Drug proves effective in opioid-induced constipation

At a fixed dose of 12 mg, methylnaltrexone bromide (Relistor, Progenics Pharmaceuticals) subcutaneous injection proved generally safe and well tolerated in non-malignant pain patients with opioid-induced constipation (OIC), according to a 1,034-patient, 1-year phase 3 study.  The safety profile was similar to that from a previously reported, shorter-duration efficacy study.

Patients experienced consistent results across all monthly intervals, and 34.1% of methylnaltrexone 12-mg subcutaneous injections resulted in bowel movements within 4 hours during the treatment period.  Subjective assessments by patients showed statistically significant reductions from baseline in straining and the number of bowel movements accompanied by the sensation of complete evacuation.

“The study yielded safety and efficacy data that support the potential utility of subcutaneous methylnaltrexone for use by patients who take opioids for pain over extended periods,” said Robert Israel, MD, senior vice president of medical affairs at Progenics Pharmaceuticals..  “We found that the 4-hour response rate remained durable over the course of the 1-year study period.”

Patients in the study included those with a history of chronic, non-malignant pain (including back pain, joint/extremity pain, neurologic/neuropathic pain, and fibromyalgia), and who experienced constipation during opioid pain medication use for at least 1 month prior to screening.  Of the patients in the study, 624 were treated for 6 months or more, and 477 completed the 48-week study and post-treatment follow-up periods.  Patients received a median of 6 subcutaneous injections per week of methylnaltrexone 12 mg for up to 48 weeks. 

There were no unexpected adverse effects and pain scores confirmed that the drug did not interfere with analgesia or cause opioid withdrawal symptoms.

A supplemental New Drug Application is being prepared for submission to FDA by the end of June.  Results of the study were presented at the recent annual meeting of the American Pain Society in Austin, Texas.