, and the potential for bleeding complications, is increasing. Rivaroxaban acts to prevent and treat thrombosis by potently inhibiting coagulation Factor Xa in the blood. Factor Xa converts prothrombin to thrombin, which initiates the formation of blood clots by converting fibrinogen to clot-forming fibrin and leads to platelet activation. After a large and novel clinical development program in over 75,000 patients to date, rivaroxaban has received approval for multiple indications in the United States, European Union, and other countries worldwide to prevent and treat several thrombosis-mediated conditions. This review will highlight some of the unique aspects of the rivaroxaban development program.

Investigation of Pharmacodynamic and Pharmacokinetic Interactions Between Rivaroxaban and Enoxaparin in Healthy Male Subjects

Rivaroxaban, an oral, direct factor Xa inhibitor, is currently used in clinical practice for the prevention and treatment of thromboembolic disorders. This single-center, three-way crossover study was designed to investigate the pharmacodynamic effects of rivaroxaban (10 mg) and enoxaparin (40 mg) alone and in combination as well as the influence of enoxaparin on the pharmacokinetics of rivaroxaban in healthy male subjects. When given alone, both drugs exhibited similar, rapid anti-factor Xa activity. Combined administration resulted in an increase of ∼50% in anti-factor Xa activity and a lesser increase in activated partial thromboplastin time, compared with either drug alone. Enoxaparin had no additional effect on prolongation of the prothrombin time induced by rivaroxaban and did not affect the pharmacokinetic parameters of rivaroxaban. The results showed that rivaroxaban (10 mg) and enoxaparin (40 mg) had a similar and rapid onset of action, as indicated by the similar anti-factor Xa activity-time curves, suggesting that both drugs have a similar duration of pharmacological activity at the factor X site. Co-administration of rivaroxaban and enoxaparin is associated with enhanced pharmacodynamic effects.

Model-based drug development: a rational approach to efficiently accelerate drug development

The pharmaceutical industry continues to face significant challenges. Very few compounds that enter development reach the marketplace, and the investment required for each success can surpass $1.8 billion. Despite attempts to improve efficiency and increase productivity, total investment continues to rise whereas the output of new medicines declines. With costs increasing exponentially through each development phase, it is failure in phase II and phase III that is most wasteful. In today's development paradigm, late-stage failure is principally a result of insufficient efficacy. This is manifested as either a failure to differentiate sufficiently from placebo (shown for both novel and precedented mechanisms) or a failure to demonstrate sufficient differentiation from existing compounds. Set in this context, this article will discuss the role model-based drug development (MBDD) approaches can and do play in accelerating and optimizing compound development strategies through a series of illustrative examples.

Safety, Tolerability, Pharmacodynamics, and Pharmacokinetics of Rivaroxaban-an Oral, Direct Factor Xa Inhibitor-Are Not Affected by Aspirin

Rivaroxaban (BAY 59-7939) is an oral, direct Factor Xa inhibitor in advanced clinical development for the prevention and treatment of thromboembolic disorders. This was a randomized, 2-way crossover study in healthy male subjects, with an aspirin run-in period, to examine whether aspirin influences the safety, tolerability, pharmacodynamics, and pharmacokinetics of rivaroxaban. All treatments were well tolerated; drug-related adverse events were mild and transient. Aspirin did not alter the effects of rivaroxaban on Factor Xa activity or clotting tests. Platelet aggregation and bleeding time were not affected by rivaroxaban, and rivaroxaban did not influence the effects of aspirin on these parameters to a clinically relevant extent. Aspirin did not affect the pharmacokinetics of rivaroxaban, including the fraction unbound. This study suggests that there is no clinically relevant interaction between rivaroxaban and aspirin and that the 2 drugs could be administered concomitantly at the doses used in this study.

