Apixaban, an oral direct factor Xa inhibitor, inhibits human clot-bound factor Xa activity in vitro

In Vivo pharmacokinetic interactions of ribociclib with rivaroxaban and apixaban in rats: implications for increased drug exposure and dose adjustments

Background

Apixaban (API) and rivaroxaban (RIVA) are orally available inhibitors of coagulation factor Xa and are commonly used to treat cancer-related venous thrombosis. Ribociclib (RIBO), a first-line treatment for hormone receptor-positive/human epidermal growth factor receptor 2 negative (HR+/HER2-) advanced breast cancer, is an inhibitor of CYP3A4, P-gp, and BCRP. Given the potential for these drugs to be co-administered in clinical settings, there is limited information regarding the pharmacokinetic drug-drug interactions (DDIs) between ribociclib and these anticoagulants. This study aimed to evaluate the extent of DDIs between ribociclib and rivaroxaban or apixaban in rats and to explore the optimization of drug dosing strategies.

Methods

Male Sprague-Dawley rats were divided into 9 groups (n = 6), receiving ribociclib, apixaban, rivaroxaban, ribociclib with rivaroxaban, ribociclib with apixaban, and combinations with reduced doses and time intervals. Blood concentrations were measured using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Pharmacokinetic parameters such as AUC, Cmax, CLz/F, and Vz/F.

Results

Ribociclib significantly increased exposure to both rivaroxaban and apixaban, with a greater impact on rivaroxaban. Specifically, ribociclib increased the AUC0-t, AUC0-∞ and Cmax of rivaroxaban (normal dose) by about 2.4-fold, 2.1-fold and 1.8-fold, while increasing apixaban exposure by about 60.82%, with a trend towards an increase in Cmax that was not statistically significant. When co-administered with ribociclib, even at a reduced dosage of 1 mg/kg, rivaroxaban exhibited a significant increase in exposure, with the AUC increasing by 2.3-fold and Cmax by 1.3-fold. Despite the reduction in dosage, the pharmacokinetic effect of ribociclib on rivaroxaban persisted. While administration of rivaroxaban 12 h after ribociclib resulted in a less pronounced increase in exposure compared to the normal-dose group. The results of qRT-PCR showed that ribociclib reduced the expression of Cyp3a1 and Abcg2 in rat intestine.

Discussion

This research highlights the need for careful consideration of dosing regimens to minimize toxicity risk and optimize the safety of clinical co-administration of ribociclib with rivaroxaban.

Treating cancer-associated venous thromboembolism: A practical approach

Venous thromboembolism (VTE) is a common and potentially life-threatening complication in patients with cancer. Both cancer and its treatments increase the risk of developing VTE. Specific cancer types and individual patient comorbidities increase the risk of developing cancer-associated VTE, and the risk of bleeding is increased with anticoagulation therapies. The aims of this article are to summarize the latest evidence for treating cancer-associated VTE, discuss the practical considerations involved, and share best practices for VTE treatment in patients with cancer. The article pays particular attention to challenging contexts including patients with brain, lung, gastrointestinal, and genitourinary tumors and those with hematological malignancies. Furthermore, the article summarizes specific clinical scenarios that require additional treatment considerations, including extremes of body weight, nausea and gastrointestinal disturbances, compromised renal function, and anemia, and touches upon the relevance of drug-drug interactions. Historically, vitamin K antagonists and low-molecular-weight heparins (LMWHs) have been used as therapy for cancer-associated VTE. The development of direct oral anticoagulants has provided additional treatment options, which, in certain instances, offer advantages over LMWHs. There are numerous factors that need to be considered when treating cancer-associated VTE, and although various treatment guidelines are helpful, they do not reflect each unique scenario that may arise in clinical practice. This article provides a summary of the latest evidence and a practical approach for treating cancer-associated VTE.

Apixaban Pharmacokinetics and Bioequivalence of Two Tablet Formulations: A Randomized, Open-Label, Crossover Study, Fasting Condition in Healthy Indonesian Volunteers

The present study aimed to assess the bioequivalence of a new apixaban generic with reference formulation. Twenty-six healthy volunteers were recruited for an open-label, balanced, randomized, 2-treatment, 2-sequence, 2-period, single oral dose study. Following overnight fasting, each volunteer received 5 mg of apixaban test and reference formulations as single doses, separated by a 1-week washout period. Twenty blood samples were collected at predose and multiple time points between 0.5 and 72 hours after dosing. A validated ultra-performance liquid chromatography-tandem mass spectrometry detection method following a protein precipitation step was implemented to determine apixaban concentrations. Noncompartmental analysis was used to derive the pharmacokinetic parameters, which were then compared between the test and reference products using a multivariate analysis of variance. The pharmacokinetic parameters of the test product were not statistically different from the reference product, and the 90% confidence intervals of apixaban natural log-transformed area under the concentration-time curve from time 0 to infinity, area under the concentration-time curve from time 0 to the last measurable concentration, and maximum concentration were within 80%-125% based on the bioequivalence acceptance range criteria. The test and reference formulations of apixaban are bioequivalent in healthy subjects under fasting conditions.

Physiologically based absorption modeling to predict the bioequivalence of two apixaban formulations

The equivalence of absorption rates and extents between generic drugs and their reference formulations is crucial for ensuring therapeutic comparability. Bioequivalence (BE) studies are widely utilized and play a pivotal role in substantiating the approval and promotional efforts for generic drugs. Virtual BE simulation is a valuable tool for mitigating risks and guiding clinical BE studies, thereby minimizing redundant in vivo BE assessments. Herein, we successfully developed a physiologically based absorption model for virtual BE simulations, which precisely predicts the BE of the apixaban test and reference formulations. The modeling results confirm that the test and reference formulations were bioequivalent under both fasted and fed conditions, consistent with clinical studies. This highlights the efficacy of physiologically based absorption modeling as a powerful tool for formulation screening and can be adopted as a methodological and risk assessment strategy to detect potential clinical BE risks.

