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

The Efficacy and Safety of Pharmacological Prophylaxis of Venous Thromboembolism Following Elective Knee or Hip Replacement

The present systematic review was conducted to assess the efficacy and safety of apixaban versus other anticoagulants, for the prevention of venous thromboembolism (VTE) following total hip replacement (THR) and total knee replacement (TKR) surgery. Electronic databases were interrogated to identify relevant randomized controlled trials. A series of direct/indirect comparisons and a network meta-analysis were conducted. Indirect comparisons found that the odds ratio of “all VTE and all-cause death” were significantly higher for dabigatran than for apixaban in patients with THR (odds ratio [OR], 2.51; 95% confidence interval [CI], 1.50-4.21) and TKR (OR, 1.72; 95% CI, 1.22-2.42). Rivaroxaban showed similar efficacy to apixaban in patients with THR and TKR (OR, 0.69; 95% CI, 0.38-1.25 and OR, 0.83; 95% CI, 0.57-1.19, respectively). No significant differences were observed in bleeding outcomes between treatments. The novel anticoagulants apixaban, rivaroxaban, and dabigatran demonstrated similar or improved efficacy and similar safety compared with current therapies in this indication.

Effect of co-administration of rivaroxaban and clopidogrel on bleeding time, pharmacodynamics and pharmacokinetics: a phase I study

Dual antiplatelet therapy with acetylsalicylic acid and a thienopyridine, such as clopidogrel, is effective for the secondary prevention of cardiovascular events in patients with acute coronary syndrome, but there is still a substantial residual risk of recurrence. Although anticoagulant therapy with a vitamin K antagonist (e.g. warfarin) in conjunction with antiplatelet therapy has been shown to reduce the risk of cardiovascular events, the rates of bleeding were increased with these combination therapies; hence, triple therapy with warfarin is currently only recommended in patients at low risk of bleeding. In addition, there are other limitations associated with vitamin K antagonist therapy, including the need for routine coagulation monitoring and dose adjustment to maintain the treatment within the therapeutic range. Rivaroxaban is an oral, direct Factor Xa inhibitor; in clinical practice, it is likely that rivaroxaban will be given to patients who also receive antiplatelet therapy, such as clopidogrel. This randomized, non-blinded, three-way crossover study investigated the effect of rivaroxaban on bleeding time when co­administered with clopidogrel. In addition, the influence of clopidogrel on the safety, tolerability, pharmacodynamics and pharmacokinetics of rivaroxaban was investigated. Of 27 healthy male subjects who received a single 300 mg dose of clopidogrel, 14 were identified as clopidogrel responders and were then randomized to the following three treatments: (A) two doses of clopidogrel on two consecutive days (300 mg on day 1; 75 mg on day 2); (B) one dose of rivaroxaban (15 mg); or (C) a combination of treatments A and B (rivaroxaban given on day 2). All treatments were well tolerated. Bleeding time with co­administration of rivaroxaban and clopidogrel was significantly prolonged in four subjects, compared with either drug alone: combination treatment increased the overall least squares-means to 3.77 times baseline (90% confidence interval [CI] 2.82–4.73), compared with 1.13 times baseline (90% CI 0.17–2.09) with rivaroxaban and 1.96 times baseline (90% CI 0.10–2.91) with clopidogrel. Co-administration of clopidogrel had no significant effect on the pharmacokinetics of rivaroxaban and, when compared with rivaroxaban alone, had no further effects on Factor Xa activity or prothrombin time. Inhibition of ADP-stimulated platelet aggregation by clopidogrel was not affected by rivaroxaban. As expected, owing to the mode of action of each study drug, the results of this study demonstrated that co­administration of the Factor Xa inhibitor rivaroxaban and the antiplatelet clopidogrel increased the bleeding time in healthy subjects without affecting other pharmacokinetic or pharmacodynamic parameters of each drug.

Oral thromboprophylaxis in pelvic trauma: a standardized protocol

BACKGROUND

Thromboprophylaxis for deep vein thrombosis (DVT) after lower-extremity trauma could include rivaroxaban, an oral medication that does not need laboratory monitoring.

OBJECTIVE

To assess rivaroxaban's efficacy in preventing DVTs after pelvic trauma compared to its historical incidence.

MATERIALS AND METHODS

All patients admitted with pelvic fractures in a 12-month period followed a standardized thromboprophylaxis protocol: 1) rivaroxaban 10 mg/day within 24 h of injury or upon hemodynamic stability; 2) pre-operative, post-operative, and 30-day extremity ultrasound; 3) ventilation-perfusion scintigraphy for clinical signs of pulmonary embolus; and 4) a 45-, 90-, and 120-day re-evaluation. Rivaroxaban administration ceased the day of surgery and restarted 12 h post-operatively or upon hemodynamic stability, continuing for 30 days. Excluded patients had severe neurological or hepatosplenic injuries, heparin hypersensitivity, or hemodynamic instability.

RESULTS

Of 113 patients assessed, 84 patients (66 males), average age 46.6 years (range 19-69 years), were included. They had isolated pelvic trauma (n = 37), associated lower limb injuries (n = 47), average Injury Severity Score 21.4 (range 16-50), and average Glasgow Coma Scale score 13.6 (range 9-15). Patients receiving thromboprophylaxis soon after their fracture (n = 64) had a lower incidence of DVT than those receiving delayed thromboprophylaxis (n = 20) (p = 0.02). One patient (1.2%) died from a pulmonary embolus; 13 had asymptomatic below-the-knee DVTs. Rivaroxaban did not increase intra- or post-operative bleeding in surgical wounds.

CONCLUSIONS

DVT incidence after pelvic fractures is reduced by administering antithrombotics within 24 h of injury or, if the patient is hemodynamically unstable, 24 h after stabilization. Rivaroxaban is a safe and effective method of providing this thromboprophylaxis.

Determination of rivaroxaban by different factor Xa specific chromogenic substrate assays: reduction of interassay variability

Rivaroxaban and other oral direct factor Xa inhibitors (ODiXa) are currently developed for prophylaxis and treatment of thromboembolic diseases using fixed doses. Although routine monitoring is not required, assessing the intensity of anticoagulation may be useful under certain clinical conditions. ODiXa prolong coagulation times of several clotting assays and, thus, their concentration may be determined in factor Xa specific chromogenic substrate assays. So far, no standardized and validated assay is commercially available. Here, five methods (A through E) are studied and optimized to reduce interassay variability. Human pooled plasma was spiked by a serial dilution of rivaroxaban (25–900 ng/ml). The release of para-nitroaniline from the chromogenic substrates was measured by the optical density (OD) at 405 nm. Method B was identified to yield the lowest sum of deviations from the mean value of the OD concentration curve calculated from all assays. Spline functions were developed for OD versus concentration curves for all methods. The calculated OD versus concentration curves overlapped for all methods. The coefficient of variation for all assays and concentrations of rivaroxaban decreased from 25.3 ± 11.4% using the original data to 3.8 ± 2.2% using the calculated data (P < 0.0001). The robustness of the chromogenic assay (method B) remains to be corroborated in interlaboratory comparisons.

