New oral anticoagulants: discussion on monitoring and adherence should start now!

Comparative analysis of andexanet alfa and prothrombin complex concentrate in reversing anticoagulation by rivaroxaban ex vivo

BACKGROUND

The comparative effectiveness of the specific antidote andexanet alfa vs the nonspecific therapy four-factor prothrombin complex concentrates (4F-PCCs) as reversal agents for direct factor Xa (FXa) inhibitors in severely bleeding patients is unclear. We hypothesised that specific reversal using andexanet alfa would be more effective than a high dose of PCC (50 IU kg-1) for reversing the FXa inhibitor rivaroxaban.

METHODS

The reversal potential of andexanet alfa, various 4F-PCCs, and activated PCC was investigated ex vivo in human blood anticoagulated with rivaroxaban (37.5, 75, 150, and 300 ng ml-1) using a panel of coagulation parameters, including conventional coagulation assays, thrombin generation, and a newly developed viscoelastometric device. We simulated in vivo conditions of coagulation activation and fibrin formation using flow chamber experiments of thrombogenicity potential under arterial flow conditions.

RESULTS

The 4F-PCCs normalised clotting profiles only at low rivaroxaban concentrations, whereas andexanet alfa and activated PCC significantly shortened clotting time at all rivaroxaban concentrations. Only andexanet alfa restored thrombin generation to baseline. Flow chamber results showed that various 4F-PCCs concentration-dependently restored clot formation.

CONCLUSIONS

In contrast to thrombin generation measurements, haemostatic reversal of rivaroxaban using high-dose 4F-PCCs exhibited similar efficacy as andexanet alfa in flow chamber experiments. The haemostatic effects of 4F-PCCs and andexanet alfa in the context of bleeding patients taking FXa inhibitors requires further study.

Methodological considerations for investigating oral anticoagulation persistence in atrial fibrillation

AIMS

Reports of long-term oral anticoagulant (OAC) therapy for atrial fibrillation (AF) reveal highly variable, and generally suboptimal estimates of medication persistence. The objective of this review is to summarize current literature and highlight important methodological considerations for interpreting persistence research and designing studies of persistence on OAC treatment.

METHODS AND RESULTS

We summarize differences in study methodology, setting, timing, treatment, and other factors associated with reports of better or worse persistence. For example, prospective compared with retrospective study designs are associated with higher reported persistence. Similarly, patient factors such as permanent AF or high stroke risk, and treatment with non-vitamin K oral antagonists relative to vitamin K antagonists are associated with higher persistence. Persistence has also been reported to be higher in Europe compared with North America and higher when the treating physician is a general practitioner compared with a specialist. We propose a framework for assessing and designing persistence studies. This framework includes aspects of patient selection, reliability and validity of measures, persistence definitions, clinical utility of measurements, follow-up periods, and analytic approaches.

CONCLUSIONS

Differences in study design, patient selection, treatments, and factors such as the countries/regions where studies are conducted or the type of treating physician may help explain the variability in OAC persistence estimates. A framework is proposed to assess persistence studies. This may have utility to compare and interpret published studies as well as for planning of future studies.

The relationship between DOAC levels and clinical outcomes: The measures tell the tale

Direct oral anticoagulants (DOACs) are increasingly used for treatment and prevention of thromboembolic diseases, used in fixed dose regimens. Although their safety and efficacy profiles are considered optimal, clinical events still occur. Given that anticoagulation treatment is a delicate balance between clotting and bleeding, it is possible that an optimal target spot exists where the effect of anticoagulation achieves both the lowest possible risk of bleeding and thrombosis. Other currently available anticoagulants (ie, vitamin K antagonists and heparins) provide important clues for this. If such a target spot exists, tailored DOAC therapy may further benefit patients. This opinion article summarizes the current available evidence that suggests that such a tailored strategy could work. It also describes research suggestions for conducting studies in patient populations such as patients with extremes of body weight or impaired kidney function to evaluate whether tailored treatment with DOACs could lead to better patient outcomes.

Venous Thromboembolism: Role of the Clinical Laboratory in Diagnosis and Management

Background

Venous thromboembolism (VTE) is the third most common cause of cardiovascular illness and is projected to double in incidence by 2050. It is a spectrum of disease that includes deep venous thrombosis (DVT) and pulmonary embolism (PE). In February 2016, the American College of Chest Physicians provided updated management guidelines for DVT and PE to address some of the unresolved questions from the previous version and to provide recommendations related to newer anticoagulants.

Content

Here we review current concepts for screening, diagnosis, thromboprophylaxis, and management of DVT and PE. We also describe the management of VTE in acute, long-term, and extended phases of treatment. Thrombophilia testing is rarely necessary and should be used judiciously; the laboratory can serve an important role in preventing unnecessary testing. The direct oral anticoagulants are as effective as conventional treatment and are preferred agents except in the case of cancer. The initial management of PE should be based on risk stratification including the use of D-dimer testing. Thrombolysis is used in cases of hemodynamically unstable PE and not for low-risk patients who can be treated on an outpatient basis.

Summary

This review is intended to provide readers with updated guidelines for screening, testing, prophylaxis, and management from various organizations.

