Oral Anticoagulants in Development

Hip disease in Mucopolysaccharidoses and Mucolipidoses: A review of mechanisms, interventions and future perspectives

The hips are frequently involved in inheritable diseases which affect the bones. The clinical and radiological presentation of these diseases may be very similar to common hip disorders as developmental dysplasia of the hip, osteoarthritis and avascular necrosis, so the diagnosis may be easily overlooked and treatment may be suboptimal. Mucopolysaccharidosis (MPS) and Mucolipidosis (ML II and III) are lysosomal storage disorders with multisystemic involvement. Characteristic skeletal abnormalities, known as dysostosis multiplex, are common in MPS and ML and originate from intra-lysosomal storage of glycosaminoglycans in cells of the cartilage, bones and ligaments. The hip joint is severely affected in MPS and ML. Hip pathology results in limitations in mobility and pain from young age, and negatively affects quality of life. In order to better understand the underlying process that causes hip disease in MPS and ML, this review first describes the normal physiological (embryonic) hip joint development, including the interplay between the acetabulum and the femoral head. In the second part the factors contributing to altered hip morphology and function in MPS and ML are discussed, such as abnormal development of the pelvic- and femoral bones (which results in altered biomechanical forces) and inflammation. In the last part of this review therapeutic options and future perspectives are addressed.

Thromboprophylaxis across orthopaedic surgery: Bibliometric analysis of the most cited articles

PURPOSE

One of the most common adverse events after orthopaedic surgery, with a potential for subsequent serious morbidity and mortality is venous thromboembolism (VTE). Bibliometric analysis has been performed regarding many topics and across orthopaedics. As DVT prophylaxis is a major component of both orthopaedic surgery considerations and research, a bibliometric analysis in this area would prove beneficial in not only in understanding the research done in the field thus far, but would also direct future research efforts.

METHODS

The Web of Science (WoS) database from the Institute of Scientific Information (ISI) was used to compile articles for bibliometric analysis using Boolean search: ((Orthopaedic∗ OR Orthopaedic∗) AND (thromboprophylaxis OR Thromboembolism OR Deep vein thrombosis OR thrombus OR embolism OR anticoagulation OR Embolus OR prophylaxis)).

RESULTS

The Top 100 cited articles included in the final list generated a total of 21,099 citations. The highest cited article was Prevention of venous thromboembolism by Geerts et al. published in Chest, which had a total of 2802 on WoS, and a calculated citation density of 215.54 of citations/years since publication. Comparing the overall citation against the year of publication there was a slight positive trend favoring more recent publications (R-value: 0.142; adjusted R-squared: 0.01; p = 0.16). Analysis of an articles Level of Evidence (LOE), 17 were grade with a level of I.

CONCLUSIONS

Orthopaedic thromboprophylaxis is an ever-changing field that is at the forefront of orthopaedic literature. The significant trend favoring high quality research within orthopaedic thromboprophylaxis demonstrates the importance of this topic and there was a need for a guide to best understand the evolution of DVT prophylaxis.

Direct oral anticoagulants for the treatment and prevention of venous thromboembolism in patients with cancer: current evidence

Venous thromboembolic disease (VTED) is a common and clinically important complication in patients with cancer, contributing to its mortality and morbidity. Direct oral anticoagulant agents (DOACs), including direct thrombin inhibitors and direct factor Xa inhibitors, are as effective as vitamin K antagonists for the treatment of VTED and are associated with less frequent and severe bleeding. They have advantages over low-molecular-weight heparin, but comparative long-term efficacy and safety data are lacking for these compounds. Recent randomized clinical trials suggest a role for DOACs in the treatment of VTED in patients with cancer. This review will discuss the existing evidence and future perspectives on the role of DOACs in the treatment of VTE based on the current evidence about their overall efficacy and safety and the limited information in patients with cancer; in addition, we will briefly review their pharmacokinetic properties with special reference to potential interactions.

