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

New oral anticoagulants: their advantages and disadvantages compared with vitamin K antagonists in the prevention and treatment of patients with thromboembolic events

Despite the discovery and application of many parenteral (unfractionated and low-molecular-weight heparins) and oral anticoagulant vitamin K antagonist (VKA) drugs, the prevention and treatment of venous and arterial thrombotic phenomena remain major medical challenges. Furthermore, VKAs are the only oral anticoagulants used during the past 60 years. The main objective of this study is to present recent data on non-vitamin K antagonist oral anticoagulants (NOACs) and to analyze their advantages and disadvantages compared with those of VKAs based on a large number of recent studies. NOACs are novel direct-acting medications that are selective for one specific coagulation factor, either thrombin (IIa) or activated factor X (Xa). Several NOACs, such as dabigatran (a direct inhibitor of FIIa) and rivaroxaban, apixaban and edoxaban (direct inhibitors of factor Xa), have been used for at least 5 years but possibly 10 years. Unlike traditional VKAs, which prevent the coagulation process by suppressing the synthesis of vitamin K-dependent factors, NOACs directly inhibit key proteases (factors IIa and Xa). The important indications of these drugs are the prevention and treatment of deep vein thrombosis and pulmonary embolisms, and the prevention of atherothrombotic events in the heart and brain of patients with acute coronary syndrome and atrial fibrillation. They are not fixed, and dose-various strengths are available. Most studies have reported that more advantages than disadvantages for NOACs when compared with VKAs, with the most important advantages of NOACs including safety issues (ie, a lower incidence of major bleeding), convenience of use, minor drug and food interactions, a wide therapeutic window, and no need for laboratory monitoring. Nonetheless, there are some conditions for which VKAs remain the drug of choice. Based on the available data, we can conclude that NOACs have greater advantages and fewer disadvantages compared with VKAs. New studies are required to further assess the efficacy of NOACs.

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

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

Of men and meals

Rivaroxaban is increasingly used to treat patients with acute venous thromboembolism (VTE), a potentially life-threatening condition. Because absorption of rivaroxaban decreases from nearly 100% to 66% under fasting conditions, it is recommended that VTE patients take rivaroxaban with a meal. However, this recommendation is based on preclinical pharmacokinetic (PK) studies in healthy volunteers. So far, no clinical evidence is available to support this recommendation. We describe a case of a compliant young patient who developed recurrent pulmonary embolism during rivaroxaban treatment. PK studies provided evidence that malabsorption of rivaroxaban 20 mg due to irregular intake of meals during shift work was the leading cause of recurrent pulmonary embolism. When the patient was instructed to take rivaroxaban with a regular meal, peak plasma concentrations increased from 115 to 318 ng mL(-1) (+ 176%). Consequently, the importance of taking rivaroxaban with food may have a greater clinical relevance than data from preclinical PK studies suggest.

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

CONTEXT

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

OBJECTIVE

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

DESIGN

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

RESULTS

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

CONCLUSIONS

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

Peri-procedural use of rivaroxaban in elective percutaneous coronary intervention to treat stable coronary artery disease. The X-PLORER trial

Patients on rivaroxaban requiring percutaneous coronary intervention (PCI) represent a clinical conundrum. We aimed to investigate whether rivaroxaban, with or without an additional bolus of unfractionated heparin (UFH), effectively inhibits coagulation activation during PCI. Stable patients (n=108) undergoing elective PCI and on stable dual antiplatelet therapy were randomised (2:2:2:1) to a short treatment course of rivaroxaban 10 mg (n=30), rivaroxaban 20 mg (n=32), rivaroxaban 10 mg plus UFH (n=30) or standard peri-procedural UFH (n=16). Blood samples for markers of thrombin generation and coagulation activation were drawn prior to and at 0, 0.5, 2, 6-8 and 48 hours (h) after start of PCI. In patients treated with rivaroxaban (10 or 20 mg) and patients treated with rivaroxaban plus heparin, the levels of prothrombin fragment 1 + 2 at 2 h post-PCI were 0.16 [0.1] nmol/l (median) [interquartile range, IQR] and 0.17 [0.2] nmol/l, respectively. Thrombin-antithrombin complex values at 2 h post-PCI were 3.90 [6.8]µg/l and 3.90 [10.1] µg/l, respectively, remaining below the upper reference limit (URL) after PCI and stenting. This was comparable to the control group of UFH treatment alone. However, median values for thrombin-antithrombin complex passed above the URL with increasing tendency, starting at 2 h post-PCI in the UFH-alone arm but not in rivaroxaban-treated patients. In this exploratory trial, rivaroxaban effectively suppressed coagulation activation after elective PCI and stenting.

