Andexanet alfa is a recombinant, modified factor Xa (FXa) molecule that is used for the reversal of the anticoagulant effect of oral anti-FXa anticoagulants in patients with major haemorrhage. Here we present a case of an 85-year-old man taking rivaroxaban for atrial fibrillation, who presented with an acute, upper gastrointestinal bleed. He was stabilised with red cell transfusion and then received a 400 mg bolus of andexanet alfa. Within minutes of this, he developed chest tightness, shortness of breath, ischaemic electrocardiographic changes, and then cardiac arrest from which he could not be resuscitated. The onset of symptoms was clearly temporally related to andexanet alfa administration and the differential diagnosis includes anaphylaxis with Kounis syndrome, or myocardial infarction. Although infusion site reactions have been reported and are relatively common, this is to date the first case of a fatal drug reaction andexanet alfa. This knowledge can be factored into physicians’ risk-benefit decisions when treating patients with oral anti-FXa anticoagulant-associated major haemorrhage