Concomitant use of medication with antiplatelet effects in patients receiving either rivaroxaban or enoxaparin after total hip or knee arthroplasty

INTRODUCTION

The RECORD programme compared oral rivaroxaban with enoxaparin for prevention of venous thromboembolism after elective total hip or knee replacement. This analysis compared the safety of concomitant use of specified medications with rivaroxaban and enoxaparin by evaluating postoperative bleeding rates from the pooled RECORD1-4 data.

MATERIALS AND METHODS

The co-medications were non-steroidal anti-inflammatory drugs and platelet function inhibitors, including acetylsalicylic acid (no dose restriction). The endpoints evaluated were the composite of major and non-major clinically relevant bleeding and any bleeding occurring after first oral study drug intake. The time relative to surgery was stratified into three time periods: day 1-3, day 4-7 and after day 7. Relative bleeding rate ratios for co-medication use versus non-use were derived using stratified Mantel-Haenszel methods and compared between rivaroxaban and enoxaparin groups.

RESULTS

Co-medication use with rivaroxaban or enoxaparin resulted in non-significant increases in bleeding events. Respective rate ratios were not significantly different between rivaroxaban and enoxaparin for all bleeding endpoints with concomitant use of non-steroidal anti-inflammatory drugs (any bleeding, 1.22 vs 1.22; major and non-major clinically relevant bleeding, 1.28 vs 0.90) and with concomitant use of platelet function inhibitors/acetylsalicylic acid (any bleeding, 1.32 vs 1.40; major and non-major clinically relevant bleeding, 1.11 vs 1.13).

CONCLUSIONS

This explorative analysis indicates that there is no significant increase in bleeding risk for rivaroxaban compared with enoxaparin when co-administered with non-steroidal anti-inflammatory drugs or acetylsalicylic acid, although, because of low usage, the experience with platelet function inhibitors (except acetylsalicylic acid) was limited.

Conflict of interest in the assessment of thromboprophylaxis after total joint arthroplasty: a systematic review

BACKGROUND

The choice of modalities for thromboprophylaxis after total joint arthroplasty is controversial. To address this issue, an evidence-based review of previous studies was performed. The characteristics of the studies selected for review can affect the final conclusion of an evidence-based review. One such characteristic, financial conflict of interest related to medical research, is a widespread concern. The purpose of the present study was to determine what proportion of studies on thromboprophylaxis after total joint arthroplasty were sponsored by industry and whether the assessments of thromboprophylaxis after total joint arthroplasty were associated with industry support.

METHODS

We searched PubMed for prospective, original, English-language studies, published from 2004 to 2010, on thromboprophylaxis after total joint arthroplasty. The funding sources of the articles were reviewed, and qualitative conclusions regarding the modality of interest for thromboprophylaxis after total joint arthroplasty were classified as being favorable, neutral, or unfavorable.

RESULTS

Seventy-one eligible articles were identified; fifty-two were funded by industry, and fourteen were not. The other five studies did not include information about the funding source. A significant association was observed between the funding source and qualitative conclusions (p = 0.033). Only two (3.8%) of the fifty-two industry-sponsored studies had unfavorable conclusions, whereas three (21.4%) of the fourteen non-industry-sponsored studies indicated that, depending on the clinical scenario, the modality examined was neither effective nor safe.

CONCLUSIONS

Most studies on thromboprophylaxis after total joint arthroplasty are sponsored by industry. Moreover, the qualitative conclusions in those studies are favorable to the use of the sponsored prophylactic agent.

Adverse effects of heparin

All the adverse effects of heparins are related to their wide variety of biological activities, with bleeding being the most important safety issue, resulting directly from the potency of heparin as an anticoagulant. However, it is hard to define the bleeding risk, since it depends on numerous parameters including the indication, dosage, method, and duration of heparin application, the clinical study design and definition of bleeding as well as patient characteristics and determinants of bleeding such as type of surgery and co-medication. Nonbleeding complications of heparins are caused by binding of heparin molecules to proteins other than antithrombin and to cells, which is generally more pronounced with unfractionated heparin than with low-molecular-weight heparins. Accordingly, heparin-induced thrombocytopenia, the most severe nonbleeding adverse reaction, occurs about 10 times less with low-molecular-weight heparins than with unfractionated heparin. Frequent and therefore important adverse reactions of heparins are skin lesions resulting from delayed-type hypersensitivity reactions. All the other undesirable effects are discussed as well, but they are mostly clinically irrelevant.

Safety, pharmacokinetics and pharmacodynamics of multiple ascending doses of R1663, an oral factor Xa inhibitor, in healthy young subjects coupled with exploration of influence of gender and age

This study investigated the safety, pharmacokinetics and pharmacodynamics of multiple oral doses of R1663, a factor Xa inhibitor, and explored the influence of age and gender on pharmacokinetics and pharmacodynamics of R1663. This was a single-blind, randomised, placebo-controlled, dose escalation study in 48 healthy male volunteers aged 18 to 44 years. R1663 doses up to 300 mg twice daily or 400 mg once daily were administered for seven days. The exploration of gender and age effect was carried out in separate cohorts of eight male and eight female volunteers aged 45 to 65 years. Multiple oral doses of R1663 were safe and well tolerated. Pharmacokinetics was linear and showed moderate variability. Plasma concentrations peaked at 3 hour. Terminal half-life at steady state was 3–5 hours. Accumulation of R1663 was minimal. R1663 prolonged clotting times, inhibited thrombin generation (peak height and endogenous thrombin potential [ETP]) and anti-factor Xa activity in a concentration-dependent manner without increasing bleeding time. Pharmacodynamic parameters were strongly correlated to R1663 plasma concentrations. The inhibition was more pronounced on peak height (IC50 = 194 ng/ml) than on ETP (2790 ng/ml). Pharmacokinetics and pharmacodynamics of R1663 appeared not to be substantially affected by age or gender but remained to be confirmed in larger clinical trials including older patients. Meanwhile, dose adjustments based on age and gender are not anticipated.

Apixaban and rivaroxaban safety after hip and knee arthroplasty: a meta-analysis

Direct experimental safety comparisons of Xa coagulation factor direct inhibitors, apixaban and rivaroxaban, on their approved therapeutic indications have not been identified. Due to recently raised safety concerns, a meta-analysis was carried out pooling data from studies identified on a Medline and Cochrane Library search in order to better evaluate the safety profile of both drugs. Abstracts from scientific meetings were also searched from 2003 to 2011. Primary and secondary outcome measures were major bleeding and total bleeding, respectively. Relative risks (RRs) were estimated using random effects models and statistical heterogeneity was estimated with I(2) statistics. Of the 160 screened publications, 12 clinical trials were included in which enoxaparin was the active control. For knee arthroplasty, apixaban was associated with significantly fewer major bleeding events (6496 patients, RR 0.56, 95% confidence interval [CI] 0.32-0.96) and fewer total bleeding events (6496 patients, RR 0.81, 95% CI 0.67-0.97). There were no significant differences in the incidence of major bleeding events (5699 patients, RR 1.40, 95% CI 0.56-3.52) or in the incidence of total bleeding events for rivaroxaban (5699 patients, RR 1.09, 95% CI 0.91-1.30). No differences were found when thromboprophylaxis after hip replacement was the case. Apixaban seems to be associated with a lower risk of the incidence of hemorrhagic events after total knee arthroplasty. For hip arthroplasty, no differences were found between the studied drugs.

