AUSTIN, TX—Methylnaltrexone bromide, a selective peripherally acting mu-opioid receptor antagonist, is effective for the long-term treatment of opioid-induced constipation (OIC) resulting from chronic opioid therapy in chronic non-cancer pain, as demonstrated by study data presented at the American Pain Society’s 30th Annual Scientific Meeting. OIC is one of the most common dose-limiting adverse effects associated with prolonged use of opioid analgesics for the treatment of chronic pain. Methylnaltrexone decreases the peripheral adverse side effects of opioids without altering the centrally mediated analgesic effects.

Lynn Webster, MD, FACPM, FASAM, from Lifetree Clinical Research & Pain Clinic, Salt Lake City, UT, and colleagues conducted a Phase 3, 48-week, multicenter, open-label study to evaluate the long-term efficacy, safety, and tolerability of subcutaneous (SQ) methylnaltrexone in alleviating OIC in patients with chronic non-cancer pain. Study endpoints include the percentage of injections resulting in a bowel movement within 4 hours and the change from baseline in the number of weekly bowel movements. Additional assessments included Bristol Stool Form, Straining, and Evacuation Scales.

The study enrolled a total of 1,034 patients ≥18 years who demonstrated constipation 1 month prior to screening. Other inclusion criteria: ≤3 bowel movements per week, at least 25% of BMs characterized by hard or lumpy stools, straining, sensation of incomplete evacuation, or use of manual maneuvers. Following a 14-day screening period, eligible patients received methylnaltrexone SQ at least once weekly and up to once daily for 48 weeks (477/1034 of patients who received ≥1 dose of methylnaltrexone completed 48 weeks of the study ). Patients were permitted to use routine laxatives for the duration of the study.

Data presented by Dr. Webster showed that 34% of methylnaltrexone SQ injections per patient resulted in a BM within 4 hours over the open-label period, with a monthly mean response rate ranging from 33% to 37.4% of injections. Methylnaltrexone bromide also demonstrated an increase of 1.5 BMs per week compared with baseline. Additionally, patients showed improvements from baseline in straining and stool consistency.

Study investigators concluded that the results of this study support the long-term efficacy of SQ methylnaltrexone in providing rapid laxation in patients with chronic non-cancer pain and OIC. This study was supported by a grant from Wyeth Research, Collegeville, PA.