Measurements of endogenous thrombin potential using the CAT method in cats: Reference values and influence of the direct factor Xa inhibitor apixaban

The aim of this study was to establish a thrombin generation assay (calibrated automated thrombogram, CAT) in cats by determining the precision (repeatability), reference values, and the sensitivity to anticoagulant treatment with the factor Xa inhibitor apixaban. The CAT method was performed on citrated plasma with different commercial tissue factor (TF) reagents (PPP Reagent 1 pM [LOW], PPP Reagent 5 pM, PPP Reagent 20 pM [HIGH]) according to the manufacturers` test instruction. Measurements in triplicate were performed in platelet poor plasma (PPP) of 58 healthy cats and in 6 cats at different times following the oral administration of 2.5 mg apixaban. The median CVs in healthy cats usually were < 10% with the exception of thrombin peak height measured using PPP Reagent 1 pM (14.6%). Reference values of all parameters showed marked inter-individual variability and depended largely on the TF concentration of the used activating reagent. Thrombin generation was significantly influenced by apixaban and reacted more sensitively than other tests of haemostasis including the prothrombin time, aPTT, and rotational elastometry. In conclusion, thrombin generation measured by the CAT method using commercially available reagents seems suitable for the examination of feline PPP and may be a valuable method to establish effective anticoagulant therapies for the feline patient and monitoring of such therapies in cats.

An assay to measure levels of factor Xa inhibitors in blood and plasma

Essentials Direct oral anticoagulants (DOAC) are used for stroke and venous thromboembolism prevention. We report a new assay that measures anti-factor Xa DOAC levels in plasma and whole blood. Rivaroxaban and apixaban can be accurately quantified below trough levels. The ease and accuracy of the assay demonstrate its potential for point-of-care applications.

BACKGROUND

Rivaroxaban and apixaban are the most commonly used anti-factor (F) Xa direct oral anticoagulants (DOAC), with indications for prevention of stroke in nonvalvular atrial fibrillation as well as treatment and prevention of venous thromboembolism. However, lacking is accessibility to a detection method that is able to quantify low levels of anti-FXa DOACs.

OBJECTIVE

We report a new assay that measures anti-FXa DOAC levels in plasma and whole blood.

METHODS

This is achieved by the use of a prothrombin derivative that is labeled with a fluorescent probe (Flu-II), which then acts as the macromolecular substrate to measure residual FXa activity. The Flu-II cleavage is then initiated by the addition of a solution containing FXa, FVa, and phospholipid vesicles composed of 75% PC and 25% PS (PCPS) vesicles with calcium, in the presence of hirudin to prevent feedback activity by the native thrombin generated. The Flu-II cleavage is monitored by fluorescence in real time where the initial rate of fluorescence change is inversely proportional to DOAC levels.

RESULTS

In plasma systems, the assay demonstrates dose-response between 0 and 5 nmol/L rivaroxaban and between 0 and 10 nmol/L apixaban. Corn trypsin inhibitor did not affect this assay. With individual plasma samples, the assay showed excellent consistency and reproducibility. From 2 μL of whole blood, the assay showed dose-response between 0 and 2 nmol/L of DOACs in the final mixture of 100 μL, thus representing up to 100 nmol/L in circulating blood.

CONCLUSION

The assay is ideal for rapidly and accurately measuring DOAC levels in plasma and blood, demonstrating its potential for point-of-care applications.

Direct oral anticoagulants: a review of common medication errors

Stroke and venous thromboembolism continues to be a major cause of morbidity and mortality worldwide. The use of anticoagulation therapy has proven effective in the prevention of stroke and management of thromboembolism; however, initiating treatment may bear clinical burden given the capacity of these agents to cause bleeding. Originally, warfarin has been primarily used, but with the approval of direct oral anticoagulants, therapeutic recommendations have shifted to direct oral anticoagulants for first line therapy for venous thromboembolism for patients without cancer. As compared to warfarin, direct oral anticoagulants are associated with predictable pharmacokinetic profiles, lower bleeding risks, and minimal drug interactions. Complexities in the medication use process can however heighten the risks of causing adverse events. The purpose of this article is to describe common medication errors associated with direct oral anticoagulants, provide practical guidance on the management of direct oral anticoagulants, and suggest strategies to reduce errors. Efforts to minimize medication errors involve the participation of an interdisciplinary team that has standardized policies, risk reduction strategies, and guiding principles to achieve optimal therapeutic outcomes. Current primary literature is not robust in assessment of clinical impact of medication errors associated with DOACs but reports of adverse drug events have been noted. Future studies should be guided to assess clinical outcomes associated with medication errors and identify potential clinical interventions to optimize therapy.

New antiplatelet drugs and new oral anticoagulants

In our daily anaesthetic practice, we are confronted with an increasing number of patients treated with either antiplatelet or anticoagulant agents. During the last decade, changes have occurred that make the handling of antithrombotic medication a challenging part of anaesthetic perioperative management. In this review, the authors discuss the most important antiplatelet and anticoagulant drugs, the perioperative management, the handling of bleeding complications, and the interpretation of some laboratory analyses related to these agents.