Rivaroxaban

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Venous thromboembolism: classification, risk factors, diagnosis, and management

Venous thromboembolism (VTE) is categorised as deep venous thrombosis (DVT) and pulmonary embolism (PE). VTE is associated with high morbidity and causes a huge financial burden on patients, hospitals, and governments. Both acquired and hereditary risks factors contribute to VTE. To diagnose VTE, noninvasive cost-effective diagnostic algorithms including clinical probability assessment and D-dimer measurement may be employed followup by compression ultrasonography for suspected DVT patients and multidetector computed tomography angiography for suspected PE patients. There are pharmacological and mechanical interventions to manage and prevent VTE. The pharmacological approaches mainly target pathways in coagulation cascade nonspecifically: conventional anticoagulants or specifically: new generation of anticoagulants. Excess bleeding is one of the major risk factors for pharmacological interventions. Hence, nonpharmacological or mechanical approaches such as inferior vena cava filters, graduated compression stockings, and intermittent pneumatic compression devices in combination with pharmacological interventions or alone may be a good approach to manage VTE.

Inhibitors of propagation of coagulation: factors V and X

Cardiovascular diseases are still the most important cause of morbidity and mortality in western countries and antithrombotic treatment is nowadays widely used. Drugs able to reduce coagulation activation are the treatment of choice for a number of arterial and/or venous thromboembolic conditions. Some of the drugs currently used for this purpose, such as heparins (UFH or LMWH) and VKA, have limitations consisting of a narrow therapeutic window and an unpredictable response with the need of laboratory monitoring in order to assess their efficacy and safety. These drawbacks have stimulated an active research aimed to develop new drugs able to act on single factors involved in the coagulation network, with predictable response. Intense experimental and clinical work on new drugs has focused on synthetic agents, which could preferably be administered orally and at fixed doses. The most advanced clinical development with new anticoagulants has been achieved for those inhibiting FXa and some of them, like fondaparinux, are already currently used in clinical practice. Other agents, such as rivaroxaban, apixaban, otamixaban and edoxaban are under development and have already been studied or are currently under investigation in large scale phase III clinical trials for prevention and treatment of venous thromboembolism, atrial fibrillation and acute coronary syndromes. Some of them have proved to be more effective than conventional therapy. Data on some agents inhibiting FVa are still preliminary and some of these drugs have so far been considered only in patients with disseminated intravascular coagulation secondary to sepsis.

Tissue factor, blood coagulation, and beyond: an overview

Emerging evidence shows a broad spectrum of biological functions of tissue factor (TF). TF classical role in initiating the extrinsic blood coagulation and its direct thrombotic action in close relation to cardiovascular risks have long been established. TF overexpression/hypercoagulability often observed in many clinical conditions certainly expands its role in proinflammation, diabetes, obesity, cardiovascular diseases, angiogenesis, tumor metastasis, wound repairs, embryonic development, cell adhesion/migration, innate immunity, infection, pregnancy loss, and many others. This paper broadly covers seminal observations to discuss TF pathogenic roles in relation to diverse disease development or manifestation. Biochemically, extracellular TF signaling interfaced through protease-activated receptors (PARs) elicits cellular activation and inflammatory responses. TF diverse biological roles are associated with either coagulation-dependent or noncoagulation-mediated actions. Apparently, TF hypercoagulability refuels a coagulation-inflammation-thrombosis circuit in “autocrine” or “paracrine” fashions, which triggers a wide spectrum of pathophysiology. Accordingly, TF suppression, anticoagulation, PAR blockade, or general anti-inflammation offers an array of therapeutical benefits for easing diverse pathological conditions.

Extended-duration rivaroxaban thromboprophylaxis in acutely ill medical patients: MAGELLAN study protocol

Patients with acute medical illnesses are at increased risk of venous thromboembolism (VTE), a significant cause of morbidity and mortality. Thromboprophylaxis is recommended in these patients but questions remain regarding the optimal duration of therapy. The aim of this study is to determine whether oral rivaroxaban is non-inferior to standard-duration (approximately 10 days) subcutaneous (s.c.) enoxaparin for the prevention of VTE in acutely ill medical patients, and whether extended-duration (approximately 5 weeks) rivaroxaban is superior to standard-duration enoxaparin. Patients aged 40 years or older and hospitalized for various acute medical illnesses with risk factors for VTE randomly receive either s.c. enoxaparin 40 mg once daily (od) for 10 ± 4 days or oral rivaroxaban 10 mg od for 35 ± 4 days. The primary efficacy outcomes are the composite of asymptomatic proximal deep vein thrombosis (DVT), symptomatic DVT, symptomatic non-fatal pulmonary embolism (PE), and VTE-related death up to day 10 + 4 and up to day 35 + 4. The primary safety outcome is the composite of treatment-emergent major bleeding and clinically relevant non-major bleeding. As of July 2010, 8,101 patients from 52 countries have been randomized. These patients have a broad range of medical conditions: approximately one-third were diagnosed with acute heart failure, just under one-third were diagnosed with acute infectious disease, and just under one-quarter were diagnosed with acute respiratory insufficiency. MAGELLAN will determine the efficacy, safety, and pharmacological profile of oral rivaroxaban for the prevention of VTE in a diverse population of medically ill patients and the potential of extended-duration therapy to reduce incidence of VTE.

Emerging anticoagulants

INTRODUCTION

Thromboembolic disease encompasses a spectrum of conditions extending from deep vein thrombosis to stroke and myocardial infarction. The current anticoagulation therapy is cumbersome and characterized by several important drawbacks.

AREAS COVERED

Existing treatments and latest breakthroughs on emerging anticoagulants are presented. Oral and parenteral novel anticoagulants are being developed and tested for efficacy and safety and results are being published regularly. The introduction of novel anticoagulants marks a new era in the management of anticoagulated patients. It is important for the healthcare provider to understand the benefits and risks of the armamentarium of anticoagulants that will be available in the very near future. The critical conclusions drawn will help the reader look past what is the most highlighted feature of the new anticoagulantion era: the non-necessity for monitoring.

EXPERT OPINION

Currently, novel anticoagulants seem to lack the indefinable 'charm' of weakness. However, important questions remain unanswered and will require in-depth evaluations.

[Incidence and distribution of venous thrombosis of the lower limbs diagnosed by duplex ultrasonography after total hip or total knee arthroplasty, and hip fracture surgery. Results from 5981 exams and 2123 cases of venous thrombosis over 10 years]

AIM

To determine the incidence and distribution of lower limb venous thrombosis diagnosed by duplex ultrasonography, including calf exploration, after total hip or knee replacement or hip fracture, and to compare them with the venographic results reported by recent randomized control trials testing new antithrombotic drugs.

