Rare Disease Report

FDA Rejects Antidote for Factor Xa Inhibitors

AUGUST 17, 2016
Andrew Black
The FDA has issued a Complete Response Letter to Portola Pharmaceuticals for its orphan drug Andexxa (andexanet alfa). The drug was being developed as an antidote for patient with uncontrolled bleeding while taking a Factor Xa inhibitor.  
While details are limited, Portola stated that the FDA requested additional information about the manufacturing of the drug. The FDA also asked for additional data to support the inclusion of edoxaban and enoxaparin in AndexXa’s label, and indicated that they need to finalize its review of the clinical amendments to Portola’s post-marketing commitments that recently were submitted.
Portola’s submission to the FDA for Andexxa was based on positive data from two Phase 3 Anexxa studies which evaluated the safety and efficacy of AndexXa in reversing the anticoagulant activity of the Factor Xa inhibitors rivaroxaban and apixaban in 50-75 year old patient volunteers.

Complete Response Letter

The FDA send a Complete Reponse letter when it had determined that the drug will not get approved based on the application they received.  In this instance, the FDA has completely reviewed the application and has concluded that the data in the application is insufficient for them to make a decision on its efficacy and safety.  This does not mean the drug will never get approved but that the company needs to provide more data – in this case manufacturing details and a data set looking at Factor Xa inhibitors edoxaban and enoxaparin if they want those drugs included in the labeling.


AndexXa (andexanet alfa) is the first compound being studied as an antidote for Factor Xa inhibitors that directly and specifically reverses anti-Factor Xa activity. Approximatley 1-4% of patients treated with Factor Xa inhibitors (e.g., (apixaban, rivaroxaban, edoxaban, enoxaparin) develop life-threatening or uncontrollable bleeding that requires Factor Xa inhibition reversal.  It is a modified human Factor Xa molecule that acts as a decoy to target and sequester with high specificity both oral and injectable Factor Xa inhibitors in the blood.

Stock Watch

Portola's shares began trading today at $19 which is a 30% drop since yesterday’s price of $27

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