Associations between illness beliefs, medication beliefs, anticoagulation-related quality of life, and INR control: Insights from the Switching Study

BACKGROUND

Anticoagulation control with vitamin-K antagonists (VKAs) in patients with atrial fibrillation (AF) or venous thromboembolism (VTE) can be measured using time in therapeutic range (TTR), where TTR >65% is considered good and low TTR may be associated with low adherence.

METHODS

This cross-sectional observational study compared illness beliefs, treatment beliefs, and treatment satisfaction of patients with TTR >75% and TTR <50% using validated tools to determine their association with TTR. Adults requiring chronic VKA therapy were recruited from 2 hospital anticoagulation clinics in London, UK.

RESULTS

311 patients with TTR >75% and 214 with TTR <50% were recruited. TTR >75% patients had been taking warfarin on average over 2 years longer than TTR <50% patients (P < .001). Statistically significant differences in beliefs were found in all subscales other than in treatment control, general harm, and general overuse. Cluster analysis determined there were 4 distinct clusters of beliefs among patients. Multivariate binary logistic regression found VTE patients were least likely to have poor TTR (OR = 0.49; 95% CI 0.29, 0.77). Patients in the "cautious of therapy and fearful of illness" cluster were most likely to have low TTR (OR = 4.75; 95% CI 2.75, 8.77).

CONCLUSION

Illness perceptions, medication beliefs and treatment satisfaction were associated with INR control. VTE patients and those who were accepting of both illness and treatment were most likely to have optimal INR control.

Contemporary utilization of antithrombotic therapy for stroke prevention in patients with atrial fibrillation: an audit in an Australian hospital setting

BACKGROUND

To document antithrombotic utilization in patients with nonvalvular atrial fibrillation (NVAF), particularly, recently approved NOACs (nonvitamin K antagonist oral anticoagulants) and warfarin; and identify factors predicting the use of NOACs versus warfarin.

METHODS

A retrospective audit was conducted in an Australian hospital. Data pertaining to inpatients diagnosed with atrial fibrillation (AF) admitted between January and December 2014 were extracted. This included patient demographics, risk factors (stroke, bleeding), social history, medical conditions, medication history, medication safety issues, medication adherence, and antithrombotic prescribed at admission and discharge.

RESULTS

Among 199 patients reviewed, 84.0% were discharged on antithrombotics. Anticoagulants (± antiplatelets) were most frequently (52.0%) prescribed (two-thirds were prescribed warfarin, the remainder NOACs), followed by antiplatelets (33.0%). Among 41 patients receiving NOACs, 59.0% were prescribed rivaroxaban, 24.0% dabigatran, and 17.0% apixaban. Among patients aged 75 years and over, antiplatelets were most frequently used (37.0%), followed by warfarin (33.0%), then NOACs (14.0%). Compared with their younger counterparts, patients aged 75 years and over were significantly less likely to receive NOACs (14.0% versus 28.0%, p = 0.01). Among the 'most eligible' patients (Congestive Cardiac Failure, Hypertension (, Age ⩾ 75 years, Age= 65-74 years, Diabetes Mellitus, Stroke/ Transient Ischaemic Attack/ Thromboembolism, Vascular disease, Sex female[CHA2DS2-VASc] score ⩾2 and no bleeding risk factors), 46.0% were not anticoagulated on discharge. Patients with anaemia (68.0% versus 86.0%, p = 0.04) or a history of bleeding (65.0% versus 87.0%, p = 0.01) were less likely to receive antithrombotics compared with those without these risk factors. Warfarin therapy was less frequently prescribed among patients with cognitive impairment compared with patients with no cognitive issues (12.0% versus 23.0%, p = 0.01). Multivariate logistic regression modelling identified that patients with renal impairment were 3.6 times more likely to receive warfarin compared with NOACs (odds ratio = 3.6, 95% confidence interval = 0.08-0.90, p = 0.03, 60.0% correctly predicted; Cox and Snell R2 = 0.51, Nagelkerke R2 = 0.69).

CONCLUSION

Despite the availability of NOACs, warfarin remains a preferred treatment option, particularly among patients with renal impairment. The high proportion of eligible patients still being prescribed antiplatelet therapy or 'no therapy' needs to be addressed.

Treatment of venous thromboembolism with rivaroxaban in relation to body weight

The pharmacokinetics of oral rivaroxaban are highly predictable and only affected to a limited extent by bodyweight; therefore, dose adjustments for bodyweight are not required. However, this raises concerns among physicians for potential under- or overdosing. This substudy of the randomised EINSTEIN DVT and EINSTEIN PE trials, which compared rivaroxaban with enoxaparin/vitamin K antagonist (VKA) therapy, aimed to determine the incidence of major bleeding in patients with a low bodyweight and recurrent venous thromboembolism (VTE) in patients with a high bodyweight during rivaroxaban or enoxaparin/VKA therapy. More than 8,000 patients with objectively diagnosed deepvein thrombosis or pulmonary embolism were included. Adjusted hazard ratios for recurrent VTE and bleeding were calculated using the Cox proportional hazards model. Analyses were performed for both the first 21 days of treatment and the whole treatment period. For rivaroxaban recipients, there was no association between bodyweight or body mass index (BMI) and risk of recurrent VTE (ptrend=0.87 and 0.62, respectively), major bleeding (ptrend=0.24 and 0.36, respectively) or clinically relevant bleeding (ptrend=0.17 and 0.63, respectively). Major bleeding events were numerically lower in rivaroxaban patients across all bodyweight and BMI categories. Hazard ratios for rivaroxaban vs enoxaparin/VKA were similar in all bodyweight and BMI categories, both during the first 21 days and the whole treatment period. The fixed-dose rivaroxaban regimen is not associated with an increased risk of major bleeding or recurrent VTE in patients with either a low or high bodyweight. A high BMI was not associated with an increased risk of recurrent VTE during anticoagulation.