PATIENTS AND METHODS

From January 2001 to December 2009, 30,510 standardized report forms incremented a database from which files corresponding to major orthopaedic surgery were selected: 1652 after total hip replacement (THR), 1440 after total knee replacement (TKR) and 2889 after hip fracture (HF). Base-line characteristics, incidence and anatomic distribution of venous thrombosis were analysed in the three populations.

RESULTS

Systematic screening was applied for 95.1% of the exams (n=5689). Incidence of total and proximal venous thrombosis was, respectively, 27.8% (n=460) and 2.8% (n=46) for THR, 32.5% (n=939) and 4.4% (n=126) for HF, and 50.3% (n=724) and 3.8% (n=55) for TKR. Venous thrombosis was distal in 89.3% (n=1896). More than half (n=1014) of distal venous thromboses were strictly muscular soleal locations. Ilio-caval thrombosis incidence was 0.18% (n=11), and superficial venous thrombosis incidence was 1.5% (n=89).

CONCLUSION

This study shows that incidence and distribution of venous thromboses diagnosed with a complete and standardized duplex ultrasonographic screening are very close to the rates published with venographic screening in recent trials.

Arylsulfonamidopiperidone derivatives as a novel class of factor Xa inhibitors

The design, synthesis and SAR of a novel class of valerolactam-based arylsulfonamides as potent and selective FXa inhibitors is reported. The arylsulfonamide-valerolactam scaffold was derived based on the proposed bioisosterism to the arylcyanoguanidine-caprolactam core in known FXa inhibitors. The SAR study led to compound 46 as the most potent FXa inhibitor in this series, with an IC(50) of 7 nM and EC(2×PT) of 1.7 μM. The X-ray structure of compound 40 bound to FXa shows that the sulfonamide-valerolactam scaffold anchors the aryl group in the S1 and the novel acylcytisine pharmacophore in the S4 pockets.

Dabigatran and rivaroxaban for prevention of venous thromboembolism--systematic review and adjusted indirect comparison

WHAT IS KNOWN AND OBJECTIVE

Dabigatran and rivaroxaban are new oral anticoagulants for thromboprophylaxis after elective orthopaedic surgery. We aimed to systematically compare their relative benefits and harms through meta-analysis, and adjusted indirect comparison.

METHODS

We searched PubMed, EMBASE, trial registries and regulatory documents through May 2009 for randomized controlled trials (RCTs) of dabigatran (150 and 220 mg daily) and rivaroxaban (10 mg daily) compared with enoxaparin (40-60 mg daily) in elective orthopaedic surgery. We used random effects meta-analysis to calculate pooled relative risks (RRs) and 95% confidence intervals (95% CI) for the outcomes of total venous thromboembolism, VTE (deep venous thrombosis, non-fatal pulmonary embolism and all-cause mortality), and haemorrhagic adverse events (major and clinically relevant non-major bleeds). Adjusted indirect comparison was used for the pooled RRs of dabigatran and rivaroxaban with enoxaparin as the common control.

RESULTS

Rivaroxaban was superior to enoxaparin for the prevention of venous thromoboembolism (RR 0.56, 95% CI 0.43-0.73, P<0.0001), with a trend for increased haemorrhage (RR 1.26, 95% CI 0.94-1.69, P=0.13). Dabigatran was not superior to enoxaparin for prevention of VTE (RR 1.12, 95% 0.97-1.29, P=0.12), and did not reduce haemorrhage risk (RR 1.10, 95% 0.90-1.35, P=0.32). Adjusted indirect comparison showed that rivaroxaban was superior to dabigatran in preventing VTE, RR 0.50 (95% CI 0.37-0.68), but with a slight trend towards increased haemorrhage RR 1.14 (95% CI 0.80-1.64).

WHAT IS NEW AND CONCLUSION

Rivaroxaban may be more effective than dabigatran for prevention of VTE after elective orthopaedic surgery but might also slightly increase the risk of haemorrhage.

Preventing venous thromboembolism following orthopedic surgery in the United States: impact of special populations on clinical outcomes

Clinical trials of anticoagulants often exclude special populations. We assessed the proportion of special populations in real-world orthopedic surgery and the incidence of venous thromboembolism (VTE)-related outcomes. Data on patients with hip (n = 11 483) or knee replacement (n = 19 390) were extracted from IMS' PharMetrics Patient-Centric Database. There was high prevalence of patients aged ≥75 years (20.3%), CYP3A4-inhibitor use (21.5%), and chronic warfarin use (9.5%). Venous thromboembolism events were increased with each increasing year of age (hip: odds ratio [OR] 1.02, 95% confidence interval [CI] = 1.01-1.03; knee: OR 1.01, 95%CI = 1.00-1.02) and chronic warfarin use (hip: OR 1.56, 95%CI = 1.13-2.17; knee: OR 1.33, 95%CI = 1.03-1.72); in hip patients with renal insufficiency (OR1.61, 95%CI=1.11-2.36); and in knee patients with atrial fibrillation (OR 1.41, 95%CI = 1.06-1.88). Major bleeding was higher in hip patients with hepatic impairment (OR 21.99, 95%CI = 2.04-236.62), each increasing year of age (OR 1.08, 95%CI = 1.01-1.15), and chronic warfarin use (OR 7.11, 95%CI = 1.16-43.46). Special populations are prevalent in real-world orthopedic surgery, which may impact VTE-related outcomes.

Crossover dose escalation study to assess safety, pharmacokinetics, and pharmacodynamics of single doses of R1663, an oral factor Xa inhibitor, in healthy male volunteers

This study investigated the safety, pharmacokinetics, and pharmacodynamics of single oral doses of R1663, a factor Xa inhibitor, in healthy volunteers. It was a single-blind, randomized, crossover, placebo-controlled, dose escalation study in 33 healthy male volunteers aged 18 to 45 years. Each volunteer was dosed on 3 occasions with R1663 or placebo. Single oral doses of R1663 were safe and well tolerated. R1663 did not affect bleeding time. Pharmacodynamic effects (prothrombin time [PT], activated partial thromboplastin time [aPTT]), parameters of thrombogram, and anti-factor Xa activity) and plasma concentrations of R1663 were dose-dependent and showed low to moderate (<40%) intersubject and intrasubject variability. Maximum factor Xa inhibition was achieved 3 hours post dose (time to maximum concentration of R1663): clotting times were prolonged up to 2.5-fold, whereas endogenous thrombin potential (ETP) and peak height were decreased by 48% and 85% from their baseline values, respectively. Pharmacodynamic parameters were strongly correlated to R1663 plasma concentrations, with IC50 values of 182 and 2680 ng/mL for peak height and ETP, respectively. Oral doses of R1663 up to 480 mg were well tolerated, with predictable pharmacodynamics and pharmacokinetics. R1663 prolonged clotting times (PT, aPTT) and inhibited thrombin generation without increasing bleeding time.

