XenoPort Reports Positive Results from a Phase 2 Trial of Arbaclofen Placarbil in Spinal Cord Injury Patients with Spasticity

SANTA CLARA, Calif.--(Business Wire)--
XenoPort, Inc. (Nasdaq:XNPT) announced today positive preliminary results from a
Phase 2 clinical trial of arbaclofen placarbil (AP), also known as XP19986, for
the treatment of patients with spasticity due to spinal cord injury (SCI). Doses
of 20 and 30 mg of AP, given twice daily (BID), demonstrated statistically
significant improvements compared to placebo for the primary endpoint of the
study. AP was well tolerated during the trial.

"Currently available medications for treating spasticity are often limited by
their short duration of action and significant central nervous system side
effects," said David A. Stamler, M.D., XenoPort`s chief medical officer. "The
efficacy and tolerability of AP that were observed in this trial was
encouraging, and we believe that AP offers the potential to address important
medical needs for SCI patients."

This Phase 2 clinical trial was a randomized, double-blind, placebo-controlled,
crossover study that enrolled 37 subjects at ten sites in the United States and
Canada. Subjects with SCI between C-5 and T-12 discontinued spasticity therapy
during a one-week washout period prior to a one-week placebo run-in period, at
the end of which baseline assessments were conducted. Subjects had an Ashworth
Scale score of at least 2 in one of six assessed muscle groups (hip
abductors/adductors, knee flexors/extensors and ankle flexors/extensors) on the
most affected leg. Subjects received either AP (10, 20 or 30 mg BID) or placebo
in the first treatment segment of the two-segment crossover design. Each
treatment segment included a titration period, followed by at least one week at
the target dose, at which time efficacy assessments were performed (day 17 of
each treatment segment). Each treatment segment also included a down-titration
period, and there was a three-day washout between treatment segments.

The primary endpoint in this study was the difference in Ashworth Scale score
during the placebo and AP treatment segments for the muscle group with the
highest Ashworth Scale score at baseline. Ashworth Scale scores were determined
by the investigator prior to dosing, and again two, four and six hours after the
morning dose. The primary analysis used a repeated-measures analysis of variance
model and included data from the 35 subjects who completed both treatment
segments.

Mean maximum baseline Ashworth Scale scores were 3.2 (n=10), 3.1 (n=12) and 3.1
(n=13) for the 10, 20 and 30 mg BID AP dose cohorts, respectively. For the
primary endpoint, the overall adjusted mean differences between placebo and AP
over the six-hour assessment period for these cohorts were -0.17 (not
significant), -0.60 (p=0.0059) and -0.88 (p=0.0007), respectively. AP treatment
was associated with statistically significant differences from placebo at all
time points in the 20 and 30 mg BID AP dose cohorts, indicating a treatment
effect over the 12-hour dosing interval. In a secondary analysis, 20 and 30 mg
BID of AP also showed a statistically significant difference from placebo in the
average Ashworth Scale score for all six muscle groups.

AP was well tolerated at all dose levels. There were no withdrawals due to
adverse events during the trial. The most commonly reported adverse events while
on any AP dose were urinary tract infection (11% AP; 9% placebo), pain in
extremity (8% AP; 0% placebo), insomnia (8% AP, 0% placebo) and nasopharyngitis
(8% AP; 3% placebo). Side effects were generally mild to moderate in intensity.
There were no drug-related serious adverse events.

"These results add to a growing body of evidence suggesting the efficacy and
safety of AP in multiple indications," said Ronald W. Barrett, Ph.D., XenoPort`s
chief executive officer. "We believe AP offers the potential for a
differentiated treatment of spasticity in SCI patients. We intend to seek
guidance from regulatory authorities regarding future trial designs and safety
database requirements for a clinical program leading to a new drug application
for AP as a potential treatment of spasticity in SCI patients and possibly other
spasticity populations."

Conference Call

XenoPort will host a conference call at 9:00 a.m. Eastern Time today. 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 12:00 p.m. Eastern Time
today via the Internet, at www.XenoPort.com, or via phone at 1-800-642-1687 for
domestic callers or 1-706-645-9291 for international callers. The reference
number to enter the call and the replay of the call is 18012057.

About AP

AP (arbaclofen placarbil) is a Transported Prodrug of R-baclofen that is
designed to engage natural nutrient transport mechanisms found on intestinal
cell membranes, thereby gaining efficient entrance into the bloodstream. AP is
then rapidly converted by high-capacity enzymes to R-baclofen and natural
substances that have well-studied, favorable safety characteristics. The current
sustained-release tablet formulation of AP could enable convenient once- or
twice-daily dosing of subjects in future clinical trials.

R-baclofen is an agonist of the target known as gamma amino-butyric acid(B), or
GABA(B), receptor. Racemic baclofen (a mixture of R and S isomers) has been
approved for the treatment of spasticity and has been shown in clinical studies
to have efficacy in a number of other therapeutic indications, including
gastroesophageal reflux disease (GERD) and acute back spasms.

About Spasticity

Spasticity is a debilitating condition that is associated with some common
neurological disorders, such as multiple sclerosis, stroke and cerebral palsy,
as well as spinal cord injury. Spasticity is a condition in which certain
muscles are continuously contracted, interfering with movement or speech.
According to data from Wolters Kluwer Health, Source® Pharmaceutical Audit
Suite, for the 12 months ended December 31, 2008, there were approximately 7.0
million prescriptions written in the United States for the two most widely
prescribed drugs for the treatment of spasticity, racemic baclofen and
tizanidine.

About XenoPort

XenoPort, Inc. is a biopharmaceutical company focused on developing a portfolio
of internally discovered product candidates that utilize the body`s natural
nutrient transport mechanisms to improve the therapeutic benefits of existing
drugs. XenoPort is developing its lead product candidate, XP13512, in
collaboration with Astellas Pharma Inc. and GlaxoSmithKline. The Food and Drug
Administration is currently reviewing the new drug application for this product
candidate as a potential treatment for moderate-to-severe primary restless legs
syndrome. XenoPort`s product candidates are also being studied for the potential
treatment of GERD, migraine headaches, neuropathic pain, spasticity related to
spinal cord injury, acute back spasms and Parkinson`s disease.

To learn more about XenoPort, please visit the Web site at www.XenoPort.com.

Forward-Looking Statements

This press release contains "forward-looking" statements, including, without
limitation, all statements related to our future clinical development program
for AP and the timing thereof; the therapeutic and commercial potential of AP;
the suitability of AP as a treatment for spasticity; and our future clinical
trials and the timing thereof. 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 "believe," "could," "intend," "potential,"
"suggesting" 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, risks related to the
uncertain results of future clinical trials; XenoPort`s ability to successfully
conduct future clinical trials for AP; the uncertainty of the FDA approval
process and other regulatory requirements; and the uncertain therapeutic and
commercial value of AP. These and other risk factors are discussed under the
heading "Risk Factors" in XenoPort`s Quarterly Report on Form 10-Q for the
quarter ended March 31, 2009, filed with the Securities and Exchange Commission
on May 7, 2009. 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.

XenoPort and Transported Prodrug are trademarks of XenoPort, Inc.

XNPT2C

XenoPort, Inc.
Jackie Cossmon, 408-616-7220
ir@xenoport.com

Copyright Business Wire 2009