Synthetic Xylosides: Probing the Glycosaminoglycan Biosynthetic Machinery for Biomedical Applications

Glycosaminoglycans (GAGs) are polysaccharides ubiquitously found on cell surfaces and in the extracellular matrix (ECM). They regulate numerous cellular signaling events involved in many developmental and pathophysiological processes. GAGs are composed of complex sequences of repeating disaccharide units, each of which can carry many different modifications. The tremendous structural variations account for their ability to bind many proteins and thus, for their numerous functions. Although the sequence of GAG biosynthetic events and the enzymes involved mostly were deduced a decade ago, the emergence of tissue or cell specific GAGs from a nontemplate driven process remains an enigma. Current knowledge favors the hypothesis that macromolecular assemblies of GAG biosynthetic enzymes termed "GAGOSOMEs" coordinate polymerization and fine structural modifications in the Golgi apparatus. Distinct GAG structures arise from the differential channeling of substrates through the Golgi apparatus to various GAGOSOMEs. As GAGs perform multiple regulatory roles, it is of great interest to develop molecular strategies to selectively interfere with GAG biosynthesis for therapeutic applications. In this Account, we assess our present knowledge on GAG biosynthesis, the manipulation of GAG biosynthesis using synthetic xylosides, and the unrealized potential of these xylosides in various biomedical applications. Synthetic xylosides are small molecules consisting of a xylose attached to an aglycone group, and they compete with endogenous proteins for precursors and biosynthetic enzymes to assemble GAGs. This competition reduces endogenous proteoglycan-bound GAGs while increasing xyloside-bound free GAGs, mostly chondroitin sulfate (CS) and less heparan sulfate (HS), resulting in a variety of biological consequences. To date, hundreds of xylosides have been published and the importance of the aglycone group in determining the structure of the primed GAG chains is well established. However, the structure-activity relationship has long been cryptic. Nonetheless, xylosides have been designed to increase HS priming, modified to inhibit endogenous GAG production without priming, and engineered to be more biologically relevant. Synthetic xylosides hold great promise in many biomedical applications and as therapeutics. They are small, orally bioavailable, easily excreted, and utilize the host cell biosynthetic machinery to assemble GAGs that are likely nonimmunogenic. Various xylosides have been shown, in different biological systems, to have anticoagulant effects, selectively kill tumor cells, abrogate angiogenic and metastatic pathways, promote angiogenesis and neuronal growth, and affect embryonic development. However, most of these studies utilized the commercially available one or two β-D-xylosides and focused on the impact of endogenous proteoglycan-bound GAG inhibition on biological activity. Nevertheless, the manipulation of cell behavior as a result of stabilizing growth factor signaling with xyloside-primed GAGs is also reckonable but underexplored. Recent advances in the use of molecular modeling and docking simulations to understand the structure-activity relationships of xylosides have opened up the possibility of a more rational aglycone design to achieve a desirable biological outcome through selective priming and inhibitory activities. We envision these advances will encourage more researchers to explore these fascinating xylosides, harness the GAG biosynthetic machinery for a wider range of biomedical applications, and accelerate the successful transition of xyloside-based therapeutics from bench to bedside.

Rivaroxaban for venous thromboembolism prevention after major orthopedic surgery: translating trial data into routine clinical practice

An established standard of care for the prevention of venous thromboembolism after major orthopedic surgery has been subcutaneous low-molecular-weight heparin. The non-vitamin K antagonist oral anticoagulant rivaroxaban has demonstrated superior efficacy and similar safety to all tested regimens of enoxaparin in large Phase III clinical studies of venous thromboembolism prevention after elective hip and knee arthroplasty. Despite regulatory approval of rivaroxaban for this indication, concerns remain among physicians regarding its optimal and effective use in routine clinical practice. Real-life studies, such as XAMOS and ORTHO-TEP, are providing physicians with more information on the routine use of rivaroxaban for venous thromboembolism prevention after orthopedic surgery, helping to establish its safety and effectiveness in everyday clinical care. Among the most important issues are the risk of bleeding complications, wound healing, timing of first dose, impact of type of anesthesia on thromboprophylaxis effectiveness, patient comorbidities and comedication use, periprocedural management, associated costs, and clinical outcomes in trauma-related fractures. Many of these issues are difficult to study in randomized, double-blind, Phase III trials, and can be assessed more readily using real-life data. In particular, real-life or noninterventional studies lack many of the strict inclusion and exclusion criteria associated with Phase III trials and involve unselected patients who often present with significant comorbidities or comedication use.