Evaluation of the efficacy and safety of rivaroxaban using a computer model for blood coagulation

Rivaroxaban is an oral, direct Factor Xa inhibitor approved in the European Union and several other countries for the prevention of venous thromboembolism in adult patients undergoing elective hip or knee replacement surgery and is in advanced clinical development for the treatment of thromboembolic disorders. Its mechanism of action is antithrombin independent and differs from that of other anticoagulants, such as warfarin (a vitamin K antagonist), enoxaparin (an indirect thrombin/Factor Xa inhibitor) and dabigatran (a direct thrombin inhibitor). A blood coagulation computer model has been developed, based on several published models and preclinical and clinical data. Unlike previous models, the current model takes into account both the intrinsic and extrinsic pathways of the coagulation cascade, and possesses some unique features, including a blood flow component and a portfolio of drug action mechanisms. This study aimed to use the model to compare the mechanism of action of rivaroxaban with that of warfarin, and to evaluate the efficacy and safety of different rivaroxaban doses with other anticoagulants included in the model. Rather than reproducing known standard clinical measurements, such as the prothrombin time and activated partial thromboplastin time clotting tests, the anticoagulant benchmarking was based on a simulation of physiologically plausible clotting scenarios. Compared with warfarin, rivaroxaban showed a favourable sensitivity for tissue factor concentration inducing clotting, and a steep concentration–effect relationship, rapidly flattening towards higher inhibitor concentrations, both suggesting a broad therapeutic window. The predicted dosing window is highly accordant with the final dose recommendation based upon extensive clinical studies.

Safety and efficacy of rivaroxaban for thromboprophylaxis following lower limb surgery: an update

INTRODUCTION

Thromboprophylaxis in orthopedic surgery remains a controversial issue despite recent changes to NICE guidelines, particularly with the addition of oral factor Xa inhibitors. The healthcare burden of venous thromboembolism is substantial and needs frequent academic and clinical appraisal.

AREAS COVERED

The authors review the available relevant literature on the use of rivaroxaban in orthopedic surgery, identified using an EMBASE (1980 - 2010) and Ovid MEDLINE (1950 - 2010) search of published articles up to August 2010. This includes clinical studies, case reports and experimental studies where applicable. Search terms include: 'rivaroxaban', 'safety', 'efficacy', 'bleeding', 'toxicity', 'tolerability' and 'complication'.

EXPERT OPINION

Rivaroxaban is a safe and effective choice of thromboprophylactic agent following lower limb arthroplasty surgery. More research is required to expand the application of this novel agent to other areas of orthopedic surgery.

Investigational factor Xa inhibitors for thrombosis and acute coronary syndromes

INTRODUCTION

A number of new oral anticoagulant drugs that selectively and directly inhibit factor Xa (FXa) appear as promising alternatives to the existing anticoagulant agents. These compounds present a convenient route of administration with predictable pharmacokinetics and pharmacodynamics that allow fixed dosing regimens without requiring coagulation monitoring. Rivaroxaban is the first of this new class of drugs that was approved for the prevention of venous thromboembolism (VTE) after elective total hip replacement or total knee replacement surgery in the EU, Canada and several other countries. Clinical trials with rivaroxaban in patients with acute VTE and in patients with atrial fibrillation have been recently completed. Numerous other compounds are under different developing stages (apixaban, edoxaban, otamixaban, LY517717, PRT-054021, YM150).

AREAS COVERED

This review provides an overview of the two oral anti-FXa drugs at the most advanced stage of development (rivaroxaban and apixaban) and briefly describes and comments on the results of the most important studies.

EXPERT OPINION

Undoubtedly, these new drugs will offer several advantages over the previous compounds, but a number of issues still require some attention during the phase of translation from clinical trials into daily clinical practice.

Effects of renal impairment on the pharmacokinetics, pharmacodynamics and safety of rivaroxaban, an oral, direct Factor Xa inhibitor

AIM

This study evaluated the effects of impaired renal function on the pharmacokinetics, pharmacodynamics and safety of rivaroxaban (10mg single dose), an oral, direct Factor Xa inhibitor.

METHODS

Subjects (n= 32) were stratified based on measured creatinine clearance: healthy controls (≥80ml min(-1) ), mild (50-79mlmin(-1) ), moderate (30-49mlmin(-1) ) and severe impairment (<30mlmin(-1) ).

RESULTS

Renal clearance of rivaroxaban decreased with increasing renal impairment. Thus, plasma concentrations increased and area under the plasma concentration-time curve (AUC) LS-mean values were 1.44-fold (90% confidence interval [CI] 1.1, 1.9; mild), 1.52-fold (90% CI 1.2, 2.0; moderate) and 1.64-fold (90% CI 1.2, 2.2; severe impairment) higher than in healthy controls. Corresponding values for the LS-mean of the AUC for prolongation of prothrombin time were 1.33-fold (90% CI 0.92, 1.92; mild), 2.16-fold (90% CI 1.51, 3.10 moderate) and 2.44-fold (90% CI 1.70, 3.49 severe) higher than in healthy subjects, respectively. Likewise, the LS-mean of the AUC for Factor Xa inhibition in subjects with mild renal impairment was 1.50-fold (90% CI 1.07, 2.10) higher than in healthy subjects. In subjects with moderate and severe renal impairment, the increase was 1.86-fold (90% CI 1.34, 2.59) and 2.0-fold (90% CI 1.44, 2.78) higher than in healthy subjects, respectively.

CONCLUSIONS

Rivaroxaban clearance is decreased with increasing renal impairment, leading to increased plasma exposure and pharmacodynamic effects, as expected for a partially renally excreted drug. However, the influence of renal function on rivaroxaban clearance was moderate, even in subjects with severe renal impairment.

Blood coagulation factor Xa as an emerging drug target

INTRODUCTION

Factor (F)Xa is well-known as an important player in the coagulation cascade responsible for thrombin generation. More recently, FXa emerged as an essential player in cell biology via activation of protease-activated receptors (PAR)-1 and -2. This pleiotropic role of FXa forms the basis for its potential contribution to the pathogenesis of several diseases.

AREAS COVERED

The role of FXa in pathophysiology is reviewed with special emphasis on its signal transduction properties. To this end, we first discuss the important role of FXa in the coagulation cascade, we continue with recent data on FXa induced signaling in pathophysiology with special emphasis on tissue remodeling and fibrosis and discuss the potential of FXa as an emerging drug target.

EXPERT OPINION

FXa is more than a passive intermediate in the coagulation cascade and FXa may in fact orchestrate fundamental processes during pathophysiology. Targeting FXa may be an exciting new therapeutic strategy in the treatment of (fibro)proliferative diseases for which current treatment options are limited.

