Valeant and Progenics announced that the Food and Drug Administration (FDA) has approved Relistor (methylnaltrexone bromide) tablets for the treatment of opioid-induced constipation (OIC) in adults with chronic non-cancer pain. 

Relistor was initially approved in 2008 as a subcutaneous injection for the treatment of OIC in adults with advanced illness who are receiving palliative care, and in 2014,  for the treatment of OIC in adults with chronic non-cancer pain. Methylnaltrexone is a selective antagonist of opioid binding at the mu-opioid receptor. The ability of methylnaltrexone to cross the blood-brain barrier is restricted. This allows it to function as a peripherally-acting mu-opioid receptor antagonist in tissues such as the gastrointestinal tract, thereby decreasing the constipating effects of opioids without impacting opioid-mediated analgesic effects on the central nervous system. 

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The FDA approval was based on data from a Phase 3 randomized, double-blind trial that evaluated once-daily methylnaltrexone 450mg tablets (n=200) vs. placebo (n=201) in adults with chronic non-cancer pain. Patients in the 450mg treatment group showed statistically significant improvements in rescue-free bowel movement (RFBM) within 4 hours of administration over 28 days vs. placebo, meeting the primary endpoint. Also, the 450mg treatment group achieved statistical significance for the first key secondary efficacy endpoint where a higher percentage of responders was seen with methylnaltrexone treatment vs. placebo. 

The efficacy of oral methylnaltrexone was similar to that observed in clinical studies of subcutaneous methylnaltrexone in patients with chronic, non-cancer pain. The overall safety profile was also comparable to placebo in patients treated with oral methylnaltrexone.

Relistor tablets will be available as a 450mg strength in the 3rd quarter of 2016. Relistor for subcutaneous injection is already available as 8mg/0.4mL and 12mg/0.6mL strength solutions.

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