Development of ADX10059 ended for long-term use

Conference call and webcast at 2pm CET / 8am ET

Geneva, Switzerland, 15 December 2009 - Addex Pharmaceuticals
(SIX:ADXN) announced today that based on preliminary review of the
unblinded data from study 206, it has terminated development of
ADX10059 for chronic indications, including long term treatment of
gastroesophageal reflux disease and migraine prophylaxis.

In study 206 the incidence of alanine transaminase (ALT) levels
greater than five times the upper limit of normal (>5xULN) levels was
6% (16 of 257 patients); however, bilirubin remained normal in all
but one patient. The elevation of ALT occurred in all dose groups and
appears to be related to the duration of dosing. The incidence was
3.9% (10 patients) in the 100 mg group; 0.8% (2 patients) in the 50
mg group; 1.6% (4 patients) in the 25 mg group. No abnormalities of
liver function were observed in the placebo group.

A rise in transaminases to >5x ULN is considered to be predictive of
a potential for drug induced liver injury. As these significant
elevations in ALT have been observed in all the dose groups, Addex
considers that future development of ADX10059 for long term use
appears unlikely. The company will evaluate potential development
options based on the complete analysis of the data from study 205, a
4-week study in GERD patients, which will report top-line data in
early January.

Study 205 is still blinded however, a review of blinded safety data
show an incidence of ALT >5x ULN of 0.6% (2 of 295 patients). This is
in-line with expectations for this type of study.

"The occurrence of liver function abnormalities in patients receiving
the lowest dose, makes future development of this compound difficult,
especially for long term use," said Charlotte Keywood, chief medical
officer.

"We have cash for operations until the end of 2011 and plan to focus
our efforts on development of ADX48621, which has completed Phase I
testing and is scheduled to start Phase II testing for the treatment
of Parkinson's disease levodopa induced dyskinesia in the fourth
quarter of 2010," said Vincent Mutel, chief executive officer. "We
also will accelerate development of selected programs in discovery
and preclinical development and continue to leverage our unique
discovery and development platform for allosteric modulator drugs."

No liver function abnormalities have been seen in any of the
previously reported clinical trials, several of which explored higher
doses, including the recently reported study ADX10059-204, a 2-week
study of monotherapy in 103 GERD patients. Study 205 a 4-week study
of ADX10059 as an add-on therapy to PPIs in GERD patients, is due to
un-blind around the end of the year and data will be reported in
January.

A webcast and conference call will be held at 2pm CET (8am ET) today,
December 15. Please see www.addexpharma.com or use the following
dial-in numbers:

+41 91 610 56 00 (Europe)
+44 207 107 06 11 (UK)
+1 866 291 41 66 (USA)

Study ADX10059-206 is a double-blind, placebo-controlled, dose range
finding, multi-center European Phase IIb trial in 240 patients who
suffer from three or more migraine attacks per month. Following a
one-month baseline period, patients take study medication for 3
months. The primary endpoint compares migraine frequency and severity
in the last month of treatment with the baseline. The data are being
un-blinded and will be analyzed and any indications of efficacy will
be reported in early January.

Study ADX10059-205 is a double-blind, placebo-controlled,
multi-center U.S. and European Phase IIb trial in 280 GERD patients
who are partial responders to proton pump inhibitors (PPIs). In Study
205 ADX10059 is being used as an add-on therapy to the patients'
existing PPI treatment. There was a baseline symptom evaluation
period followed by four weeks of administration of twice-daily
ADX10059 (50mg, 100mg or 150mg). The primary endpoint is patient
reported symptom control compared to baseline. Data are expected to
be communicated in early January.

Study ADX10059-204 was a double-blind, placebo-controlled,
multi-center European Phase IIb trial in 103 GERD patients known to
respond well to PPIs. There was a two-week baseline symptom
evaluation period followed by two weeks of administration of ADX10059
120 mg twice daily. ADX10059 achieved the co-primary endpoints of
patient reported symptom control compared to baseline and the effects
of ADX10059 on lower esophageal sphincter (LES) function as well as
multiple secondary endpoints. There were no serious adverse events in
the study and safety monitoring parameters were within normal limits.
Mild or moderate adverse events included dizziness, vertigo and sleep
disturbance.

Migraine is a condition distinguished by recurrent episodes of a
characteristic headache, which can be accompanied by a variety of
other symptoms such as nausea, and sensitivity to light and sound.
The average migraine patient suffers 12 attacks a year. The
International Headache Society estimates that about 25% of migraine
patients have three or more attacks per month and could benefit from
migraine prevention treatment. A migraine attack, which typically
lasts about 24 hours but can range from 4-72 hours, has three
distinct phases: the prodrome phase, when an array of individual
warning signs - like blurred vision or tingling of the skin - may
begin to appear; the headache phase; and the postdrome phase, when
many patients report fatigue or other "hangover-like" symptoms. As
migraine attacks are prolonged, many patients and especially those
with frequent attacks, lose a significant amount of work and family
time to suffering caused by the disease. Indeed, migraine is
currently estimated to cost employers $13 billion annually in lost
productivity in the United States. Prevalence of migraine is
estimated at 12% in the United States, where about 30 million people
suffer from migraine.

