Methylnaltrexone for Opioid-Induced Constipation in Advanced Illness

Background Constipation is a distressing side effect of opioid treatment. As a quaternary amine, methylnaltrexone, a μ-opioid–receptor antagonist, has restricted ability to cross the blood–brain barrier. We investigated the safety and efficacy of subcutaneous methylnaltrexone for treating opioid-induced constipation in patients with advanced illness. Methods A total of 133 patients who had received opioids for 2 or more weeks and who had received stable doses of opioids and laxatives for 3 or more days without relief of opioid-induced constipation were randomly assigned to receive subcutaneous methylnaltrexone (at a dose of 0.15 mg per kilogram of body weight) or placebo every other day for 2 weeks. Coprimary outcomes were laxation (defecation) within 4 hours after the first dose of the study drug and laxation within 4 hours after two or more of the first four doses. Patients who completed this phase were eligible to enter a 3-month, open-label extension trial. Results In the methylnaltrexone group, 48% o...