# Paraquat and Organochlorine Poisoning

> Paraquat and organochlorine poisoning for NEET-PG Medicine covering pulmonary fibrosis, the dithionite urine test, oxygen withholding and seizures.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/paraquat-and-organochlorine-poisoning
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Goldfrank's Toxicologic Emergencies; Harrison's Principles of Internal Medicine; Robbins and Cotran Pathologic Basis of Disease
- How to cite: "Paraquat and Organochlorine Poisoning", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/paraquat-and-organochlorine-poisoning

## Direct answer

Paraquat is a bipyridyl herbicide whose main danger is progressive pulmonary fibrosis, while organochlorine insecticides such as lindane and endosulfan cause hyperexcitability and seizures. Paraquat exposure is confirmed by the sodium dithionite urine test, and oxygen is withheld where possible because it accelerates free radical injury to the lung. Organochlorine poisoning is managed with benzodiazepines for seizures, and oil-based purgatives are avoided because these fat-soluble chemicals are absorbed more readily in fat.

## What you must remember

- **Paraquat mechanism:** Redox cycling generates superoxide radicals that injure alveolar type I and II pneumocytes, leading to fibrosis.
- **Sodium dithionite test:** Urine treated with sodium dithionite and alkali turns blue in the presence of paraquat, a useful bedside confirmation.
- **Oxygen rule:** High inspired oxygen accelerates lung injury, so oxygen is minimised, but hypoxia is still corrected to the lowest effective concentration.
- **Early decontamination:** Fuller's earth adsorption is used in the early hours after ingestion, while the value of steroids and cyclophosphamide remains uncertain.
- **Organochlorines:** lindane, endosulfan and aldrin block GABA-A chloride channels, while DDT prolongs sodium channel opening; both routes produce hyperexcitability, seizures and myoclonus.
- **Organochlorine management:** Benzodiazepines are first line for seizures, and fatty foods or oil-based purgatives are avoided.

## A worked course of paraquat poisoning over days

A farmer presents four hours after drinking a paraquat formulation, with burning in the mouth, vomiting and mild dyspnoea. Early injury is dominated by corrosive gastrointestinal damage, and the volume and time of ingestion are recorded because prognosis depends on the amount taken.

1. **Bind the herbicide early:** Fuller's earth is considered in the early hours to bind the herbicide.
2. **Confirm exposure:** A urine sodium dithionite test confirms exposure.
3. **Estimate lung risk:** A plasma paraquat concentration, read against a nomogram, estimates the risk of lung injury.
4. **Track organ function:** Kidney and liver function are repeated daily.
5. **Limit oxygen:** Supplemental oxygen is kept to the minimum needed, since high inspired oxygen accelerates lung injury.
6. **Anticipate fibrosis:** The patient may seem to improve over the following days. Progressive respiratory failure and pulmonary fibrosis develop over days to weeks, and no antidote has been shown to reliably reverse the lung injury.

## Where the examiner tests the oxygen rule

Three traps separate the two poisonings in examination questions.

- **Trap:** treating hypoxia with high-flow oxygen by reflex. — **Correct:** in paraquat poisoning the examiner expects oxygen to be withheld or limited, while hypoxia is still corrected to the lowest effective concentration.
- **Trap:** choosing atropine and pralidoxime for paraquat. — **Correct:** organophosphates produce miosis, bronchorrhoea and fasciculations and respond to these drugs, whereas paraquat has no such antidote.
- **Trap:** giving atropine for organochlorine seizures. — **Correct:** atropine is the wrong drug for hyperexcitability, and the absence of cholinergic features should redirect the thinking to benzodiazepines.

Lindane, used topically for scabies and lice, can cause seizures in its own right, which examiners often test.

## Frequently asked questions

### Which urine test confirms paraquat poisoning?

The sodium dithionite test confirms paraquat exposure, because urine treated with sodium dithionite and alkali turns blue when the herbicide is present. It is a qualitative bedside test, and a plasma concentration is used for prognosis.

### Why is oxygen withheld in paraquat poisoning?

Oxygen is withheld or limited because high oxygen concentrations increase reactive oxygen species generation in the lungs, worsening paraquat-induced injury. Hypoxia is still corrected, but the aim is the lowest oxygen concentration that maintains adequate saturation.

### Which drug treats seizures in organochlorine poisoning?

Benzodiazepines such as diazepam are the first-line treatment for seizures caused by organochlorines like lindane and endosulfan, which block GABA-A chloride channels. Oil-based purgatives are avoided because these fat-soluble chemicals are absorbed more readily in fat.

### Why is death in paraquat poisoning often delayed?

Death is often delayed because the main cause is progressive pulmonary fibrosis that develops over days to weeks after the initial gastrointestinal and renal injury. Survivors of large ingestions frequently need prolonged respiratory support.