San Diego, California and Research Triangle Park, North Carolina, November 7, 2007

Prometheus Laboratories Inc., a speciality pharmaceutical company has signed an agreement with GlaxoSmithKline to acquire exclusive rights to Lotronex^® (alosetron hydrochloride) Tablets in the United States. Lotronex is the only prescription drug approved by the FDA for use in adult female patients with severe diarrhea-predominant irritable bowel syndrome who meet the conditions stated in the label. Prometheus will market and sell Lotronex under an exclusive distribution agreement until the acquisition is completed, which is expected in January 2008. Prometheus will continue to offer Lotronex exclusively through the currently established Prescribing Program for Lotronex (PPL). Lotronex may be prescribed only by physicians who have enrolled in the PPL.

“The acquisition of Lotronex is a significant opportunity for Prometheus and an important next step in continuing to build our portfolio of proprietary pharmaceutical products,” said Joseph M. Limber, President and Chief Executive Officer of Prometheus. “Lotronex fits well with our long-term plans to grow through acquisitions of meaningful therapeutic products and enhances Prometheus’ position as a leading provider of therapeutics and diagnostics for physicians and their patients who suffer from severe gastrointestinal diseases.”

Commenting from GlaxoSmithKline, Stan Hull, Senior Vice President, US Pharmaceuticals said, “We believe that Prometheus is ideally positioned with their strong franchise and relationships with gastroenterologists to market Lotronex and to educate patients and physicians on its proper use.”

Lotronex is indicated for use only in women with severe diarrhea-predominant irritable bowel syndrome who have failed to respond to conventional therapy, whose irritable bowel syndrome, or IBS, symptoms are chronic, and who have had other gastrointestinal medical conditions that could explain their symptoms ruled out. Diarrhea-predominant IBS is severe if in addition to diarrhea the patient experiences at least one of the following symptoms: frequent and severe abdominal pain/discomfort; frequent bowel urgency/fecal incontinence; or disability/restriction of daily activities because of IBS. Clinical studies have not been performed to adequately confirm the benefits of Lotronex in men or patients under the age of 18.

Serious gastrointestinal adverse events have been reported with the use of Lotronex. These events, including ischemic colitis and serious complications of constipation, have resulted in hospitalizations, blood transfusions, surgery and fatalities. Lotronex should be discontinued immediately in patients who develop constipation or symptoms of ischemic colitis. Lotronex should not be resumed in patients who develop ischemic colitis. Physicians should instruct patients who report constipation to immediately contact them if the constipation does not resolve after discontinuation of Lotronex. Patients with resolved constipation should resume Lotronex only on the advice of their treating physician.

About IBS

According to the American Gastroenterology Association, IBS is one of the most common gastrointestinal disorders in the United States affecting more than 58 million people. IBS affects all races and both men and women; however, approximately 4 out of 5 (or 80 percent) of IBS sufferers are women. Although the cause is currently unknown, IBS is characterized by multiple symptoms that include chronic or recurrent abdominal pain and discomfort together with irregular bowel function, such as diarrhea, constipation or alternating diarrhea and constipation. Approximately 30% of women with IBS have diarrhea-predominant IBS.

About Prometheus

Prometheus is a specialty pharmaceutical company committed to developing new ways to help physicians individualize patient care. Prometheus focuses on the treatment, diagnosis and detection of gastrointestinal, autoimmune and inflammatory diseases and disorders. Prometheus' strategy includes the marketing and delivery of pharmaceutical products complemented by its proprietary, high-value diagnostic testing services. By integrating therapeutics and diagnostic services, Prometheus addresses the continuum of patient care, thereby providing physicians with a comprehensive solution to treat chronic diseases. Prometheus' corporate offices are located in San Diego, California. Additional information about Prometheus can be found at www.prometheuslabs.com.

About GSK

GlaxoSmithKline is one of the world's leading research-based pharmaceutical and healthcare companies and is committed to improving the quality of human life by enabling people to do more, feel better and live longer. For more information, visit GlaxoSmithKline at www.gsk.com.

Prometheus forward-looking statements
This press release contains certain “forward looking” statements within the meaning of the Private Securities Litigation Reform Act of 1995. To the extent that any statements made in the news release contain information that is not historical, these statements are essentially forward-looking and are subject to risks and uncertainties. Actual events or results may differ materially from those projected in any of such statements due to various factors. Prometheus cautions that any forward-looking information is not a guarantee of future performance. The acquisition of Lotronex is subject to certain conditions of closing, including the accuracy of specific representations and warranties. Assuming the acquisition closes successfully, the Company may not successfully maintain or grow the market for Lotronex for a variety of reasons. For example, the Company is aware of other products under development and in clinical testing for the treatment of IBS. In addition, to market Lotronex, the Company plans to expand its sales force and the product must be successfully manufactured in compliance with current good manufacturing practices. Under the acquisition agreement, the Company will be required to transfer manufacturing from GlaxoSmithKline to other suppliers over a two to three year period. If unsuccessful, the Company may not have product available to sell. The market for personnel is competitive, and there is no assurance that the Company can recruit new personnel on a timely basis. It is difficult to predict the impact of competitive products and pricing. The number of products available for acquisition is limited and the market for such products is competitive and expensive. There can be no assurance that the Company will successfully complete the acquisition of Lotronex or acquire any other new products.

GlaxoSmithKline forward-looking statements
Under the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995, GSK cautions investors that any forward-looking statements or projections made by GSK, including those made in this announcement, are subject to risks and uncertainties that may cause actual results to differ materially from those projected. Factors that may affect GSK's operations are described under 'Risk Factors' in the Operating and Financial Review and Prospects in the company's Annual Report on Form 20-F for 2006.

The Prescribing Program for Lotronex and full prescribing information are available by calling 1-888-423-5227 or visiting www.Lotronex.com.

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