Risperidone toxicity

Risperidone is an atypical antipsychotic agent associated with tachycardia and acute dystonic reactions.

Toxic Mechanism:

Risperidone antagonises the mesolimbic dopamine (D2), serotonin and alpha 1 + 2 receptors. Compared with other antipsychotics it has a low affinity for histamine the muscarninic receptors, meaning less CNS depression and anticholinergic features.

Toxicokinetics: 

  • Rapidly absorbed
  • Moderate volume of distribution 1.5 L/kg
  • Highly protein bound
  • Metabolised in the liver and excreted in the urine

Resuscitation:

  • Rarely required

Risk Assessment

  • Dose related risk assessment is poorly defined
  • Children: >1 mg is associated with clinical features. Acute dystonic reactions are more common in children.
  • Clinical features should manifest within 4 hours and resolve by 24 hours
    • Sinus tachycardia 50%
    • Acute dystonia 10%
    • Mild sedation
    • QT prolongation but no reports of Torsades de pointes
    • CNS depression is rare

Supportive Care

  • General supportive care

Investigations

  • Screening: 12 lead ECG, BSL, Paracetamol level
  • Specific:
    • ECG at presentation and 4 hours (if normal no further ECGs required)
    • Sinus tachycardia is common
    • Reports of minor QT prolongation but no Torsades de pointes.

Decontamination:

  • Not routinely indicated

Enhanced Elimination

  • Not clinical useful

Antidote

  • Benztropine for acute dystonic reactions.
    • Over 3 yrs 0.02 mg/kg IM or IV.
    • Adults 1mg.
    • May repeat in 15 minutes.

Disposition

  • Children who are symptomatic all need review
  • Patients who are well with a normal baseline ECG can be medically cleared at 4 hours post ingestions
  • Symptomatic patients need supportive care until toxicity resolves
  • Patients should be warned that extrapyramidal movements may occur up to 3 days later.

References:


toxicology library antidote 700 1

Toxicology Library

DRUGS and TOXICANTS

Dr Neil Long BMBS FACEM FRCEM FRCPC. Emergency Physician at Burnaby Hospital in Vancouver Emergency. Loves the misery of alpine climbing and working in austere environments. Supporter of FOAMed, toxicology, tropical medicine, sim and ultrasound

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.