Core shell stationary phase for a novel separation of some COVID-19 used drugs by UPLC-MS/MS Method: Study of grapefruit consumption impact on their pharmacokinetics in rats

A sensitive and selective UPLC-MS/MS method was developed for the synchronized determination of four drugs used in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), namely, azithromycin, apixaban, dexamethasone, and favipiravir in rat plasma. using a Poroshell 120 EC-C18 column (50 mm × 4.6 mm, 2.7 m) with a high-resolution ESI tandem mass spectrometer detection with multiple reaction monitoring. We used an Agilent Poroshell column, which is characterized by a stationary phase based on non-porous core particles. With a remarkable improvement in the number of theoretical plates and low column backpressure. In addition, the developed method was employed in studying the potential food-drug interaction of grapefruit juice (GFJ) with the selected drugs which affects their pharmacokinetics in rats. The LC-MS/MS operated in positive and negative ionization mode using two internal standards: moxifloxacin and chlorthalidone, respectively. Liquid- liquid extraction of the cited drugs from rat plasma was accomplished using diethyl ether: dichloromethane (70:30, v/v). The analytes were separated using methanol: 0.1 % formic acid in water (95: 5, v/v) as a mobile phase in isocratic mode of elution pumped at a flow rate of 0.3 mL/min. A detailed validation of the bio-analytical method was performed in accordance with US-FDA and EMA guidelines. Concerning the in vivo pharmacokinetic study, the statistical significance between the results of the test groups receiving GFJ along with the cited drugs and the control group was assessed demonstrating that GFJ increased the plasma concentration of azithromycin, apixaban, and dexamethasone. Accordingly, this food-drug interaction requires cautious ingestion of GFJ in patients using (SARS-CoV-2) medications as it can produce negative effects in the safety of the drug therapy. A potential drug-drug interaction is also suggested between those medications requiring a suitable dose adjustment.

Uninterrupted DOACs Approach for Catheter Ablation of Atrial Fibrillation: Do DOACs Levels Matter?

Most patients present for catheter ablation of atrial fibrillation (CAAF) with residual or full effect of vitamin K antagonists (VKAs) or direct oral anticoagulants (DOACs). In daily practice, it has been observed that the activated clotting time (ACT) was actually poorly sensitive to the effect of DOACs and that patients on DOACs required more unfractionated heparin (UFH) to achieve the ACT target of 300 s during the procedure, leading some authors to worry about potential overdosing. Conversely, we hypothesize that these higher doses of UFH are necessary to achieve adequate hemostasis during CAAF regardless of the residual effect of DOACs. During CAAF, thrombosis is promoted mainly by the presence of thrombogenic sheaths and catheters in the bloodstream. Preclinical data suggest that only high doses of DOACs are able to mitigate catheter-induced thrombin generation, whereas low dose UFH already do so. In addition, the effect of UFH seems to be lower in patients on DOACs, compared to patients on VKAs, explaining part of the differences observed in heparin requirements. Clinical studies could not identify increased bleeding risk in patients on DOACs compared to those on VKAs despite similar efficacy during CAAF procedures. Moreover, targeting a lower ACT was associated with an increased periprocedural thrombotic risk for both DOAC and VKA patients. Therefore, the low sensitivity of the ACT to the residual effect of DOACs should not be a major concern in its use in the interventional cardiology laboratory.

Effect of Apixaban Pretreatment on Alteplase-Induced Thrombolysis: An In Vitro Study

Benefit of thrombolytic therapy in patients with acute stroke, who are on anticoagulant treatment, is not well addressed. The aim of this study was to investigate whether apixaban can modify the thrombolytic efficacy of alteplase in vitro. Static and flow models and two variants of red blood cell (RBC) dominant clots, with and without apixaban, were used. Clots were prepared from the blood of healthy human donors and subsequently exposed to alteplase treatment. Apixaban and alteplase were used in clinically relevant concentrations. Clot lysis in the static model was determined both by clot weight and spectrophotometric determination of RBC release. Clot lysis in the flow model was determined by measuring recanalization time, clot length and spectrophotometric determination of RBC release. In the static model, clots without apixaban; compared to those with apixaban had alteplase-induced mass loss 54 ± 8% vs. 53 ± 8%, p = 1.00; RBC release 0.14 ± 0.04 vs. 0.12 ± 0.04, p = 0.14, respectively. Very similar results were obtained if plasma was used instead of physiological buffered saline as the incubation medium. In the flow model, clot lysis without apixaban; compared to those with apixaban was as follows: recanalization time 107 ± 46 min vs. 127 ± 31 min, p = 1.00; recanalization frequency 90 ± 22% vs. 90 ± 22%, p = 1.00; clot volume reduction 32 ± 15% vs. 34 ± 10%, p = 1.00; RBC release 0.029 ± 0.007 vs. 0.022 ± 0.007, p = 0.16, respectively. Apixaban had no positive effect on alteplase-induced thrombolysis in both the in vitro static and flow models. Our data support current clinical practice, such that thrombolysis is contraindicated in stroke treatment for patients who have been treated with anticoagulants.

Blue Rubber Bleb Nevus Syndrome Complicated by Enhanced-Fibrinolytic-Type DIC: A Case Report

A 54-year-old Japanese man was diagnosed with blue rubber bleb nevus syndrome (BRBNS) due to venodilation in the lower extremities at birth and gastrointestinal vascular malformations. He also had small bowel bleeding and enhanced-fibrinolytic-type disseminated intravascular coagulation (DIC). Endoscopic sclerotherapy for intestinal hemangioma could not be performed because of bleeding concerns; instead, a combined anticoagulant and antifibrinolytic treatment was performed. Although combination treatment with unfractionated heparin and tranexamic acid proved ineffective for small bowel bleeding, combination treatment with apixaban and tranexamic acid dramatically improved enhanced-fibrinolytic-type DIC. In BRBNS, treatment strategies should be considered after performing detailed coagulation tests.

