Salix Pharmaceuticals, Ltd. (NASDAQ:SLXP) and Progenics Pharmaceuticals (NASDAQ:PGNX) today received at approximately 5:00 p.m. ET a Complete Response Letter (CRL) from the U.S. Food and Drug Administration (FDA) following its review of a Supplemental New Drug Application (sNDA) for RELISTOR ® (methylnaltrexone bromide) injection for subcutaneous use for the treatment of opioid-induced constipation (OIC) in adult patients with chronic, non-cancer pain. The CRL requests additional clinical data. Salix and Progenics intend to request an End-of-Review meeting with the Division of Gastroenterology and Inborn Errors Products to better understand the contents of the CRL. RELISTOR is a peripherally acting mu–opioid receptor antagonist specifically designed to block the constipating effects of opioid pain medications in the gastrointestinal tract. RELISTOR does not cross the blood-brain barrier, therefore relieving the distressing effects of the constipation while retaining the analgesic effect of the opioid. RELISTOR Subcutaneous Injection has been FDA approved since 2008 to treat constipation in patients with advanced illness and receiving palliative care, when response to laxative therapy has not been sufficient. About Opioids, Constipation and RELISTOR (methylnaltrexone bromide) Opioid analgesics are frequently prescribed for patients with chronic pain. Constipation, a common side effect, occurs in patients receiving opioid therapy. RELISTOR is the first approved medication that specifically targets the underlying cause of opioid-induced constipation in these patients. Opioids relieve pain by specifically interacting with mu–opioid receptors within the brain and spinal cord. However, opioids also interact with mu–opioid receptors found outside the central nervous system, such as those within the gastrointestinal tract, resulting in constipation that can be debilitating. RELISTOR is a peripherally acting mu–opioid receptor antagonist that does not cross the blood-brain barrier and was specifically designed to block mu-opioid receptors in the GI tract, therefore decreasing the constipating effects of opioid pain medications without affecting their ability to relieve pain.