Paraquat Poisoning
Lesson Objectives
By the end of this lesson, learners should be able to:
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Define Paraquat and describe its mechanism of toxicity.
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Recognize the clinical signs and symptoms of paraquat poisoning.
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Identify appropriate laboratory and imaging investigations for diagnosis and monitoring.
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Describe the treatment and precautions required in managing paraquat poisoning.
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Understand the rationale for avoiding oxygen therapy in affected patients.
Description
Paraquat (1,1′-dimethyl-4,4′-dipyridylium) is a broad-spectrum liquid herbicide associated with both accidental and intentional ingestion, leading to severe and often fatal toxicity.
It is rapidly but incompletely absorbed from the gastrointestinal tract and is largely eliminated unchanged in urine within 12 to 24 hours.
Toxicity arises because paraquat generates reactive oxygen species (ROS) that cause cellular injury via lipid peroxidation, mitochondrial damage, and apoptosis. The lungs, kidneys, liver, and pancreas are most affected.
Clinical Features
| System | Signs and Symptoms |
|---|---|
| General | Vomiting, fever, tachycardia, tachypnoea, occasional diarrhoea, and drowsiness |
| Respiratory | Pneumonitis and progressive lung fibrosis due to active uptake of paraquat into lung tissue |
| Renal | Acute kidney injury due to tubular necrosis |
| Hepatic | Hepatic injury and transaminitis |
| Gastrointestinal | Nausea, vomiting, abdominal pain, oral or oesophageal ulceration |
| Pancreatic | Possible acute pancreatitis with raised amylase or lipase |
| Neurological | Drowsiness and confusion (in severe cases) |
Investigations
| Test Type | Purpose / Findings |
|---|---|
| Electrolytes | Assess dehydration and acid–base balance |
| Renal and liver function tests | Evaluate organ injury |
| Full blood count | Monitor for systemic involvement |
| Chest radiograph | Identify pneumonitis, pneumomediastinum, pneumothorax, or fibrosis |
| Chest CT scan | Detect early lung fibrosis or assess long-term damage |
| Amylase and lipase | Detect acute pancreatitis (if abdominal pain and hyperglycaemia present) |
| Plasma paraquat levels | Confirm diagnosis and guide prognosis |
| Urine and plasma dithionite tests | Rapid bedside screening for paraquat exposure |
Treatment
| Step | Management Details |
|---|---|
| 1. Decontamination | Perform gastric lavage as soon as possible after ingestion. |
| 2. Activated Charcoal | Administer 1 g/kg by gastric tube every 2 hours for 3–4 doses to minimize further absorption. |
| 3. Oxygen Therapy | Withhold supplemental oxygen, as it accelerates lung damage through free radical generation. |
| 4. Supportive Care | Maintain adequate hydration, monitor electrolytes and renal function, and manage complications as they arise. |
| 5. Monitoring | Observe for respiratory distress, renal failure, or hepatic dysfunction. Continuous vital sign monitoring is essential. |
Summary
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Paraquat is a highly toxic herbicide that causes multi-organ injury, particularly to the lungs, kidneys, and liver.
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Toxicity results from reactive oxygen species causing oxidative cellular damage.
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Gastric lavage and repeated doses of activated charcoal can reduce absorption.
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Supplemental oxygen should be avoided unless absolutely necessary, as it worsens lung injury.
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Prognosis is poor in severe poisoning, and management is mainly supportive.