Injections may Provide New Therapy for Opioid-induced Constipation

At the annual meeting of the American Pain Society, May 7-9 in San Diego, CA, E. Richard Blonsky, MD, director of the Pain and Rehabilitation Clinic of Chicago and clinical professor of neurology (http://www.neurology.northwestern.edu/index.html) at Northwestern University's Feinberg School of Medicine (http://www.medschool.northwestern.edu/), described the positive impact that injections of Relistor (methylnaltrexone) may have for patients with constipation due to opioid therapy for non-cancer pain.

Blonsky was discussing the results of a study that examined the effectiveness of injections of Relistor in comparison with a placebo. According to Blonsky, 34.3% of patients given Relistor accomplished laxation within four hours of the injection, compared to 9.9% of patients given placebo. In addition, about 46% of people given methylnaltrexone achieved laxation within 24 hours, seen in 25% of those in the placebo group.

Blonsky said that the drug “decreases the constipating effects of opioids without affecting centrally mediated analgesia.” Though the FDA has not yet approved the drug for the treatment of opioid-induced constipation in patients without cancer, the agent is currently used to treat opioid-induced constipation as a result of cancer treatments.

For the current study, researchers performed a double blind, placebo controlled, phase 3 randomized trial of 460 patients. Participants were divided into three groups: one given subcutaneous methylnaltrexone every day, one given the drug every other day, and one given placebo. Of patients in the “active treatment group,” 81% finished the trial, with the 7.7% of the individuals who did withdraw citing adverse events.

"These results suggest that subcutaneous methylnaltrexone is an effective and generally well-tolerated treatment for opioid-induced constipation in patients with chronic nonmalignant pain," Blonsky said.

He said that the goal of the treatment is to allow patients to freely leave their homes without being concerned about “the urge to void” that comes from the “unpredictable nature of their constipation and of common laxatives.”

Side effects seen with the injections of Relistor included abdominal pain, dizziness, nausea, vomiting, and diarrhea. Blonsky noted that these were seen with “frequency notably different” from the placebo.

Patients who have already suffered from constipation before receiving treatment for pain should avoid opioid therapy if possible, Blonsky added.