Evaluation of Anti-Xa Apixaban and Rivaroxaban Levels With Respect to Known Doses in Relation to Major Bleeding Events

BACKGROUND

Although not routinely recommended, anti-Xa level monitoring for apixaban or rivaroxaban may be useful in certain clinical scenarios. There are currently no laboratory standards, therapeutic ranges, or proven correlation between anti-Xa levels and clinical outcomes.

OBJECTIVE

This study describes the utilization, application, and association of anti-Xa levels with clinical outcomes in patients receiving apixaban or rivaroxaban.

METHODS

This retrospective, descriptive study included adult inpatients within the Houston Methodist System on apixaban or rivaroxaban with at least one anti-Xa level ordered subsequent to administered doses. The primary endpoint was major bleeding according to International Society on Thrombosis and Haemostasis criteria. Secondary endpoints included reasons for anti-Xa level ordering, anti-Xa levels at different time intervals post-dose, and thrombotic events. Pre-specified subgroup analyses were performed to further evaluate the primary endpoint.

RESULTS

The study population consisted of 169 patients and 234 anti-Xa levels. Twenty-nine levels were obtained in context of major bleeding. The majority of levels were not drawn as peak levels 2-4 hours post-dose, however remained quantifiable above typical observed levels within this timeframe and well beyond 24 hours post-dose. Patient characteristics with major bleeding included elderly age, acute renal impairment, and low body weight. At least 14 unique reasons for anti-Xa level ordering were identified. Twenty-nine levels were associated with thrombotic events.

CONCLUSION

Anti-Xa levels may be useful for assessment of current drug concentrations, immediate safety of therapy, and guidance for possible clinical interventions. Dose titration and reversal therapies based on anti-Xa level results in major bleeding warrant further research.

Evaluation of characteristics and dosing regimens in patients with new or recurrent thrombosis on apixaban and rivaroxaban

Direct factor Xa inhibitors, such as apixaban and rivaroxaban, are widely used for treatment and prevention of venous thromboembolism; however, recent cases of therapeutic failure have been reported. Potential risk factors associated with therapeutic failure such as dose deviations outside of package labeling recommendations, and the use of direct factor Xa-specific inhibitor levels to guide clinical decision making continue to be areas of further investigation. Our study aimed to describe characteristics and dosing regimens in patients on apixaban or rivaroxaban who experienced a new or recurrent thrombosis. We performed a retrospective chart review on 190 patients on either apixaban or rivaroxaban presenting to our institution with new or breakthrough thromboembolism. Evaluation of prescribed anticoagulation regimens compared to package labeling recommendations, direct factor Xa inhibitor-specific anti-Xa levels, anticoagulation interruptions, use of parenteral bridge anticoagulation, final anticoagulation regimen disposition, and thrombosis-associated mortality were recorded. In patients presenting with breakthrough thromboembolism, 78% were on a regimen that matched package labeling recommendations. Anti-Xa levels were documented in 66 patients, the majority of which fell within institutional expected ranges at time of thrombosis. Therapy interruptions immediately prior to thrombosis were observed in 22% of patients and 21% of those patients received parenteral anticoagulation during interruption. Upon discharge, 46% of patients continued the same anticoagulation regimen with no changes. The mortality rate was 6%. In patients who present with new thromboembolism on apixaban or rivaroxaban, a thorough review of risks and benefits should be conducted to mitigate future risk of recurrent thrombosis.

Thrombin Generation in a patient with Triple Positive Antiphospholipid Syndrome Treated with Three Different Anticoagulants

INTRODUCTION

Venous and arterial thrombosis is one of the hallmarks of Antiphospholipid Antibody Syndrome (APS). The traditional treatment for individuals with APS and venous thrombosis has been vitamin K antagonists. However, with the widespread use of direct oral anticoagulants (DOACs) there has been conflicting evidence regarding their safety and failure rate as alternatives to warfarin. Reasons for this failure remain elusive. We utilized the thrombin generation assay (TGA) to investigate the anticoagulation efficacy of three different agents in a patient with triple-positive APS to acquire a better understanding of the pathophysiology of APS.

METHODS

Blood samples were obtained from a single patient with APS at five distinct time points while on three different anticoagulants: rivaroxaban, warfarin, and enoxaparin. The effects of these anticoagulants on TG potential were evaluated using the TGA.