A liquid chromatography-tandem mass spectrometry method for the determination of apixaban in human plasma and its application to pharmacokinetics studies in the Indian population

Apixaban is a novel oral anticoagulant intended to treat and prevent blood clots and to prevent strokes in patients with nonvalvular atrial fibrillation. The development and validation of a fast, selective, accurate, and precise method using high-performance liquid chromatography tandem mass spectrometry is described for the estimation of apixaban in human plasma, with apixaban ¹³CD₃ as an internal standard (IS). Using a reverse phase Gemini C18 column (50 mm × 4.6 mm, 3 μm) and a mixture of acetonitrile (2 mM) and ammonium formate buffer (50 : 50 v/v) as the mobile phase, chromatographic separation was achieved following extraction via a solid-phase extraction process. To track multiple reaction monitoring transitions set at 460/443 (m/z) and 464/447 (m/z) for apixaban and apixaban ¹³CD₃, respectively, liquid chromatography coupled with triple quadrupole mass spectrometry was employed. A concentration linearity range between 1.01 and 280.00 ng mL^-1 was validated with regression ≥0.99, and the method was successfully applied to apixaban pharmacokinetics analysis. At a flow rate of 1.0 mL min^-1, the run time was around 1.8 min, which is short. With an extraction recovery of >73% for both apixaban and apixaban ¹³CD₃, the method was sensitive, with a limit of quantitation of 1.01 ng mL^-1. The inter-day/between-run precision ranged from 1.21% to 3.21%, while the accuracy ranged from 96.5% to 102%. For pharmacokinetics analysis, the validated method was applied. The percentage difference between findings from samples that were reanalyzed and samples that were initially analyzed was within ±20%. With high-quality assay specificity and accuracy in relation to apixaban analysis in human plasma under the experimental conditions used, the method provided is accurate.

Development and validation of LC-MS/MS method for determination of plasma apixaban

Oral anticoagulants are a group of drugs used for the prevention and treatment of venous thrombosis and venous thromboembolism. For the last ten years, direct oral anticoagulants (DOAC) have been available and are equally effective, but significantly safer than vitamin K antagonists. In the case of an overdose, their most important side effect is still bleeding. Due to their widespread use, as well as increased toxicological importance there is a need to develop an analytical method for the determination of DOAC in biological material.

The aim of this paper was to establish a method for the quantification of apixaban as one of the representatives of DOAC. The methodology of the study included the measurement of apixaban in the plasma of patients treated in the intensive care unit. Plasma apixaban concentrations were determined by LC-MS/MS technique using carbamazepine as an internal standard. Obtained validation parameters indicate that the introduced method is sensitive, reliable, precise and accurate. Using this method, apixaban can be quickly and easily detected and quantified in plasma in patients who are suspected of overdosing with this drug.

Using Pharmacogenetics of Direct Oral Anticoagulants to Predict Changes in Their Pharmacokinetics and the Risk of Adverse Drug Reactions

Dabigatran, rivaroxaban, apixaban, and edoxaban are direct oral anticoagulants (DOACs) that are increasingly used worldwide. Taking into account their widespread use for the prevention of thromboembolism in cardiology, neurology, orthopedics, and coronavirus disease 2019 (COVID 19) as well as their different pharmacokinetics and pharmacogenetics dependence, it is critical to explore new opportunities for DOACs administration and predict their dosage when used as monotherapy or in combination with other drugs. In this review, we describe the details of the relative pharmacogenetics on the pharmacokinetics of DOACs as well as new data concerning the clinical characteristics that predetermine the needed dosage and the risk of adverse drug reactions (ADRs). The usefulness of genetic information before and shortly after the initiation of DOACs is also discussed. The reasons for particular attention to these issues are not only new genetic knowledge and genotyping possibilities, but also the risk of serious ADRs (primarily, gastrointestinal bleeding). Taking into account the effect of the carriership of single nucleotide variants (SNVs) of genes encoding biotransformation enzymes and DOACs metabolism, the use of these measures is important to predict changes in pharmacokinetics and the risk of ADRs in patients with a high risk of thromboembolism who receive anticoagulant therapy.

Laboratory Monitoring of Direct Oral Anticoagulants (DOACs)

The introduction of direct oral anticoagulants (DOACs), such as dabigatran, rivaroxaban, apixaban, edoxaban, and betrixaban, provides safe and effective alternative to previous anticoagulant therapies. DOACs directly, selectively, and reversibly inhibit factors IIa or Xa. The coagulation effect follows the plasma concentration-time profile of the respective anticoagulant. The short half-life of a DOAC constrains the daily oral intake. Because DOACs have predictable pharmacokinetic and pharmacodynamic responses at a fixed dose, they do not require monitoring. However in specific clinical situations and for particular patient populations, testing may be helpful for patient management. The effect of DOACs on the screening coagulation assays such as prothrombin time (PT), activated partial thromboplastin time (APTT), and thrombin time (TT) is directly linked to reagent composition, and clotting time can be different from reagent to reagent, depending on the DOAC's reagent sensitivity. Liquid chromatography-mass spectrometry (LC-MS/MS) is considered the gold standard method for DOAC measurement, but it is time consuming and requires expensive equipment. The general consensus for the assessment of a DOAC is clotting or chromogenic assays using specific standard calibrators and controls. This review provides a short summary of DOAC properties and an update on laboratory methods for measuring DOACs.

