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

Steffany N. Nguyen, Melanie C. Ruegger, Eric Salazar, Diane Dreucean, Alexandra W. Tatara, Kevin R. Donahue

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)836-845
Number of pages10
JournalJournal of Pharmacy Practice
Issue number6
StatePublished - Dec 2022


  • anti-Xa apixaban
  • anti-Xa level
  • anti-Xa rivaroxaban
  • bleeding
  • factor Xa inhibitor

ASJC Scopus subject areas

  • Pharmacy
  • Pharmacology (medical)


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