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FDA Expands Indication for Methylnaltrexone Bromide (Relistor)

Treatment approved for opioid-induced constipation in patients with non-cancer pain

The FDA has given the nod to methylnaltrexone bromide (Relistor, Salix Pharmaceuticals) subcutaneous injection, 12 mg/0.6 mL, for the treatment of opioid-induced constipation (OIC) in patients receiving opioids for chronic non-cancer pain.

The treatment is the only available peripherally acting mu opioid receptor antagonist (PAMORA) that is approved for treating OIC at the cause without interfering with the centrally acting analgesic properties of the opioid.

Traditional laxative treatments are often ineffective for many patients with chronic pain who experience opioid-induced constipation. Approximately 80% of chronic pain patients with OIC that were receiving laxative therapy continued to report difficulties dealing with their constipation symptoms, as documented by a large patient survey published in 2008 in Pain Medicine. One third of these chronic pain patients reported stopping or lowering their opioid dose to relieve their opioid-induced constipation, resulting in increased pain levels.

A randomized, double blind, placebo-controlled trial was conducted to evaluate the efficacy and safety of methylnaltrexone bromide 12 mg once daily for the treatment of opioid-induced constipation in patients with chronic non-cancer pain.

A total of 312 patients with a history of non-cancer pain and receiving opioids for at least 1 month before study entry were eligible for enrollment. The patients also had confirmed OIC (defined as fewer than three spontaneous bowel movements [BMs] per week during the screening period). Constipation due to opioid use had to be associated with one or more of the following: a Bristol Stool Form Scale score of 1 or 2 for at least 25% of the BMs, straining during at least 25% of the BMs, or a sensation of incomplete evacuation after at least 25% of the BMs.

The median duration of opioid-induced constipation at baseline was 59 months. The median daily baseline oral morphine equivalent dose was 161 mg. The patients were randomly assigned to receive methylnaltrexone bromide 12 mg or placebo once daily for 4 weeks, followed by an 8-week open-label phase, during which patients could take medications as needed.

A significantly greater portion of patients treated with methylnaltrexone bromide 12 mg daily reported having three or more spontaneous bowel movements (SBMs) per week during the 4-week double blind period compared with placebo (59% vs. 38%, respectively). After the first dose, 33% of patients in the methylnaltrexone bromide group had an SBM within 4 hours, and approximately half of patients had an SBM before the second dose of study drug.

The treatment was well tolerated. The most common side effects included abdominal pain (21%), diarrhea (6%), nausea (9%), and hyperhidrosis (6%).

Relistor (methylnaltrexone bromide) subcutaneous injection was approved by the FDA in 2008 for the treatment of OIC in patients with advanced illness who are receiving palliative care when the response to laxative therapy has not been sufficient.

Source: Salix Pharmaceuticals; September 29, 2014.

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