naltrexone

introduction

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