Epidemiology

• Paraquat is a widely-used and toxic herbicide
• Used widely to spray marijuana fields (however, there is not believed to be a risk of illness with smoking paraquat-sprayed marijuana)

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Exposure

• Accidental or Intentional Ingestion: most deaths occur due to suicide attempts (few in USA though)
• Transdermal Skin Exposure: through pesticide spraying
  • Requires either soaking of the skin or contact with skin breached by injury (burn, wounds, etc)

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Physiology

• Unique Superoxide Radical-Mediated Pulmonary Fibrosis
  • Does not cause immediate caustic irritant injury to the lung
  • Mechanism of injury may be partly iron-dependent
  • Due to oxidant-related mechanism: supplemental oxygen (and radiation therapy) exacerbate the degree of injury
  • Interestingly, the related pesticide Diquat does not manifest pulmonary toxicity

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Diagnosis

• Blood/Urine Paraquat Level: may reveal diagnosis (although history is usually the best)
  • May have a role in predicting survival

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Clinical Manifestations

Cardiovascular Manifestations

• Myocarditis (see Myocarditis, [[Myocarditis]])

Endocrinologic Manifestations

• Adrenal Necrosis (see Adrenal Insufficiency, [[Adrenal Insufficiency]])

Gastrointestinal/Hepatic Manifestations

• Acute Gastrointestinal Necrosis (see Intestinal Perforation, [[Intestinal Perforation]])
  • Physiology: caustic injury to GI mucosa
• Fulminant Hepatic Failure (see Fulminant Hepatic Failure, [[Fulminant Hepatic Failure]])

Neurologic Manifestations

• Seizures (see Seizures, [[Seizures]])

Pulmonary Manifestations

• Acute Lung Injury-ARDS (see Acute Lung Injury-ARDS, [[Acute Lung Injury-ARDS]])
  • Diagnosis
    • Pathology: diffuse alveolar damage
  • Clinical: usually occurs within 24-48 hrs of ingestion
• Subsequent Pulmonary Fibrosis (see Interstitial Lung Disease-Etiology, [[Interstitial Lung Disease-Etiology]])
  • Diagnosis
    • PFT’s: restriction with decreased DLCO
    • ABG: hypoxemia
  • Clinical
    • Progresses after initial ingestion, resulting in death from respiratory failure within days-weeks
    • Survivors may manifest modest and slow improvement in lung function

Renal Manifestations

• Acute Kidney Injury (AKI) (see Acute Kidney Injury, [[Acute Kidney Injury]])

Toxicologic Manifestations

• Methemoglobinemia (see Methemoglobinemia, [[Methemoglobinemia]])

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Treatment

• Supplemental Oxygen/XRT: may worsen outcome
• Hemodialysis: useful
• Charcoal Hemoperfusion(see Hemoperfusion, [[Hemoperfusion]]): may provide better clearance than hemodialysis, but its benefit is unproven
• Steroids + Cyclophosphamide: single trial demonstrated mortality benefit in moderate-severe ingestions

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Prognosis

• May be predicted by paraquat level
• Death from multi-organ failure typically occurs within 1-2 wks (but may occur up to 6 wks later)

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References

• Winchester JF. Active methods for detoxification. In: Haddad LM, Shannon MW, Winchester JF, eds. Clinical management of poisoning and drug overdose. Third edition. Philadelphia: WB Saunders; 1997, 175-188
• Winchester JF. Paraquat and the bipyridyl herbacides. In: Haddad LM, Shannon MW, Winchester JF, eds. Clinical management of poisoning and drug overdose. Third edition. Philadelphia: WB Saunders; 1997, 845-853
• Am J Resp Crit Care Med 1999; 159:357-360