Novel anticoagulant therapy: principle and practice

Currently, there are several lines of evidence supporting the interplay between coagulation and inflammation in the propagation of various disease processes, including venous thromboembolism (VTE) and inflammatory diseases. Major advances in the development of oral anticoagulants have resulted in considerable progress toward the goal of safe and effective oral anticoagulants that do not require frequent monitoring or dose adjustment and have minimal food/drug interactions. Indirect inhibitors such as low-molecular-weight heparin (LMWH) and the pentasaccharide fondaparinux represent improvements over traditional drugs such as unfractionated heparin for acute treatment of VTE, constituting a more targeted anticoagulant approach with predictable pharmacokinetic profiles and no requirement for monitoring. Vitamin K antagonist, with its inherent limitations in terms of multiple food and drug interactions and frequent need for monitoring, remains the only oral anticoagulant approved for long-term secondary thromboprophylaxis in VTE. The oral-direct thrombin inhibitor ximelagatran was withdrawn from the world market due to safety concerns. Newer anticoagulant drugs such as parenteral pentasaccharides (idraparinux, SSR126517E), novel oral-direct thrombin inhibitors (dabigatran), oral-direct factor Xa inhibitors (rivaroxaban, apixaban, YM-150, DU-176b), and tissue factor/factor VIIa complex inhibitors have been "tailor-made" to target specific procoagulant complexes and have the potential to greatly expand oral antithrombotic targets for both acute and long-term treatment of VTE, acute coronary syndromes, and for the prevention of stroke in atrial fibrillation patients.

Rivaroxaban versus enoxaparin for thromboprophylaxis after total hip or knee arthroplasty: a meta-analysis of randomized controlled trials

PURPOSE

Rivaroxaban is a newly developed oral medicine that direct inhibits factor Xa for the prevention and treatment of thromboembolic disorders. The objective of this study was to compare the efficacy and safety of rivaroxaban versus enoxaparin, a medicine routinely used for thromboprophylaxis after total hip or knee arthroplasty.

METHODS

We performed a meta-analysis of relevant randomized controlled trials (RCTs) identified in PubMed, Cochrane library, and Embase. The primary efficacy outcome for our meta-analysis was total venous thromboembolism (VTE) and all-cause mortality. The primary safety outcome was bleeding events, which were categorized as major, clinically relevant non-major, or minor events.

RESULTS

Eight RCTs, involving 15,586 patients, were included in our meta-analysis. Compared to enoxaparin, thromboprophylaxis with rivaroxaban was associated with significantly fewer VTE and all-cause mortality [9,244 patients, risk ratio (RR) 0.56, 95% confidence interval (CI) 0.39-0.80] cases and a similar incidence of bleeding cases (major bleeding events: 13,384 patients, RR 1.65, 95% CI 0.93-2.93; clinically relevant non-major bleeding events: 13,384 patients, RR 1.21, 95% CI 0.98-1.50; total bleeding events, 13,384 patients, RR 1.10, 95% CI 0.97-1.24). The total hip or knee arthroplasty subgroup analysis revealed consistent efficacy and safety findings.

CONCLUSIONS

Rivaroxaban was more effective than the recommended dose of enoxaparin and had a similar safety profile for thromboprophylaxis after hip and knee arthroplasty.

New oral antithrombotic agents for the prevention of deep venous thrombosis and pulmonary embolism in orthopedic surgery

As the population ages and medical care, along with a functional life style, continues to improve the health of this group, the number of joint replacement surgeries will continue to rise each year in the United States. This growing volume carries with it the risk of venous thromboembolism associated with joint replacement surgery. The American College of Chest Physicians and the American Academy of Orthopedic Surgery have provided guidelines for preventing this complication with the use of warfarin, low molecular weight heparins, pentasaccharides, and aspirin. These agents have had variable efficacy and safety preventing postoperative and out-of-hospital venous thromboembolism. New classes of oral agents, which inhibit Factor II or Factor X, have been shown to be an effective and safe class of anticoagulants that do not require monitoring or have food and drug interactions. This paper will review the current data on the new oral anticoagulants in joint replacement surgery.

Anticoagulation by factor Xa inhibitors

BACKGROUND

Therapeutic agents that regulate blood coagulation are critical to the management of thrombotic disorders, with the selective targeting of factor (F) Xa emerging as a promising approach.

OBJECTIVE

To assess anticoagulant strategies targeting FXa.

METHODS

A deterministic computational model of tissue factor (Tf)-initiated thrombin generation and two empirical experimental systems (a synthetic coagulation proteome reconstruction using purified proteins and a whole blood model) were used to evaluate clinically relevant examples of the two available types of FXa-directed anticoagulants [an antithrombin (AT)-dependent agent, fondaparinux, and an AT-independent inhibitor, Rivaroxaban] in experimental regimens relevant to long-term (suppression of new Tf-initiated events) and acute (suppression of ongoing coagulation processes) clinical applications.

RESULTS

Computational representations of each anticoagulant's efficacy in suppressing thrombin generation over a range of anticoagulant concentrations in both anticoagulation regimens were validated by results from corresponding empirical reconstructions and were consistent with those recommended for long-term and acute clinical applications, respectively. All three model systems suggested that Rivaroxaban would prove more effective in the suppression of an ongoing coagulation process than fondaparinux, reflecting its much higher reactivity toward the prothrombinase complex.

CONCLUSION

The success of fondaparinux in acute settings in vivo is not explained solely by its properties as an FXa inhibitor. We have reported that FIXa contributes to the long-term capacity of clot-associated catalysts to restart a coagulation process, suggesting that the enhanced anti-FIXa activity of fondaparinux-AT may be critical to its success in acute settings in vivo.

New oral anticoagulants for thromboprophylaxis after elective total hip and knee arthroplasty

Anticoagulant drugs reduce the risk of venous thromboembolic events after total hip and knee arthroplasty. However, the use of current drugs, such as low molecular weight heparins, is hampered by their subcutaneous route of administration. The use of vitamin K antagonists is hampered by the requirement for routine coagulation monitoring and dose titration to provide effective anticoagulation without an increased risk of bleeding and numerous food and drug interactions. Clearly, there is a need for new oral, fixed-dose anticoagulant drugs that do not require coagulation monitoring, while demonstrating similar or better efficacy and safety profiles when compared with current agents.

Drug and dietary interactions of the new and emerging oral anticoagulants

Oral warfarin is associated with extensive food and drug interactions, and there is a need to consider such interactions with the new oral anticoagulants (OACs) dabigatran etexilate, rivaroxaban and apixaban. A literature survey was conducted using PubMed, EMBASE and recent abstracts from thrombosis meetings to identify publications related to food, drug and dietary supplement interaction studies with dabigatran etexilate, rivaroxaban and apixaban. Clinical experience regarding food interactions is currently limited. Regarding drug-drug interactions, dabigatran requires caution when used in combination with strong inhibitors or inducers of P-glycoprotein, such as amiodarone or rifampicin. Rivaroxaban (and possibly apixaban) is contraindicated in combination with drugs that strongly inhibit both cytochrome P450 3A4 and P-glycoprotein, such as azole antimycotics, and caution is required when used in combination with strong inhibitors of only one of these pathways. Important drug interactions of the new OACs that can lead to adverse clinical reactions may also occur with non-steroidal anti-inflammatory drugs and antiplatelet drugs, such as aspirin and clopidogrel. Over-the-counter (OTC) medications and food supplements (e.g. St. John's Wort) may also interact with the new OACs. Given the common long-term use of drugs for some chronic disorders, the frequent use of OTC medications and the need for multiple treatments in special populations, such as the elderly people, it is essential that the issue of drug interactions is properly evaluated. New OACs offer significant potential advantages to the field of venous thromboprophylaxis, but we should not fail to appreciate their lack of extensive clinical experience.