Investigation of the effect of macitentan on the pharmacokinetics and pharmacodynamics of warfarin in healthy male subjects

BACKGROUND AND OBJECTIVES

Macitentan is a novel dual endothelin receptor antagonist recently approved for the treatment of pulmonary arterial hypertension (PAH). Warfarin, an anticoagulant often prescribed to patients with PAH, has a narrow therapeutic index and is prone to potential interactions with drugs. This study assessed the effects of macitentan on the pharmacokinetics and pharmacodynamics of single-dose warfarin in healthy subjects.

METHODS

This was a randomised, open-label, single-centre, two-way crossover (treatment A followed by treatment B, or vice versa), phase I study in 14 healthy male subjects. Treatment A was a loading dose of macitentan 30 mg on Day 1 followed by 10 mg once daily for 8 days, with a single 25 mg dose of warfarin on Day 4. Treatment B was a single dose of warfarin on Day 1. Blood samples were assessed for warfarin pharmacokinetics (R- and S-warfarin) and pharmacodynamics [international normalised ratio (INR) and factor VII]. Plasma trough concentrations of macitentan and its active metabolite (ACT-132577) and the safety and tolerability of each treatment were also assessed.

RESULTS

Plasma concentrations of R- and S-warfarin were similar in both treatment periods. Warfarin did not affect the mean trough plasma concentrations of macitentan or ACT-132577. Macitentan did not affect the pharmacodynamics of warfarin; the mean INR and factor VII activity versus time profiles were similar with and without macitentan.

CONCLUSIONS

The absence of effect of macitentan on the pharmacokinetics and pharmacodynamics of a single dose of warfarin suggests that both drugs can be concomitantly administered without need for dose adjustment.

Global assays and the management of oral anticoagulation

Coagulation tests range from global or overall tests to assays specific to individual clotting factors and their inhibitors. Whether a particular test is influenced by an oral anticoagulant depends on the principle of the test and the type of oral anticoagulant. Knowledge on coagulation tests applicable in monitoring status and reversal of oral anticoagulation is a prerequisite when studying potential reversal agents or when managing anticoagulation in a clinical setting. Specialty tests based on the measurement of residual activated factor X (Xa) or thrombin activity, e.g., are highly effective for determining the concentration of the new generation direct factor Xa- and thrombin inhibitors, but these tests are unsuitable for the assessment of anticoagulation reversal by non-specific prohemostatic agents like prothrombin complex concentrate (PCC) and recombinant factor VIIa (FVIIa). Global coagulation assays, in this respect, seem more appropriate. This review evaluates the current status on the applicability of the global coagulation assays PT, APTT, thrombin generation and thromboelastography in the management of oral anticoagulation by vitamin K antagonists and the direct factor Xa and thrombin inhibitors. Although all global tests are influenced by both types of anticoagulants, not all tests are useful for monitoring anticoagulation and reversal thereof. Many (pre)analytical conditions are of influence on the assay readout, including the oral anticoagulant itself, the concentration of assay reagents and the presence of other elements like platelets and blood cells. Assay standardization, therefore, remains an issue of importance.

Clinical utility of apixaban in the prevention and treatment of venous thromboembolism: current evidence

Anticoagulation with heparin and vitamin K antagonist has been the mainstay of prevention and treatment of venous thromboembolism (VTE) for many years. In recent years, novel oral anticoagulants such as dabigatran etexilate (a direct thrombin inhibitor) and rivaroxaban, apixaban, and edoxaban (a direct factor Xa inhibitor) have emerged for the prevention and treatment of VTE. Novel oral anticoagulants have been shown to be noninferior to vitamin K antagonist or heparin in the prevention and treatment of VTE. This review specifically examines the role of apixaban in the prevention and treatment of VTE based on the available literature. The management of apixaban in the perioperative setting is also explored because some patients on apixaban may require surgical intervention. Finally, we discuss the management of apixaban-induced major bleeding complications, the relevance of drug–drug interactions, and patient education.