Effect of Food, an Antacid, and the H2Antagonist Ranitidine on the Absorption of BAY 59-7939 (Rivaroxaban), an Oral, Direct Factor Xa Inhibitor, in Healthy Subjects

To investigate the influence of food and administration of an antacid (aluminum-magnesium hydroxide) or ranitidine on the absorption of BAY 59-7939 (rivaroxaban), 4 randomized studies were performed in healthy male subjects. In 2 food interaction studies, subjects received BAY 59-7939, either as two 5-mg tablets (fasted and fed), four 5-mg tablets (fasted), or one 20-mg tablet (fasted and fed). In 2 drug interaction studies, BAY 59-7939 (six 5-mg tablets) was given alone or with ranitidine (150 mg twice daily, preceded by a 3-day pretreatment phase) or antacid (10 mL). Plasma samples were obtained to assess pharmacokinetic and pharmacodynamic parameters of BAY 59-7939. In the presence of food, time to maximum concentration (t(max)) was delayed by 1.25 hours; maximum concentration (C(max)) and area under the curve (AUC) were increased, with reduced interindividual variability at higher doses of BAY 59-7939. Compared with baseline, BAY 59-7939 resulted in a relative increase in maximum prothrombin time (PT) prolongation of 44% (10 mg) and 53% (20 mg) in the fasted state, compared with 53% and 83% after food. Time to maximum PT prolongation was delayed by 0.5 to 1.5 hours after food, with no relevant influence of food type. No significant difference in C(max) and AUC was observed with coadministration of BAY 59-7939 and ranitidine or antacid.

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.

Characterisation of exposure versus response of edoxaban in patients undergoing total hip replacement surgery

Edoxaban is an oral direct factor Xa inhibitor approved for the prevention of venous thromboembolism (VTE) in Japan. The objectives of this analysis were to characterise the population pharmacokinetics (PK) of edoxaban and the relationships between edoxaban exposure and clinical outcomes in a phase IIb study of surgical patients following total hip replacement (THR). A total of 1,795 subjects from a phase IIb study, 10 phase I studies, and three phase IIa studies were included in the PK analysis. The exposure-response analysis included data from surgical patients assigned to edoxaban in the phase IIb study. Edoxaban disposition in healthy and post-surgical patients was well-described with a linear, two-compartment model. Creatinine clearance was significantly correlated with edoxaban clearance and the rate of oral absorption was affected by surgery. The probability of a post-operative VTE was significantly correlated with steady-state metrics of edoxaban exposure estimated for each subject by Bayesian post-hoc methods with age and gender being the significant and expected covariates. The incidence of bleeding was low in these studies and hence no exposure-response relationship could be identified. These analyses suggest that edoxaban has a predictable anticoagulant effect in this patient population leading to dose-proportional reduction in incidence of VTE with low incidence of bleeding.

Practical management of anticoagulants in family medicine after orthopedic surgery

In order to prevent postoperative venous thromboembolism, prophylactic anticoagulant therapy is routinely administered to hospitalized patients after total hip arthroplasty (THA) and total knee arthroplasty (TKA). However, after hospital discharge, anticoagulant therapy is primarily managed by a primary care physician (PCP). The agents traditionally used for this purpose are associated with certain limitations that affect anticoagulation management. The new, fixed-dose oral anticoagulants have predictable pharmacokinetic and pharmacodynamic profiles, no requirement for coagulation monitoring, and a low propensity for food and drug interactions. As a result, they have the potential to simplify and improve postoperative outcomes in patients who have undergone THA or TKA and allow for simpler management of anticoagulation in these patients. This article examines the clinical evidence for benefits of the new oral anticoagulants, discusses caveats regarding their appropriate use, and provides some guidance regarding bleeding management with these agents.

[Rivaroxaban in the prevention and treatment of thromboembolic disorders]

Rivaroxaban (Xarelto(®)) is a new anticoagulant for the prevention and treatment of thromboembolic disorders. Rivaroxaban inhibits coagulation factor Xa directly, has high oral bioavailability, shows low propensity for drug-drug interactions and requires no routine coagulation monitoring. In patients undergoing elective knee or hip replacement surgery rivaroxaban (10 mg/d) is highly effective to prevent venous thromboembolism. In patients with non-valvular atrial fibrillation rivaroxaban (20 mg/d) has been approved to prevent stroke or systemic embolism. The favourable benefit-risk profile of rivaroxaban in the treatment of deep vein thrombosis (DVT) was shown in EINSTEIN-DVT and led to its clinical approval (twice daily 15 mg for 3 weeks, followed by 20 mg/d). Based on ATLAS-ACS-TIMI-51 which has shown that rivaroxaban (2.5 mg twice daily) reduced thrombotic cardiovascular events and mortality in patients with a recent acute coronary syndrome, the approval of low dose rivaroxaban has been submitted for this indication. Taken together, rivaroxaban may become an effective alternative to standard anticoagulants in the prevention and treatment of thromboembolic disorders.

