Pharmacokinetics of rivaroxaban after bariatric surgery: a case report.

Rivaroxaban is a direct factor Xa inhibitor, which is rapidly absorbed in the upper gastrointestinal (GI) tract. In large trials, it has been shown to be effective and safe in VTE treatment. However, in these trials patients with morbid obesity were not reported and it is unknown if the standard dosage of 20 mg rivaroxaban is sufficient for bariatric patients, especially after bariatric surgery, which may impact the resorption of rivaroxaban. We report the case of a bariatric patient with high venous thromboembolism risk and instable INR after recent bariatric surgery, who was switched from Vitamin-K antagonists to rivaroxaban. After intake of 20 mg rivaroxaban, plasma concentration were repeatedly measured until 3 h after the second dose using a commercially available chromogenic aXa-assay. Furthermore, INR and aPTT were measured. Peak concentrations of 224.22 ng/ml were observed. After 6 h, plasma concentration decreased to 86.9 ng/ml and remained stable until 12 h (86.32 ng/ml). After 24 h, a trough level of 35.54 ng/ml was observed. The patients INR did immediately increase and remained significantly elevated throughout the day with a slow decrease. Since peak values of rivaroxaban plasma concentrations were in the expected range of published data, we conclude that resorption of rivaroxaban was immediate and not significantly impaired by bariatric surgery of the upper GI tract. Consequently, no dose adjustments seem to be necessary in this high-risk population.