Direct oral anticoagulants (DOACs) and neck of femur fractures: Standardising the perioperative management and time to surgery

Demographic projections for hip fragility fractures indicate a rising annual incidence by virtue of a multimorbid, ageing population with more noncommunicable diseases (NCDs). NCDs are characterised by slow progression and long duration ranging from ischaemic cardiovascular disease, cerebrovascular disease, diabetes, chronic obstructive pulmonary disease to various cancers. Management of this disease burden often involves commencing patients on oral anticoagulants to reduce the risk of thromboembolic events. The use of direct oral anticoagulants (DOACs) in clinical practice has increased due to their rapid onset of action, short half-life and predictable anticoagulant effects, without the need for routine monitoring. Safe and timely surgical intervention relies on reversal of anticoagulants. However, the lack of specific evidence-based guidelines for the perioperative management of patients on DOACs with hip fractures has proved challenging; in particular, the accessibility of DOAC-specific assays, justification of the cost-benefit ratio of targeted reversal agents and indications for neuraxial anaesthesia. This has led to potentially avoidable delays in surgical intervention. Following a literature review of the pharmacokinetic and pharmacodynamics of commonly used DOACs in our region including the role of surrogate markers, we propose a systematic, evidence-based guideline to the perioperative management of hip fractures DOACs. We believe this standardised protocol can be easily replicated between hospitals. We recommend that if patients are deemed suitable for a general anaesthesia, with satisfactory renal function, optimal surgical time should be 24 h following the last ingested dose of DOAC.

Pharmacokinetics and Pharmacogenetics of Apixaban

Apixaban is oral anticoagulant, it is widely used in prevention of stroke in non-valvular atrial fibrillation and treatment of deep vein thrombosis and pulmonary embolism. Its main mechanism of action is through reversible inhibition of factor Xa. It specifically binds and inhibits both free and bound factor Xa which ultimately results in reduction in the levels of thrombin formation. Apixaban is mainly metabolized by CYP3A4 with minor contributions from CYP1A2, CYP2C8, CYP2C9, CYP2C19 and CYP2J2 isoenzymes. Some of the major metabolic pathways of apixaban include o-demethylation, hydroxylation, and sulfation, with o-demethylapixabansulphate being the major metabolite. The aim of this review is analysis of associated researches of single nucleotide variants (SNV) of CYP3A5 and SULT1A1 genes and search for new candidate genes reflecting effectiveness and safety of apixaban. The search for full-text publications in Russian and English languages containing key words “apixaban”, “pharmacokinetics”, “effectiveness”, “safety” was carried out amongst literature of the past twenty years with the use of eLibrary, PubMed, Web of Science, OMIM data bases. Pharmacokinetics and pharmacogenetics of apixaban are considered in this review. The hypothesis about CYP и SULT1A enzymes influence on apixaban metabolism was examined. To date, numerous SNVs of the CYP3A5 and SULT1A1 genes have been identified, but their potential influence on pharmacokinetics apixaban in clinical practice needs to be further studies. The role of SNVs of other genes encoding beta-oxidation enzymes of apixaban (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2J2) and transporter proteins (ABCB1, ABCG2) in its efficacy and safety are not well understood, and ABCB1 and ABCG2 genes may be potential candidate genes for studies of the drug safety.

Apixaban: A Clinical Pharmacokinetic and Pharmacodynamic Review

Apixaban is an oral, direct factor Xa inhibitor that inhibits both free and clot-bound factor Xa, and has been approved for clinical use in several thromboembolic disorders, including reduction of stroke risk in non-valvular atrial fibrillation, thromboprophylaxis following hip or knee replacement surgery, the treatment of deep vein thrombosis or pulmonary embolism, and prevention of recurrent deep vein thrombosis and pulmonary embolism. The absolute oral bioavailability of apixaban is ~ 50%. Food does not have a clinically meaningful impact on the bioavailability. Apixaban exposure increases dose proportionally for oral doses up to 10 mg. Apixaban is rapidly absorbed, with maximum concentration occurring 3–4 h after oral administration, and has a half-life of approximately 12 h. Elimination occurs via multiple pathways including metabolism, biliary excretion, and direct intestinal excretion, with approximately 27% of total apixaban clearance occurring via renal excretion. The pharmacokinetics of apixaban are consistent across a broad range of patients, and apixaban has limited clinically relevant interactions with most commonly prescribed medications, allowing for fixed dosages without the need for therapeutic drug monitoring. The pharmacodynamic effect of apixaban is closely correlated with apixaban plasma concentration. This review provides a summary of the pharmacokinetic, pharmacodynamic, biopharmaceutical, and drug–drug interaction profiles of apixaban. Additionally, the population-pharmacokinetic analyses of apixaban in both healthy subjects and in the target patient populations are discussed.

Thrombin Aptamer-Modified Metal-Organic Framework Nanoparticles: Functional Nanostructures for Sensing Thrombin and the Triggered Controlled Release of Anti-Blood Clotting Drugs

This paper features the synthesis of thrombin-responsive, nucleic acid-gated, UiO-68 metal-organic framework nanoparticles (NMOFs) loaded with the drug Apixaban or rhodamine 6G as a drug model. Apixaban acts as an inhibitor of blood clots formation. The loads in the NMOFs are locked by duplex nucleic acids that are composed of anchor nucleic acids linked to the NMOFs that are hybridized with the anti-thrombin aptamer. In the presence of thrombin, the duplex gating units are separated through the formation of thrombin-aptamer complexes. The unlocking of the NMOFs releases the drug (or the drug model). The release of the drug is controlled by the concentration of thrombin. The Apixaban-loaded NMOFs revealed improved inhibition, as compared to free Apixaban, toward blood clot formation. This is reflected by their longer time intervals for inducing clot formation and the decreased doses of the drug required to affect clots formation. The beneficial effects of the Apixaban-loaded NMOFs are attributed to the slow-release mechanism induced by the NMOFs carriers, where the inhibition of factor Xa in the blood clotting cycle retards the formation of thrombin, which slows down the release of the drug.

Insight into the perioperative management of direct oral anticoagulants: concerns and considerations

INTRODUCTION

Direct oral anticoagulants (DOACs) have gained momentum in recent years in patients requiring anticoagulation for the prevention and management of venous thromboembolism and thromboembolic events caused by atrial fibrillation. The use of these agents involves potential bleeding complications, particularly during invasive procedures. With increasing use of DOACs, adequate knowledge regarding the perioperative management of patients on DOACs has become indispensable.

AREAS COVERED

This review covers the indications, mechanism of action, and pharmacokinetics of DOACs and their management in different perioperative settings based on various current guidelines and practices. The role of bridging therapy with heparin and the recently developed reversal agents are also discussed.