Note: This study was presented at the 25th Congress of the International Society on Thrombosis and Haemostasis; June, 2015, Toronto, Canada. Trial registration: EINSTEIN DVT (NCT00440193), EINSTEIN PE (NCT00439777).

Rapid liquid chromatography tandem mass spectrometry determination of rivaroxaban levels in human plasma for therapeutic drug monitoring

A rapid, sensitive, high-throughput liquid chromatography coupled with tandem mass spectrometry method for the quantification of rivaroxaban from human plasma has been developed and validated. For the analytical separation a Zorbax SB-C18 column with isocratic flow of mobile phase composed of 0.2% formic acid in water and acetonitril (65:35, V/V) with a flow rate of 1 mL/min at a temperature of 45ºC was used. Detection of rivaroxaban was performed using positive electrospray ionization and MS/MS mode (sum of m/z 231.1; 289.2 and 318.2 from m/z 436.3). Plasma samples were prepared using single-step protein precipitation with methanol. Method validation was performed with regards to selectivity, linearity (r >0.9927), within-run and between-run precision (CV< 13.1 %) and accuracy (bias< 9.4 %) over a concentration range of 24.00 - 960.00 ng/mL plasma. Recovery was between 96.5 - 108.5% and the lower limit of quantification of rivaroxaban was 24.00 ng/mL. The developed method is simple, rapid, and selective, requires small plasma sample volumes, and was successfully applied for therapeutic drug monitoring of rivaroxaban in treated patients.

Using Artificial Intelligence to Reduce the Risk of Nonadherence in Patients on Anticoagulation Therapy

BACKGROUND AND PURPOSE

This study evaluated the use of an artificial intelligence platform on mobile devices in measuring and increasing medication adherence in stroke patients on anticoagulation therapy. The introduction of direct oral anticoagulants, while reducing the need for monitoring, have also placed pressure on patients to self-manage. Suboptimal adherence goes undetected as routine laboratory tests are not reliable indicators of adherence, placing patients at increased risk of stroke and bleeding.

METHODS

A randomized, parallel-group, 12-week study was conducted in adults (n=28) with recently diagnosed ischemic stroke receiving any anticoagulation. Patients were randomized to daily monitoring by the artificial intelligence platform (intervention) or to no daily monitoring (control). The artificial intelligence application visually identified the patient, the medication, and the confirmed ingestion. Adherence was measured by pill counts and plasma sampling in both groups.

RESULTS

For all patients (n=28), mean (SD) age was 57 years (13.2 years) and 53.6% were women. Mean (SD) cumulative adherence based on the artificial intelligence platform was 90.5% (7.5%). Plasma drug concentration levels indicated that adherence was 100% (15 of 15) and 50% (6 of 12) in the intervention and control groups, respectively.

CONCLUSIONS

Patients, some with little experience using a smartphone, successfully used the technology and demonstrated a 50% improvement in adherence based on plasma drug concentration levels. For patients receiving direct oral anticoagulants, absolute improvement increased to 67%. Real-time monitoring has the potential to increase adherence and change behavior, particularly in patients on direct oral anticoagulant therapy.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02599259.

The assessment of anticoagulant activity to predict bleeding outcome in atrial fibrillation patients receiving dabigatran etexilate

Special circumstances may require the measurement of the anticoagulant effect of dabigatran etexilate. No data currently link any given coagulation test to bleeding outcomes in patients receiving dabigatran etexilate for atrial fibrillation. Nonvalvular atrial fibrillation patients receiving dabigatran etexilate of 110 mg (DE110) or 150 mg (DE150) were consecutively enrolled. The hemoclot thrombin inhibitor (HTI) assay, prothrombin time, and activated partial thromboplastin time (APTT) measurements were correlated with bleeding events during a prospective follow-up. There were 17 bleeding events (8.2%) in 208 patients (74.7 ± 10.3 years old, 67.9% male, median follow-up: 364 days), whereas 15 patients with bleeding events used DE110. Compared with DE110, the patients receiving DE150 were younger and more often male and had lower HAS-BLED and CHA2DS2VASc scores and better renal function. Patients' HTI levels were very variable (DE110, 10-90th percentile: 20.5-223.9 ng/ml). A receiver-operator characteristic curve gave a median cutoff HTI level of 117.7 ng/ml to predict bleeding events (C-statistics: 0.65; P = 0.036), but no cutoff could be determined for prothrombin time or APTT. Based on the Kaplan-Meier analysis, a dabigatran etexilate level greater than 117.7 ng/ml was associated with a higher bleeding rate (15.4% vs. 4.9%, P = 0.01). After multivariate Cox regression analysis, HTI levels, history of stroke, and male sex were independent risk factors for bleeding events. Dabigatran etexilate-HTI levels were independently associated with bleeding in patients receiving routine clinical care. Blood sampling at multiple time points might be needed to increase reliability because of high variation of dabigatran etexilate-HTI levels.

