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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. (Nasdaq: PTIE), announced today that PTI-901, the

first of a new class of drugs developed to treat irritable bowel

syndrome, 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):

GlaxoKline's Lotronex and Novartis' Zelnorm. According

to Physicians' Desk Reference, the response rate and placebo rate for

women on Lotronex are approximately 50% and 35% respectively at

Week 4. The response rate and placebo rate for women on Zelnorm

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, 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