– Excellent or Good Hemostasis Achieved in 82 Percent of Evaluable Patients –

–Thrombotic Event Rate of 9.7 Percent Across All Patients, No Thrombotic Events Observed Among Patients Who Re-started Oral Anticoagulation Therapy –

– Data Presented as a Late-Breaking Oral Presentation at the International Stroke Conference 2019 and Published in The New England Journal of Medicine –

SOUTH SAN FRANCISCO, Calif., Feb. 07, 2019 (GLOBE NEWSWIRE) — Portola Pharmaceuticals, Inc.^® (Nasdaq: PTLA) today announced full results from ANNEXA-4, the Company’s Phase 3b/4 trial of its Factor Xa inhibitor antidote Andexxa^® [coagulation factor Xa (recombinant), inactivated-zhzo] in patients experiencing acute major bleeding while taking a Factor Xa inhibitor. Data are being presented as a late-breaking oral presentation today at the International Stroke Conference 2019 and published simultaneously online by The New England Journal of Medicine (NEJM). 

Full data from 352 patients (249 of which were evaluable for hemostatic efficacy; all 352 were evaluable for safety) showed that Andexxa rapidly and significantly reversed anti-Factor Xa activity when administered as a bolus, and sustained this reversal when followed by a 120-minute infusion. Anti-Factor Xa activity is a measure of the anticoagulant activity of apixaban, rivaroxaban, edoxaban and enoxaparin, the anticoagulants studied in ANNEXA-4. Among all 352 patients, 64 percent (n=227) were treated for intracranial hemorrhage (ICH) and 26 percent (n=90) were treated for a gastrointestinal bleed. Of those evaluated for efficacy 82 percent (n=204) achieved excellent or good hemostasis (stoppage of bleeding) over the 12-hour period following treatment with Andexxa, as determined by an independent adjudication committee.

Within 30 days of enrollment, thrombotic events occurred in 34 patients (9.7 percent) and death occurred in 49 patients (13.9 percent), consistent with previous ANNEXA-4 trial results and with the high background thrombotic risk of the enrolled patient population. The majority of thrombotic events occurred in patients who delayed or did not re-start anticoagulation therapy with a Factor Xa inhibitor during the follow-up period. Among the 100 patients who re-started oral anticoagulation therapy, no thrombotic events were observed. Two patients experienced an infusion reaction and none developed antibodies to Factor Xa or Factor X or neutralizing antibodies to Andexxa.

“The consistency of the hemostatic efficacy and safety – regardless of age, dose, type of Factor Xa inhibitor and type of bleed – confirms the potential of Andexxa to address life-threatening bleeding associated with the use of the Factor Xa inhibitors apixaban or rivaroxaban,” said Truman J. Milling Jr., M.D., FACEP, Seton Dell Medical School Stroke Institute and ANNEXA-4 Executive Committee member. “We now also have new data demonstrating no observed thrombotic events after resumption of oral anticoagulation. This is a particularly significant finding given the clinical importance of re-initiating therapy as soon as possible, even in the wake of a major bleeding event.”

The worldwide use of Factor Xa inhibitors is rapidly growing because of their efficacy and safety profile compared to warfarin and enoxaparin in preventing and treating thromboembolic conditions such as stroke, pulmonary embolism and venous thromboembolism (VTE). This growth has come with a proportional increase in the incidence of hospital admissions and deaths related to bleeding, the major complication of anticoagulation. In the U.S. alone in 2017, there were approximately 140,000 hospital admissions attributable to Factor Xa inhibitor-related bleeding.

“The need for a specific Factor Xa inhibitor reversal agent is clear. As Factor Xa inhibitor use continues to grow, so does the prevalence of life-threatening bleeds such as an ICH, which carries a mortality rate of nearly 50 percent,” said John Curnutte, M.D., Ph.D., head of research and development at Portola. “The consistency of the ANNEXA-4 data, the strong response from the international medical societies that have already added Andexxa to their guidelines and the initial demand following the approval of Andexxa in May 2018 highlight its potential to benefit thousands of patients facing life-threatening bleeding associated with the use of rivaroxaban or apixaban.”

