methylnaltrexone (Relistor)

Indications

• opioid-induced constipation in palliative care patients who aren't getting relief from laxatives

Contraindications

• intestinal obstruction

Dosage

• given SC every other day
• oral formulation available
• laxative therapy should be discontinued before starting methylnaltrexone
  • if symptoms persist with methylnaltrexone therapy, laxative therapy can be reinitiated.

Pharmacokinetics

• methyl group keeps it from crossing into the CNS
• about 1/2 of patients will have a response within 4 hours after the 1st dose

Adverse effects

• generally mild
• nausea, dizziness, diarrhea

Mechanism of action

• opioid antagonist
• blocks opioid effects on the gut without blocking its CNS analgesic effects

More general terms

• gastrointestinal agent
• naltrexone (ReVia, Trexan, Vivitrol, Vivitrex)

Database

• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=5361918
• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=5361917