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