Prevention of stroke and systemic embolism with rivaroxaban compared with warfarin in Chinese patients with atrial fibrillation

This study assessed the effects and safety of rivaroxaban versus warfarin in Chinese patients with atrial fibrillation. In this double-blind clinical trial, a total of 353 consecutive patients with atrial fibrillation who were at risk of stroke or systemic embolism were enrolled to receive either rivaroxaban or warfarin. The primary effect endpoint occurred in five patients in the rivaroxaban group (2.29% per year) and in seven patients in the warfarin group (2.91% per year) (hazard ratio with warfarin, 0.76, 95% CI, 0.64-0.91; p = 0.03). Major and non-major clinically relevant bleeding occurred in 38 patients (14.3% per year) in the rivaroxaban group and in 36 patients (13.7% per year) in the warfarin group (hazard ratio rivaroxaban versus warfarin, 1.07; 95% CI, 0.93-1.14; p = 0.39). Adverse events were similar between these two arms (p > 0.05). In conclusion, oral administration of rivaroxaban reduced the risk of stroke or systemic embolism without significantly increasing the safety concern.

Prevention and treatment of venous thromboembolism with new oral anticoagulants: a practical update for clinicians

Traditional anticoagulants, such as warfarin and enoxaparin, have several limitations, including parenteral administration, need for laboratory monitoring, and ongoing dose adjustment, which may limit optimal patient care. Newer oral anticoagulants, such as direct thrombin inhibitors (e.g., dabigatran etexilate) and direct factor Xa inhibitors (e.g., rivaroxaban, apixaban, and edoxaban), have been developed to overcome these drawbacks, and thereby improve patient care. Several of these agents have been approved for use in the prevention and treatment of venous and/or systemic thromboembolism. The objective of this paper is to provide an overview of the available clinical trial data for these new oral anticoagulants in the prevention and treatment of venous thromboembolism and a practical update for clinicians.

Darexaban for the Prevention of Venous Thromboembolism in Asian Patients Undergoing Orthopedic Surgery

Objective:

To evaluate the efficacy and safety of darexaban (YM150) in Asian patients undergoing total hip or total knee arthroplasty.

Methods:

In 2 phase II/III multicenter, randomized, double-blind, placebo-controlled, parallel-group studies, patients were randomized to oral darexaban 15 mg twice daily (bid), darexaban 30 mg bid, oral placebo bid, or subcutaneous enoxaparin 20 mg bid. Primary efficacy outcome for both studies was total venous thromboembolism (VTE) incidence.

Results:

Both darexaban doses were statistically significantly superior to placebo for total VTE incidence (hip study: darexaban 15 mg bid [2.9%] vs placebo [17.1%], P < .001; darexaban 30 mg bid [5.2%] vs placebo [17.1%], P = .003; and knee study: darexaban 15 mg bid [27.2%] vs placebo [52.8%], P = .002; darexaban 30 mg bid [15.5%] vs placebo [52.8%], P < .001). In both studies, the incidence of bleeding events was low across all treatment groups.

Conclusion:

Darexaban is effective and well tolerated as VTE prophylaxis in Asian patients undergoing elective major orthopedic surgery.

Novel 1,2,4-triazolo[1,5-a]pyridines and their fused ring systems attenuate oxidative stress and prolong lifespan of Caenorhabiditis elegans

In this paper we report the synthesis of some novel 1,2,4-triazolo[1,5-a]pyridine and azolotriazolopyridine ring systems. The products were screened for various types of activity like antibacterial, antifungal, and antioxidative activity. Compound 13 was found to pose an antioxidative activity. In addition, this compound was found to extend the life span of Caenorhabiditis elegans under standard laboratory conditions and reduces both heat and chemical induced oxidative stress in C. elegans in a dose-dependent manner. Furthermore, treatment of worms with compound 13 was found to significantly attenuate the formation of advanced glycation end products and malondialdehyde in a dose-dependent manner.

