A Factor Xa Inhibitor Antidote (andexanet alfa) is Capable of Neutralizing the Anticoagulant Effects of Unfractionated Heparin of Bovine, Ovine and Porcine Origin in a Comparable Manner as Protamine Sulfate
Authors: Siddiqui Fakiha , Tafur Alfonso , Bontekoe Emily , Iqbal Omer , Hoppensteadt Debra , Jeske Walter , Kouta Ahmed , Zorriasateyn Kambiz , Ramacciotti Eduardo , Fareed Jawed 
Published: June 2021

IntroductionAndexanet alfa (zhzo, coagulation factor Xa recombinant) is approved for such factor Xa inhibitors as apixaban and rivaroxaban. Unfractionated heparin (UFH) is commonly used for therapeutic, interventional and surgical indications. Protamine sulfate is commonly used to neutralize UFH. The study investigated the comparative neutralization profiles of andexanet alfa and protamine sulfate for heparins of bovine, ovine or porcine origin.Materials and MethodPowdered form of pharmaceutical grade heparins of bovine (140 U/mg), ovine (200 U/mg) and porcine (190 U/mg) origin were obtained from commercial vendors. Andexanet alfa was obtained from the hospital pharmacy (Skokie Hospital, Skokie, Illinois) and reconstituted at 10 mg/ml according to the manufacturer's instructions. Powdered protamine sulfate (USP grade) was reconstituted at 1.0 mg/ml in saline. To investigate the neutralization profile of these two antidotes for various heparins, each of the bovine, ovine and porcine heparins was supplemented to plasma over a concentration range of 0–10 ug/ml. The effect of protamine sulfate at 10 ug/ml was studied in the activated partial thromboplastin time (aPTT), anti‐Xa and anti‐IIa assays. Similar studies were carried out with andexanet alfa at a concentration of 100 ug/ml. The neutralization effect of protamine sulfate and andexanet alfa was also studied on an approximate surgical/interventional concentration of heparin by supplementing freshly drawn whole blood from healthy individuals (n=5–10) with each of the heparins at a concentration of 25 ug/ml. The neutralization effect of andexanet alfa was studied at 100 ug/ml and protamine sulfate was studied at 25 ug/ml.ResultsBoth andexanet alfa (100 ug/ml) and protamine sulfate (10 ug/ml) completely neutralized the anticoagulant effects of all three heparins in the aPTT assay. However, protamine sulfate was more effective in neutralizing the amidolytic anti‐Xa and anti‐IIa effects in comparison to andexanet alfa which only partially neutralized these effects. In the whole blood clotting ACT studies, all three heparins produced a strong anti‐coagulant effects (400–450 seconds) in comparison to saline (130–150 seconds). Both andexanet alfa (100 ug/ml) and protamine sulfate (25 ug/ml) almost completely neutralized the anti‐coagulant effects of heparins (140–160 seconds).ConclusionThese results clearly suggest that andexanet alfa at 100 ug/ml is effective in neutralizing both the therapeutic and surgical/interventional concentrations of heparins in the in‐vitro settings. While differences in the anti‐Xa and anti‐IIa effects between heparins are noted, the anti‐coagulant effect of these agents in the aPTT assay were comparable and similar neutralization profile was observed in the ACT assays by both agents. The pharmacologic implication of these observations require further investigations.Support or Funding InformationN/AThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.