EXPERT OPINION

The perioperative management of DOACs is influenced by drug pharmacokinetics, potential comorbidities of the patient and perioperative thrombotic and bleeding risk. In low bleeding risk and minor procedures, continuing DOACs seems to be safe. Interrupting DOACs in high-risk procedures might be necessary and should be based on the elimination half-life of the drug and renal function of the patient. Further research is needed to better clarify the role of recently developed reversal agents in the perioperative setting and to identify specific laboratory tests to guide the perioperative management of DOACs.

Vitamin K antagonists

For the last decades, anticoagulation for stroke prevention in atrial fibrillation (AF) as well as for the prophylaxis and long-term treatment of venous thromboembolism has been entirely based on vitamin K antagonists (VKA). Although very effective under optimal conditions, long-term treatment with these drugs is flawed by the fact that the time in the therapeutic range frequently is suboptimal due to biological factors, drug interactions and compliance.

The direct thrombin inhibitor dabigatran, as well as the direct FXa inhibitors rivaroxaban and apixaban provide more consistent anticoagulation and have proven their efficacy and safety against VKAs in several large scale randomized clinical trials for stroke prevention in atrial fibrillation as well as for the treatment and prevention of venous thromboembolism. In view of these convincing data and other advantages such as the lack of mandatory monitoring and only few drug interactions,VKAs will most likely be replaced in a majority of patients for these indications. Based on the most recent trial evidence, the current review discusses the role of VKA treatmentand that of the novel anticoagulants.

Venous and arterial thrombosis – pathogenesis and the rationale for anticoagulation

Thromboembolic disorders are major causes of morbidity and mortality. It is well-recognised that the pathogenesis is different for arterial and venous thrombosis; however, both involve coagulation activation. Anticoagulants are used for the prevention and treatment of a wide variety of thromboembolic and related conditions. Agents with anti-inflammatory properties in addition to anticoagulation may be particularly beneficial. Traditional anticoagulants, although effective, are associated with certain limitations. Understanding the pathological processes associated with thrombosis and the rational target for anticoagulation is essential, not only for the development of safer and more effective agents, but also for better clinical management of patients who require anticoagulation therapy. In recent years, new oral agents that target single enzymes of the coagulation cascade have been developed – some of those are in advanced stages of clinical development. Based on scientific rationale, both factor Xa and thrombin are viable targets for effective anticoagulation.

The effect of a dual or a triple antithrombotic therapy with apixaban on thrombus formation in vivo and in an ex vivo perfusion chamber model: An open-label, controlled, sequential study

BACKGROUND

There is a need to optimize pharmacological treatment in patients with acute coronary syndrome and concomitant atrial fibrillation, in particular with newer antithrombotic medicines. We have therefore studied if dual or triple combination of antithrombotic agents exert similar effects on coagulation activation in an in vivo model in the skin microvasculature and in an ex vivo perfusion chamber.

METHODS AND RESULTS

Shed blood platelet activation (β-thromboglobulin [β-TG]), thrombin generation (thrombin-antithrombin complex [TAT]) and volume as well as markers of thrombus size (D-dimer) and its platelet content (P-selectin) in a perfusion chamber were studied in a sequential, open-label, parallel group trial in 40 healthy male volunteers (n = 20 per group). Subjects received ticagrelor and apixaban without or with acetylsalicylic acid (ASA). Outcome parameters were assessed at 3 hours after therapy dosing, and at steady-state trough and peak conditions.A triple or dual therapy induced a comparable decrease in shed blood β-TG at 3 hours after therapy dosing but was more pronounced at steady-state conditions with the more intense treatment combination. During both antithrombotic regimens a similarly sustained inhibition in thrombin generation was observed which was accompanied by comparable increases in shed blood volume. In contrast, no treatment effect could be observed in the perfusion chamber experiment.

CONCLUSION

Ticagrelor and apixaban with or without ASA inhibit platelet activation and thrombin formation in vivo in healthy subjects. Platelet inhibition was greater at steady-state conditions after triple therapy administration.

Examining the transplacental passage of apixaban using the dually perfused human placenta

Essentials Apixaban is a novel oral anticoagulant that has not been studied in pregnant patients. Our objective was to determine the rate and extent of the placental transfer of apixaban. Apixaban rapidly crosses the ex vivo term human placenta from maternal to fetal circulation. Fetal apixaban levels in vivo are estimated to be 35-90% of the corresponding maternal levels.

SUMMARY

Background Apixaban is a novel oral anticoagulant that is increasingly being prescribed to women of reproductive age. However, information regarding its placental transfer is non-existent. Objective To determine the rate and extent of placental transfer of apixaban, using the human placenta ex vivo. Methods Placentae collected after Caesarean or vaginal delivery of healthy term infants were perfused in the respective maternal and fetal circulation. At the start of the experiment, apixaban was added to the maternal circulation at a concentration of 150 ng mL(-1) , and samples from maternal and fetal reservoirs were collected over 3 h. Results There was a rapid decline of apixaban in the maternal compartment, followed by emergence in the fetal compartment with a median fetal-to-maternal drug concentration ratio of 0.77 (interquartile range [IQR], 0.76-0.81) and fetal concentration of 39.0 ng mL(-1) (IQR, 36.8-40.6) after 3 h (n = 5). The perfusion results were subsequently adjusted to account for differences in the concentration of plasma proteins in maternal and fetal blood, as apixaban remains highly bound to albumin and alpha-1 acid glycoprotein. After the adjustment, the predicted fetal-to-maternal ratio of total (bound plus unbound) apixaban concentrations in vivo ranged from 0.35 to 0.90. Conclusions We conclude that unbound apixaban rapidly crosses from the maternal to fetal circulation. We further predict that total apixaban concentrations in cord blood in vivo are 35-90% of the corresponding maternal levels, suggesting that apixaban could have a possible adverse effect on fetal and neonatal coagulation.