A Novel Prothrombin Time Assay for Assessing the Anticoagulant Activity of Oral Factor Xa Inhibitors

Conventional prothrombin time (PT) assays have limited sensitivity and dynamic range in monitoring the anticoagulant activity of direct factor Xa inhibitors. Hence, new assays are needed. We modified a PT assay by adding calcium chloride (CaCl2) to the thromboplastin reagent to increase assay dynamic range and improve sensitivity. Effects of calcium and sodium ion concentrations, and sample handling, were evaluated to optimize assay performance. Increasing concentrations of calcium ions produced progressive increases in PT across the factor Xa inhibitor concentrations of 0 to 2500 nmol/L for razaxaban and apixaban. The greatest effect was seen when the thromboplastin reagent was diluted 1:2.25 with 100 mmol/L CaCl2 (thus selected for routine use). The optimized assay showed an interassay precision of 1.5 to 9.3 percentage coefficient of variation (%CV) for razaxaban and 3.1 to 4.6 %CV for apixaban. We conclude that the modified PT assay is likely to be suitable as a pharmacodynamic marker for activity at therapeutic concentrations of factor Xa inhibitors.

Dabigatran etexilate: an oral direct thrombin inhibitor for the management of thromboembolic disorders

BACKGROUND

Until recently, warfarin was the only oral anticoagulant available in the United States. Its narrow therapeutic index, interpatient variability in dose response, and drug and food interactions make it difficult to use. Dabigatran etexilate (DE) is a new oral direct thrombin inhibitor that was approved in the US and in Canada for the prevention of thromboembolic events in patients with atrial fibrillation (AF), as well as in Europe and Canada for the prevention of venous thromboembolism (VTE).

OBJECTIVE

To discuss the role of DE for the prevention and treatment of VTE, as well as for the prevention of stroke in patients with AF.

METHODS

Peer-reviewed clinical trials, review articles, and treatment guidelines were identified from MEDLINE and the Current Contents database (both 1966-February 15, 2012) using the search terms dabigatran, VTE, Afib, pharmacokinetics, pharmacodynamics, pharmacoeconomics, and cost-effectiveness. Citations from available articles were also reviewed for additional references.

RESULTS

For VTE prophylaxis, DE 150 or 220 mg orally daily has demonstrated either superiority or noninferiority to subcutaneous enoxaparin once daily in most studies. However, one study failed to demonstrate noninferiority to subcutaneous enoxaparin dosed BID in the composite end point of VTE, and all-cause mortality. For VTE treatment, DE 150 mg BID orally was shown to be noninferior to warfarin in preventing recurrent events. For AF, DE 150 mg BID orally is superior to warfarin in the prevention of thromboembolism, whereas 110 mg BID is noninferior to warfarin. Pharmacoeconomic analyses performed in the United Kingdom and Ireland found that DE can be cost-saving compared with enoxaparin in the prevention of VTE. Adverse effects of DE reported in clinical studies include dyspepsia (12%-13%) and bleeding (minor bleeding: 6%-22%).

CONCLUSIONS

DE exhibited a safety profile and efficacy comparable to enoxaparin for VTE prophylaxis; comparable safety profile and efficacy to warfarin for VTE treatment; and superiority (150 mg BID orally) in the prevention of stroke and systemic embolism compared with warfarin in patients with AF. The relative ease of oral administration, no need for routine monitoring, and lack of significant drug interactions, may favor use of DE over other anticoagulants. However, there is no antidote for DE currently available.

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.

Dabigatran etexilate prevents venous thromboembolism after total knee arthroplasty in Japanese patients with a safety profile comparable to placebo

We assessed the efficacy, safety, and dose-response of dabigatran etexilate (DAB) in preventing venous thromboembolism (VTE) in Japanese patients undergoing total knee arthroplasty (TKA). Five hundred twelve patients received DAB (110, 150, or 220 mg) or placebo once daily for 11 to 14 days, starting the day after surgery. The primary efficacy end point was the incidence of total VTE and all-cause mortality; the primary safety end point was incidence of major, clinically relevant, and minor bleeding events. Total VTE and all-cause mortality were lower in patients receiving DAB (39.6%, 32.7%, and 24.0%) than placebo (56.4%). There was no difference in the incidence of major bleeding between the DAB and placebo groups. Overall, DAB reduced the incidence of VTE in Japanese patients undergoing TKA, with a comparable safety profile vs placebo.