Search For The Ideal Antithrombotic Drug: Utopian Task Likely Is Implemented Already

Atrial fibrillation is the most prevalent cardiac arrhythmia with a high risk of ischemic stroke. Thromboprophylaxis plays a key role in prevention of cardioembolic and non-cardioembolic events. Oral antithrombotic drugs are most often used to reduce hypercoagulable state. Patients may suffer from both under- and overtreatment compromising the outcomes. Medication peculiarities at large are well-known and widely debated. Non-adherence to antithrombotic drug regimen poses a significant risk of stroke. There is a pressing need for more detailed delineation of risk factors, namely by incorporation of the letter "N" (meaning "Non-adherence to drug therapy") into the well-known risk score alphanumeric display: CHA₂DS₂N-VASc. Better delineation of risk factors related to antithrombotic treatment as well as those related to treatment for congestive heart failure, hypertension, diabetes are desirable. Similarly, the bleeding risk score formula HAS-BLED might be improved by an additional risk factor, marked as the symbol "E", meaning "Excessive antithrombotic dosing" i.e. HAS-BLEDE. Improved formulas would help raise the predictive scores value and awareness for clinicians facing the problem of non-adherence to treatment regimen. If patients properly followed the prescribed drug therapy regimen it would potentially reveal that we already have ideal or near ideal antithrombotic drug(s). These drugs, herein non-specified, are widely used, but due to non-adherence they are not categorized as the best ones. That is why considerable efforts are focused on continued research and new developments.

Laboratory Monitoring: A Turning Point in the Use of New Oral Anticoagulants

Large clinical trials have demonstrated that new oral anticoagulants (NOACs) are at least as efficient as vitamin K antagonists (VKAs) in preventing thromboembolic events, while providing a better safety profile. The relatively stable pharmacokinetics and pharmacodynamics, the reduced reports on food and drug interactions, and the wide therapeutic windows of NOACs appear to provide a more predictable anticoagulant effect than that observed with VKAs, enabling the use of fixed doses without the need for monitoring. However, the safe implementation of NOACs may require additional judgment, and one should not have the erroneous impression that NOACs are free from interactions or that inter- and intra-individual variability is absent with NOACs. In fact, a consensus seems to have been reached concerning the usefulness of "circumstantial" testing in certain clinical scenarios. Recent data also suggest that factors such as intercurrent diseases, drug interactions, and inexplicable variability may occasionally alter the anticoagulant effect of NOACs. Furthermore, the issue of nonadherence, already high in VKA-treated patients, may represent an even greater clinical concern with NOACs, given their short half-lives. This review aims to underline the main arguments that support the need for NOAC monitoring, at least in selected categories of patients. Additionally, an overview of classic coagulation assays and novel laboratory techniques that may provide a tool for NOAC monitoring is also provided.

The modification of the thrombin generation test for the clinical assessment of dabigatran etexilate efficiency

A new oral anticoagulant, dabigatran etexilate (DE, a prodrug of direct thrombin inhibitor (DTI) dabigatran), has been used clinically to prevent thrombosis. The assessment of dabigatran efficiency is necessary in some clinical cases, such as renal insufficiency, risk of bleeding, and drug interactions. However, a specific thrombin generation test (TGT) that is one of the most informative and sensitive to anticoagulant therapy (calibrated automated thrombinography (САТ)) shows a paradoxical increase of test parameters, such as endogenous thrombin potential (ETP) and peak thrombin, in patients receiving DE. The paradoxical behaviour of ETP and peak thrombin in these patients in the presence of DTIs is mostly caused by a decrease in the activity of thrombin in the α₂-macroglobulin-thrombin complex that is used as a calibrator in CAT. For a correct estimation of the TGT parameters in patient’s plasma containing DTIs we proposed to use our previously described alternative calibration method that is based on the measurement of the fluorescence signal of a well-known concentration of the reaction product (7-amino-4-methylcoumarin). In this study, the validity of such approach was demonstrated in an ex vivo study in patients with knee replacement and two special patients with multiple myeloma, who received DE for thrombosis prophylaxis.

Once-daily rivaroxaban for long-term stroke prevention in patients with atrial fibrillation

Oral anticoagulation is the long-term standard of care for preventing stroke in patients with atrial fibrillation (AF). However, anticoagulation is associated with an increased risk of bleeding, such that its use should be based on the absolute risks of stroke and bleeding, and the relative benefit-risk profile of the individual patient. Non-vitamin K antagonist oral anticoagulants, including rivaroxaban, are alternatives to vitamin K antagonists such as warfarin in this setting, and are supported in treatment guidelines as the optimal choice for patients with AF at moderate to high risk of stroke. Rivaroxaban can be given in fixed doses without routine coagulation monitoring, and phase III studies have demonstrated its safety profile and efficacy in patients with non-valvular AF, including the elderly and those with co-morbidities. Moreover, rivaroxaban is administered once daily, which has advantages for optimal patient adherence to medication over the long term. The established efficacy and safety profile of rivaroxaban, together with its convenient once-daily dosing schedule, may contribute to improved patient outcomes and lead to sustained benefits for patients with non-valvular AF at risk of stroke.

