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A New Drug for Irritable Bowel Syndrome Proves Successful in Clinical Trial

Pain Therapeutics' New Drug Markedly Improved Patients with Irritable Bowel Syndrome (IBS): Company's First Clinical Results in IBS With a New Class of Drugs.  SOUTH SAN FRANCISCO, Calif., May 29 /PRNewswire-FirstCall/ –

– Pain Therapeutics, Inc. announced that PTI-901, the first of a new class of drugs developed to treat irritable bowel syndrome (IBS), significantly improved all the common symptoms associated with IBS.

In a 50 patient pilot clinical study, patients of both gender reported a response rate of 76.2% at the conclusion of the four-week study (N=42). The magnitude of the benefit far exceeded what this pilot study was designed to demonstrate. The study also met the secondary endpoints of improving daily abdominal pain, bowel habits and stool consistency. These improvements were observed in patients whose baseline symptoms were either diarrhea or constipation, or both. No drug-related adverse events were observed.

"This study met its primary endpoint," said Remi Barbier, president and chief executive officer of Pain Therapeutics, Inc. "These results reinforce our faith that PTI-901 has the potential to become the standard drug therapy for patients who suffer from IBS. We believe a safe and effective drug to treat both men and women who suffer from IBS represents a $1 billion market opportunity in the United States alone."

The male and female response rate was 76.5% (N=17) and 75.0% (N=25) respectively. In addition, patients on PTI-901 reported a 193% increase in number of pain-free days at Week 4 compared to baseline (N=37). Significant clinical improvements in bowel urgency, stool consistency and number of stools per day were also reported at Week 4 in both genders. PTI-901 was well tolerated by all patients during the entire treatment period.

"In this study, PTI-901 had a clean safety profile and provided rapid and sustained relief of abdominal pain for patients with IBS," added Nadav Friedmann, Ph.D., MD, chief medical and operating officer of Pain Therapeutics, Inc. "Significantly, these clinical benefits were observed in IBS patients regardless of gender. These data encourage us to evaluate PTI-901 in a Phase III trial designed to support product approval."

Pain Therapeutics believes this study presents clinical validation of the novel hypothesis that IBS patients suffer from an abnormal imbalance of opioid activity in the gut. Such an imbalance may be triggered by emotional stress, metabolic disorders or intrinsic release of opioids from gut neurons.

The Company and its scientific collaborators believe that chronic administration of very low doses of an opioid antagonist, such as the investigational new drug PTI-901, restores the proper level of opioid activity in the gut. This relieves abdominal pain and other symptoms frequently observed in patients with IBS. The Company holds exclusive, worldwide commercial rights in a family of issued patents and patent applications, including two issued U.S. patents in this area.

Pain Therapeutics and its principal investigator intend to submit an abstract of this trial to the Annual Scientific Meeting of the American College of Gastroenterology, which will be held in Baltimore in October 2003. The Company plans to follow-up this pilot clinical study with a 600 patient Phase III pivotal trial in the United States. The Company's registration strategy will ultimately depend on PTI-901's level of activity in pivotal Phase III studies and on discussions with regulatory agencies.

Study Detail

The purpose of this open-label study was to evaluate the clinical effects of PTI-901 (low-dose naltrexone HCI) in patients with IBS. A total of 50 patients were enrolled. All patients were diagnosed with IBS by a gastroenterologist according to Rome II Criteria. Treatment consisted of 0.5 mg dose of PTI-901 daily over a four-week period.

Patients were evaluated for abdominal pain, bowel habits and stool consistency at baseline and at the end of weeks 1 through 4. The primary efficacy endpoint was the patients' observations of Global Assessment of Adequacy of Treatment. Secondary efficacy endpoints included abdominal pain and bowel habits. The study was conducted at the Sourasky Medical Center in Israel under an Investigational New Drug (IND) Application filed with the U.S. Food and Drug Administration (FDA).

Existing IBS Drugs

The FDA has approved two drugs to treat women with certain types of IBS (no drug therapy is currently FDA approved for men with IBS): GlaxoSmithKline's Lotronex(TM) and Novartis' Zelnorm(TM). According to Physicians' Desk Reference, the response rate and placebo rate for women on Lotronex(TM) are approximately 50% and 35% respectively at Week 4. The response rate and placebo rate for women on Zelnorm(TM) are approximately 58% and 50% respectively at Week 4.

About Irritable Bowel Syndrome (IBS)

IBS is a chronic, painful abdominal disorder that leads to major changes in bowel habits. IBS causes some patients to have constipation, diarrhea or in some cases both. The cause of IBS is not known, and as yet there is no cure. People with chronic IBS may be unable to attend social events, hold a job, or travel away from home. Over 10 percent of the U.S. population suffers from IBS. For unknown reasons, IBS predominantly affects women.

About Pain Therapeutics, Inc.

We are a medical research company specializing in the discovery and development of novel proprietary painkillers. We believe one of our lead drug candidates, Oxytrex(TM), may offer more pain relief (with no increase in side-effects) or lower tolerance/dependence, withdrawal effects or addiction potential compared to conventional forms of oxycodone. The market for oxycodone exceeded $1.5 billion in the United States in 2002. Another drug candidate, PTI-901, is aimed at treating patients who suffer from abdominal pain associated with Irritable Bowel Syndrome.

For more information, please visit our website at www.paintrials.com.
Note Regarding Forward-Looking Statements: This press release contains forward-looking statements for purposes of the Private Securities Litigation Reform Act of 1995 and it is Pain Therapeutics' intent that such statements be protected by the safe harbor created thereby. Examples of such statements include, but are not limited to, any statements relating to the potential benefits of PTI-901 for the treatment of IBS, the size, scope, goals, or timing of the Company's pivotal trial with PTI-901, the benefits that may be derived from the Company's patents or technology, the potential benefits of the Company's drug candidates, and the size of the potential market for the Company's products.

Such statements are based on management's current expectations, but actual results may differ materially due to various factors, including, but not limited to, risks and uncertainties relating to difficulties or delays in development, enrolling and conducting clinical trials such as the IBS study, regulatory approval, production and marketing of the Company's drug candidates, unexpected adverse side effects or inadequate therapeutic efficacy of the Company's drug candidates that could slow or prevent product approval (including the risk that current and past results of clinical trials are not necessarily indicative of future results of clinical trials), the uncertainty of patent protection for the Company's intellectual property or trade secrets and the Company's ability to obtain additional financing if necessary.

For further information regarding these and other risks related to the Company's business, investors should consult the Company's filings with the Securities and Exchange Commission, including its Form 10-K for the year ended December 31, 2002 and its subsequent quarterly filings.

Source: Pain Therapeutics, Inc.