Oral IIa inhibitors

Direct oral factor IIa inhibitors represent a new class of anticoagulants for the prevention and treatment of venous and selected arterial thomboembolisms. Dabigatran etexilate is the most studied and promising of the oral direct thrombin inhibitors. Preclinical and early-phase clinical studies show it to have a predictable and reliable pharmacokinetic and pharmacodynamic profile, whereas advanced phase 3 trials prove it to be noninferior to traditional anticoagulants in selective conditions for the prevention and treatment of venous and arterial thromboembolism. Other advantages of this drug, including a lack of interaction with cytochrome P450 enzymes or with food and drugs, rapid onset of action, good safety profile, lack of need for routine monitoring, broad therapeutic window, and fixed-dose administration, make this a competitive oral anticoagulant.

Simplifying thromboprophylaxis could improve outcomes in orthopaedic surgery

Venous thromboembolism is a serious complication after total hip or knee surgery, and there is a well-established clinical need for thromboprophylaxis. However, in a large number of cases adequate administration of thromboprophylaxis does not seem to occur after total joint arthroplasty. A major challenge in the management of thromboprophylaxis is to balance the benefits of treatment with the risks, including bleeding complications. Another potential barrier to the optimal use of thromboprophylaxis could be the inconvenience of currently available agents. Many surgeons therefore adopt a conservative approach towards thromboprophylaxis. Simplifying therapy with more convenient, efficacious, and safe anticoagulants could change attitudes to anticoagulant use and improve adherence to thromboprophylactic guidelines.

Forecasting drug utilization and expenditure in a metropolitan health region

BACKGROUND

New pharmacological therapies are challenging the healthcare systems, and there is an increasing need to assess their therapeutic value in relation to existing alternatives as well as their potential budget impact. Consequently, new models to introduce drugs in healthcare are urgently needed. In the metropolitan health region of Stockholm, Sweden, a model has been developed including early warning (horizon scanning), forecasting of drug utilization and expenditure, critical drug evaluation as well as structured programs for the introduction and follow-up of new drugs. The aim of this paper is to present the forecasting model and the predicted growth in all therapeutic areas in 2010 and 2011.

METHODS

Linear regression analysis was applied to aggregate sales data on hospital sales and dispensed drugs in ambulatory care, including both reimbursed expenditure and patient co-payment. The linear regression was applied on each pharmacological group based on four observations 2006-2009, and the crude predictions estimated for the coming two years 2010-2011. The crude predictions were then adjusted for factors likely to increase or decrease future utilization and expenditure, such as patent expiries, new drugs to be launched or new guidelines from national bodies or the regional Drug and Therapeutics Committee. The assessment included a close collaboration with clinical, clinical pharmacological and pharmaceutical experts from the regional Drug and Therapeutics Committee.

RESULTS

The annual increase in total expenditure for prescription and hospital drugs was predicted to be 2.0% in 2010 and 4.0% in 2011. Expenditures will increase in most therapeutic areas, but most predominantly for antineoplastic and immune modulating agents as well as drugs for the nervous system, infectious diseases, and blood and blood-forming organs.

CONCLUSIONS

The utilisation and expenditure of drugs is difficult to forecast due to uncertainties about the rate of adoption of new medicines and various ongoing healthcare reforms and activities to improve the quality and efficiency of prescribing. Nevertheless, we believe our model will be valuable as an early warning system to start developing guidance for new drugs including systems to monitor their effectiveness, safety and cost-effectiveness in clinical practice.

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.

Coagulation factor IXa as a target for treatment and prophylaxis of venous thromboembolism

Venous thromboembolism remains a frequent cause of vascular death. Despite advances in anticoagulant drug development, unmet needs remain, including limited treatment options for patients with severe renal impairment and the inability to fully reverse the effects of anticoagulants approved or in late-stage development. Because coagulation factor IXa plays a pivotal role in tissue factor-mediated thrombin generation, it represents an attractive target for anticoagulant development. This article discusses the rationale for factor IXa as an anticoagulant target and the potential role in venous thromboembolism prevention or management of the 2 factor IXa inhibitors that have undergone testing in phase 1 or 2 trials: TTP889, an oral, small-molecule compound, and RB006, an aptamer-based compound, the intravenous and subcutaneous formulations of which are the anticoagulant components of the REG1 and REG2 anticoagulation systems, respectively.

