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

References

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