Dabigatran, rivaroxaban, or apixaban versus enoxaparin for thromboprophylaxis after total hip or knee replacement: systematic review, meta-analysis, and indirect treatment comparisons

OBJECTIVE

To analyse clinical outcomes with new oral anticoagulants for prophylaxis against venous thromboembolism after total hip or knee replacement.

DESIGN

Systematic review, meta-analysis, and indirect treatment comparisons.

DATA SOURCES

Medline and CENTRAL (up to April 2011), clinical trials registers, conference proceedings, and websites of regulatory agencies.

STUDY SELECTION

Randomised controlled trials of rivaroxaban, dabigatran, or apixaban compared with enoxaparin for prophylaxis against venous thromboembolism after total hip or knee replacement. Two investigators independently extracted data. Relative risks of symptomatic venous thromboembolism, clinically relevant bleeding, deaths, and a net clinical endpoint (composite of symptomatic venous thromboembolism, major bleeding, and death) were estimated using a random effect meta-analysis. RevMan and ITC software were used for direct and indirect comparisons, respectively.

RESULTS

16 trials in 38,747 patients were included. Compared with enoxaparin, the risk of symptomatic venous thromboembolism was lower with rivaroxaban (relative risk 0.48, 95% confidence interval 0.31 to 0.75) and similar with dabigatran (0.71, 0.23 to 2.12) and apixaban (0.82, 0.41 to 1.64). Compared with enoxaparin, the relative risk of clinically relevant bleeding was higher with rivaroxaban (1.25, 1.05 to 1.49), similar with dabigatran (1.12, 0.94 to 1.35), and lower with apixaban (0.82, 0.69 to 0.98). The treatments did not differ on the net clinical endpoint in direct or indirect comparisons.

CONCLUSIONS

A higher efficacy of new anticoagulants was generally associated with a higher bleeding tendency. The new anticoagulants did not differ significantly for efficacy and safety.

The emergence of factor Xa inhibitors for the treatment of cardiovascular diseases: a patent review

INTRODUCTION

Factor Xa (FXa) is a critical enzyme in the coagulation cascade responsible for thrombin generation, the final enzyme that leads to fibrin clot formation. Significant success has recently been reported with compounds such as rivaroxaban, apixaban and edoxaban in the treatment and prevention of venous thromboembolism (VTE) and more recently in the prevention of stroke in atrial fibrillation (AF). The success these agents have demonstrated is now being reflected by a narrowing of new FXa patents over the past few years. The new patents appear to be structural modifications of previously published, small molecule inhibitors and bind in a similar manner to the FXa enzyme.

AREAS COVERED

SciFinder®, PubMed and Google websites were used as the main source of literature retrieval. Patent searches were conducted in the patent databases: HCAPlus, WPIX and the full text databases (USPAT2, USPATFULL, EPFULL, PCTFULL) using the following keywords: ((FXa) OR (F OR factor) (W) (Xa)) (S) (inhibit? or block? or modulat? or antagonist? or regulat?). The search was restricted to patent documents with the entry date on or after 1 January 2009. Literature and information related to clinical development was retrieved from Thomson Reuter's Pharma.

EXPERT OPINION

A large body of Phase II and Phase III data is now available for FXa inhibitors such as rivaroxaban, apixaban, edoxaban and betrixaban. The clinical data demonstrate favorable benefit-risk profiles compared with the standards of care for short- and long-term anticoagulation (i.e., low molecular weight heparins (LMWHs) and wafarin). The potential exists that these agents will eventually be the agents of choice for the treatment of a host of cardiovascular disease states, offering improved efficacy, safety, and ease of use compared with existing anticoagulants.

