UMEM Educational Pearls

Title: Naltrexone vs. Methylnaltrexone

Category: Pharmacology & Therapeutics

Keywords: naltrexone, methylnaltrexone, constipation, opioid dependence (PubMed Search)

Posted: 6/1/2012 by Bryan Hayes, PharmD (Updated: 6/15/2012)
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Naltrexone and methylnaltrexone are both mu-receptor antagonists that look similar and have similar names. But, they have very different uses.

Naltrexone (ReVia, Vivitrol)
- Used to treat opioid/alcohol dependence or to prevent relapse following opioid detoxifcation
- Dose: 25 to 100 mg PO daily or 380 IM every 4 weeks
- Crosses blood-brain-barrier and can precipitate withdrawal

Methylnaltrexone (Relistor)
- Used to treat opioid-induced constipation
- Dose (weight-based): 8 to 12 mg (or 0.15 mg/kg) subcutaneously once daily
- Peripherally acting, does not cross blood brain barrier

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