Direct oral anticoagulants and heparins: laboratory values and pitfalls in 'bridging therapy'

Application of anti-Xa assay in monitoring unfractionated heparin therapy in contemporary antithrombotic management

INTRODUCTION

Unfractionated heparin remains the most widely used agent in the prevention and acute treatment of thrombosis. Pharmacological complexities of this intriguing agent mandate frequent monitoring of its anticoagulant properties to maintain safe and effective hematological outcomes. Although activated partial thromboplastin time has been the standard test to monitor unfractionated heparin therapy for many decades, the anti-Xa assay has emerged as a substitute or adjunct in many institutions.

AREAS COVERED

This brief report outlines the key features of anti-Xa assay in monitoring unfractionated heparin in acute management of thrombosis in various contemporary settings, with emphasis on evidence for clinical outcomes. PubMed.gov database was utilized to obtain the pertinent literature.

EXPERT OPINION

The anti-Xa activity is primarily a reflection of UFH concentration and does not account for other hematological variables frequently present in contemporary anticoagulation management. The advantage of the anti-Xa assay in monitoring UFH therapy is predicated upon its limitations to account for global physiological hemostasis. There are significant disease and drug interactions that may potentially result in false in-vitro analysis of anti-Xa activity. Routine application of the anti-Xa assay is not evidence-based at this time.

An update of the efficacy and comparative characteristics of direct (new) oral anticoagulants (DOACs)

Direct (New-generation) Oral Anticoagulants (DOACs) have emerged as effective agents which are used in place of vitamin-K antagonists in treatment and prophylaxis of Venous Thromboembolism (VTE), atrial fibrillation and other thrombotic diseases. Among them, the FIIa-direct thrombin inhibitor dabigatran and FXa inhibitors (rivaroxaban, apixaban, edoxaban) are the most broadly used. Anticoagulant dosing may differ under special considerations. The patients' physiological reserves, organ functional status and failures should be taken into account in clinical decision-making processes. The advantages and drawbacks of each specific agent should be weighed with special regard to metabolism, pharmacokinetics and pharmacodynamics, along with the efficiency of the agents in different indications. This article aims to review the most recent literature to highlight the usage and efficacy of the agents in different clinical conditions.

An in vitro study to investigate the interference of enoxaparin on plasma levels of direct oral factor Xa inhibitors measured by chromogenic assays

INTRODUCTION

Co-administration of enoxaparin and a direct oral factor Xa inhibitor (xabans: apixaban, edoxaban, rivaroxaban) could give rise to the problem of overlapping the anti-Xa activity when measuring direct oral anticoagulant (DOAC) levels. We aimed to evaluate in vitro the degree of the interference of increasing enoxaparin concentrations on xaban plasma levels measured by different chromogenic anti-Xa assays with drug-specific calibrators and controls.

METHODS

Seven plasma samples were spiked with apixaban, edoxaban, or rivaroxaban at fixed concentration, and enoxaparin at increasing concentrations (0, 0.125, 0.250, 0.50, 1.0, 1.50, and 2.0 IU/mL). The evaluated chromogenic assays were as follows: Biophen DiXaI and Biophen Heparin LRT (Hyphen BioMed), Berichrom Heparin and Innovance Heparin (Siemens), STA-Liquid Anti-Xa (Stago Diagnostics), Technochrom anti-Xa (Technoclone), and HemosIL Liquid Anti-Xa (Werfen).

RESULTS

The presence of enoxaparin caused increased DOAC levels, with over-estimation depending on the anti-Xa assay and on the heparin concentration in the sample. The smallest over-estimation was in the sample with enoxaparin 0.125 IU/mL and the greatest in the sample with enoxaparin 2.0 IU/mL (0%, 3.1%, and 7.4% vs 583.8%, 526.1%, and 415.2% for apixaban, edoxaban, and rivaroxaban, respectively). Biophen DiXaI showed lower interference compared to other methods (maximum over-estimation in the presence of enoxaparin 2.0 IU/mL: 56.4% dosing rivaroxaban by Biophen DIXaI vs 583.8% dosing apixaban by Berichrom Heparin).

CONCLUSION

The presence of enoxaparin interferes with xabans measurement by chromogenic anti-Xa assays causing falsely elevated DOAC levels, the over-estimation being dependent on the anti-Xa assay and on the heparin concentration in the sample.

Residual rivaroxaban exposure after discontinuation of anticoagulant therapy in patients undergoing cardiac catheterization

PURPOSE

Patients treated with direct oral anticoagulants (DOACs) frequently undergo interventional procedures requiring temporary discontinuation of anticoagulant therapy. Little is known about remaining peri-procedural exposure to rivaroxaban in real-world patients.

METHODS

Fifty-six patients with rivaroxaban treatment and scheduled cardiac catheterization were included in this prospective, observational, and single-center study. Rivaroxaban concentrations were determined by LC-MS/MS and a chromogenic anti-Xa assay. Population pharmacokinetic modeling was carried out on LC-MS/MS concentration data using NONMEM software, and results were applied to Monte Carlo simulations to predict appropriate rivaroxaban discontinuation intervals.

RESULTS

Rivaroxaban concentrations ranged from <LLOQ to 300.6 ng/ml at the time of admission to hospital and from <LLOQ to 55.5 ng/ml at the beginning of the procedure. Times since last rivaroxaban intake were (mean ± SD) 51.0 ± 31.7 h (admission) and 85.5 ± 36.8 h (start catheterization). LC-MS/MS and anti-Xa assay results were in good agreement (r = 0.958); however, the anti-Xa assay may underestimate low rivaroxaban concentrations and overestimate rivaroxaban exposure when performed on plasma samples contaminated with heparins. Pharmacokinetics of rivaroxaban were adequately described, and simulations predicted that 95% of patients will have rivaroxaban concentrations ≤ 28.4 ng/ml (15 mg dose group) and ≤ 31.9 ng/ml (20 mg dose group) after 48 h of discontinuation.

CONCLUSIONS

In the majority of patients, rivaroxaban plasma concentrations dropped below 30 ng/ml after 48 h of treatment discontinuation which is considered hemostatically safe before surgery with high bleeding risk. For accurate determination of low rivaroxaban concentrations, LC-MS/MS is the preferred choice.