New anticoagulants for the prevention of venous thromboembolism

Anticoagulant drugs have an essential role in the prevention and treatment of thromboembolic diseases. Currently available anticoagulants substantially reduce the incidence of thromboembolic events in a number of clinical conditions. However, these agents have limitations that strengthen the case for the development of new anticoagulants. An ideal anticoagulant should be at least as effective as those currently in use, as well as safe, simple to use, and widely applicable.The majority of new anticoagulants currently under investigation are small molecules with a selective and direct anti-Xa or antithrombin action, allowing oral administration in fixed doses. These new agents are in different phases of clinical development. The anti-Xa agent rivaroxaban and the antithrombin agent dabigatran are already available for the prophylaxis of venous thromboembolism in some countries. Apixaban is in an advanced phase of clinical development and several anti-Xa agents are currently approaching phase III clinical trials. Promising results in terms of efficacy and safety profiles have been obtained with these agents in different clinical conditions. Differences in pharmacokinetics and pharmacodynamics could offer the potential for individualized anticoagulant therapies in the near future.

Dabigatran versus enoxaparin for prevention of venous thromboembolism after hip or knee arthroplasty: a pooled analysis of three trials

BACKGROUND

Three randomized, double-blind trials compared dabigatran, an oral direct thrombin inhibitor, with enoxaparin for the primary prevention of venous thromboembolism (VTE) in patients undergoing elective total hip and knee arthroplasty.

OBJECTIVES AND METHODS

We conducted a pre-specified pooled analysis of these trials. 8,210 patients were randomized, of whom 8,135 were treated (evaluable for safety) with dabigatran 220 mg or 150 mg once-daily, or subcutaneous enoxaparin (40 mg once-daily or 30 mg twice-daily). Efficacy analyses were based on the modified intention-to-treat population of 6,200 patients with an evaluable outcome. The common risk difference (RD) of treatment effect between each dabigatran dose and enoxaparin was estimated using fixed-effects models, and statistical heterogeneity was estimated using the I2 statistic.

RESULTS

The composite outcome of major VTE (proximal deep vein thrombosis and/or pulmonary embolism) and VTE-related mortality occurred in 3.3% of the enoxaparin group versus 3.0% of the dabigatran 220 mg group (RD vs. enoxaparin -0.2%, 95% CI -1.3% to 0.9%, I2=37%) and 3.8% of the 150 mg group (RD vs. enoxaparin 0.5%, -0.6% to 1.6%, I2=0%). Major bleeding occurred in 1.4% of the enoxaparin group versus 1.4% of the dabigatran 220 mg group (RD vs. enoxaparin -0.2%, -0.8% to 0.5%, I2=40%) and 1.1% of the 150 mg group (RD vs. enoxaparin -0.4%, -1.0% to 0.2%, I2=0%).

CONCLUSIONS

Oral dabigatran was as effective as subcutaneous enoxaparin in reducing the risk of major VTE and VTE-related mortality after hip or knee arthroplasty and has a similar bleeding profile.

Rivaroxaban and dabigatran etexilate: two new oral anticoagulants for extended postoperative prevention of venous thromboembolism after elective total hip arthroplasty

Extended thromboprophylaxis is vital in patients undergoing total hip arthroplasty (THA) because of the prolonged risk of venous thromboembolism (VTE). Despite evidence that extended prophylaxis can reduce the incidence of symptomatic VTE in this high-risk patient population and the evidence-based guideline recommendations, a large proportion of patients still do not receive an adequate duration of thromboprophylaxis. This is partly due to the limitations of conventional anticoagulants, such as the subcutaneous route of administration or the requirement for routine coagulation monitoring and dose adjustment. New oral anticoagulants (such as the direct thrombin inhibitor dabigatran etexilate and the Factor Xa inhibitor rivaroxaban) could address the current unmet need. Phase III clinical studies in VTE prevention in patients undergoing THA and total knee arthroplasty (TKA) showed that dabigatran etexilate was non-inferior to the EU regimen of enoxaparin, but did not achieve non-inferiority to the US regimen of enoxaparin. In contrast, rivaroxaban demonstrated superiority to both enoxaparin regimens for the prevention of VTE after THA and TKA, without a significant increase in major bleeding rates. Their convenient, once-daily, fixed dosing, with no need for routine coagulation monitoring, could facilitate adherence to evidence-based guideline recommendations of extended thromboprophylaxis after THA.

Safety, pharmacokinetics and pharmacodynamics of single/multiple doses of the oral, direct Factor Xa inhibitor rivaroxaban in healthy Chinese subjects

AIMS

To investigate the safety, pharmacokinetics and pharmacodynamics of rivaroxaban, an oral, direct Factor Xa (FXa) inhibitor, in healthy, male Chinese subjects.

METHODS

Two randomized, single-blind, placebo-controlled, dose-escalation studies were conducted in healthy Chinese men aged 18-45 years. In the single-dose study, subjects received single, oral doses of rivaroxaban 2.5, 5, 10, 20 and 40 mg. In the multiple-dose study, oral rivaroxaban was administered in doses of 5, 10, 20 and 30 mg twice daily for 6 days.

RESULTS

Rivaroxaban, in single and multiple doses up to 60 mg, was well tolerated. Rapid absorption was observed in both studies (time to C(max) 1.25-2.5 h). In the multiple-dose study, rivaroxaban exposure increased dose-proportionally after the first dose and at steady state (for the 5-20-mg doses). The half-life of rivaroxaban was up to 7.9 h in the single-dose study. Maximal inhibition of FXa activity was achieved within 1-3 h of dosing in the single-dose study [at 20 mg FXa inhibition as a median percentage change from baseline, 45.92; 95% confidence interval (CI) 44.64, 50.70] and 2-3 h after administration at steady state in the multiple-dose study (at 20 mg median FXa inhibition as a median percentage change from baseline, 60.25; 95% CI 56.16, 63.05), in line with maximum rivaroxaban plasma concentrations.

CONCLUSIONS

Rivaroxaban demonstrated predictable pharmacokinetics and pharmacodynamics in healthy Chinese subjects, in line with findings observed previously in White subjects. This suggests that fixed doses of rivaroxaban may be administered to all patients, regardless of their ethnic origin.

Direct thrombin inhibitors versus vitamin K antagonists or low molecular weight heparins for prevention of venous thromboembolism following total hip or knee replacement

BACKGROUND

Patients who have undergone total hip or knee replacement (THR, TKR) have a high risk of developing venous thromboembolism (VTE) following surgery, despite appropriate anticoagulation with warfarin or low molecular weight heparin (LMWH). New anticoagulants are under investigation.