Rivaroxaban, an oral, direct factor Xa inhibitor: a new option for thromboprophylaxis

Patients undergoing major orthopedic surgery, including total hip arthroplasty (THA) and total knee arthroplasty (TKA), are at high risk for developing venous thromboembolism (VTE). Although largely a preventable complication, VTE develops in a significant proportion of patients, highlighting the need for improved methods of VTE prevention. Current thromboprophylactic options are limited by unpredictable pharmacokinetics and pharmacodynamics (vitamin K antagonists), parenteral/subcutaneous administration (heparin and low-molecular-weight heparins), complicated dosing, and increased risk of bleeding.Rivaroxaban is an oral, direct Factor Xa inhibitor that has recently received marketing authorization in the United States for prophylaxis of deep vein thrombosis in patients undergoing hip or knee replacement surgery. The clinical pharmacology of rivaroxaban supports a convenient, oral, once-daily dosing regimen without the need for routine coagulation monitoring after THA or TKA. A comprehensive phase II and III study program supports its safety and efficacy for VTE prevention after THA or TKA. Phase III results have demonstrated the superior efficacy of rivaroxaban regimens compared with enoxaparin regimens, with similar rates of major bleeding. This article provides an overview of the phase II and III results that support the use of this agent for the prevention of VTE after elective total hip or knee replacement.

Pharmacokinetic evaluation of rivaroxaban for the treatment of acute coronary syndromes

INTRODUCTION

Arterial and venous thrombotic states, including myocardial infarction (MI), stroke and deep vein thrombosis with subsequent pulmonary embolism, are a significant cause of cardiovascular mortality and morbidity. Factor Xa (FXa) plays a pivotal role in thrombus formation. Its inhibition following acute coronary syndromes (ACS) blocks amplification of thrombin generation and subsequent clot formation, resulting in a risk reduction in recurrent MI, stroke and death. For this reason, a predictable form of oral anticoagulation continues to be an ongoing need. Rivaroxaban , the first oral FXa inhibitor, acts by direct inhibition of FXa and does not require an antithrombin cofactor for its activity.

AREAS COVERED

This paper describes the pharmacokinetics (PK) of low-dose rivaroxaban tested in patients with ACS. Age, gender, renal function and body weight have no clinically significant effects on the PK of the drug in treatment of ACS. Caution should be maintained during co-administration of strong CYP3A4 inducers and inhibitors. Among patients with moderate and severe hepatic impairment and in those with associated coagulopathies, rivaroxaban however is contraindicated.

EXPERT OPINION

The mortality benefit with low-dose rivaroxaban in ACS patients was first demonstrated in ATLAS ACS2 TIMI-51 trial. With its rapid oral bioavailability, predictable PK, low drug-drug interaction and no need for monitoring, the use of low-dose rivaroxaban in addition to dual antiplatelet therapy offers an appealing new option in improving outcomes following ACS in the modern era of novel oral FXa inhibitors.

Prevention of VTE in orthopedic surgery patients: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

VTE is a serious, but decreasing complication following major orthopedic surgery. This guideline focuses on optimal prophylaxis to reduce postoperative pulmonary embolism and DVT.

METHODS

The methods of this guideline follow those described in Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement.

RESULTS

In patients undergoing major orthopedic surgery, we recommend the use of one of the following rather than no antithrombotic prophylaxis: low-molecular-weight heparin; fondaparinux; dabigatran, apixaban, rivaroxaban (total hip arthroplasty or total knee arthroplasty but not hip fracture surgery); low-dose unfractionated heparin; adjusted-dose vitamin K antagonist; aspirin (all Grade 1B); or an intermittent pneumatic compression device (IPCD) (Grade 1C) for a minimum of 10 to 14 days. We suggest the use of low-molecular-weight heparin in preference to the other agents we have recommended as alternatives (Grade 2C/2B), and in patients receiving pharmacologic prophylaxis, we suggest adding an IPCD during the hospital stay (Grade 2C). We suggest extending thromboprophylaxis for up to 35 days (Grade 2B). In patients at increased bleeding risk, we suggest an IPCD or no prophylaxis (Grade 2C). In patients who decline injections, we recommend using apixaban or dabigatran (all Grade 1B). We suggest against using inferior vena cava filter placement for primary prevention in patients with contraindications to both pharmacologic and mechanical thromboprophylaxis (Grade 2C). We recommend against Doppler (or duplex) ultrasonography screening before hospital discharge (Grade 1B). For patients with isolated lower-extremity injuries requiring leg immobilization, we suggest no thromboprophylaxis (Grade 2B). For patients undergoing knee arthroscopy without a history of VTE, we suggest no thromboprophylaxis (Grade 2B).

CONCLUSIONS

Optimal strategies for thromboprophylaxis after major orthopedic surgery include pharmacologic and mechanical approaches.