Paraquat

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)

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)

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

Diagnosis

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

Clinical Manifestations

Cardiovascular Manifestations

Endocrinologic Manifestations

Gastrointestinal/Hepatic Manifestations

Neurologic Manifestations

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

Toxicologic Manifestations


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

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)

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