SAN DIEGO, May 12 — Subcutaneous injections of methylnaltrexone (Relistor) can relieve constipation caused by opioid treatment for noncancer pain — often within four hours — researchers said here

• Remind patients that the use of methylnaltrexone for noncancer pain is not yet approved by the Food and Drug Administration .
• This study was published as an abstract at a conference. These data and conclusions should be considered to be preliminary until they are reviewed and published in a peer-reviewed publication.

“As many as 40% of people who are taking opioids for pain relief experience constipation that is severe enough to cause major limitations to their quality of life,” said E. Richard Blonsky, M.D., director of the Pain and Rehabilitation Clinic of Chicago and clinical professor of neurology at Northwestern University’s Feinberg School of Medicine.

The problem is especially severe during social occasions, because patients must always be near toilet facilities to deal with the uncertainty of the condition, Dr. Blonsky told colleagues here at the American Pain Society annual meeting.

Dr. Blonsky reported that, overall, 34.3% of patients in his study accomplished laxation within four hours of a subcutaneous methylnaltrexone injection, compared with 9.9% of patients on placebo (P<0.001).

Some 46% in the methylnaltrexone group accomplished laxation within 24 hours, compared to 25% placebo, he reported.

He said methylnaltrexone decreases the constipating effects of opioids without affecting centrally mediated analgesia. The drug is currently FDA approved for treatment of opioid-induced constipation among patients with advanced illness who are receiving palliative care.

To determine if methylnaltrexone can relieve opioid-induced constipation in patients with noncancer pain, researchers enrolled 460 patients in a double-blind, placebo-controlled phase 3 randomized trial.

They were randomized to subcutaneous methylnaltrexone daily, the same drug every other day, or placebo.

Among the 150 patients taking methylnaltrexone every day, 28.9% achieved laxation within four hours, compared with 9.4% of the 162 patients on placebo (P<0.001). Likewise, 30.2% of 148 patients taking methylnaltrexone every other day achieved laxation within four hours (p<.001).

Dr. Blonsky said the goal of treatment was to free patients from being tied to their homes, never certain when the urge to void would occur due to the unpredictable nature of their constipation and of common laxatives.

With methylnaltrexone, he hoped to demonstrate that patients could predict that bowel movements would occur within four hours of delivery of the subcutaneous injection.

The most common adverse events with frequency notably different from placebo were abdominal pain, dizziness, vomiting, nausea, and diarrhea.

Dr. Blonsky noted, however, that 81.2% of patients in the active treatment group completed the trial, and just 7.7% of the withdrawals cited adverse events.

“These results suggest that subcutaneous methylnaltrexone is an effective and generally well-tolerated treatment for opioid-induced constipation in patients with chronic nonmalignant pain,” Dr. Blonsky said.

Carlton Dampier, M.D., a pediatrician at Emory University, said constipation can be “quite disturbing” to some patients taking opioids for pain.

Dr. Dampier, who was not involved in the study, noted that subcutaneous self- injection might be a problem for some people but said “patients are becoming more used to this type of delivery.”

He said that patients who already have problems with constipation prior to treatment for pain probably should avoid treatment with opioids if possible.

The study was funded by Wyeth Research of Collegeville, Pa. Dr. Blonsky has disclosed possible conflicts with Abbott, Allergan, Astellas, Bristol-Myers Squibb, Cephalon, Eisai, Endo, Lilly, NeurogesX, Pfizer, Schwarz, Takeda, and Wyeth. Dr. Dampier said he had no disclosures.

Primary source: The Journal of Pain

Source reference:
Blonsky R, et al “Subcutaneous methylnaltrexone for the treatment of opioid-induced constipation in patients with chronic non-malignant pain” J Pain 2009; 10 (4 suppl): S52.

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