Switching between oral anticoagulants

Until about 4 years ago, warfarin was the only oral anticoagulant approved in the United States, and switching between oral anticoagulants has become an option since the emergence of the novel oral anticoagulants dabigatran, rivaroxaban, and apixaban. What are the reasons one may switch between the agents and how is this done? Discussed in this article are the 4 agents approved in the United States, their characteristics, reasons one may switch, and methods for conversion. After a thorough search of original trial data and recent expert review articles, we have summarized the most recent recommendations below and briefly discuss upcoming oral anticoagulants that show promise.

Common GI Drug Interactions in the Elderly

OPINION STATEMENT

The careful review of drug-drug interactions is vital to the safe prescribing of medications for chronic medical conditions. The elderly population suffers from multiple medical problems, and polypharmacy leads to further morbidity in this vulnerable group of patients. We discuss gastrointestinal conditions such as GERD, peptic ulcer disease, gastroparesis, diarrhea, constipation, irritable bowel syndrome, inflammatory bowel disease, chronic liver disease and the commonly used medications in these conditions. Treatment options must be individualized and tailored to accommodate the underlying pharmacokinetics and known drug-drug interactions. The indication for the use of a therapeutic agent in the elderly and the duration of use must be frequently readdressed to help prevent polypharmacy and adverse drug reactions. Medications should be started at a low dose with careful titration to achieve a clinical response to prevent toxicity. The aim of this article is to increase awareness of important drug-drug interactions of commonly prescribed gastrointestinal medications in the elderly.

Periprocedural management of patients on anticoagulants

Every year, new studies are undertaken to address the complex issue of periprocedural management of patients on anticoagulants and antiplatelet medications. In addition, newer drugs add to the confusion among clinicians about how to best manage patients taking these agents. Using the most recent data, guidelines, and personal experience, this article discusses recommendations and presents simplified algorithms to assist clinicians in the periprocedural management of patients on anticoagulants.

New oral anticoagulants in patients with nonvalvular atrial fibrillation: a review of pharmacokinetics, safety, efficacy, quality of life, and cost effectiveness

Atrial fibrillation (AF) continues to be a leading cause of cerebrovascular morbidity and mortality resulting from cardioembolic stroke. Oral anticoagulation therapy has been shown to decrease the incidence of cardioembolic stroke in patients with AF by more than 50%. Appropriate use of anticoagulation with vitamin K antagonists requires precise adherence and monitoring. A number of factors that potentially induce patients’ dissatisfaction reduce quality of patient life. New direct oral anticoagulants, such as the direct factor Xa inhibitors rivaroxaban, apixaban, edoxaban, and the thrombin inhibitor dabigatran, were developed to overcome the limitations of the conventional anticoagulant drugs. However, models to optimize the benefit of therapy and to ensure that therapy can be safely continued are missing for the new oral anticoagulants. This review will briefly describe the new oral anticoagulants dabigatran, rivaroxaban, apixaban, and edoxaban with focus on their use for prevention of embolic events in AF. Moreover, it will discuss the safety, efficacy, cost data, and benefit for patients’ quality of life and adherence.

Prolonged anticoagulant activity of rivaroxaban in a polymorbid elderly female with non-convulsive epileptic state

OBJECTIVES AND BACKGROUND

Rivaroxaban, an oral direct factor Xa-inhibitor was non-inferior to adjusted dose warfarin in the prevention of stroke and embolism among patients with atrial fibrillation (AF) in the ROCKET-AF trial and has been approved for stroke prevention in AF.

