Progenics Pharmaceuticals, Inc. and Wyeth Pharmaceuticals, a division of Wyeth, said the US Food and Drug Administration (FDA) has approved Relistor (methylnaltrexone bromide) subcutaneous injection for the treatment of opioid-induced constipation (OIC) in patients with advanced illness who are receiving palliative care, when response to laxative therapy has not been sufficient.

In clinical studies, Relistor significantly decreased the constipating effects of opioids without interfering with pain relief. Wyeth expects to make Relistor available in the United States in early June.

"The approval of Relistor is a transformative event for Progenics Pharmaceuticals," said, Paul J. Maddon, M.D., Ph.D., founder, chief executive officer and chief science officer, Progenics Pharmaceuticals, Inc. "This is our first US product approval. I am proud of what our company has achieved and especially want to thank our patients and investigators who participated in the Relistor development programme. This programme has greatly benefited from our collaboration with Wyeth to develop and commercialize the Relistor platform of products."

Each year, more than 1.5 million Americans receive palliative care due to an advanced illness, such as incurable cancer, end-stage heart and lung disease, or AIDS. Many of these patients are prescribed opioids to manage their pain, and experts have stated that constipation that can be debilitating occurs in practically all of them.

"We are pleased to make Relistor available to patients to address this serious unmet medical need," said, Bernard Poussot, president and chief executive officer, Wyeth. "As Wyeth's third new medicine to receive FDA approval in 2008, Relistor is an excellent example of Wyeth's continuing commitment to develop and deliver medicines that work in novel ways and provide important new treatment options for patients."

Jay Thomas, M.D., Ph.D., an investigator in the subcutaneous Relistor clinical trial programme and clinical medical director of San Diego Hospice and the Institute of Palliative Medicine, said, "Opioid analgesics are the mainstay therapy for pain management in advanced-illness patients receiving palliative care. Side effects associated with opioids, such as constipation, can be severe enough to limit pain management. I am pleased that we now have a new treatment option to provide relief to advanced-illness patients with OIC."

Relistor, administered via subcutaneous injection, is a peripherally acting mu-opioid receptor antagonist that counteracts the constipating effects of opioid pain medications in the gastrointestinal tract without affecting their ability to relieve pain.

Opioids provide pain relief by specifically interacting with mu-opioid receptors within the central nervous system (CNS) - the brain and spinal cord. However, opioids also interact with mu-opioid receptors found outside the CNS, such as those within the gastrointestinal tract, resulting in constipation that can be debilitating. Relistor selectively displaces opioids from the mu-opioid receptors outside the CNS, including those located in the gastrointestinal tract, thereby decreasing their constipating effects. Because of its chemical structure, Relistor does not affect the opioid-mediated analgesic effects on the CNS. The efficacy and safety profile of Relistor was established in two phase III clinical trials. Use of Relistor beyond four months has not been studied.

In December 2005, Wyeth and Progenics Pharmaceuticals entered into an exclusive, worldwide agreement for the joint development and commercialization of methylnaltrexone for the treatment of opioid-induced side effects. In accordance with the terms of the collaboration, this US marketing approval triggers a $15 million milestone payment to Progenics from Wyeth.