Rivaroxaban is an oral, reversible, direct Factor Xa inhibitor used for anticoagulation.

How to measure

  • At steady state (consider practicalities such as testing on weekdays, etc)
    • Consider the half-life in that person
    • In healthy young subjects the average half-life is 7 hours meaning steady state is reached approximately 36 hours after commencing or changing dose
    • In some patients e.g. those with low clearance, the half-life can increase up to 13 hours
  • Trough – i.e. prior to next dose being due
  • Rivaroxaban concentrations are measured in the toxicology laboratory routinely once a week. See Canterbury Health Labs rivaroxaban assay information
  • Use a purple top (EDTA plasma) or blue top (citrate) tube

How to interpret

Reference Range

  • For patients taking 20 mg daily, the median (5th – 95th centiles) trough concentration is 32 (5 – 155) microg/L. This provides context regarding where the individual patient is in relation to the population of patients on rivaroxaban. Results outside the 5-95th centiles indicate an extreme outlier

Factors affecting interpretation

  • Rivaroxaban is highly protein bound (to albumin). Total rivaroxaban concentration is measured, which comprises the bound and unbound concentrations
  • With low serum albumin for a given unbound concentration the total rivaroxaban concentration will be lower
      – Caution if the total concentration is ‘normal’, the unbound (active) concentration may be high

Coagulation tests

  • INR increases in a concentration dependent manner
  • APTT and TT are not affected by rivaroxaban
    NB. Anti-factor Xa assays will increase in a concentration dependent manner. However, the CHL assay is not calibrated to rivaroxaban use is not currently recommended.

Dose individualisation and adjustment

  • Rivaroxaban concentrations increase proportional to dose
  • Defined dose forms can lead to issues with practical prescribing. Where possible use whole tablet dosing (rounding to the nearest whole tablet)
  • Dose adjustment may result in dosing outside of that which is Medsafe-approved.
  • Select the initial dose based on clinical factors, such as indication for treatment and renal function. See Hospital HealthPathway Dabigatran and Rivaroxaban

Contacts for help with interpretation

  • Medicines Information

Key references

Foerster KI, Hermann S, Mikus G & Haefeli WE. Drug-drug interactions with direct oral anticoagulants. Clinical pharmacokinetics 2020;59: 967-980. https://link.springer.com/content/pdf/10.1007/s40262-020-00879-x.pdf
Chin PKL (2015). Which Patients May Benefit from Dose Adjustments of Non-Vitamin K Antagonist Oral Anticoagulants? Semin Thromb Hemost 2015;41:195–207.

Mueck W, Lensing AWA, Agnelli G, Decousus H, Prandoni P, Misselwitz. Rivaroxaban. Population Pharmacokinetic Analyses in Patients Treated for Acute Deep-Vein Thrombosis and Exposure Simulations in Patients with Atrial Fibrilation Treated for Stroke Prevention. Clin Pharmacokinet 2011; 50 (10): 675-686.

Mueck W, Stampfuss J, Kubitza D, Becka M. Clinical Pharmacokinetic and Pharmacodynamic Profile of Rivaroxaban. Clin Pharmacokinet 2014;53:1-16.

https://www.medsafe.govt.nz/profs/Datasheet/x/Xareltotab

Author | Date
TW, PC, MD 2021