Arena Pharmaceuticals, Inc. Initiates Phase 2b Clinical Trial of APD125 for the Treatment of Insomnia

SAN DIEGO, April 8, 2008 /PRNewswire-FirstCall/ -- Arena Pharmaceuticals, Inc. (Nasdaq: ARNA - News) announced today that it initiated screening in a Phase 2b clinical trial of APD125 in patients with primary insomnia. APD125 is an oral drug candidate discovered by Arena with the potential to reduce insomnia symptoms and improve sleep maintenance and quality.

The Phase 2b trial of APD125 is a double-blind, randomized, placebo- controlled subjective study evaluating the efficacy and tolerability of APD125 in patients with primary insomnia characterized by difficulty maintaining sleep. The trial, which is expected to enroll a total of approximately 675 male and female patients in about 70 clinical sites in the United States, will evaluate two doses (20 mg and 40 mg) and placebo over 14 nights of treatment. The trial will evaluate standard subjective measurements of sleep, including change from baseline in subjective number of awakenings after sleep onset (sNAASO), which is the primary endpoint.

“We are very encouraged by the emerging profile of APD125. We believe APD125 has the potential to significantly improve sleep maintenance and quality for patients with insomnia without the potential for dependence or impairing psychomotor function,” said Jack Lief, Arena’s President and Chief Executive Officer. “Results from this trial are expected around year end, and we believe they will increase our understanding of APD125 while supporting ongoing partnership efforts.”

In a Phase 2a trial, when compared to placebo, patients treated with APD125 achieved statistically significant improvements in objective measurements of sleep maintenance, or the ability to maintain sleep during the night after falling asleep, and sleep architecture. The improvements were achieved without any limiting next day cognitive effects. In both the Phase 1 program and the Phase 2a trial, APD125 was well tolerated at all doses investigated.

About APD125

Discovered by Arena, APD125 is a novel and oral selective inverse agonist of the 5-HT2A serotonin receptor. The vast majority of approved drugs for insomnia activate the GABA-A receptor complex in the brain, causing a general suppressive effect on the central nervous system, or CNS. These GABAergic drugs are generally associated with CNS side effects, including a sensation of dullness and lethargy upon awakening, often referred to as the “hangover effect.” Other potential problems associated with the GABAergic drugs include the risk of developing tolerance and drug dependency in at-risk populations. In addition, GABAergic drugs are scheduled controlled substances by the Drug Enforcement Administration due to their potential for abuse.

By selectively targeting the 5-HT2A receptor, APD125 acts through a different mechanism than currently marketed insomnia drugs and blocks one of several CNS activating pathways. Because of the different mechanism of action, APD125 may not have the side effects or abuse potential generally associated with currently approved GABAergic drugs. Through its novel mechanism, APD125 has the potential to reduce insomnia symptoms by improving sleep maintenance.

About Insomnia

Insomnia is characterized by inadequate or poor sleep due to nonrefreshing sleep, frequent wakening with difficulty falling back to sleep, difficulty falling asleep or waking too early. Most insomnia complaints relate to sleep maintenance issues, such as waking frequently or awakening too early, as opposed to problems with sleep latency (i.e. falling asleep). About 30% of US adults report some level of insomnia in the course of a year, and about 10% of US adults indicate that their condition is chronic. In these cases, the lack of restful sleep impairs the person’s ability to carry out their daily responsibilities because they are too tired or have trouble concentrating.

Insomnia has a variety of causes. It is often a symptom of some other disease or condition (e.g. life stress, psychiatric and medical disorders, or use of certain medications), but it can also be a distinct disorder. The prevalence of insomnia increases with age and is more common in women. Common symptoms of acute insomnia are sleepiness, negative mood and impairment of performance. Chronic insomnia is often associated with fatigue, mood changes, difficulty concentrating and impaired daytime functioning.

About Arena Pharmaceuticals

Arena is a clinical-stage biopharmaceutical company focused on discovering, developing and commercializing oral drugs in four major therapeutic areas: cardiovascular, central nervous system, inflammatory and metabolic diseases. Arena’s most advanced drug candidate, lorcaserin, is being investigated in a Phase 3 clinical trial program for the treatment of obesity. Arena’s broad pipeline of novel compounds targeting G protein-coupled receptors, an important class of validated drug targets, includes compounds being evaluated independently and with its partners, Merck & Co., Inc. and Ortho-McNeil Pharmaceutical, Inc.

Arena Pharmaceuticals® and Arena® are registered service marks of the company. “APD” is an abbreviation for Arena Pharmaceuticals Development.

Forward-Looking Statements

Certain statements in this press release are forward-looking statements that involve a number of risks and uncertainties. Such forward-looking statements include statements about the continued development of APD125; the protocol, design, scope, enrollment, number, timing and other aspects of clinical trials of APD125; the timing of the results from the Phase 2b clinical trial of APD125 and expectations related to such results; the tolerability, side effects, safety profile, efficacy and the commercial and other potential of APD125 and other of Arena’s drug candidates; the possibility of APD125 to be a non-scheduled treatment; the relevance of indicators of sleep maintenance; the advancement and content of Arena’s pipeline; and other statements about Arena’s vision, outlook, strategy, preclinical and internal and partnered clinical programs, and ability to develop compounds and commercialize drugs. For such statements, Arena claims the protection of the Private Securities Litigation Reform Act of 1995. Actual events or results may differ materially from Arena’s expectations. Factors that could cause actual results to differ materially from the forward-looking statements include, but are not limited to, clinical trials and studies may not proceed at the time or in the manner Arena expects or at all, the results of clinical trials or preclinical studies may not be predictive of future results, Arena’s ability to partner lorcaserin, APD125, APD791 or other of its compounds or programs, the timing, success and cost of Arena’s research, out- licensing endeavors and clinical trials, Arena’s ability to obtain additional financing, Arena’s ability to obtain and defend its patents, the timing and receipt of payments and fees, if any, from Arena’s collaborators, and Arena’s ability to redeem with common stock any outstanding shares of its series B convertible preferred stock. Additional factors that could cause actual results to differ materially from those stated or implied by Arena’s forward- looking statements are disclosed in Arena’s filings with the Securities and Exchange Commission. These forward-looking statements represent Arena’s judgment as of the time of this release. Arena disclaims any intent or obligation to update these forward-looking statements, other than as may be required under applicable law.

Contacts: Jack Lief Mary Claire Duch President and CEO WeissComm Partners Media Relations David Walsey 212.301.7228 Director, Corporate Communications Arena Pharmaceuticals, Inc. 858.453.7200, ext. 1682 http://www.arenapharm.com

Source: Arena Pharmaceuticals, Inc.

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