GERD (gastroesophageal reflux disease) is a chronic condition caused
by stomach contents flowing back into the esophagus on a regular
basis. The underlying cause of this is an abnormally functioning
lower esophageal sphincter (LES) muscle that allows stomach contents
to pass back into the esophagus too easily. GERD leads to painful
symptoms like heartburn and can also damage the lining of the
esophagus. It is a common disorder with prevalence at about 15% in
the United States and between 10% and 25% in EU. Marketed GERD
products work by reducing the acidity of the stomach contents but do
nothing to reduce reflux events, so that in many patients symptoms of
GERD persist.

ADX10059 is a metabotropic glutamate receptor 5 (mGluR5) negative
allosteric modulator (NAM). Glutamate overstimulation is thought to
contribute via different mechanisms to pathology in both migraine and
GERD. ADX10059 has been shown in clinical studies to reduce symptoms
of acute migraine and, separately, to reduce reflux and GERD
symptoms.

Addex Pharmaceuticals (www.addexpharma.com) discovers and develops
allosteric modulators for human health. Allosteric modulators are a
different kind of orally available small molecule therapeutic agent,
which we believe will offer a competitive advantage over classical
drugs. Our lead allosteric modulator product, ADX10059, an mGluR5
negative allosteric modulator (NAM), has achieved clinical proof of
concept and is in Phase IIb testing for the treatment of GERD and,
separately, migraine prevention. ADX48621, our next-stage mGluR5 NAM,
has completed Phase I testing and will enter Phase II for Parkinson's
disease levodopa-induced dyskinesia (PD-LID) in 2010.
Our products and technology already have proven their value through
our relationships with four of the top 10 pharmaceutical companies in
the world. Specifically, under an agreement with Ortho-McNeil-Janssen
Inc., a Johnson & Johnson company, ADX71149, an mGluR2 positive
allosteric modulator (PAM), is undergoing Phase I clinical testing
and has potential for treatment of schizophrenia and anxiety. Under
two separate agreements with Merck & Co., Inc., we are developing
PAMs of mGluR4 and mGluR5 as drugs to treat Parkinson's disease and
schizophrenia, respectively. In addition, SR-One, the corporate
venture arm of GlaxoSmithKline, and Roche Venture Fund have made
equity investments in Addex.

Chris Maggos
Investor Relations & Communications
Addex Pharmaceuticals
+41 22 884 15 11
chris.maggos@addexpharma.com

Disclaimer: The foregoing release contains forward-looking statements
that can be identified by terminology such as "not approvable",
"continue", "believes", "believe", "will", "remained open to
exploring", "would", "could", or similar expressions, or by express
or implied discussions regarding Addex Pharmaceuticals Ltd, its
business, the potential approval of its products by regulatory
authorities, or regarding potential future revenues from such
products. Such forward-looking statements reflect the current views
of Addex Pharmaceuticals Ltd regarding future events, and involve
known and unknown risks, uncertainties and other factors that may
cause actual results with allosteric modulators of mGluR4, mGluR2,
mGluR5 or other therapeutic targets to be materially different from
any future results, performance or achievements expressed or implied
by such statements. There can be no guarantee that allosteric
modulators of mGluR4, mGluR2 or mGluR5 will be approved for sale in
any market or by any regulatory authority. Nor can there be any
guarantee that allosteric modulators of mGluR4, mGluR2, mGluR5 or
other therapeutic targets will achieve any particular levels of
revenue (if any) in the future. In particular, management's
expectations regarding allosteric modulators of mGluR4, mGluR2,
mGluR5 or other therapeutic targets could be affected by, among other
things, unexpected actions by our partners, unexpected regulatory
actions or delays or government regulation generally; unexpected
clinical trial results, including unexpected new clinical data and
unexpected additional analysis of existing clinical data; competition
in general; government, industry and general public pricing
pressures; the company's ability to obtain or maintain patent or
other proprietary intellectual property protection. Should one or
more of these risks or uncertainties materialize, or should
underlying assumptions prove incorrect, actual results may vary
materially from those anticipated, believed, estimated or expected.
Addex Pharmaceuticals is providing the information in this press
release as of this date and does not undertake any obligation to
update any forward-looking statements contained in this press release
as a result of new information, future events or otherwise.

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