acute hydroxychloroquine or chloroquine overdose / toxicity (Plaquenil)

see also:

• hydroxychloroquine (Plaquenil)

• hydroxychloroquine and chloroquine have relatively narrow therapeutic windows and acute toxicity is a risk, particularly for those who self-prescribe
• cardiovascular and neurologic toxicity may present within 1-3 hours of ingestion of doses > 10mg/kg of chloroquine (hydroxychloroquine is 2-3x less toxic in animal models)
• ingestion of > 5g chloroquine may be fatal in adults without intervention, while the average dose causing fatalities is around 8g of chloroquine

• hypotension
• hypokalaemia from intracellular shift
• prolonged QTc
• widened QRS
• ST depression
• U waves (hypokalaemia)
• AV block
• ventricular arrhythmias
• visual disturbances including reversible blindness
• diplopia
• photophobia
• +/- myopathies, neuropathies
• CNS depression
• seizures and coma in pre-arrest status
• death usually occurs within 12hrs, but may be delayed up to 48hrs

• discuss with a clinical toxicologist
• decontaminate if within 2hrs ingestion:
  • consider intubation and then activated charcoal via NG if obtunded or if > 5g ingested
• avoid over-treating hypokalaemia as risk of rebound hyperkalaemia
• IV fluid 20mL/kg for hypotension +/- IV adrenaline
  • consider high dose diazepam infusion following adrenaline eg. 2mg/kg IV over 30minutes then 1-2mg/kg over 24hrs
• Rx ventricular arrhythmias:
  • consider IV sodium bicarbonate although this may exacerbate hypokalaemia
• Rx seizures with benzodiazepines
• no role for dialysis as large Vd
• consider ECMO if refractory shock
• if significant toxicity, admit to a critical care area for 48hrs
• if clinically well, asymptomatic for 6hrs post ingestion with a normal ECG then clinically clear for MH assessment and Mx