Salix and Progenics announced that the Food and Drug Administration (FDA) has approved Relistor (methylnaltrexone) subcutaneous injection for the treatment of opioid-induced constipation (OIC) in patients taking opioids for chronic noncancer pain.

The approval was based on a Phase 3, randomized, double-blind, placebo-controlled trial evaluating the efficacy and safety of Relistor 12mg once daily in 312 patients. Patients had confirmed OIC defined as <3 spontaneous bowel movements per week during the screening period.

The study showed that a significantly greater portion of patients taking Relistor 12mg daily reported having >3 spontaneous bowel movements (SBM) per week during the 4-week double blind period compared to placebo (59% vs. 38%). After the first dose, 33% of patients in the Relistor 12 mg once daily treatment group had a SBM within 4 hours and approximately half of patients had a SBM prior to the second dose of Relistor.

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Relistor is a peripherally acting mu opioid receptor antagonist (PAMORA) specifically designed to block the constipating effects of opioids in the gastrointestinal tract. The molecular structure of Relistor restricts it from crossing the blood-brain barrier and interfering with the analgesic effect of opioids. Relistor was initially approved in 2008 for the treatment of OIC in patients with advanced illness who are receiving palliative care, when response to laxatives has been insufficient.

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