Edoxaban, a direct factor Xa inhibitor, suppresses tissue-factor induced human platelet aggregation and clot-bound factor Xa in vitro: Comparison with an antithrombin-dependent factor Xa inhibitor, fondaparinux

INTRODUCTION

Tissue factor-induced platelet aggregation and factor Xa (FXa) activity bound to clot contribute to the formation and growth of thrombus. The effects of edoxaban, a direct FXa inhibitor, on these responses were determined and compared with that of fondaparinux, an antithrombin-dependent (indirect) FXa inhibitor.

MATERIAL AND METHODS

Human platelet aggregation was induced by human tissue factor (Dade Innovin or RecombiPlasTin) in platelet-rich plasma spiked with edoxaban or fondaparinux. Clot formed from human whole blood was incubated with 0.9μM prothrombin in the absence or presence of FXa inhibitors. As the index of FXa activity, the amount of prothrombin fragment F1+2 was measured with an ELISA. Free FXa activity was measured using human FXa and its chromogenic substrate S-2222.

RESULTS

Edoxaban inhibited tissue factor-induced platelet aggregation in a concentration-dependent manner with the IC50 values of 150 and 110nM for Dade Innovin and RecombiPlasTin-induced platelet aggregation, respectively. At 1μM, edoxaban completely inhibited the aggregation. Fondaparinux inhibited RecombiPlasTin-induced aggregation with the IC50 of 9.3μM, but did not show complete inhibition up to 30μM and had no effect on Dade Innovin-induced aggregation. Edoxaban inhibited both free and clot-bound FXa with the IC50 of 2.3 and 8.2nM, respectively. Fondaparinux inhibited free FXa (IC50 5.4nM), but 40-times higher concentration were required to inhibit clot-bound FXa (IC50 217nM).

CONCLUSIONS

Edoxaban, a direct FXa inhibitor, was a more potent inhibitor of tissue factor-induced platelet aggregation and clot-bound FXa than fondaparinux, an indirect FXa inhibitor.

Effects of the oral, direct factor Xa inhibitor apixaban on routine coagulation assays and anti-FXa assays

INTRODUCTION

Apixaban is an oral direct factor Xa inhibitor developed for the prophylaxis and treatment of thromboembolic disorders. Laboratory monitoring is not necessary, but the effects on common coagulation reagents and assays constitute clinically valuable information.

OBJECTIVES

To investigate the effects of apixaban on commonly used coagulation methods, and to evaluate anti-FXa assays for specific determination of the drug concentration.

MATERIALS AND METHODS

Apixaban was added to plasma from healthy subjects in the concentration range 0-1000 μg L(-1) , and analyses were performed with different reagents for activated partial thromboplastin time (APTT), prothrombin time (PT), antithrombin, protein C, and protein S. A lupus anticoagulant assay and an APTT assay with varying phospholipid concentrations were used to study the phospholipid dependence.

RESULTS

In general, apixaban showed fewer effects in vitro than have been shown for rivaroxaban, another direct FXa inhibitor. The concentration needed to double the APTT varied between 2200 and 4700 μg L(-1) , and the concentration needed to double the PT varied between 700 and 3900 μg L(-1) . The effects on antithrombin, protein C and protein S assays were dependent on the type of reagent. Apixaban did not cause false-positive lupus anticoagulant results. Chromogenic anti-FXa assays showed linear dose-response curves with apixaban.

CONCLUSIONS

Therapeutic concentrations of apixaban variably affect different assay groups, and even different reagents within an assay group. The effects were much smaller than with rivaroxaban. The use of APTT and/or PT assays to screen the anticoagulant activity of apixaban cannot be recommended. A chromogenic anti-FXa assay can be used for reliable measurements of apixaban concentration.

Safety, pharmacokinetics and pharmacodynamics of multiple oral doses of apixaban, a factor Xa inhibitor, in healthy subjects

AIM

Apixaban is an oral factor Xa inhibitor approved for stroke prevention in atrial fibrillation and thromboprophylaxis in patients who have undergone elective hip or knee replacement surgery and under development for treatment of venous thromboembolism. This study examined the safety, pharmacokinetics and pharmacodynamics of multiple dose apixaban.

METHOD

This double-blind, randomized, placebo-controlled, parallel group, multiple dose escalation study was conducted in six sequential dose panels - apixaban 2.5, 5, 10 and 25 mg twice daily and 10 and 25 mg once daily- with eight healthy subjects per panel. Within each panel, subjects were randomized (3:1) to oral apixaban or placebo for 7 days. Subjects underwent safety assessments and were monitored for adverse events (AEs). Blood samples were taken to measure apixaban plasma concentration, international normalized ratio (INR), activated partial thromboplastin time (aPTT) and modified prothrombin time (mPT).

RESULTS

Forty-eight subjects were randomized and treated (apixaban, n = 36; placebo, n = 12); one subject receiving 2.5 mg twice daily discontinued due to AEs (headache and nausea). No dose limiting AEs were observed. Apixaban maximum plasma concentration was achieved ~3 h post-dose. Exposure increased approximately in proportion to dose. Apixaban steady-state concentrations were reached by day 3, with an accumulation index of 1.3-1.9. Peak : trough ratios were lower for twice daily vs. once daily regimens. Clotting times showed dose-related increases tracking the plasma concentration-time profile.

CONCLUSION

Multiple oral doses of apixaban were safe and well tolerated over a 10-fold dose range, with pharmacokinetics with low variability and concentration-related increases in clotting time measures.

How I treat target-specific oral anticoagulant–associated bleeding

Target-specific oral anticoagulants (TSOACs) that directly inhibit thrombin (dabigatran) or factor Xa (rivaroxaban, apixaban) are effective and safe alternatives to vitamin K antagonists (VKAs) and low-molecular-weight heparin (LMWH). Although these agents have practical advantages compared with VKAs and LMWH, there are no antidotes that reverse their anticoagulant effect. Clinical evidence for the efficacy of nonspecific therapies that promote formation of fibrin (prothrombin complex concentrate [PCC], activated PCC [aPCC], and recombinant factor VIIa) in the setting of TSOAC-associated bleeding is lacking, and these prohemostatic products are associated with a risk of thrombosis. In the absence of specific antidotes, addition of PCC or aPCC to maximum supportive therapy may be reasonable for patients with severe or life-threatening TSOAC-associated bleeding. Targeted antidotes for these agents are in development.