Barriers to the optimal use of anticoagulants after orthopaedic surgery

Venous thromboembolism (VTE) and the consequent morbidity and mortality associated with this condition continue to be a problem following orthopaedic surgery. The vast majority of patients undergoing orthopaedic surgery receive some form of thromboprophylaxis. However, the use of inappropriate thromboprophylaxis is an important factor which may explain why the clinical burden of VTE is still considerable. Barriers to the use of appropriate thromboprophylaxis include the belief by some surgeons that pharmacological thromboprophylaxis increases the risk of bleeding and the asymptomatic nature of deep vein thrombosis. In addition, in patients at risk of VTE, thromboprophylaxis should be given beyond the standard duration recommended in international or national guidelines, and many surgeons have concerns about adherence and adverse events in the outpatient setting. Furthermore, currently available anticoagulants have drawbacks, including the need for monitoring, or a subcutaneous route of administration. The introduction and implementation of multi-faceted and integrated approaches to thromboprophylaxis could improve adherence with current guidelines, extend appropriate thromboprophylaxis according to risk factors, and improve patient outcomes in this setting. In addition, the development of new anticoagulants with more convenient administration regimens and no need for monitoring may help to achieve these objectives.

Dabigatran etexilate for the prophylaxis of venous thromboembolism after hip or knee replacement rationale for dose regimen

Dabigatran etexilate is an oral reversible direct thrombin inhibitor that offers potential practical advantages over existing anticoagulants for the prevention of venous thromboembolism after major joint replacement surgery. These include oral administration, rapid onset of action, and a predictable anticoagulant effect that obviates the need for laboratory monitoring. Evidence from 3 phase II dose-finding trials showed that dabigatran etexilate, 100 to 300 mg daily, had similar efficacy, risk of bleeding, and tolerability compared with enoxaparin. Using pharmacokinetic modeling and taking into account efficacy/safety considerations, dabigatran etexilate 150 mg and 220 mg once daily, with a half-dose on the day of surgery, were selected for further evaluation in phase III trials. These doses were selected to ensure that the risk of bleeding did not exceed that of enoxaparin. This review discusses the rationale for selection of these dose regimens based on results from phase II trials.

3-(3-Chloro-anilino)-1-(3,5-dimethyl-1H-pyrazol-1-yl)propan-1-one

In the mol­ecule of the title compound, C₁₄H₁₆ClN₃O, the benzene and pyrazole rings are oriented at a dihedral angle of 3.50 (3)°. In the crystal structure, inter­molecular N—H⋯O hydrogen bonds link the mol­ecules into chains. A π–π contact between the benzene and pyrazole rings [centroid–centroid distance = 3.820 (3) Å] may further stabilize the structure.

Economic evaluation of dabigatran etexilate for the prevention of venous thromboembolism after total knee and hip replacement surgery

OBJECTIVE

This was an evaluation of the cost-effectiveness of oral dabigatran etexilate compared with subcutaneous low-molecular-weight heparin (enoxaparin) for the prevention of venous thromboembolism (VTE) after total knee replacement (TKR) and total hip replacement (THR) surgery from the perspective of the UK National Health Service.

METHODS

Dabigatran etexilate (220 mg once daily) was compared with enoxaparin (40 mg once daily) in patients undergoing TKR (duration of prophylaxis, 6-10 days) and THR (duration of prophylaxis, 28-35 days). The 10-week acute postsurgical phase was modeled using a decision tree. A Markov process (1-year cycle length) was used to model long-term events (recurrent VTE, postthrombotic syndrome, and consequences of intracranial hemorrhage) for patients' remaining lifetimes. Relative risks for VTE and bleeding events were derived from 2 Phase III studies that compared dabigatran etexilate with enoxaparin 40 mg once daily. The probabilities of long-term events were estimated using data from published longitudinal studies.

