AGS: Methylnaltrexone Demonstrates Efficacy for Treatment of Opioid-Induced Constipation

SEATTLE, May 7 -- Opioid-induced constipation in advanced cancer may be relieved for more than half of patients within four hours by a subcutaneous injection of methylnaltrexone, researchers here reported.

Moreover, the methylnatrexone treatment was not associated with significant changes in pain scores, which suggested that "blocking the opioid receptors in the gut did not affect receptors in the brain," said Gary M. Garner, M.D., R.Ph., of Harmony Home Health in Murray, Utah.

Dr. Garner reported results of two phase III trials of methylnatrexone, an investigational compound, at the meeting of the American Geriatrics Society.

Sixty-two percent of patients given a single injection of methylnaltrexone achieved laxation within four hours of treatment as did 48.4% of patients in the second study that lasted two-weeks and involved every-other-day dosing (P

The single-dose study enrolled 154 patients and the two-week dosing trail enrolled 133 patients. Patients in both studies were 18 or older and all had had advanced disease with a life expectancy of less than six months. All patients had been receiving opioid therapy for at least two weeks.

Opioid-induced constipation was defined as less than three bowel movements a week or no bowel movement for more than 48 hours.

Patients received methylnaltrexone or placebo on top of best medical care, which included laxative management.

The most common side effect was transient abdominal pain, cramping, and flatulence, he said. "But I regard that as a positive because these patients are very often relieved when they develop those symptoms because they take it as evidence that 'something is happening,'" he said.