SOUTH SAN FRANCISCO, Calif., Nov. 25, 2013 (GLOBE NEWSWIRE) -- Portola Pharmaceuticals, Inc. (Nasdaq:PTLA) today announced that it has been granted breakthrough therapy designation by the U.S. Food and Drug Administration (FDA) for andexanet alfa, its investigational Factor Xa inhibitor antidote. The FDA's breakthrough therapy designation is intended to expedite the development and review of drugs for serious or life-threatening conditions. i Portola is pursuing an Accelerated Approval pathway for andexanet alfa, a first-in-class agent, and plans to initiate registration-enabling studies in 2014. By the year 2020, Portola estimates that the number of patients presenting to the hospital who could benefit from an antidote could approach 500,000 in the United States, Japan and the five largest European Union countries alone. "The FDA's decision to designate andexanet alfa as a breakthrough therapy reaffirms the urgent need for an antidote to Factor Xa inhibitors, and we believe it demonstrates that andexanet alfa's properties and data distinguish it from currently used agents or others in development," said William Lis, Portola's chief executive officer. "Pro-coagulant agents being used in the absence of an antidote are unproven, have limited biological rationale for their effectiveness to reverse Factor Xa inhibitors, and have been shown to cause serious blood clots. Therefore, andexanet alfa marks an important advance in the field, and our goal is to bring it to market as quickly as possible." The Company has previously reported data from its ongoing Phase 2 proof-of-concept studies of andexanet alfa and the Factor Xa inhibitors Eliquis ® and XARELTO ®. Additional studies are ongoing with Lovenox ® (enoxaparin), Lixiana ® and Portola's investigational oral Factor Xa inhibitor, betrixaban, which is being studied in a Phase 3 clinical trial and has the potential to be the first oral Factor Xa inhibitor approved for venous thromboembolism (VTE) prevention in acute medically ill patients. Phase 2 results to date have demonstrated andexanet alfa's ability to immediately reverse the anticoagulant activity of Factor Xa inhibitors by the administration of a short intravenous bolus. Additional data have shown that this reversal can be prolonged when necessary by the addition of an extended infusion of andexanet alfa. Unlike pro-coagulant agents or other compounds in development, once administration is stopped, andexanet alfa is rapidly cleared and anticoagulant therapy can be re-initiated, which is critical for patients who have pre-existing (underlying) prothrombotic conditions. Andexanet alfa's specific mechanism of action may also reduce the potential for serious adverse events and interactions with other commonly used drugs. No serious adverse events or antibodies to Factor Xa or Factor X have been observed in the ongoing Phase 2 studies.