Non-
vitamin K oral
anticoagulant (
NOAC)
therapy may be inappropriate if prescription was incorrect, the patient's physiological parameters change, or interacting concomitant medications are erroneously added. The aim of this report was to illustrate inappropriate
NOAC prescription in a 78-year-old woman with non-valvular
atrial fibrillation and borderline renal dysfunction who was switched from
warfarin to
rivaroxaban and subsequently developed bruising with
hemorrhagic shock and acute on
chronic renal failure. Administration of 4-factor
prothrombin complex concentrate effectively reversed coagulopathy and stopped
bleeding. Retrospective determination of circulating plasma levels of
rivaroxaban and
warfarin confirmed that excessive anticoagulation was likely due to
warfarin that the patient probably continued to take although
rivaroxaban was initiated. Pharmacodynamic interaction between
rivaroxaban and
warfarin may not only be additive but synergistic. In patients at high risk of complications, judicious prescribing and dosing of NOACs, and regular monitoring of concomitant medications and renal function are highly recommended.