Methylnaltrexone (MNTX) is a peripheral opioid receptor antagonist that is designed to treat rapidly the side effects of opioids without interfering with pain relief. Progenics is developing the treatment with Wyeth Pharmaceuticals, a division of Wyeth, under an agreement made in 2005.
In this second phase III clinical study, subcutaneous administration of MNTX induced laxation (bowel movement) within four hours in 51.2% of severely constipated advanced-medical-illness patients at more than three times the rate of placebo on average over a two-week period.
All primary and secondary efficacy endpoints of the phase III study were positive and highly statistically significant. The drug was generally well tolerated, and there were no serious adverse events attributed to MNTX.
“Treatment of the complications and discomfort of opioid-induced constipation is often a greater problem than the treatment of pain in these patients. MNTX has the potential to improve significantly the care of patients who require opioids for pain relief”, said Dr Charles von Gunten, editor-in-chief of Journal of Palliative Medicine and medical director, Center for Palliative Studies, San Diego Hospice, a participating site in MNTX clinical trials.