ARYx Therapeutics, Inc. Provides Additional Data on Atrial Fibrillation Clinical Trial on ATI-2042

Washout Data and Secondary End Points Reinforce Top-Line Efficacy
FREMONT, Calif.--(Business Wire)--
ARYx Therapeutics, Inc. (NASDAQ:ARYX), a biopharmaceutical company, today
announced further results from a Phase 2b clinical trial testing the safety and
efficacy of its oral anti-arrhythmic therapy, ATI-2042, in patients with atrial
fibrillation. This follows the December 18, 2008 press release reporting that
ATI-2042 reached statistical significance at its primary end point in the two
highest of three doses tested. Those results are now reinforced by these
additional findings indicating, in part, that patients in the study quickly
returned to their pre-treatment level of atrial fibrillation once the treatment
ended. The complete safety results from this study are still not finalized and
are expected by the end of March 2009.

"These additional results broaden our confidence about the effectiveness of
ATI-2042. We believe these incremental data provide additional clinical evidence
that ATI-2042 does not accumulate in the body which is known to be a major
liability with the treatment of choice, amiodarone," stated Dr. Paul Goddard,
chairman and chief executive officer of ARYx Therapeutics. "Our product has been
designed to be as effective as amiodarone in a broad atrial fibrillation patient
population, including those with congestive heart failure, but without its known
safety problems. These additional Phase 2b results should support our efforts to
find the right partner for the full development and eventual commercialization
of ATI-2042."

Our Study Design and Analyses

The clinical trial, which enrolled 72 patients, was a multi-centered,
randomized, double blind, placebo-controlled study of the efficacy and safety of
ATI-2042 in patients with paroxysmal atrial fibrillation (PAF). Patients
entering this study all had previously implanted permanent pacemakers with
appropriate diagnostic and recording capabilities. These devices were used to
collect comprehensive cardiac data, including the percentage of time each
patient spent in atrial fibrillation (their "burden"), as well as other aspects
of cardiac function that will be incorporated in the complete results analysis.
Patients were entered into a baseline screening period of up to 30 days during
which their burden was measured to establish if they were eligible for the
trial. Qualifying subjects were randomized to receive twice-a-day (BID) oral
doses of 200 mg, 400 mg, or 600 mg ATI-2042, or placebo for a treatment period
of 12 weeks. This treatment period was followed by a further 4-week observation
period; the "washout period." During this washout period, no new antiarrythmic
drugs were permitted. Each patient`s burden during the 12-week treatment period
was measured and compared to their own baseline measurement. These results were
then compared to the response in the placebo group.

As previously announced, the primary statistical efficacy analysis showed
significance for ATI-2042 at the 400 mg (p=0.015) and 600 mg (p=0.005) doses.
The atrial fibrillation burden in these two treatment groups was reduced from
baseline by 54% and 75%, respectively. Subsequent to the release of these
top-line results, additional data have been generated.

Our Washout Period Results

Data related to the level of atrial fibrillation burden that existed in the
treated patients during the 4-week washout period is now available. At the end
of the washout period, pacemakers were interrogated and the atrial fibrillation
burden data were analyzed in the same way as the active treatment data. In each
of the three ATI-2042 dose groups, the atrial fibrillation burden returned to
essentially their baseline values within the one-month washout period. The
washout data show no evidence of accumulation or of a rebound effect in the
atrial fibrillation burden.

Additional Indication of Lack of Drug Accumulation

In this study, we utilized slit-lamp examinations to measure whether crystal
deposits, so-called microdeposits, were formed in the patients` eyes as a result
of treatment with ATI-2042. These microdeposits are thought to be an indication
of whether drug accumulation occurs. For example, published studies have shown
these corneal microdeposits appear in approximately 90% of patients treated with
amiodarone for 3 months (HL Green, et al. JACC 1983;2:1114). While the safety
data is still blinded, a review of the over-all results of the slit-lamp eye
examinations conducted on patients in this Phase 2b study reveal that, after up
to three months of treatment, 56 of 57 patients were free of corneal
microdeposits. Along with the washout period data, these slit-lamp examination
results provide evidence of the lack of tissue accumulation of ATI-2042 and its
metabolites.

Our Secondary Endpoint Results

In addition to providing measurement of atrial fibrillation burden, the
pacemakers used in this Phase 2b trial also provided study data on the secondary
efficacy endpoints such as the duration of atrial fibrillation episodes and the
total number of atrial fibrillation episodes. A significant benefit in terms of
reductions in both the number and duration of atrial fibrillation episodes was
demonstrated in the 600 mg BID dose group. Commensurate with the reduced
duration of atrial fibrillation there was a significant increase in the duration
of normal sinus rhythm. The goal of anti-arrhythmic therapies is to maintain
patients in normal sinus rhythm. These improvements in the secondary endpoints
were supportive of the primary endpoint, and provide a plausible biological
explanation for the established dose-dependent reduction in atrial fibrillation
burden seen in this trial`s top-line results. We believe these full efficacy
results help explain how ATI-2042 will be of clinical benefit to patients with
atrial fibrillation.