Validation of an LC–MS/MS method for the simultaneous quantification of dabigatran, rivaroxaban and apixaban in human plasma

Aim: Novel oral anticoagulants are characterized by a wide therapeutic window, yet the determination of their plasma–drug concentrations may be useful in some clinical conditions. Results: An LC–MS/MS method for the analysis of dabigatran, apixaban and rivaroxaban in human plasma has been successfully developed and validated. The analysis of plasma samples from patients given other concomitant drugs revealed no significant interference. By reanalysis of samples from patients on anticoagulant therapy, we found the percentage difference in results between the concentration of repeat and the original sample to be within the threshold limit of 20% in 60 of 63 specimens. Conclusion: The developed LC–MS/MS assay is easily applicable in the clinical management of patients on anticoagulation therapy.

Genetic risk for atrial fibrillation could motivate patient adherence to warfarin therapy: a cost effectiveness analysis

Background

Atrial fibrillation (AF) increases risk of stroke, and although this stroke risk can be ameliorated by warfarin therapy, some patients decline to adhere to warfarin therapy. A prospective clinical study could be conducted to determine whether knowledge of genetic risk for AF could increase adherence to warfarin therapy for patients who initially declined therapy. As a prelude to a potential prospective clinical study, we investigated whether the use of genetic information to increase adherence could be cost effective.

Methods

Markov model assessed costs and utilities of two care strategies for AF patients who declined warfarin therapy. In the usual care strategy patients received aspirin. In the test strategy genetic risk for AF was assessed (genotype of the 4q25 locus) and some patients with a positive genetic test (≥1 risk allele) were assumed to adhere to warfarin therapy. The remaining patients received aspirin. The incremental cost-effectiveness ratio (ICER) was the ratio of the costs differential and the quality adjusted life-years (QALYs) differential for the two strategies.

Results

We found that the 4q25 genetic testing strategy, compared with the usual care strategy (aspirin therapy), would be cost-effective (ICER $ 47,148) if 2.1 % or more of the test positive patients were to adhere to warfarin therapy. The test strategy would become a cost saving strategy if 5.3 % or more of the test positive patients were to adhere to warfarin therapy. If 20 % of test positive patients were to adhere to warfarin therapy in a hypothetical cohort of 1000 patients, 7 stroke events would be prevented and 3 extra-cranial major bleeding events would be caused over 5 years, resulting in a cost savings of ~ $250,000 and a net gain of 9 QALYs.

Discussion

A clinical study to assess the impact of patient knowledge of genetic risk of AF on adherence to warfarin therapy would be merited because even a modest increase in patient adherence would make a genetic testing strategy cost-effective.

Conclusion

Providing patients who declined warfarin therapy with information about their genetic risk of AF would be cost effective if this genetic risk information resulted in modest increases in adherence.

Supporting the use of a coagulometric method for rivaroxaban control: a hypothesis-generating study to define the safety cut-offs

Aims

Although quantitative anti-FXa assays can be used to measure rivaroxaban plasma levels, they are not widely performed or available. We aimed to tentatively determine the cut-off for thromboembolism and bleeding prevention based on the clotting effect of non-rivaroxaban conjugate-activated FX plasma levels in patients with rivaroxaban using a coagulometric method.

Methods and results

Rivaroxaban was added in vitro to normal plasma at a range of 0 to 241 μg/L to cover expected peak and trough levels. Rivaroxaban chromogenic (μg/L) and RVV-confirm as a ratio were determined. Patient plasma samples were assayed with the RVV-confirm reagent. The appropriate rivaroxaban plasma concentration to inhibit clotting mechanisms was based on the remaining FXa in plasma, which was expressed as the ratio of patients/normal, R-C. There is a high correlation between R-C in vitro and spiked normal plasma rivaroxaban concentration (R-Square 0.910, linear equation; 0.971 quadratic equation, p < 0.0001 for both) but not with plasma rivaroxaban chromogenic assays. We propose a cut-off R-C value of 1.65 and 4.5 for safety. Based on the proposed therapeutic range, in 158 assays performed in 58 patients, 6.3 % assays were above the level of bleeding tendency at the peak (R-C 5.39 ± 1.01, median 5.13) and 42 % assays were below the prevention cut-off at the trough (R-C 1.31 ± 0.18, median 1.35).

Conclusions

RVVconfirm® is fast and sensitive to measure the effect of rivaroxaban. Clinical studies are needed to establish whether this cut-off is useful for identifying patients at increased risk of hemorrhage or those who exhibit a low level of anticoagulation.

Dose tailoring of dabigatran etexilate: obvious or excessive?

INTRODUCTION

Dabigatran etexilate is used for preventing blood clots and tends to replace older anticoagulants in many of their indications. However, the 'one dose fits all' policy is subject to criticism. Recent findings assert the anxiety of the scientific community concerning the pharmacokinetic properties of dabigatran etexilate, that is, an important interindividual variability including an important genetic variant with a significant dependence of the renal function as route of elimination.