RESULTS

Rates of VTE and bleeding events did not differ significantly between dabigatran etexilate and enoxaparin. Dabigatran etexilate was less costly than enoxaparin in TKR and substantially less costly in THR, primarily due to differences in administration costs. The cost of prophylaxis for THR patients, including drugs and administration costs, was estimated at pound 137 for dabigatran etexilate and pound 237 for enoxaparin ( pound 7 for nursing time during the hospital stay, pound 91 for nurse home visits for administration after hospital discharge, and an additional pound 2 in drug costs). At a willingness-to-pay threshold of pound 20,000 per quality-adjusted life-year, the probability of cost-effectiveness for dabigatran etexilate was 75% in TKR and 97% in THR. These results were robust across a range of sensitivity analyses.

CONCLUSION

From the perspective of the UK National Health Service, thromboprophylaxis with dabigatran etexilate was cost-saving compared with enoxaparin 40 mg once daily, with comparable efficacy and safety profiles.

Characterization of total plasma glycosaminoglycan levels in healthy volunteers following oral administration of a novel antithrombotic odiparcil with aspirin or enoxaparin

Odiparcil is a novel, orally active beta-d-thioxyloside analog with antithrombotic activity associated with a reduced risk of adverse bleeding events. Its unique mechanism of action is postulated by means of an elevation in circulating endogenous chondroitin sulfate-related glycosaminoglycans (GAGs) levels. The purpose of these 2 separate clinical studies was to evaluate plasma GAG levels in healthy subjects administered odiparcil with either aspirin (ASA) or enoxaparin. Clinical plasma samples were processed and analyzed using validated HPLC bioassays that indirectly estimate GAG levels based on the simultaneous detection of the chondroitin disaccharide derivatives. The concomitant administration of odiparcil with or without ASA resulted in a significant elevation in GAG levels over baseline for both treatment groups. In the other clinical study, the concomitant administration of odiparcil with or without enoxaparin displayed significant increases in plasma DeltaDi-OS, DeltaDi-4S, and total disaccharide levels versus control group. Neither plasma GAG levels nor odiparcil plasma levels were correlated with a rise in hepatic transaminases, an adverse drug event observed in several subjects; and plasma odiparcil levels were indirectly correlated with plasma GAG levels. These clinical studies were proof of concept of preclinical rat studies indicating that chronic odiparcil treatment elevates endogenous GAG levels in human subjects.

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

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

Discovery of imidazo[1,5-c]imidazol-3-ones: weakly basic, orally active factor Xa inhibitors

The coagulation enzyme factor Xa (FXa) has been recognized as a promising target for the development of new antithrombotic agents. We previously found compound 1 to be an orally bioavailable FXa inhibitor in fasted monkeys; however, 1 showed poor bioavailability in rats and fed monkeys. To work out the pharmacokinetic problems, we focused our synthetic efforts on the chemical conversion of the 4-(imidazo[1,2- a]pyridin-5-yl)piperazine moiety of 1 to imidazolylpiperidine derivatives (fused and nonfused), which resulted in the discovery of the weakly basic imidazo[1,5- c]imidazol-3-one 3q as a potent and selective FXa inhibitor. Compound 3q showed favorable oral bioavailability in rats and monkeys under both fasted and fed conditions and antithrombotic efficacy in a rat model of venous thrombosis after oral administration, without a significant increase in bleeding time (unlike warfarin). On the basis of these promising properties, compound 3q was selected for further evaluation.

Partial factor IXa inhibition with TTP889 for prevention of venous thromboembolism: an exploratory study

BACKGROUND

Inhibitors of factor (F) IXa show potent antithrombotic activity with a low risk of bleeding in preclinical models. We investigated the anticoagulant potential of oral TTP889, a small molecule that inhibits up to 90% of FIXa activity at therapeutic doses, using a clinical model of extended prophylaxis in hip fracture surgery (HFS).

METHODS

In this multicenter, randomized, double-blind study, 261 patients received oral TTP889 (300 mg once daily) or placebo starting 6-10 days after HFS, and standard thromboprophylaxis for 5-9 days. Treatment was continued for 3 weeks and all patients then underwent mandatory bilateral venography. The primary efficacy outcome was venous thromboembolism (VTE; venographic or symptomatic deep vein thrombosis or pulmonary embolism) during treatment, and it was evaluated centrally by an independent adjudication panel. The main safety outcome was bleeding (major, clinically relevant non-major, and minor events).