About Atrial Fibrillation

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia, or
abnormal heart rhythm, affecting greater than 6.4 million people in the United
States, Europe and Japan. It is estimated that AF is responsible for more than
75,000 strokes per year in the United States alone. AF affects about 5% of
people older than 65 years of age, and as the population ages, the prevalence of
AF is projected to double by the year 2050. The prevalence of AF rises to 9% in
people over 80 years of age. AF episodes may be self-terminating, paroxysmal
atrial fibrillation (PAF), or may be prolonged and require cardioversion to
terminate the episode (persistent AF), or may be constant with the person in AF
at all times (permanent AF). PAF and persistent atrial fibrillation are closely
related and, for this reason, the same anti-arrhythmic drugs are used to treat
both types of atrial fibrillation. Atrial fibrillation is caused when the atria
quiver instead of beat. During atrial fibrillation, the atria contract and relax
erratically between 350 and 600 times per minute versus normal heart rhythm of
60 to 80 beats per minute. Patients with atrial fibrillation experience
debilitating symptoms and suffer a compromised quality of life. Because the
pumping function of the atria does not work properly in atrial fibrillation
patients, blood is not completely emptied from the heart's chambers, causing it
to pool and sometimes clot. In patients with atrial fibrillation, clotted blood
can dislodge from the atria and flow to the brain, causing stroke.

About ATI-2042

ATI-2042 is an oral anti-arrhythmic therapy modeled on amiodarone, the "gold
standard" anti-arrhythmic therapy for the treatment of atrial fibrillation (AF).
Approximately 6.4 million people in the United States, Europe and Japan are
diagnosed with AF. No other therapy has demonstrated the efficacy of amiodarone
in the treatment of persistent and paroxysmal AF and its avoidance of dangerous
proarrhythmic effects. However, amiodarone is dependent upon cytochrome P450
enzymes for metabolism and this slow clearance pathway leads to substantial
organ accumulation which is believed to be responsible for its potentially
life-threatening and toxic side effects. Through its metabolism by an alternate
and high capacity pathway, ATI-2042 is designed to maintain amiodarone's unique,
balanced pharmacological effect on various ion channels in the heart while
avoiding its very slow elimination and resulting side effects.

About ARYx Therapeutics, Inc.

ARYx Therapeutics is a biopharmaceutical company focused on developing a
portfolio of internally discovered products designed to eliminate known safety
issues associated with well-established, commercially successful drugs. ARYx
uses its RetroMetabolic Drug Design technology to design structurally unique
molecules that retain the efficacy of these original drugs but are metabolized
through a potentially safer pathway to avoid specific adverse side effects
associated with these compounds. ARYx currently has four products in clinical
trials: an oral anticoagulant agent for patients at risk for the formation of
dangerous blood clots, ATI-5923; an oral anti-arrhythmic agent for the treatment
of atrial fibrillation, ATI-2042; a prokinetic agent for the treatment of
various gastrointestinal disorders, ATI-7505; and, an agent for the treatment of
schizophrenia and other psychiatric disorders, ATI-9242. Please visit our web
site at www.aryx.com for additional information.

Forward-looking Statements

This press release contains forward-looking statements, including, without
limitation, statements related to the results from the Phase 2b clinical trial
of ATI-2042 as well as the potential safety and efficacy and further development
of ATI-2042, the likelihood and timing of entering into a potential
collaboration arrangement involving ATI-2042 on acceptable terms or at all, the
timing and availability of our clinical results, the initiation of new clinical
trials, the ability of a product candidate to be more predictable than currently
available therapies regarding dosing and response to treatment, and the ability
of a product candidate to avoid the dangers existing in currently available
therapies. Words such as "expected," "believe," "designed," "should," "will,"
and similar expressions are intended to identify forward-looking statements.
These forward-looking statements are based upon ARYx`s current expectations.
Forward-looking statements involve risks and uncertainties. ARYx`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, the risk that our product candidates may not
demonstrate safety and efficacy or lead to regulatory approval, the risk that we
may be unable to raise additional capital when needed which would force us to
limit or cease our operations and related product development programs, the risk
that any failure or delay in commencing or completing clinical trials for our
product candidates could severely harm our business, the risk that third party
manufacturers could delay or prevent the clinical development of our product
candidates, the risk that potential collaborative arrangements will likely place
the development of our product candidates outside of our control and the risk
that we may have to alter our development and commercialization plans if
collaborative relationships are not established for ATI-5923, ATI-2042 and
ATI-7505. These and other risk factors are discussed under "Risk Factors" and
elsewhere in the ARYx`s Quarterly Report on Form 10-Q for the quarter ended
September 30, 2008, the Registration Statement on Form S-3 filed with the U.S.
Securities and Exchange Commission on December 18, 2008 and ARYx`s other filings
with the U.S. Securities and Exchange Commission. ARYx expressly disclaims any
obligation or undertaking to release publicly any updates or revisions to any
forward-looking statements contained herein.

ARYx Therapeutics, Inc.
David Nagler, 510-585-2200 ext. 211
Vice President Corporate Affairs
dnagler@aryx.com

Copyright Business Wire 2009