OBJECTIVES

To examine the efficacy and safety of prophylactic anticoagulation with direct thrombin inhibitors (DTIs) versus LMWH or vitamin K antagonists in the prevention of VTE in patients undergoing THR or TKR.

SEARCH STRATEGY

The Cochrane Peripheral Vascular Disease Group searched their Specialized Register (last searched 12 March 2010) and CENTRAL (last searched 2010, Issue 2).

SELECTION CRITERIA

Randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Three reviewers independently assessed methodological quality and extracted data in pre-designed tables. The reported follow-up events were included

MAIN RESULTS

We included 14 studies included involving 21,642 patients evaluated for efficacy and 27,360 for safety. No difference was observed in major VTE in DTIs compared with LMWH in both types of operations (odds ratio (OR) 0.91; 95% confidence interval (CI) 0.69 to 1.19), with high heterogeneity (I(2) 71%). No difference was observed with warfarin (OR 0.85; 95% CI 0.63 to 1.15) in TKR, with no heterogeneity (I(2) 0%).More total bleeding events were observed in the DTI group (in ximelagatran and dabigatran but not in desirudin) in patients subjected to THR (OR 1.40; 95% CI 1.06, 1.85; I(2) 41%) compared with LMWH. No difference was observed with warfarin in TKR (OR 1.76; 95% CI 0.91 to 3.38; I(2) 0%). All-cause mortality was higher in the DTI group when the reported follow-up events were included (OR 2.06; 95% CI 1.10 to 3.87).Studies that initiated anticoagulation before surgery showed less VTE events; those that began anticoagulation after surgery showed more VTE events in comparison with LMWH. Therefore, the effect of the DTIs compared with LMWH appears to be influenced by the time of initiation of coagulation more than the effect of the drug itself.The results obtained from sensitivity analysis, did not differ from the analysed results; this strengthens the value of the results.

AUTHORS' CONCLUSIONS

Direct thrombin inhibitors are as effective in the prevention of major venous thromboembolism in THR or TKR as LMWH and vitamin K antagonists. However, they show higher mortality and cause more bleeding than LMWH. No severe hepatic complications were reported in the analysed studies. Use of ximelagatran is not recommended for VTE prevention in patients who have undergone orthopedic surgery. More studies are necessary regarding dabigatran.

Prevention of venous thromboembolism with an oral factor Xa inhibitor, YM150, after total hip arthroplasty. A dose finding study (ONYX-2)

BACKGROUND

Anticoagulant prophylaxis substantially reduces the risk of venous thromboembolism (VTE) after major orthopedic surgery. The direct factor Xa inhibitor YM150 is currently under investigation for the prevention of VTE, stroke and ischemic vascular events in patients after orthopedic surgery, with atrial fibrillation and with acute coronary syndrome, respectively.

OBJECTIVES

To investigate the efficacy and safety of YM150 for the prevention of VTE following elective total hip arthroplasty.

PATIENTS/METHODS

Patients were randomized to postoperative, once-daily, oral YM150 (5, 10, 30, 60 or 120 mg) (double-blind) or preoperative subcutaneous (open label) enoxaparin (40 mg) for 5 weeks. The primary efficacy endpoint comprised VTE diagnosed by mandatory bilateral venography or verified symptomatic deep vein thrombosis (DVT) plus all deaths up to 9 days after surgery. The primary safety outcome was major bleeding up to 9 days after surgery.

RESULTS

Primary efficacy endpoint: of 1017 patients randomized, 960 patients were evaluable for safety and 729 patients for efficacy. A dose-related decrease in VTE incidence from YM150 5 to 60 mg (P = 0.0005) and from 5 to 120 mg (P = 0.0002) was found. The VTE incidence was 27.4%, 31.7%, 19.3%, 13.3% and 14.5% for 5, 10, 30, 60 and 120 mg YM150, respectively, and 18.9% for enoxaparin. Primary safety endpoint: there was one major bleed with YM150 (60 mg) and one with enoxaparin.

CONCLUSIONS

The oral direct FXa inhibitor YM150 demonstrated a significant dose response regarding efficacy. Doses from 30 to 120 mg had comparable efficacy to enoxaparin, without compromising safety regarding major bleeding events.

Rivaroxaban: A New Oral Factor Xa Inhibitor

Rivaroxaban is a direct inhibitor of factor Xa, a coagulation factor at a critical juncture in the blood coagulation pathway leading to thrombin generation and clot formation. It is selective for human factor Xa, for which it has >10 000-fold greater selectivity than for other biologically relevant serine proteases (half-maximal inhibitory concentration [IC 50 ], >20 μmol/L). Rivaroxaban inhibits factor Xa in a concentration-dependent manner (inhibitory constant [K i ], 0.4 nmol/L) and binds rapidly (kinetic association rate constant [k on ], 1.7×10 7 mol/L −1 s −1 ) and reversibly (kinetic dissociation rate constant [k off ], 5×10 −3 s −1 ). By inhibiting prothrombinase complex-bound (IC 50 , 2.1 nmol/L) and clot-associated factor Xa (IC 50 , 75 nmol/L), rivaroxaban reduces the thrombin burst during the propagation phase. In animal models of venous and arterial thrombosis, rivaroxaban showed dose-dependent antithrombotic activity. In healthy individuals, rivaroxaban was found to have predictable pharmacokinetics and pharmacodynamics across a 5- to 80-mg total daily dose range, inhibiting factor Xa activity and prolonging plasma clotting time. In phase III clinical trials, rivaroxaban regimens reduced rates of venous thromboembolism in patients after total hip or knee arthroplasty compared with enoxaparin regimens, without significant differences in rates of major bleeding, showing that rivaroxaban has a favorable benefit-to-risk profile.

Role of orally available antagonists of factor Xa in the treatment and prevention of thromboembolic disease: focus on rivaroxaban

Interpatient variability in the safety and efficacy of oral anticoagulation with warfarin presents several challenges to clinicians, thus underscoring the emergent need for new orally available anticoagulants with predictable pharmacokinetic and pharmacodynamic profiles and ability to target circulating clotting factors. Seven compounds including rivaroxaban, apixaban, betrixaban, and eribaxaban are orally available direct inhibitors of activated factor X currently in development for the prevention and treatment of venous thromboembolism and for thromboprophylaxis in patients with atrial fibrillation or following an acute coronary syndrome. At doses used in phase 2 and 3 clinical trials, rivaroxaban and apixaban demonstrated a predictable onset of effect, maximal plasma concentration, and half-life that was unaffected by age, renal, or hepatic disease. In clinical trials for the treatment and prevention of venous thromboembolism, rivaroxaban and apixaban produced equivalent or superior reductions in the development or progression of venous thromboembolism compared with either low molecular weight heparin or warfarin. Trials comparing the efficacy of rivaroxaban or apixaban to standard therapy for stroke prophylaxis in patients with atrial fibrillation are in process. Rivaroxaban, the sentinel compound in this class, is already approved in the European Union and Canada. It is likely to be approved for use in the United States in 2010.