ORGANOPHOSPHORUS AND CARBAMATE COMPOUNDS POISONING

Organophosphorus (OP) and carbamate compounds are widely used agricultural pesticides and are among the commonest causes of life-threatening poisoning in developing countries. Toxicity occurs after inhalation, ingestion, or dermal absorption and may develop rapidly.

Common Agents

Organophosphates

• Malathion

• Parathion

• Tetraethyl pyrophosphate (TEPP)

• Mevinphos

• Chlorpyrifos

• Diazinon

Carbamates

• Carbaryl

• Methiocarb

• Propoxur

2. Mechanism of Toxicity (Pathophysiology)

Both compounds inhibit acetylcholinesterase (AChE) causing accumulation of acetylcholine at:

• Muscarinic receptors

• Nicotinic receptors

• Central nervous system receptors

Difference

Accumulated acetylcholine causes cholinergic crisis.

3. Risk Factors

• Agricultural workers / farmers

• Pesticide sprayers

• Children in rural households

• Suicidal ingestion

• Storage in beverage containers

• Poor protective equipment

• Contaminated clothing

• Food contamination

4. Clinical Features

Classic Mnemonic: DUMBELS / SLUDGE

Early Symptoms

• Vomiting

• Diarrhea

• Blurred vision

• Weakness

Signs of Excess Parasympathetic Activity

• Salivation

• Sweating

• Lacrimation

• Bradycardia

• Miosis (pinpoint pupils)

• Bronchorrhea

• Bronchospasm

• Convulsions

• Muscle twitching

• Paralysis

• Pulmonary edema

• Respiratory depression

Intermediate Syndrome (24–96 hours)

• Neck flexor weakness

• Proximal limb weakness

• Respiratory muscle paralysis

Delayed Neuropathy (2–3 weeks)

• Peripheral neuropathy

• Foot drop

• Sensory loss

5. Diagnostic Criteria

Diagnosis is primarily clinical — treatment must NOT wait for lab confirmation.

Suggestive findings:

• Pesticide exposure history

• Garlic-like odor

• Pinpoint pupils

• Copious secretions

• Fasciculations

• Bradycardia

6. Investigations

Essential

• Plasma cholinesterase level

• RBC acetylcholinesterase level (best marker)

• Blood gases (respiratory failure)

• Serum electrolytes

• Glucose

• Renal & liver function tests

Additional

• Chest X-ray (aspiration/pulmonary edema)

• ECG monitoring

• Continuous pulse oximetry

7. Management

EMERGENCY PRIORITY:

Treat immediately — do NOT delay for investigations

8. Non-Pharmacological Treatment

Decontamination

1. Remove patient from exposure

2. Remove contaminated clothing

3. Wash skin with soap & water

4. Irrigate eyes with saline

Healthcare workers must wear PPE

Gastrointestinal

• Activated charcoal within 1 hour

• DO NOT induce vomiting

• NG aspiration only if airway protected

Supportive Care

• Airway suction

• Oxygen if SpO₂ < 90%

• Continuous monitoring

• Intubation if needed

9. Pharmacological Treatment

A. Atropine — Life Saving Drug

Blocks muscarinic receptors

Adult Dose

5 mg IV bolus

Repeat every 5–10 minutes until atropinization

End-points of Atropinization

• Dry chest (no bronchial secretions)

• HR > 80 bpm

• SBP > 80 mmHg

• Pupils not pinpoint

• Dry axillae

Then start infusion:10–20% of loading dose per hour

Pediatric Dose

0.05 mg/kg IVDouble every 5 minutes until atropinized

B. Oximes (Cholinesterase Reactivators)

Pralidoxime (Preferred)

Restores acetylcholinesterase activity

Loading 50 mg/kg IV over 30 min

Repeat Once or twice

Maintenance 10–20 mg/kg/hr infusion

Obidoxime

5 mg/kg IV (within 24 hours)Give after first atropine dose

C. Seizure Control

• Diazepam 0.1–0.3 mg/kg IV

• Also reduces neurotoxicity

10. Monitoring

Continuous monitoring of:

• Respiratory rate

• Secretions

• Oxygen saturation

• Heart rate

• Level of consciousness

Measure cholinesterase daily if available

11. Complications

• Respiratory failure

• Aspiration pneumonia

• Intermediate syndrome paralysis

• Peripheral neuropathy

• Cardiac arrhythmias

• Death

12. Prognosis

Good if treated early with atropinePoor if delayed respiratory support

Major cause of death: respiratory failure

13. Prevention

Do’s

• Store pesticides safely

• Use protective gear

• Keep chemicals in original containers

• Educate farmers

Don’ts

• Never store in drink bottles

• Never spray indoors

• Never allow children access

• Never mix chemicals without protection