Progenics Pharmaceuticals, Inc. and Wyeth Pharmaceuticals has received  US Food and Drug Administration (FDA) approval for  Relistor (methylnaltrexone bromide) subcutaneous injection for the treatment of opioid-induced constipation (OIC) in patients with advanced illness who are receiving palliative care

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. 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.