Andexanet alfa, sold under the brand name Andexxa among others, is an antidote for the medications rivaroxaban and apixaban, when reversal of anticoagulation is needed due to uncontrolled bleeding. It has not been found to be useful for other factor Xa inhibitors. It is given by injection into a vein.Common side effects include pneumonia and urinary tract infections. Severe side effects may include blood clots, heart attacks, strokes, or cardiac arrest. It works by binding to rivaroxaban and apixaban.It was approved for medical use in the United States in May 2018. It was developed by Portola Pharmaceuticals.