see also:

• opiate and opioid antagonists
• opiates and opioids

• naltrexone is a long acting opioid receptor antagonist
• 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.
• 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.
• 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

• these are an extreme form of the normal opiate withdrawal features which results in:
  • dysphoria, confusion, hallucinations and agitation +/- reduced GCS
  • severe pains such as muscle, joint and back pains, headache, and abdominal cramping pains
  • profuse diarrhoea and faecal incontinence - yes, the resus room will be a continuous code brown that shift!
  • sympathetic overdrive with tachycardia, hypertension, tachypnoea, sweating, lacrimation, piloerection, yawning, anxiety
  • pupils generally mid-size
  • vomiting may be an issue with risk of aspiration if confused
  • vomiting and diarrhoea may result in hypovolaemia and hypotension

• usually require Mx in a resuscitation area with 1:1 nursing
• ABC's as per usual
• consider iv ketamine boluses and infusion in sub-anaesthetic doses
  • is probably the best analgesic and helps to control the agitation while reducing the sympathetic cardiovascular effects and appears to reduce need for benzodiazepines in subsequent days ²⁾
  • it is thought that that N-methyl-D-aspartate (NMDA) antagonists such as ketamine attenuate the signs of opiate withdrawal (NMDA blockade presumably outweighs any direct cardiovascular stimulant effects of ketamine) and diminish progression or reverses existing opiate tolerance, and reverse the EEG changes during opiate withdrawal
  • consider 0.3-0.5mg/kg/hr infusion with titrated boluses of 0.2-0.3mg/kg as needed to allow control over iv access
• some patients may require rapid sequence induction (RSI) for emergency intubation
• iv fluids to rehydrate and replace GIT fluid losses, sweat and provide usual maintenance fluids
• monitor electrolytes, glucose, fluid balance
• adjunctive Rx as per usual Mx of opiate withdrawal:
  • anti-emetics such as:
    • ondansetron 4-8mg s/l or iv, or,
    • promethazine 25mg im or slow iv
  • anti-diarrhoeal agent such as:
    • loperamide 4mg o, or,
    • octreotide 50mcg s/c
  • agents to reduce GIT cramps such as:
    • hyoscine
  • non-opiate analgesics such as:
    • non-steroidal anti-inflammatory drugs (NSAIDs)
    • paracetamol (acetaminophen)
  • clonidine (Catapres) if hypertensive eg. 0.1-0.3mg orally each hour until hypertension controlled
  • benzodiazepines are an important adjunct - titrated iv or oral diazepam should be considered (may require 10mg diazepam iv every 5-10min until sedated)
• most patients will require transfer to HDU or ICU as Mx will need to be prolonged given the duration of action of naltrexone.