Andexxa received both U.S. Orphan Drug and U.S. Food and Drug Administration (FDA) Breakthrough Therapy designations, and was approved on May 3, 2018 under the FDA’s Accelerated Approval pathway. Andexxa is the first and only antidote indicated for patients treated with rivaroxaban or apixaban, when reversal of anticoagulation is needed due to life-threatening or uncontrolled bleeding, and it was recently added to the 2019 AHA/ACC/HRS guidelines.

ANNEXA-4 Study Design
ANNEXA-4 is a global, single-arm, open-label clinical trial designed to evaluate andexanet alfa in patients who present with an acute major bleed while receiving apixaban, rivaroxaban, edoxaban or enoxaparin. This multi-center, prospective cohort study was not randomized and all participants received andexanet alfa given as a bolus dose over 20-30 minutes followed by a two-hour (120 minute) infusion. Patients received a low or high dose infusion depending on which Factor Xa inhibitor they received and the time since they received the last dose. Patients were evaluated for 30 days following andexanet alfa administration. The co-primary efficacy endpoints are the maximum percent reduction in anti-Factor Xa activity and assessment of hemostasis over 12 hours following the infusion. Hemostatic efficacy was assessed by an independent endpoint adjudication committee using predetermined criteria as either excellent, good or poor/none. The primary safety endpoints were death, thrombotic events and development of antibodies to Andexxa or to native Factor X and Factor Xa.

IMPORTANT SAFETY INFORMATION FOR ANDEXXA [coagulation factor Xa (recombinant), inactivated-zhzo]

BOXED WARNING: THROMBOEMBOLIC RISKS, ISCHEMIC RISKS, CARDIAC ARREST AND SUDDEN DEATHS

See full prescribing information for complete boxed warning

Treatment with Andexxa has been associated with serious and life‑threatening adverse events, including:

• Arterial and venous thromboembolic events
• Ischemic events, including myocardial infarction and ischemic stroke
• Cardiac arrest
• Sudden deaths

Monitor for thromboembolic events and initiate anticoagulation when medically appropriate. Monitor for symptoms and signs that precede cardiac arrest and provide treatment as needed.

Indication
Andexxa [coagulation factor Xa (recombinant), inactivated-zhzo] is a recombinant modified human Factor Xa (FXa) protein indicated for patients treated with rivaroxaban or apixaban, when reversal of anticoagulation is needed due to life-threatening or uncontrolled bleeding.

This indication is approved under accelerated approval based on the change from baseline in anti-FXa activity in healthy volunteers. An improvement in hemostasis has not been established. Continued approval for this indication may be contingent upon the results of studies to demonstrate an improvement in hemostasis in patients.

Limitation of Use
Andexxa has not been shown to be effective for, and is not indicated for, the treatment of bleeding related to any FXa inhibitors other than apixaban or rivaroxaban.

SELECT IMPORTANT SAFETY INFORMATION

Thromboembolic and Ischemic Risk

The thromboembolic and ischemic risks were assessed in 185 patients who received the Generation 1 product and in 124 patients who received the Generation 2 product. The median time to first event was six days, and patients were observed for these events for 30 days following Andexxa infusion. Of the 86 patients who received Generation 1 product and were re-anticoagulated prior to a thrombotic event, 11 (12.7%) patients experienced a thromboembolic event, ischemic event, cardiac event or death.

Monitor patients treated with Andexxa for signs and symptoms of arterial and venous thromboembolic events, ischemic events, and cardiac arrest. To reduce thromboembolic risk, resume anticoagulant therapy as soon as medically appropriate following treatment with Andexxa.

The safety of Andexxa has not been evaluated in patients who experienced thromboembolic events or disseminated intravascular coagulation within two weeks prior to the life-threatening bleeding event requiring treatment with Andexxa. Safety of Andexxa also has not been evaluated in patients who received prothrombin complex concentrates, recombinant Factor VIIa, or whole blood products within seven days prior to the bleeding event.

Re-elevation or Incomplete Reversal of Anti-FXa Activity
The time course of anti-FXa activity following Andexxa administration was consistent among the healthy volunteer studies and the ANNEXA-4 study in bleeding patients. Compared to baseline, there was a rapid and substantial decrease in anti-FXa activity corresponding to the Andexxa bolus. This decrease was sustained through the end of the Andexxa continuous infusion. The anti-FXa activity returned to the placebo levels approximately two hours after completion of a bolus or continuous infusion. Subsequently, the anti-FXa activity decreased at a rate similar to the clearance of the FXa inhibitors.

