Opioid toxicity

Opioids are obviously our bread and butter in emergency medicine, what more is there to know? This post is designed to give you a few extra tips and some idiosyncrasies with some of the other opiates to assist you in your clinical management.

Toxic Mechanism:

Agonist to the mu receptor creating euphoria, analgesia, dependance, sedation and respiratory depression.

Toxicokinetics: 

• Oral absorption is variable, most are rapid with the exception of controlled-release.
• Large volumes of distribution 2.6 L/kg to 3.6 L/kg
• Metabolised in the liver and excreted in the urine

Resuscitation:

• Reduced GCS: Trial of naloxone but some patients may require intubation and ventilation.
• Ventricular dysrhythmias: Rarely seen with dextropropoxyphene, treatment is with sodium bicarbonate.

Risk Assessment

• Life threatening CNS and respiratory depression occur just above the analgesia dose.
• Opiate naive or taken with co-ingestants increases the severity of CNS depression
• Specific opiates:
  • Dextropropxyphene: 10 mg/kg will cause symptoms, >20 mg/kg will cause CNS depression, seizures and cardiac dysrhythmias (sodium channel blockade).
  • Methadone and oxycodone: QT prolongation (torsades is rare), prolonged toxicity which can last >24 hours.
  • Pethidine: Repeated doses increase the risk of seizures and it can also precipitate serotonin toxicity.
  • Heroin toxicity lasts approximately 6 hours.
  • Controlled release preparations can result in respiratory depression up to 12 hours post ingestion.
• Children: Opioid toxicity is the leading cause of death in children. An ingestion of a single table or a mouthful of methadone can cause respiratory depression. >2 mg/kg or codeine in children can start to cause symptoms and >5 mg/kg can cause a respiratory arrest.
• Clinical features:
  • CNS and respiratory depression with miosis is the classic toxidrome.
  • Bradycardia is common unless hypoxia or hypercarbia are present.
  • Complications include: Aspiration pneumonia, hypothermia, skin necrosis, rhabdomyolysis, compartment syndrome and hypoxic brain injury.

Supportive Care

• Patients need to be observed closely, respiratory rate should be measured while they are asleep or undisturbed and saturations on room air to help detect early signs of toxicity.
• If intubated see FASTHUGSINBED for further supportive care.

Investigations

• Screening: 12 lead ECG, BSL, Paracetamol level
• Specific: 
  • Serum and urine levels are not clinically useful.
  • Specific tests will be indicated only to assess for secondary complications.

Decontamination:

• Activated charcoals not usually clinically indicated due to having a specific antidote, however, those presenting early with a controlled release preparation can be considered.

Enhanced Elimination

• Not clinically useful.

Antidote

• Naloxone either as a bolus or sometimes as an infusion for those with CNS or respiratory depression.

Disposition

• Standard release preparations require 4 hours of observation.
• Controlled release preparations require 12 hours of observation.
• Those with mild symptoms from a standard release preparation who did not receive naloxone in the first 4 hours can be observed on a ward.
• All children who have ingested an opiate require 12 hours of observation unless it is <2 mg/kg of codeine. Discharge should not occur at night.
• Patients who require a naloxone infusions or intubation will require HDU or ICU respectively.

References and Additional Resources:

Additional Resources:

• CCC – Opioid overdose
• CCC – Opioid withdrawal
• Tox Flashcard – Opioid withdrawal

References:

• Sachdeva DK, Stadnyk JM. Are one or two dangerous? Opioid exposure in toddlers. The Journal of Emergency Medicine 2005; 29(1): 77-84