Toxin

Paraquat Poisoning

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Paraquat Poisoning, Paraquat, Paraquat Toxicity, Paraquat Lung

  • See Also
  1. Acute Poisoning
  • Epidemiology
  1. Responsible for 300,000 deaths per year in Asia-Pacific Region
  • Pathophysiology
  1. Dipyridilium compound
  2. Paraquat is an inexpensive herbicide typically used outside the U.S. (although some pockets of rural U.S. use)
    1. Paraquat is a broad-spectrum, non-selective herbicide used in reforestation and weed control
    2. Overall use is being phased out internationally due to its lethality
    3. Paraquat is typically dyed blue to prevent Accidental Ingestion
  3. Poisoning typically occurs with intentional ingestion for Suicide
    1. Severe toxicity with >1-2 gram ingestion (5-10 ml of 20% solution)
    2. Mortality 40-60% with ingestion of 15 ml (1 tbs, 0.5 oz) of 24% solution
    3. Results in multi-organ failure over the course of days
  4. Mechanism of systemic toxicity
    1. Cellular metabolism of Paraquat generates free radicals (superoxide) resulting in toxicity
    2. Inhibits NADP reduction to NADPH
    3. Mitochondrial toxicity
    4. Cell membrane dysfunction (lipid peroxidation)
    5. Most toxic to the lungs, Kidneys and Gastrointestinal Tract
  5. Pharmacokinetics
    1. Rapid oral absorption
    2. Peak serum level at 1 to 4 hours after ingestion
    3. Although skin contact reaction, minimal absorption via skin (or via inhalation)
    4. Excretion renal, with Paraquat unchanged in the urine
  • Findings
  • Skin Contact (Corrosive) to Concentrated Paraquat Solutions
  1. Skin irritation
  2. Nail shedding
  3. Skin exposure rarely causes systemic effects
  • Findings
  • Systemic (Ingestion)
  1. Gastrointestinal
    1. Nausea and Vomiting
    2. Mucosal inflammation and burns (local corrosive effects)
    3. Diarrhea
    4. Abdominal Pain
  2. Renal
    1. Acute Tubular Necrosis
  3. Hepatic
    1. Liver function abnormalities (subacute Transaminitis)
  4. Neurologic
    1. Seizures
  5. Respiratory
    1. Acute Respiratory Distress Syndrome (ARDS)
    2. Pulmonary Fibrosis (Paraquat Lung)
      1. Complication of ARDS, with onset 5-31 days after ingestion
      2. Presents with Hypoxia
  • Labs
  1. See Unknown Ingestion
  2. Complete Blood Count
    1. High White Blood Cell Count is associated with poor prognosis
  3. Comprehensive Metabolic Panel
    1. Increased Serum Creatinine is associated with poor prognosis
  4. Plasma Paraquat Level
    1. Plasma Paraquat >2.64 mcg/ml at 3 hours is lethal in 100% of cases
  5. Plasma Dithionite Level
    1. Positive test predicts very high mortality
  • Management
  1. Intravenous crystalloid
  2. Decontamination (if skin or clothing contaminated)
  3. Activated Charcoal within 2 to 4 hours of ingestion
  4. Avoid excessive Supplemental Oxygen
    1. Supplemental Oxygen may increase free radical production
  5. Start Hemoperfusion within 4 to 6 hours of large ingestion
  6. Consider other measures
    1. N-Acetylcysteine
    2. Deferoxamine
    3. Dexamethasone
    4. Acetylsalicylic Acid
    5. Vitamin E
  7. Disposition
    1. All symptomatic Paraquat exposures are admitted to hospital
    2. Observe all asymptomatic Paraquat exposures for at least 6 hours
    3. Palliative measures (oxygen, Analgesics) typically recommended for late presentations of large ingestions (>10 g)
  • Prognosis
  1. Predictors of high mortality rate
    1. Mortality 40-60% with ingestion of 15 ml (1 tbs, 0.5 oz) of 24% solution
    2. Plasma dithionite test positive
    3. Serum Creatinine >0.05 mg/dl/h in first 12 hours
  2. Reassuring findings
    1. Plasma Paraquat level (in mg/dl) X Time (in hours) <10
  • References
  1. Carroll and Yakey (2025) Crit Dec Emerg Med 39(10): 36
  2. Tomaszewski (2021) Crit Dec Emerg Med 35(5): 28
  3. Gawarammana (2011) Br J Clin Pharmacol 72(5): 745-57 +PMID:21615775 [PubMed]