Problems for Discussion - 3 - Paraquat

1. Understand the mechanism of toxicity of paraquat.
2. Understand how this explains the delayed pulmonary manifestations of moderate paraquat toxicity
3. List the most common clinical manifestations of poisoning with paraquat.
4. Recognise situations where interventions are most likely to be useful.
5. Understand the difference between a frequentist and a Bayesian approach to clinical trial evidence and how this alters what interventions you institute.

A 46-year-old man was brought to hospital one hour after intentionally swallowing approximately 70 mL of a 20% paraquat solution. The patient had no previous medical illnesses and used no therapeutic drugs or drugs of abuse. Within ten minutes of swallowing the paraquat, he vomited and continued to do so for ninety minutes. He was then given 800 mL of a 15% suspension of Fullers Earth and 200 mL 20% mannitol orally.
The patient was transferred to a larger hospital where he arrived sixty hours after the ingestion (because of deteriorating renal function and decreasing arterial blood oxygen tension). He was febrile, 37.9oC and had a sore throat, dysphagia, a distended abdomen and decreased bowel sounds. Rales were audible in the left base and air entry to the right base was decreased. The chest X-ray showed right basal atelectasis.

The plasma paraquat concentration four hours after ingestion was 3 mg/L.

1. What are the clinical features of paraquat toxicity?
2. What is the mechanism of paraquat toxicity?
3. What laboratory tests should be requested in patients with paraquat toxicity?
4. What is the kinetics of paraquat?
5. How does the paraquat concentration assist in determining prognosis? By the ninth hospital day, the chest X-ray showed diffuse alveolar shadowing, most marked in the perihilar regions. At this point, the patient had a serum creatinine of 0.27 mmol/L (normal 0.06-0.11) and the arterial PO2 on room air was 33 mmHg.
6. What do these results indicate about the patient's prognosis? He died on the twelfth day, 260 hours after the ingestion.
7. How should you manage a patient who presents having been exposed to paraquat?