Rivaroxaban: Quantification by anti-FXa assay and influence on coagulation tests: a study in 9 Swiss laboratories

Area of Science:

• Pharmacology
• Clinical Chemistry
• Laboratory Medicine

Background:

• Rivaroxaban (RXA) is prescribed for venous thromboembolism prophylaxis post-orthopaedic surgery.
• A validated inter-laboratory method for quantifying RXA plasma levels is currently unavailable.
• This study addresses the need for a reliable RXA quantification assay.

Purpose of the Study:

• To assess the feasibility of quantifying RXA using a commercial anti-FXa assay.
• To determine the accuracy and precision of RXA quantification in an inter-laboratory setting.
• To evaluate the impact of 10mg RXA on standard coagulation tests.

Main Methods:

• Utilized a standardized chromogenic anti-FXa assay across multiple laboratories.
• Prepared in vitro calibrators and blinded samples by spiking normal plasma with RXA.
• Assessed RXA content via HPLC-tandem mass spectrometry and analyzed ex vivo samples from volunteers.
• Collected plasma samples pre- and post-10mg RXA ingestion from 20 healthy volunteers.

Main Results:

• Chromogenic anti-FXa assay demonstrated feasibility for RXA quantification.
• Achieved mean accuracy of 7.0% and precision (CV) of 8.8% across laboratories.
• Measured mean RXA concentration at 114±43μg/L.
• Observed significant alterations in prothrombin time (PT) and activated partial thromboplastin time (aPTT) post-RXA ingestion.
• No significant effect on thrombin time, fibrinogen, FXIII, or D-Dimer levels.

Conclusions:

• A commercial chromogenic anti-FXa assay provides accurate and precise quantification of RXA plasma levels across different laboratories and coagulometers.
• Ingestion of 10mg RXA leads to significant changes in PT and aPTT coagulation assays.
• The validated assay supports therapeutic drug monitoring and clinical research involving rivaroxaban.