Andexanet alfa (AA) – zhzo, recombinant coagulation factor Xa, is an approved antidote for oral Xa inhibitors (apixaban and rivaroxaban). Unfractionated heparin (UFH) is commonly used for therapeutic, interventional, and surgical indications. Protamine sulfate (PrSO₄) is frequently used to neutralize UFH. This study aimed to investigate the comparative neutralization profiles of AA and PrSO₄ for heparins of bovine, ovine, and porcine origin.

The neutralization effect of PrSO₄ at 25 µg/ml and AA at 100 µg/ml was studied on an approximate surgical/interventional concentration of heparin by supplementing whole blood with each of the heparins at 25 µg/ml. For the clotting profile (activated partial thromboplastin time: aPTT), amidolytic (anti-Xa and anti-IIa), and thrombin generation assay each of the heparin were supplemented from –10–0.62 µg/ml.

In the whole blood ACT studies, all three heparins produced strong anti-coagulant effects (400–450 seconds) compared to saline (130–150 seconds). Both AA and PrSO₄ almost fully neutralized the anti-coagulant effects of heparins (140–160 seconds). Both antidotes completely reversed the anticoagulant effects of all three heparins in the aPTT and thrombin generation assay. However, PrSO₄ was more effective in neutralizing the anti-Xa, and anti-IIa effects than AA, which only partially neutralized these effects.

Andexanet alfa at 100 µg/ml effectively neutralizes the therapeutic and surgical/interventional concentrations of heparins in in-vitro settings. While differences in the anti-Xa, and anti-IIa effects between heparins were noted, anti-coagulant effect of these agents in the aPTT assay were comparable. A similar neutralization profile was observed in the ACT and thrombin generation assays by both agents.