Reversal of novel oral anticoagulants in patients with major bleeding

Novel oral anticoagulants (NOACs) that directly inhibit thrombin (dabigatran) or factor Xa (rivaroxaban, apixaban, edoxaban) are effective therapies for the prevention and treatment of thromboembolism with reduced bleeding complications compared with warfarin for some indications. However, specific antidotes to reverse the anticoagulant activity of NOACs in the event of major bleeding are not available. Evidence supporting non-specific prohemostatic therapies (prothrombin complex concentrate [PCC], activated prothrombin complex concentrate [aPCC], recombinant factor VIIa) in this setting is limited to healthy human volunteers, animal models, and in vitro studies. Clinical outcome data are lacking. Administration of PCC or aPCC may be considered in addition to supportive measures for patients with severe or life-threatening bleeding. Clinical studies are needed to establish the efficacy and safety of these treatments. Target-specific antidotes are in development and hold promise for NOAC reversal, but require further investigation.

Apixaban, an oral, direct factor Xa inhibitor: single dose safety, pharmacokinetics, pharmacodynamics and food effect in healthy subjects

Aims

To evaluate apixaban single dose safety, tolerability, pharmacokinetics and pharmacodynamics and assess the effect of food on apixaban pharmacokinetics.

Methods

A double-blind, placebo-controlled, single ascending-dose, first-in-human study assessed apixaban safety, pharmacokinetics and pharmacodynamics in healthy subjects randomized to oral apixaban (n = 43; 0.5–2.5 mg as solution or 5–50 mg as tablets) or placebo (n = 14) under fasted conditions. An open label, randomized, two treatment crossover study investigated apixaban pharmacokinetics/pharmacodynamics in healthy subjects (n = 21) administered apixaban 10 mg in fasted and fed states. Both studies measured apixaban plasma concentration, international normalized ratio (INR), activated partial thromboplastin time (aPTT) and prothrombin time (PT) or a modified PT (mPT).

Results

In the single ascending-dose study increases in apixaban exposure appeared dose-proportional. Median t_max occurred 1.5–3.3 h following oral administration. Mean terminal half-life ranged between 3.6 and 6.8 h following administration of solution doses ≤2.5 mg and between 11.1 and 26.8 h for tablet doses ≥5 mg. Concentration-related changes in pharmacodynamic assessments were observed. After a 50 mg dose, peak aPTT, INR and mPT increased by 1.2-, 1.6- and 2.9-fold, respectively, from baseline. In the food effect study: 90% confidence intervals of geometric mean ratios of apixaban C_max and AUC in a fed vs. fasted state were within the predefined no effect (80–125%) range. Apixaban half-life was approximately 11.5 h. The effect of apixaban on INR, PT and aPTT was comparable following fed and fasted administration.

Conclusions

Single doses of apixaban were well tolerated with a predictable pharmacokinetic/pharmacodynamic profile and a half-life of approximately 12 h. Apixaban can be administered with or without food.

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.

Therapeutic potential of apixaban in the prevention of venous thromboembolism in patients undergoing total knee replacement surgery

Anticoagulant prophylaxis for preventing venous thromboembolism (VTE) is a worldwide established procedure in hip and knee replacement surgery. Despite available anticoagulant prophylaxis, patients who undergo total knee arthroplasty (TKA) have a high incidence of venous VTE. In spite of their proven efficacy, the currently available anticoagulants have limitations that driven to develop new oral agents that directly target specific factors in the coagulation cascade, such as direct thrombin inhibitors and direct Factor Xa inhibitors, in an attempt to overcome some of the drawbacks with the traditional agents. Apixaban is a potent, selective direct inhibitor of the coagulation factor Xa, recently approved in Europe for the prevention of venous thromboembolism (VTE) in adult patients after total hip replacement (THR) or total knee replacement (TKR) surgery. Apixaban has been extensively studied worldwide in about 12,000 patients in four clinical studies that have demonstrated the efficacy and safety of apixaban respect to enoxaparin for the prevention of thromboembolism after major orthopedic surgery. Three of these trials involved 7,337 patients who undergo TKR: one phase II trial (APROPOS Study) and two large phase III trials (ADVANCE 1 and ADVANCE 2 Studies). ADVANCE 1 demonstrated that when compared with enoxaparin 30 mg twice daily for efficacy, apixaban did not meet the prespecified statistical criteria for noninferiority, but its use was associated with lower rates of clinically relevant bleeding. ADVANCE 2 showed that apixaban was superior to the European standard dose of enoxaparin of 40 mg once daily in term of efficacy, with a similar incidence of major bleeding. This review focuses the clinical efficacy and tolerability of oral apixaban for the prevention of VTE in adult patients following TKR surgery.

Apixaban: a novel oral inhibitor of factor Xa

PURPOSE

The pharmacology, pharmacokinetics, efficacy, and safety of apixaban are reviewed.

SUMMARY

Apixaban is an oral, direct, selective factor Xa inhibitor with a rapid onset of action. It has a plasma elimination half-life of 12 hours and has been administered in a twice-daily dosing regimen in clinical trials without the need for anticoagulation monitoring or dosage adjustment. Apixaban has multiple elimination pathways, and its pharmacokinetics is not substantially altered by patient age, sex, race, or ethnicity. The results of three Phase III trials indicated that apixaban was similar to or more effective than enoxaparin for preventing venous thromboembolism (VTE) in patients undergoing total hip or knee replacement, with similar or lower rates of bleeding. Two Phase III trials found that apixaban was more effective for stroke prevention than either aspirin or warfarin in patients with atrial fibrillation (AF), with a similar (versus aspirin) or improved (versus warfarin) safety profile. A Phase III trial evaluating apixaban plus antiplatelet monotherapy or dual-antiplatelet therapy in patients with acute coronary syndrome ended early due to clear evidence of a clinically important increase in bleeding among patients randomized to apixaban without any meaningful reduction in ischemic events. The adverse-event profiles for apixaban and comparators have been similar in studies conducted to date.