Thirty-eight patients who received the Generation 1 product were anticoagulated with apixaban and had baseline levels of anti-FXa activity > 150 ng/mL. Nineteen of these 38 (50%) patients experienced a > 93% decrease from baseline anti-FXa activity after administration of Andexxa. Eleven patients who were anticoagulated with rivaroxaban had baseline anti-FXa activity levels > 300 ng/mL. Five of the 11 patients experienced a > 90% decrease from baseline anti-FXa activity after administration of Andexxa. Anti-FXa activity levels for patients who received the Generation 2 product were not available.

Adverse Reactions
The most common adverse reactions (≥ 5%) in patients receiving Andexxa were urinary tract infections and pneumonia.

The most common adverse reactions (≥ 3%) in healthy volunteers treated with Andexxa were infusion-related reactions.

Immunogenicity
As with all therapeutic proteins, there is potential for immunogenicity. Using an electrochemiluminescence (ECL)-based assay, 145 Generation 1 Andexxa-treated healthy subjects were tested for antibodies to Andexxa as well as antibodies cross-reacting with Factor X (FX) and FXa. Low titers of anti-Andexxa antibodies were observed in 26/145 healthy subjects (17%); 6% (9/145) were first observed at Day 30 with 20 subjects (14%) still having titers at the last time point (days 44 to 48). To date, the pattern of antibody response in patients in the ANNEXA-4 study has been similar to that observed in healthy volunteers with 6% (6/98) of the patients having antibodies against Andexxa. None of these anti-Andexxa antibodies were neutralizing. No antibodies cross-reacting with FX or FXa were detected in healthy subjects (0/145) or in bleeding patients (0/98) to date. There is insufficient data to assess for the presence of anti-Andexxa antibodies for subjects received the Generation 2 product.

About Portola Pharmaceuticals, Inc.
Portola Pharmaceuticals is a commercial-stage biopharmaceutical company focused on the discovery, development and commercialization of novel therapeutics that could significantly advance the fields of thrombosis and other hematologic diseases. The Company’s two FDA-approved medicines are Andexxa^® [coagulation factor Xa (recombinant), inactivated-zhzo], the first and only antidote for patients treated with rivaroxaban and apixaban when reversal of anticoagulation is needed due to life-threatening or uncontrolled bleeding, and Bevyxxa^® (betrixaban), the first and only oral, once-daily Factor Xa inhibitor for the prevention of VTE in adult patients hospitalized for an acute medical illness. The company also is advancing cerdulatinib, a Syk/JAK inhibitor for the treatment of hematologic cancers.

Forward-Looking Statements
Statements contained in this press release regarding matters that are not historical facts are “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. Because such statements are subject to risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. These include statements relating to Portola Pharmaceuticals’ expectations regarding the potential of Andexxa to address life-threatening bleeding associated with the use of the Factor Xa inhibitors apixaban or rivaroxaban, clinical treatment of patients, the need for a specific Factor Xa inhibitor reversal agent and the number of patients who could potentially benefit from Andexxa. These statements are subject to significant risks and uncertainties, and actual results could differ materially from those projected. These risks and uncertainties include, without limitation, the risk that physicians, patients and payers may not see the benefits of utilizing Andexxa; the possibility of unfavorable results from additional clinical trials involving Andexxa; the risk that the EMA may not approve Andexxa in the currently anticipated timelines or at all, and that any marketing approvals or reimbursement limitations may have significant limitations on its use; the risk that we may not obtain additional regulatory approvals necessary to expand approved indications for Andexxa; our expectation that we will incur losses for the foreseeable future and will need additional funds to finance our operations; the accuracy of our estimates regarding expenses and capital requirements; our ability to successfully build a hospital-based sales force and commercial infrastructure; our ability to obtain and maintain intellectual property protection for our product candidates; and our ability to retain key scientific or management personnel. These and other risks and uncertainties are described more fully in our most recent filings with the Securities and Exchange Commission, including our most recent quarterly report on Form 10-Q. All forward-looking statements contained in this press release speak only as of the date on which they were made. We undertake no obligation to update such statements to reflect events that occur or circumstances that exist after the date on which they were made.

Investor Contact: Cara Miller Portola Pharmaceuticals [email protected]

Media Contact: Julie Normart Pure Communications [email protected]