Paraquat toxicity

Background

• Paraquat is an herbicide that has a rapid and large distribution and can be fatal even with small ingestions. It has a high case-fatality rate (>50%) which makes it a frequent means of suicide in the developing world, as well as a dangerous accidental occupational exposure.
• Paraquat exerts its toxic effects via multiple proposed mechanisms, including lipid peroxidation and generation of reactive oxygen species, direct mitochondrial toxicity, and apoptosis.

Clinical Features

Paraquat Tongue (Credit: wikitox.org)

Overall, pulmonary and renal toxicities predominate and are the primary cause of mortality. GI toxicity is nearly universal and is probably an under-recognized cause of mortality secondary to erosion and perforation.

• Gastrointestinal: predominate early
  • Paraquat tongue
  • Esophageal and gastric erosion
  • Nausea and vomiting
• Pulmonary: occurs due to distribution to pneumocytes
  • Pneumonitis
  • Pulmonary fibrosis (delayed)
• Multiorgan failure
  • Acute renal failure
  • Hepatic necrosis
  • Myocardial necrosis
  • Internal bleeding

Differential Diagnosis

Toxic Ingestion

• Caustic Ingestion
• Toxic Alcohols
• Foreign Body Ingestion

Oral Burns/Mucositis

• Burns
• Infectious Causes
  • [[Aphthous stomatitis|Aphthous Ulcer
  • Herpes simplex infection
  • Coxsackie virus
  • Tonsillitis
  • Methotrexate/chemotherapy toxicity

Acute dyspnea

Emergent

• Pulmonary
  • Airway obstruction
  • Anaphylaxis
  • Angioedema
  • Aspiration
  • Asthma
  • Cor pulmonale
  • Inhalation exposure
  • Noncardiogenic pulmonary edema
  • Pneumonia
  • Pneumocystis Pneumonia (PCP)
  • Pulmonary embolism
  • Pulmonary hypertension
  • Tension pneumothorax
  • Idiopathic pulmonary fibrosis acute exacerbation
  • Cystic fibrosis exacerbation
• Cardiac
  • Cardiac tamponade
  • Cardiogenic pulmonary edema (CHF)
  • Myocardial Infarction
  • Pericarditis
  • Myocarditis
• Other Associated with Normal/↑ Respiratory Effort
  • Abdominal distension
  • Anemia
  • CO Poisoning
  • Salicylate toxicity
  • Diabetic ketoacidosis (DKA)
  • Diaphragm injury
  • Electrolyte abnormalities
  • Epiglottitis
  • Flail chest
  • Hypotension
  • Metabolic acidosis
  • Pneumonia
  • Pneumothorax/hemothorax
  • Renal Failure
  • Sepsis
  • Toxic ingestion
• Other Associated with ↓ Respiratory Effort
  • Guillain-Barre syndrome
  • Multiple sclerosis
  • Myasthenia Gravis
  • Lambert-Eaton Syndrome
  • Organophosphate toxicity
  • Stroke (Main)
  • Tick paralysis

Non-Emergent

• ALS
• Ascites
• Uncorrected ASD
• Congenital heart disease
• COPD exacerbation
• Fever
• Hyperventilation
• Interstitial lung disease
• Neoplasm
• Obesity
• Panic attack
• Pleural effusion
• Polymyositis
• Porphyria
• Pregnancy
• Rib fracture
• Spontaneous pneumothorax
• Thyroid Disease
• URI

Evaluation

Workup

• Labs
  • CBC
  • BMP
  • LFTs and coagulation tests
  • VBG or ABG
  • UA: high concentrations of paraquat in the urine will cause it to appear blue
  • Urine dithionate test:
    • Add 1cc of 1% sodium dithionate (hematology labs have this solution) to 10mL urine
    • Blue color change indicates presence of paraquat
• Imaging
  • CXR
  • EKG
  • consider CT if stable to evaluate for perforation/mediastinitis

Diagnosis

• Based on urine test

Management

Patients who present in extremis after an ingestion will not survive regardless of management and should be treated palliatively. Large >50mL ingestions of paraquat are universally fatal. Aggressive resuscitation is futile.

Resuscitation

• Airway: consider early aggressive intubation for any respiratory distress or large (>100mL) ingestions
• Breathing: CXR, O2
  • Avoid aggressive oxygen therapy unless severe hypoxia due to increased free radical production
• Circulation: may develop early shock and require aggressive inotropic support

Decontamination

• Paraquat is absorbed transdermally. Unprotected first responders and healthcare workers are at risk
• Remove clothing and wash patient's skin if spillage or obvious skin involvement present
• Consider activated charcoal or Fuller's Earth if within 1-2 hrs of ingestion
• Consider NG tube for administration of activated charcoal
  • Must weigh risks as NGT placement can exacerbate caustic injury

Supportive Care

• IV fluids: patients often 2-3L fluid down
• Pain control

Antidotes/Additional Therapies

• Some centers administer glucocorticoids (typically dexamethasone 6mg-10mg IV q6h)
• Consider NAC, vitamin C, other free radical scavengers in consultation with toxicologist or poison control
• No role for extracorporeal elimination (hemodialysis/Hemoperfusion, CRRT)

Disposition

• If small/trivial exposure and patient asymptomatic at 6 hours, unlikely to manifest a significant toxicity
• Any symptomatic exposure requires admission for close hemodynamic monitoring and supportive care

See Also

• Toxicology (main)