AREAS COVERED

This meta-opinion provides an overview of the current knowledge and evidence on the dose tailoring of dabigatran etexilate. It also discusses the remaining challenges to benefit from this perspective strategy to enhance the benefit-risk balance of dabigatran etexilate. Data were searched in the published literature and on regulatory agencies' websites. Additionally, unpublished data were searched and discussed.

EXPERT OPINION

Causality between dabigatran exposure and bleeding risk is now established and recommendations on how to best estimate the drug exposure are published. Additionally, simulating studies revealed that a dose adaptation based on dabigatran plasma concentration estimations could improve the benefit-risk profile of the drug. This accumulating evidence suggests that some patients under dabigatran etexilate may benefit from a tailoring of the dose beyond the ones already proposed by the manufacturer.

Non-VKA Oral Anticoagulants: Accurate Measurement of Plasma Drug Concentrations

Non-VKA oral anticoagulants (NOACs) have now widely reached the lucrative market of anticoagulation. While the marketing authorization holders claimed that no routine monitoring is required and that these compounds can be given at fixed doses, several evidences arisen from the literature tend to demonstrate the opposite. New data suggests that an assessment of the response at the individual level could improve the benefit-risk ratio of at least dabigatran. Information regarding the association of rivaroxaban and apixaban exposure and the bleeding risk is available in the drug approval package on the FDA website. These reviews suggest that accumulation of these compounds increases the risk of experiencing a bleeding complication. Therefore, in certain patient populations such as patients with acute or chronic renal impairment or with multiple drug interactions, measurement of drug exposure may be useful to ensure an optimal treatment response. More specific circumstances such as patients experiencing a haemorrhagic or thromboembolic event during the treatment duration, patients who require urgent surgery or an invasive procedure, or patient with a suspected overdose could benefit from such a measurement. This paper aims at providing guidance on how to best estimate the intensity of anticoagulation using laboratory assays in daily practice.

Does the Russell Viper Venom time test provide a rapid estimation of the intensity of oral anticoagulation? A cohort study

BACKGROUND

Dilute Russell Viper Venom Time (DRVV-T) might be useful in urgent settings for screening patients on Non-VKA Oral Anticoagulants (NOACs).

AIM

To compare the accuracy of DRVV-T with gold standard assays for the assessment of pharmacodynamics of dabigatran, rivaroxaban and vitamin K antagonist (VKA) in plasma samples from patients.

METHODS

Sixty rivaroxaban, 48 dabigatran and 50 VKA samples from patients were included. DRVV-T was performed in all groups using STA®-Staclot®DRVV-Screen and -Confirm. For NOACs, PT and aPTT were performed using different reagents while plasma drug concentrations were measured by liquid mass-spectrometry (LC-MS/MS). For VKA, INR was performed using RecombiPlasTin 2G®.

RESULTS

For NOACs, correlations between calibrated STA®-Staclot®DRVV-Confirm and LC-MS/MS (rs=0.88 and 0.97 for rivaroxaban and dabigatran, respectively) were higher than the ones obtained with STA®-Staclot®DRVV-Screen (rs=0.87 and 0.91), PT (rs=0.83 to 0.86) or aPTT (rs=0.84 to 0.89). Bland Altman analyses showed that calibrated DRVV-T methods tend to overestimate plasma concentrations of NOACs. ROC curves revealed that cut-off to exclude supra-therapeutic levels at Ctrough (i.e. 200ng/mL) are different for dabigatran and rivaroxaban. Neither STA®-Staclot®DRVV-Screen nor -Confirm correlated sufficiently with the intensity of VKA therapy (rs=0.35 and 0.52).

CONCLUSIONS

STA®-Staclot®DRVV-Confirm provides a rapid estimation of the intensity of anticoagulation with rivaroxaban or dabigatran without specific calibrators. At Ctrough, thresholds for rivaroxaban and dabigatran can be used to identify supra-therapeutic plasma level. However, this test cannot differentiate the nature of the NOACs. The development of a point-of-care device optimising this method would be of particular interest in emergency situations.

Laboratory measurements of the oral direct factor Xa inhibitor edoxaban: comparison of prothrombin time, activated partial thromboplastin time, and thrombin generation assay

OBJECTIVES

Edoxaban, an oral direct factor Xa inhibitor, does not require routine monitoring. However, assessment of the anticoagulant effects may be required in certain situations.

METHODS

We investigated the effects of edoxaban on prothrombin time (PT), activated partial thromboplastin time (aPTT), and thrombin generation using human platelet-poor plasma (PPP) or platelet-rich plasma (PRP).

RESULTS

Edoxaban concentration-dependently prolonged PT and aPTT. There was a considerable variation in the magnitude of PT prolongation among the reagents used. The variability in aPTT prolongation among the reagents was smaller than that of PT. Edoxaban concentration-dependently inhibited thrombin generation, with a more potent effect seen in PPP than in PRP. Thrombin generation assay was three times more sensitive to edoxaban than PT and aPTT.

CONCLUSIONS

PT had disadvantages of a large variability among different PT reagents. aPTT could be used as a conventional and convenient test with a smaller variation among reagents. Thrombin generation was the most sensitive assay.

