Methylnaltrexone Brand Name– Relistor

What is Methylnaltrexone

Methylnaltrexone is a peripherally-acting mu-opioid receptor antagonist.

Methylnaltrexone is the quaternary derivative of naltrexone and is comparatively more polar.

The chemical structure restricts distribution across the blood-brain barrier and prevents methylnaltrexone from interfering with the centrally-mediated analgesic effect of the opioid agonists. The drug does not reverse opioid-induced respiratory depression.

Methylnaltrexone usually produces a bowel movement in patients receiving chronic opioid treatment within 30 minutes to 4 hours after administration. Clinical trials have reported response rates with methylnaltrexone that remain consistent with continued “as needed” dosing over several months, with most patients reporting a laxation effect similar to normal spontaneous bowel movements, with predictable timing of bowel movements following dosing.

Similar findings have been reported in the treatment of constipation in patients treated chronically with opioids for non-malignant pain.

The drug has also been used for treating opioid-induced constipation in patients in critical care settings.

The FDA approved subcutaneous methylnaltrexone in April 2008 for the treatment of opioid-induced constipation (OIC) as part of palliative care in patients with advanced illness, such as cancer.

The FDA expanded the OIC indication to include patients with chronic non-cancer pain in September 2014. In July 2016, an oral formulation received FDA approval for treatment of OIC; however, the oral formulation is only indicated for use in patients with chronic non-cancer pain.


  1. nausea/vomiting
  2. opiate agonist-induced constipation
  3. pruritus
  4. urinary retention

For the treatment of opiate agonist-induced constipation (OIC) in patients with advanced illness or pain caused by active cancer who require opioid dosage escalation for palliative care, and also for the treatment of OIC in patients taking opioids for chronic non-cancer pain (including patients with chronic pain related to prior cancer or its treatment who do not require frequent [e.g., weekly] opioid dosage escalation)

Side Effects

  1. abdominal pain
  2. anxiety
  3. chills
  4. diaphoresis
  5. diarrhea
  6. dizziness
  7. flatulence
  8. flushing
  9. GI perforation
  10. headache
  11. hyperhidrosis
  12. malaise
  13. nausea
  14. rhinorrhea
  15. tremor
  16. vomiting
  17. withdrawal

Monitoring Parameters

  • LFTs
  • serum creatinine


  • acute opioid withdrawal
  • breast-feeding
  • children
  • Crohn’s disease
  • diarrhea
  • geriatric
  • GI obstruction
  • GI perforation
  • hepatic disease
  • infants
  • intravenous administration
  • neonates
  • neoplastic disease
  • peptic ulcer disease
  • pregnancy
  • renal disease
  • renal impairment
  • ulcerative colitis


  • Alvimopan
  • Buprenorphine; Naloxone
  • Bupropion; Naltrexone
  • Naldemedine
  • Nalmefene
  • Naloxegol
  • Naloxone
  • Naltrexone
  • Opiate Antagonists
  • Pentazocine; Naloxone

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