CONCLUSION

Apixaban, a new anticoagulant, appears to offer an efficacy and safety profile comparable with that of enoxaparin for preventing VTE after orthopedic surgery, with the advantage of oral administration. In patients with AF, apixaban is more effective than either warfarin or aspirin for stroke prevention, with an acceptable safety profile.

Apixaban: a review of its use in the prevention of venous thromboembolism after knee or hip replacement surgery

Apixaban (Eliquis™) is an orally active and selective direct inhibitor of factor Xa indicated for twice-daily use in the EU for the prevention of venous thromboembolism (VTE) in adults who have had knee or hip replacement surgery. In this article, the pharmacological, clinical efficacy and tolerability data relevant to the use of apixaban in this indication are reviewed. Oral apixaban is a generally effective and well tolerated thromboprophylactic agent for use after major orthopaedic surgery. In the large, randomized, double-blind, phase III, noninferiority trials known as ADVANCE-2 and -3, apixaban 2.5 mg twice daily initiated after surgery was generally more effective in preventing VTE in patients undergoing knee or hip replacement surgery than subcutaneous enoxaparin sodium initiated before surgery at the EU recommended dosage of 40 mg once daily, with apixaban conferring this benefit without significantly increasing the risk of bleeding. However, when the same apixaban regimen was compared with the US recommended dosage regimen of subcutaneous enoxaparin sodium (30 mg twice daily, initiated after surgery) in patients undergoing knee replacement surgery in the similarly designed ADVANCE-1 trial, the thromboprophylactic efficacy of apixaban did not meet primary endpoint noninferiority criteria, although apixaban was associated with fewer major or clinically relevant nonmajor bleeds (composite endpoint) than this enoxaparin sodium regimen. Additional comparative efficacy and tolerability data are required to definitively position apixaban with respect to other anticoagulants, including rivaroxaban and dabigatran etexilate. In the meantime, currently available clinical data indicate that apixaban is an emerging option for the prevention of VTE in patients undergoing knee or hip replacement surgery.

Venous Thromboembolism in Cancer Patients Undergoing Major Abdominal Surgery: Prevention and Management

Cancer is an important risk factor for venous thrombosis. Venous thromboembolism is one of the most common complications of cancer and the second leading cause of death in these patients. Recent research has given insight into mechanism and various risk factors in cancer patients which predispose to thromboembolism. The purpose of this review is to summarize the current knowledge on the prophylaxis, diagnosis, and management of venous thromboembolism in these patients.

Implementing the new oral anticoagulants into the hospital formulary

The new oral anticoagulants may prove to be one of most significant innovations in clinical practice in the past 60 years. Apixaban and rivaroxaban are direct inhibitors of Factor Xa, while dabigatran inhibits Factor IIa. The predictable pharmacological profile of these new agents allows physicians to prescribe these drugs without the need for routine coagulation monitoring, which is the mainstay of warfarin therapy. In addition, these new agents have not been shown to have any food interactions and minimal drug-drug interactions, interactions are limited to the p-glycoprotein (p-Gp) transporter or cytochrome P450 (CYP450) system, each drug is unique in its drug interaction profile, as will be discussed below. These unique pharmacokinetics profiles may usher in for clinicians a new era of managing thromboembolic disorders. In this article, the pharmacology of these new oral anticoagulants will be reviewed along with the major clinical trials evaluating the use of these agents for thromboembolic prophylaxis in patients undergoing total hip and knee arthroplastic surgery, the treatment of venous thromboembolic disorders and stroke prevention in atrial fibrillation. Am. J. Hematol., 2012. © 2012 Wiley Periodicals, Inc.

New antithrombotic drugs: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article focuses on new antithrombotic drugs that are in or are entering phase 3 clinical testing. Development of these new agents was prompted by the limitations of existing antiplatelet, anticoagulant, or fibrinolytic drugs. Addressing these unmet needs, this article (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.

Preclinical discovery of apixaban, a direct and orally bioavailable factor Xa inhibitor

Apixaban (BMS-562247; 1-(4-methoxyphenyl)-7-oxo-6-(4-(2-oxopiperidin-1-yl)phenyl)-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-c]pyridine-3-carboxamide), a direct inhibitor of activated factor X (FXa), is in development for the prevention and treatment of various thromboembolic diseases. With an inhibitory constant of 0.08 nM for human FXa, apixaban has greater than 30,000-fold selectivity for FXa over other human coagulation proteases. It produces a rapid onset of inhibition of FXa with association rate constant of 20 μM⁻¹/s approximately and inhibits free as well as prothrombinase- and clot-bound FXa activity in vitro. Apixaban also inhibits FXa from rabbits, rats and dogs, an activity which parallels its antithrombotic potency in these species. Although apixaban has no direct effects on platelet aggregation, it indirectly inhibits this process by reducing thrombin generation. Pre-clinical studies of apixaban in animal models have demonstrated dose-dependent antithrombotic efficacy at doses that preserved hemostasis. Apixaban improves pre-clinical antithrombotic activity, without excessive increases in bleeding times, when added on top of aspirin or aspirin plus clopidogrel at their clinically relevant doses. Apixaban has good bioavailability, low clearance and a small volume of distribution in animals and humans, and a low potential for drug-drug interactions. Elimination pathways for apixaban include renal excretion, metabolism and biliary/intestinal excretion. Although a sulfate conjugate of Ο-demethyl apixaban (O-demethyl apixaban sulfate) has been identified as the major circulating metabolite of apixaban in humans, it is inactive against human FXa. Together, these non-clinical findings have established the favorable pharmacological profile of apixaban, and support the potential use of apixaban in the clinic for the prevention and treatment of various thromboembolic diseases.