CASE REPORT

A 88-years-old female (body-mass-index = 19.95) with AF, hypertension and diabetes mellitus, hospitalized because of heart failure and a non-convulsive epileptic state, was treated by valproate, mirtazepin, nebivolol, digitoxin, lisinopril, gliclazide and amlodipine. Irrespective of renal insufficiency, rivaroxaban 15 mg/d was started. After 3 days rivaroxaban was stopped because of concerns about the bleeding risk. Coagulation tests 28 h after rivaroxaban-intake showed INR 2.26, PT 35%, aPTT 38.3 s and anti-Factor Xa-activity 2.00 U/ml. Explanations for the prolonged anticoagulant activity of rivaroxaban comprise renal failure, the low body-mass-index, the advanced age and drug-drug interactions of rivaroxaban with mirtazepin, valproate and amlodipine.

CONCLUSION

Health care providers should consider renal function, concomitant medication, polymorbidity and age prior to prescribing rivaroxaban. Care has to be taken when prescribing rivaroxaban to patients who are different from those included in the ROCKET AF trial.

The epidemic of pre-injury oral antiplatelet and anticoagulant use

BACKGROUND

As the population ages, an increasing number of trauma patients are taking antiplatelet and anticoagulant medications (ACAP) prior to their injuries. These medications increase their risk of hemorrhagic complications, particularly intracerebral hemorrhage. Clopidogrel and warfarin are common and their mechanisms well understood, but optimal reversal methods continue to evolve. The novel direct thrombin and factor Xa inhibitors are less well described and do not have existing antidotes.

METHODS

This article reviews the relevant literature on traumatic outcomes with use of ACAP medications, as well as data on ideal reversal strategies. Suggested algorithms are introduced, and future research directions discussed.

RESULTS

Although they are beneficial in preventing clot formation, once bleeding occurs ACAP medications contribute to increased morbidity and mortality, particularly in geriatric patient populations. The efficacy of clopidogrel reversal with platelet transfusions and DDAVP remains unclear. Warfarin use is best treated with the algorithm-driven use of plasma, vitamin K, prothrombin complex concentrates (PCCs) and possibly recombinant factor VIIa depending upon specific patient and injury factors. Optimal treatment for direct thrombin and factor Xa inhibitors has yet to be developed, but PCCs are promising for rivaroxaban and apixaban while dabigatran is best treated with medication cessation and the possible addition of activated PCCs or hemodialysis.

CONCLUSION

New developments in reversal of the ACAP medications are promising, particularly PCCs for warfarin and the factor Xa inhibitors. Function assays and clear antidotes are needed for the thrombin and Xa inhibitors. Research on outcomes and appropriate treatments is actively ongoing.

New oral anticoagulants and oculoplastic surgery

The use of oral anticoagulants is increasing because of the rising prevalence of atrial fibrillation and other cardiovascular diseases that occur in an aging population. In the last decade, several new oral anticoagulants have emerged, comprising the direct thrombin inhibitor dabigatran and the factor Xa inhibitors apixaban and rivaroxaban. Although these new anticoagulants may not affect clear corneal cataract surgery, their use will impact the management of patients having eyelid, orbital, and nasolacrimal procedures. The objective of this review is to provide a concise and practical approach to the perioperative management of patients who require an oculoplastic procedure and are receiving these new anticoagulants.

The use of novel oral anticoagulants for thromboprophylaxis after elective major orthopedic surgery

Venous thromboembolism is a common cause of morbidity and mortality among patients undergoing elective orthopedic surgery. Due to the high incidence of venous thromboembolism in this setting, perioperative anticoagulation is the recommended approach for thromboprophylaxis. Low molecular weight heparin (LMWH), fondaparinux and warfarin are the agents commonly used for thromboprophylaxis. The well-recognized limitations of warfarin and the inconvenience and discomfort associated with the subcutaneous administration of low molecular weight heparin and fondaparinux inspired intense investigation to develop novel oral anticoagulants (NOACs) with more predictable pharmacokinetics, fewer drug interactions and no need for regular laboratory monitoring. Three NOACs have been demonstrated to be effective for thromboprophylaxis after total hip arthroplasty (THA) and total knee arthroplasty (TKA) in large randomized controlled trials. Here we review the pharmacology of rivaroxaban, dabigatran, and apixaban, summarize the major clinical trials of these agents in thromboprophylaxis after THA and TKA, and discuss the clinical factors to be considered by providers when selecting a NOAC for their patients.