Methylnaltrexone
Common brands: Relistor
Gut motility stimulator
It can treat constipation caused by narcotic pain medications.
Brands: Relistor
Availability: Prescription needed

Methylnaltrexone (brand name Relistor) is a peripherally acting μ-opioid receptor antagonist used primarily to treat opioid-induced constipation (OIC) in adults with chronic non-cancer pain or advanced illness, including those receiving palliative care, when standard laxatives are ineffective. It works by blocking opioid receptors in the gastrointestinal tract, reducing constipation without crossing the blood-brain barrier, thus preserving central opioid analgesia and avoiding withdrawal symptoms.

Key Details:

• Forms and Dosage: Available as subcutaneous injections (12 mg daily for chronic non-cancer pain; 0.15 mg/kg every other day as needed for advanced illness) or oral tablets (450 mg daily, taken on an empty stomach).
• Indications: Approved for OIC in chronic non-cancer pain, including pain related to prior cancer treatment, and in advanced illness or active cancer pain requiring opioid dose escalation.
• Side Effects: Common (>5%) include abdominal pain, flatulence, nausea, dizziness, diarrhea, and hyperhidrosis. Serious risks include gastrointestinal perforation (rare, especially in patients with compromised GI integrity like Crohn’s disease) and opioid withdrawal symptoms (e.g., anxiety, chills, diarrhea).
• Contraindications: Not for use in patients with known or suspected gastrointestinal obstruction. Use with caution in pregnancy (may cause fetal opioid withdrawal due to immature fetal blood-brain barrier) and breastfeeding (not recommended due to potential infant withdrawal).
• Efficacy: Clinical trials show 48% of patients with advanced illness achieve laxation within 4 hours of a single subcutaneous dose (vs. 15% placebo), with 50% of responders experiencing a bowel movement within 30 minutes.
• Pharmacokinetics: Rapidly absorbed (Tmax ~30 minutes for subcutaneous), metabolized to methyl-6-naltrexol isomers and methylnaltrexone sulfate, with ~44-54% excreted unchanged in urine.

Precautions:

• Discontinue maintenance laxatives before starting; resume if no response after 3 days.
• Monitor for severe abdominal pain or persistent diarrhea; stop if these occur.
• Not studied for use beyond 4 months.
• Avoid in patients with gastrointestinal perforation risk or blood-brain barrier disruptions.

Methylnaltrexone is a targeted therapy for OIC, effective in rapid laxation without compromising pain relief, but requires careful patient selection and monitoring due to potential risks. For more details, consult a healthcare provider or refer to the FDA Medication Guide (https://www.fda.gov/Drugs/DrugSafety/ucm085729.htm).[](https://medlineplus.gov/druginfo/meds/a616047.html)

Disclaimer: owerl is not a doctor; please consult one.