Methylnaltrexone for opioid-induced constipation in advanced illness

Area of Science:

• Pharmacology
• Gastroenterology
• Oncology

Background:

• Opioid-induced constipation (OIC) is a common and distressing side effect of opioid therapy.
• Methylnaltrexone, a peripherally acting mu-opioid receptor antagonist, is designed to counteract OIC without affecting central analgesia.
• This study evaluated the safety and efficacy of subcutaneous methylnaltrexone in patients with advanced illness experiencing OIC.

Purpose of the Study:

• To assess the efficacy of subcutaneous methylnaltrexone in relieving opioid-induced constipation.
• To evaluate the safety profile of methylnaltrexone in this patient population.
• To determine if methylnaltrexone affects central opioid receptor-mediated analgesia or precipitates opioid withdrawal.

Main Methods:

• A randomized, double-blind, placebo-controlled trial involving 133 patients with OIC.
• Patients received subcutaneous methylnaltrexone (0.15 mg/kg) or placebo every other day for 2 weeks.
• Coprimary outcomes included laxation within 4 hours of the first dose and within 4 hours of at least two of the first four doses without rescue laxatives.

Main Results:

• 48% of methylnaltrexone recipients experienced laxation within 4 hours of the first dose, versus 15% for placebo (P<0.001).
• 52% achieved laxation within 4 hours of two or more of the first four doses without rescue laxatives, compared to 8% for placebo (P<0.001).
• No evidence of central nervous system opioid withdrawal or changes in pain scores was observed; abdominal pain and flatulence were common adverse events.

Conclusions:

• Subcutaneous methylnaltrexone provides rapid and effective relief of OIC in patients with advanced illness.
• The treatment is safe and does not interfere with central opioid analgesia or cause opioid withdrawal.
• Methylnaltrexone represents a valuable therapeutic option for managing OIC in palliative care settings.