RESULTS

Two hundred and twelve patients with an evaluable venogram were included in the efficacy analysis. The primary efficacy outcome occurred in 32.1% (35/109) of patients who had been allocated TTP889, and 28.2% (29/103) of patients on placebo (P = 0.58). There were no major bleeding events, and only two clinically relevant non-major bleeding events with TTP889.

CONCLUSION

Partial FIXa inhibition with TTP889 300 mg daily was not effective for extended prevention of VTE after standard prophylaxis for up to 9 days. Coupled with the low incidence of bleeding episodes, this suggests a lack of antithrombotic potential. Further investigation of TTP889 in different clinical settings is needed. (Clinical trial registration information URL: http://www.clinicaltrials.gov. Unique identifier: NCT00119457).

The discovery of (2R,4R)-N-(4-chlorophenyl)-N- (2-fluoro-4-(2-oxopyridin-1(2H)-yl)phenyl)-4-methoxypyrrolidine-1,2-dicarboxamide (PD 0348292), an orally efficacious factor Xa inhibitor

Herein, we report the discovery of novel, proline-based factor Xa inhibitors containing a neutral P1 chlorophenyl pharmacophore. Through the additional incorporation of 1-(4-amino-3-fluoro-phenyl)-1H-pyridin-2-one 22, as a P4 pharmacophore, we discovered compound 7 (PD 0348292). This compound is a selective, orally bioavailable, efficacious FXa inhibitor that is currently in phase II clinical trials for the treatment and prevention of thrombotic disorders.

Lower limb contrast venography: a modified technique for use in thromboprophylaxis clinical trials for the accurate evaluation of deep vein thrombosis

Lower limb venography remains the imaging modality of choice for detection of asymptomatic deep vein thrombosis (DVT) in clinical trials of anticoagulant agents. A variety of techniques of venography have been described. Here, we describe a modified technique (the "King's" technique) developed to increase the overall adequacy of identification of lower limb veins and detection of small asymptomatic DVT. Essential elements include proper preparation of patients prior to their arrival in the radiology department, intermittent use of tourniquets to ensure complete and adequate deep vein filling, use of a consistent image acquisition sequence and visualization of all veins in at least two different planes. Use of this technique minimizes technical difficulties, provides improved patient through-put in "busy" fluoroscopy units and, ultimately, improves "off-site" levels of adjudication.

Oral dabigatran etexilate vs. subcutaneous enoxaparin for the prevention of venous thromboembolism after total knee replacement: the RE-MODEL randomized trial

BACKGROUND

Oral anticoagulants, such as dabigatran etexilate, an oral, direct thrombin inhibitor, that do not require monitoring or dose adjustment offer potential for prophylaxis against venous thromboembolism (VTE) after total knee replacement surgery.

METHODS

In this randomized, double-blind study, 2076 patients undergoing total knee replacement received dabigatran etexilate, 150 mg or 220 mg once-daily, starting with a half-dose 1-4 hours after surgery, or subcutaneous enoxaparin 40 mg once-daily, starting the evening before surgery, for 6-10 days. Patients were followed-up for 3 months. The primary efficacy outcome was a composite of total VTE (venographic or symptomatic) and mortality during treatment, and the primary safety outcome was the incidence of bleeding events.

RESULTS

The primary efficacy outcome occurred in 37.7% (193 of 512) of the enoxaparin group versus 36.4% (183 of 503) of the dabigatran etexilate 220 mg group (absolute difference, -1.3%; 95% CI, -7.3 to 4.6) and 40.5% (213 of 526) of the 150 mg group (2.8%; 95% CI, -3.1 to 8.7). Both doses were noninferior to enoxaparin based on the pre-specified noninferiority criterion. The incidence of major bleeding did not differ significantly between the three groups (1.3% versus 1.5% and 1.3% respectively). No significant differences in the incidences of liver enzyme elevation and acute coronary events were observed during treatment or follow-up.

CONCLUSIONS

Dabigatran etexilate (220 mg or 150 mg) was at least as effective and with a similar safety profile as enoxaparin for prevention of VTE after total knee-replacement surgery.

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

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