When Apixaban and Rivaroxaban Interfere With Anti-Xa Assays: A Cohort Study.

Area of Science:

• Pharmacology
• Cardiology
• Clinical Medicine

Background:

• Direct factor Xa inhibitors (e.g., apixaban, rivaroxaban) improve medication adherence.
• Transitioning patients to unfractionated heparin (UFH) during hospitalization can occur.
• Residual factor Xa inhibitor activity may affect anticoagulation monitoring, like anti-Xa assays.

Purpose of the Study:

• To evaluate the impact of residual factor Xa inhibitor activity on anticoagulation monitoring.
• To assess the incidence of thrombotic and bleeding events in patients transitioned to UFH.
• To determine the utility of baseline anti-Xa levels in managing these patients.

Main Methods:

• Retrospective chart review of admitted patients from December 2020 to June 2022.
• Inclusion of patients on apixaban or rivaroxaban transitioned to intravenous UFH.
• Measurement of baseline plasma anti-Xa levels and assessment for adverse events.

Main Results:

• 48 patients were included; common reasons for UFH bridging were NSTEMI (31%) and pre-procedure (23%).
• Mean baseline anti-Xa level was 0.92 U/mL.
• 25% of patients experienced bleeding events, and 2% had thrombotic events; 57% of those with adverse events had supratherapeutic baseline anti-Xa levels.

Conclusions:

• Baseline anti-Xa levels are important for patients on factor Xa inhibitors transitioning to UFH.
• Standardizing baseline anti-Xa measurements can guide UFH initiation timing and dosing.
• This practice may help prevent adverse thrombotic or bleeding events and inform assay selection.