Methylnaltrexone Effective for Opioid-Induced Constipation Relief
Methylnaltrexone is a peripherally acting μ-opioid receptor antagonist.
A daily subcutaneous injection of methylnaltrexone provides effective relief from opioid-induced constipation (OIC) in patients with chronic non-cancer pain, according to a phase 3 open-label trial published in Pain Medicine.1
In this study, researchers examined efficacy and tolerability results of a once-daily 12 mg subcutaneous injection of methylnaltrexone in adults with chronic non-cancer pain (n=1034) for OIC relief. Approximately half of the study population (n= 496; 48.0%) received methylnaltrexone for ≥44 weeks.
Assessments of efficacy included the weekly bowel movement (BM) rate, mean weekly BM straining scale score (rated as 0 [none] to 4 [very severe]), BM percentage with complete evacuation sensation, and weekly average BM Bristol Stool Scale score (rated as 1 [separate hard lumps] to 7 [watery with no solid pieces]). Efficacy data were recorded in a daily patient diary.
This patient population commonly reported mild to moderate gastrointestinal-related adverse events (AEs). Methylnaltrexone contributed to a successful BM within a 4-hour period in 34.1% of the injections. Of the study patients, 9 experienced serious cardiac-related AEs. There was a significant improvement in average weekly BM rate, Bristol Stool Scale score, BM Straining Scale score, and BM percentage with sensation of complete evacuation at 48 weeks (P <.001).
The investigators noted that the study's open-label design could have inadvertently affected patient-reported AEs. Laxatives, which were taken by 77.3% of patients during the study period, may have also contributed to some of the AEs experienced.
In addition, the researchers noted that the study of demographic and baseline disease characteristics should be included in future studies “to assess the effects of methylnaltrexone on diverse patient populations (eg, older patients, patients receiving both low and high opioid doses, patients receiving different types of opioids,…).”