Methylnaltrexone for treatment of opioid-induced constipation in advanced illness patients

Area of Science:

• Pharmacology
• Gastroenterology
• Palliative Care

Background:

• Opioid-induced constipation (OIC) is a common side effect in patients receiving opioid therapy, significantly impacting quality of life.
• Current laxatives may be ineffective or cause central side effects, necessitating targeted treatments.
• Methylnaltrexone, a peripherally acting mu-opioid receptor antagonist, offers a potential solution for OIC without central nervous system effects.

Purpose of the Study:

• To evaluate the efficacy and safety of subcutaneous methylnaltrexone in patients with advanced illness and OIC.
• To determine the onset and rate of laxation response to methylnaltrexone.
• To assess the impact of methylnaltrexone on pain scores and opioid withdrawal symptoms.

Main Methods:

• A double-blind, randomized, placebo-controlled trial involving 154 patients with advanced illness and OIC.
• Patients received subcutaneous injections of methylnaltrexone (0.15 mg/kg or 0.3 mg/kg) or placebo.
• Laxation response within 4 hours, time to first bowel movement, pain scores, and adverse events were recorded.

Main Results:

• Significantly higher laxation response rates were observed with methylnaltrexone (62% and 58% for 0.15 mg/kg and 0.3 mg/kg, respectively) compared to placebo (14%) (P < 0.0001).
• Approximately 50% of methylnaltrexone responders experienced a bowel movement within 30 minutes of dosing.
• No significant changes in pain scores or evidence of central opioid withdrawal were noted. Common adverse events included abdominal pain and flatulence.

Conclusions:

• Subcutaneous methylnaltrexone is an effective and rapid-acting treatment for OIC in patients with advanced illness.
• Methylnaltrexone demonstrates a favorable safety profile, with no reversal of analgesia or central opioid withdrawal.
• The drug is generally well-tolerated, offering a valuable therapeutic option for managing OIC in palliative care settings.