• Job Harenberg, Sandra Krämer, Shanshan Du, Shabnam Zolfaghari, Astrid Schulze, Roland Krämer, Christel Weiss, Martin Wehling, and Gregory Y H Lip.
• Department of Clinical Pharmacology, Medical Faculty Mannheim, Ruprecht-Karls University Heidelberg, Mannheim, Germany.
• Eur. J. Clin. Invest. 2014 Aug 1; 44 (8): 743-52.

BackgroundThe determination of rivaroxaban and apixaban from serum samples of patients may be beneficial in specific clinical situations when additional blood sampling for plasma and thus the determination of factor Xa activity is not feasible or results are not plausible.Materials And MethodsThe primary aim of this study was to compare the concentrations of rivaroxaban and apixaban in serum with those measured in plasma. Secondary aims were the performance of three different chromogenic methods and concentrations in patients on treatment with rivaroxaban 10 mg od (n = 124) or 20 mg od (n = 94) or apixaban 5 mg bid (n = 52) measured at different time.ResultsConcentrations of rivaroxaban and apixaban in serum were about 20-25% higher compared with plasma samples with a high correlation (r = 0·79775-0·94662) using all assays (all P < 0·0001). The intraclass correlation coefficients were about 0·90 for rivaroxaban and 0·55 for apixaban. Mean rivaroxaban concentrations were higher at 2 and 3 h compared with 1 and 12 h after administration measured from plasma and serum samples (all P-values < 0·05) and were not different between 1 vs. 12 h (plasma and serum).ConclusionsThe results indicate that rivaroxaban and apixaban concentrations can be determined specifically from serum samples.© 2014 The Authors. European Journal of Clinical Investigation published by John Wiley & Sons Ltd on behalf of Stichting European Society for Clinical Investigation Journal Foundation.

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