Wyeth Pharmaceuticals, a division of Wyeth, and Progenics Pharmaceuticals, Inc. said their phase III clinical study investigating Relistor (methylnaltrexone bromide) subcutaneous injection to treat opioid-induced constipation (OIC) in patients with chronic, non-cancer pain achieved statistical significance for the primary and key secondary efficacy endpoints. Adverse events observed in this study were similar to those seen in prior studies of subcutaneous Relistor.

The positive outcome reported today was from the double-blind, randomised placebo-controlled portion of a phase III clinical study.

"Many patients who take prescription opioids to help relieve their non-cancer pain experience opioid-induced constipation, which can disrupt their lives. The results of this study suggest that Relistor has the potential to help decrease the constipating effects of opioids for this patient population," said Gary L. Stiles, executive vice president, chief medical officer, Wyeth Pharmaceuticals.

Wyeth and Progenics plan to meet global regulatory agencies, including the US Food and Drug Administration, to review these data and intend to present results from both the double-blind and open-label phases of the study at an upcoming scientific meeting.

"This phase III clinical study of Relistor subcutaneous injection showed statistically significant improvements in the occurrence of bowel movements in patients with opioid-induced constipation who have chronic, non-cancer pain," said Paul J. Maddon, chief executive officer, chief science officer and founder of Progenics Pharmaceuticals, Inc.

In the double-blind phase of this study, in which Relistor or placebo were administered subcutaneously for four weeks, the endpoints included the proportion of Relistor injections resulting in bowel movements within four hours and the evaluation of the number of bowel movements per week.

This study was conducted at 80 centres in North America, and enrolled 469 patients with an established history of OIC and chronic pain, such as back pain, fibromyalgia, neuropathic pain, and osteoarthritis, among other types of non-cancer pain. The study consisted of an initial four-week, double-blind phase followed by an eight-week, open-label phase. The open-label portion of the study has recently been completed and an analysis is pending.

Approximately 10 million patients a year in the U.S. are prescribed opioids for 30 days or more to manage their pain. Opioids are considered to be effective analgesics for the management of moderate-to-severe chronic pain, and one of the most common side effects of opioids is persistent constipation.

Relistor is a peripherally acting mu-opioid receptor antagonist that decreases the constipating effects of opioid pain medications in the gastrointestinal tract without diminishing their ability to relieve pain. The use of Relistor beyond four months has not been studied. Relistor subcutaneous injection is approved in the US Europe, Canada and Australia for the treatment of OIC in patients with advanced illness receiving palliative care, when response to laxative therapy has not been sufficient.

Relistor is contraindicated in patients with known or suspected mechanical gastrointestinal obstruction.