Estimation of dabigatran plasma concentrations in the perioperative setting. An ex vivo study using dedicated coagulation assays

The perioperative management of dabigatran is challenging, and recommendations based on activated partial thromboplastin time (aPTT) and thrombin time (TT) are unsatisfactory. Dedicated coagulation tests have limitations at plasma concentrations < 50 ng/ml. Therefore, a more sensitive test, which is available 24/7, is required. It was the aim of this study to investigate the performance of the Hemoclot Thrombin Inhibitors® LOW (HTI LOW) kit, a diluted thrombin time, and the STA® - ECA II(ECA-II) kit, a chromogenic variant of the ecarin clotting time, that were developed to measure low dabigatran concentrations, compared to reference dabigatran analysis by liquid chromatography tandem mass-spectrometry (LC-MS/MS). This study included 33 plasma samples from patients treated with dabigatran etexilate who had plasma concentrations < 200 ng/ml. HTI LOW and ECA-II were performed along with HTI, aPTT (STA®-C. K.Prest® and SynthasIL®) and TT (STA® - Thrombin). All procedures were performed according to recommendations by the manufacturers. Linear (or curvilinear) correlations and Bland-Altman analyses were calculated. For free dabigatran concentrations < 50 ng/ml, the R² of linear correlations were 0.69, 0.84 and 0.61, with HTI, HTI LOW and ECA-II, respectively. The R² for TT, STA®-C. K.Prest® and SynthasIL® were 0.67, 0.42 and 0.15. For HTI, HTI LOW and ECA-II, Bland-Altman analyses revealed mean differences of -6 ng/ml (95 %CI: -25-14 ng/ml), 1 ng/ml (95 %CI: -18-19 ng/ml) and -1 ng/ml (95 %CI: -25-23 ng/ml), demonstrating that tests dedicated to measuring low concentrations are more accurate than HTI. In conclusion, the use of HTI LOW or ECA-II to assess low plasma dabigatran concentrations is supported by our findings.

Appropriateness of Prescribing Dabigatran Etexilate and Rivaroxaban in Patients With Nonvalvular Atrial Fibrillation

Background: Direct oral anticoagulants have been developed to address some of the drawbacks of vitamin-K antagonists. However, special attention should be given when using these drugs, especially in patients with renal insufficiency, questionable compliance, and those at high risk of bleeding. Objective: To evaluate the appropriateness of prescribing dabigatran etexilate (DE) and rivaroxaban in patients with nonvalvular atrial fibrillation (NVAF) in real-life clinical practice. Methods: This was a prospective study that included patients presenting to a teaching hospital from April to mid-October 2013, who were taking rivaroxaban or DE for NVAF. Appropriateness of prescribing was evaluated using 9 of the 10 criteria of the Medication Appropriateness Index. The primary outcome measure was the prevalence of inappropriate prescribing. Secondary outcome measures included ( a) categories of inappropriateness, ( b) prevalence of adverse drug events, and ( c) interventions made by a clinical pharmacist to optimize prescribing. Results: A total of 69 patients were evaluated; 16 patients (23%) had 1 inappropriate criterion, and an additional 18 (26%) had more than 1 inappropriate criterion. The most frequent inappropriate criteria were inappropriate choice (28% of patients), wrong dosage (26%), and impractical modalities of administration (26%). An adverse event (AE) was found in 51% of patients (including 8 patients with transient ischemic attack/stroke). The clinical pharmacists performed 48 interventions, and 94% were accepted by the physician. Conclusions: Inappropriate use of DE and rivaroxaban in patients with NVAF is frequent and possibly leads to AEs. Reinforcing education of health care professionals and patients is needed. Collaboration with clinical pharmacists can contribute to better use.

Preventive strategies against bleeding due to nonvitamin K antagonist oral anticoagulants

Dabigatran etexilate (DE), rivaroxaban, and apixaban are nonvitamin K antagonist oral anticoagulants (NOACs) that have been compared in clinical trials with existing anticoagulants (warfarin and enoxaparin) in several indications for the prevention and treatment of thrombotic events. All NOACs presented bleeding events despite a careful selection and control of patients. Compared with warfarin, NOACs had a decreased risk of intracranial hemorrhage, and apixaban and DE (110 mg BID) had a decreased risk of major bleeding from any site. Rivaroxaban and DE showed an increased risk of major gastrointestinal bleeding compared with warfarin. Developing strategies to minimize the risk of bleeding is essential, as major bleedings are reported in clinical practice and specific antidotes are currently not available. In this paper, the following preventive approaches are reviewed: improvement of appropriate prescription, identification of modifiable bleeding risk factors, tailoring NOAC's dose, dealing with a missed dose as well as adhesion to switching, bridging and anesthetic procedures.

[Patient with acute renal injury presenting dabigatran overdose: Hemodialysis for surgery]

Dabigatran is a direct thrombin inhibitor indicated for stroke and systemic embolism prevention in patients with non-valvular atrial fibrillation. No reversal agent exists, but hemodialysis has been proposed as dabigatran removal method. We report a case of an 80-year-old man presenting hemorrhage with dabigatran overdose caused by obstructive acute renal failure. Before nephrostomy, several hemodialysis sessions were necessary to remove dabigatran probably because of its large volume of distribution.