naltrexone

see also:

• opiate and opioid antagonists
• Mx of severe acute opiate withdrawal due to inappropriate use of naltrexone
• opiates and opioids

• naltrexone is a long acting opioid receptor antagonist used in addiction medicine
• it should NOT be used in opiate-dependent persons within 7-10 days of last opiate dose otherwise there is a high risk of a severe, potentially life threatening acute opiate withdrawal reaction.
• severe acute withdrawal reactions usually occur in the context of a IV heroin user accessing naltrexone and using it inappropriately or inadvertently while still using heroin - see Mx of severe acute opiate withdrawal due to inappropriate use of naltrexone
• naltrexone has also been used to provide Ultrarapid Opioid Detoxification (UROD), but this is a controversial procedure which exposes the patient to risks of general anaesthesia and acute severe withdrawal features without clear benefits

• peak plasma levels of naltrexone occur at ~3hrs after oral dose
• naltrexone has a half-life of ~4hrs but an active metabolite has a half-life of ~16 hrs, thus opioid receptor blockade and the withdrawal reaction usually lasts 24-72hrs and may require HDU Mx or even ICU if intubation is required.

• in Australia, naltrexone use is restricted to specialist clinics
• adult dose:
  • 25 mg o daily, increasing to 50 mg
  • courses of treatment generally last many months