XenoPort Reports Top-Line Results of Phase 3 Trial of Arbaclofen Placarbil for Spasticity in Multiple Sclerosis Patients

XenoPort, Inc. (Nasdaq: XNPT) announced today top-line results from its pivotal Phase 3 clinical trial of arbaclofen placarbil (AP) for the treatment of patients with spasticity due to multiple sclerosis (MS). The trial was unsuccessful in demonstrating that AP provided statistically significant improvement relative to placebo in the co-primary endpoints of the study.

Ronald W. Barrett, Ph.D., chief executive officer of XenoPort, stated, “We are obviously disappointed that the co-primary efficacy endpoints were not met. Based on the results of the study, we have decided to terminate further investment in this program. We will be working diligently to shut down all activities related to AP development, and plan to provide an update in the future on the impact of these expected savings on our cash burn guidance. We remain committed to allocating our resources to build value through the focused commercialization of Horizant and advancing the development of our novel fumarate product candidate, XP23829.”

About the Trial

The trial was a 13-week, multicenter, randomized, double-blind, placebo-controlled study that enrolled 228 subjects in 30 sites in the United States. There was a one-week placebo run-in period, two weeks of up-titration, eight weeks at the maintenance dose and two weeks of down-titration. Eligible subjects were randomized to one of four arms: 15 mg, 30 mg or 45 mg of AP or placebo dosed twice a day (BID) with food.

The first of the co-primary endpoints for the study was the time-matched change from baseline in Maximum Ashworth score (six hours post-dose time point) at the end of the maintenance dose period. The muscle group in the lower limbs with the highest Ashworth score at baseline was followed throughout the trial. Subjects entering the trial were required to have a Maximum Ashworth score of two or greater prior to entering the study and at the end of the placebo run-in period, which served as baseline. The second co-primary endpoint was the score on the 7-point Patient Global Impression of Change scale at the end of the maintenance period. The co-primary endpoint analysis plan examined the differences of the 30 and 45 mg BID groups from the placebo group. The co-primary endpoints and dose groups were analyzed independently. Comparison of the AP groups to the placebo group did not reach statistical significance on either of the co-primary endpoints for either of the AP doses.

The most commonly reported adverse event was somnolence (2%, 7%, 16% and 21% for placebo, 15, 30 and 45 mg AP BID, respectively). There were seven subjects with treatment emergent serious adverse events, none of which were deemed to be related to treatment.

Conference Call

XenoPort will host a conference call at 8:30 am Eastern Time today to discuss its AP Phase 3 clinical trial results and business updates. To access the conference call via the Internet, go to www.XenoPort.com. To access the live conference call via phone, dial 1-888-275-3514. International callers may access the live call by dialing 1-706-679-1417.

The replay of the conference call may be accessed after 11:30 am Eastern Time today via the Internet, at www.XenoPort.com, or via phone at 1-855-859-2056 for domestic callers or 1-404-537-3406 for international callers. The reference number to enter the call and the replay of the call is 74912690.

About XenoPort

XenoPort, Inc. is a biopharmaceutical company focused on developing and commercializing a portfolio of internally discovered product candidates for the potential treatment of neurological disorders. Horizant, XenoPort’s internally discovered drug, is approved and being marketed by XenoPort in the United States. Regnite® (gabapentin enacarbil) Extended-Release Tablets is approved and is being marketed in Japan. Astellas Pharma Inc. holds all development and commercialization rights for Regnite in Japan and five other Asian countries. XenoPort holds all other world-wide rights to gabapentin enacarbil. XenoPort's pipeline of product candidates includes potential treatments for patients with Parkinson's disease, relapsing-remitting multiple sclerosis and psoriasis.

Forward-Looking Statements

This press release contains “forward-looking” statements, including, without limitation, all statements related to the shutdown of activities related to AP development, and the timing thereof; future impact on cash burn guidance and resource allocation; building value through the focused commercialization of Horizant and advancing the development of XP23829; and the therapeutic and commercial potential of XenoPort’s product candidates. Any statements contained in this press release that are not statements of historical fact may be deemed to be forward-looking statements. Words such as “expected,” “plan,” “potential,” “will” and similar expressions are intended to identify forward-looking statements. These forward-looking statements are based upon XenoPort's current expectations. Forward-looking statements involve risks and uncertainties. XenoPort's actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include, without limitation; XenoPort’s lack of commercialization experience and its ability to successfully market and sell Horizant, including its ability to obtain uninterrupted drug supply and appropriate pricing and reimbursement for Horizant in an increasingly challenging environment; XenoPort’s ability to comply with applicable regulatory guidelines and requirements with respect to the marketing and manufacturing of Horizant or with Horizant post-marketing commitments or requirements mandated by the U.S. Food and Drug Administration (FDA); XenoPort’s need for additional funding and the risk that XenoPort could utilize its available capital resources sooner than it expects; the uncertainty of the FDA approval process and other regulatory requirements; the uncertain results and timing of clinical trials and other studies; XenoPort’s ability to successfully initiate, conduct and complete clinical trials in the anticipated timeframes, or at all; and the uncertain therapeutic and commercial value of XenoPort’s product candidates. These and other risk factors are discussed under the heading "Risk Factors" in XenoPort's Securities and Exchange Commission filings and reports, including in its Quarterly Report on Form 10-Q for the quarter ended March 31, 2013, filed with the Securities and Exchange Commission on April 24, 2013. XenoPort expressly disclaims any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in the company's expectations with regard thereto or any change in events, conditions or circumstances on which any such statements are based.

Horizant, Regnite and XENOPORT are trademarks of XenoPort, Inc.

XNPT2C