RESULTS

In the presence of thrombomodulin, rivaroxaban had the highest endogenous thrombin potential, thrombin peak, velocity index, and thrombin inactivation velocity (821.9 nMmin, 121.5 nM, 36.44 nM/min, 7.19 nM/min) when compared to warfarin (121-367 nMmin, 13.85-121.5 nM, 3.02-3.85 nM/min, 0.64-4.55 nM/min) and enoxaparin (242-378.8 nM min, 21.33-23.78 nM, 2.87-3.85 nM/min, 0.747-0.784 nM/min). This trend was also observed in the absence of thrombomodulin.

CONCLUSIONS

These results suggest that patients with APS treated with rivaroxaban may be at greater risk for thrombosis compared to warfarin or enoxaparin. The findings may provide insight into the recent studies in patients with triple positive APS randomized to different anticoagulants demonstrating high rates of thrombosis with rivaroxaban. Further studies are necessary to elucidate the clinical significance.

Role of direct oral anticoagulants in patients with kidney disease

The anticoagulation field is experiencing a renaissance that began with regulatory approval of the direct thrombin inhibitor dabigatran, a direct oral anticoagulant (DOAC), in 2010. The DOAC medication class has rapidly evolved to include the additional approval of 4 direct factor Xa inhibitors. Commensurately, DOAC use has increased and collectively account for the majority of new anticoagulant prescriptions. Despite exclusion of patients with moderate-to-severe kidney disease from most pivotal DOAC trials, DOACs are increasingly used in this setting. An advantage of DOACs is similar or improved antithrombotic efficacy with less bleeding risk when compared with traditional agents. Several post hoc analyses, retrospective studies, claims data studies, and meta-analyses suggest that these benefits extend to patients with kidney disease. However, the lack of randomized controlled trial data in specific kidney disease settings, with their unique pathophysiology, should be a call to action for the kidney community to systematically study these agents, especially because early data suggest that DOACs may pose less risk of anticoagulant-related nephropathy than do vitamin K antagonists. Most DOACs are renally cleared and are significantly protein bound in circulation; thus, the pharmacokinetics of these drugs are influenced by reduced renal function and proteinuria. DOACs are susceptible to altered metabolism by P-glycoprotein inhibitors and inducers, including drugs commonly used for the management of kidney disease comorbidities. We summarize the currently available literature on DOAC use in kidney disease and illustrate knowledge gaps that represent important opportunities for prospective investigation.

Factor Xa inhibitors for preventing recurrent thrombosis in patients with antiphospholipid syndrome: a longitudinal cohort study

OBJECTIVE

The objective of this study was to clarify the efficacy and safety of factor Xa inhibitors for antiphospholipid syndrome patients in real world utilization.

METHODS

This is a retrospective cohort study comprised of all consecutive patients with antiphospholipid syndrome in our department over a period of 28 years. Patients treated with factor Xa inhibitors were extracted from the cohort. As a control group, patients treated with warfarin were selected from the same cohort with matched age, gender, coexistence of systemic lupus erythematosus, and the presence of antiplatelet therapy, after which we used a propensity score for each of the risk factors as an additional covariate in multivariate Cox proportional hazard regression. The primary endpoint was set as thrombotic and hemorrhagic event-free survival for five years.

RESULTS

Among 206 patients with antiphospholipid syndrome, 18 had a history of anti-Xa therapy (five rivaroxaban, 12 edoxaban, one apixaban). Fourteen out of 18 patients on anti-Xa therapy had switched to factor Xa inhibitors from warfarin. Event-free survival was significantly shorter during anti-Xa therapy than that during warfarin therapy (hazard ratio: 12.1, 95% confidence interval: 1.73-248, p = 0.01) ( Figure 1(a) ). Similarly, event-free survival in patients treated with factor Xa inhibitors was significantly shorter compared with controls (hazard ratio: 4.62, 95% confidence interval: 1.54-13.6, p = 0.0075). In the multivariate Cox proportional hazard model, event-free survival in patients with anti-Xa therapy remained significantly shorter (hazard ratio: 11.9, 95% confidence interval: 2.93-56.0, p = 0.0005).

CONCLUSIONS

Factor Xa inhibitors may not be recommended for antiphospholipid syndrome.