Methylnaltrexone Improves Opioid-Induced Constipation in Patients with Chronic Nonmalignant Pain

BALTIMORE, Md.—Patients with chronic nonmalignant pain who receive methylnaltrexone for opioid-induced constipation have improved bowel movement frequency and quality, investigators reported during the American Pain Society’s 29th Annual Scientific Meeting. Opioid-induced constipation was defined as ≤2 rescue-free bowel movements (RFBMs) per week plus ≥25% of those movements with Bristol Stool form 1 or 2, straining, or sensation of incomplete evacuation.

Marc Duerden, MD, of the Indiana University School of Medicine, Indianapolis, Ind., and colleagues reported additional efficacy results from a double-blind, randomized, placebo-controlled study in patients taking daily opioid for chronic nonmalignant pain.

At baseline, patients were randomized to methylnaltrexone 12 mg/day; methylnaltrexone 12 mg every other day; or placebo for 4 weeks. During the study, only standardized rescue laxatives were allowed. Using standardized scales, patients recorded stool consistency (1-7), defecation straining (0-4), and sensation of complete evacuation. Of 460 patients who received at least one dose of study medication, chronic back pain was the primary pain condition (60.4%). Mean age was 48.8 years and 60.2% were female.

Mean change from baseline in weekly RFBMs with a sensation of complete evacuation was significantly greater in patients treated with methylnaltrexone (QD 1.9, QOD 1.2) than placebo (0.8 daily; P<0.001 and P=0.012, respectively). Both groups of methylnaltrexone-treated patients had a significantly greater decrease from baseline in mean straining of RFBMs, -1.1 compared with -0.8 placebo (P=0.008 for every day and P=0.015 for every other day).

Greater changes from baseline in mean Bristol Stool Form of RFBMs were observed with methylnaltrexone (1.4 for every day and 1.2 for every other day) vs placebo (0.9), with a significant treatment difference between methylnaltrexone once daily and placebo (P=0.002). Abdominal pain was the most frequent adverse event.