Pesticide and Insecticide Poisoning

Organophosphate & Carbamate Poisoning - AChE Attack!

• Mechanism: Inhibit Acetylcholinesterase (AChE) → ↑ Acetylcholine (ACh).
  • Organophosphates (OPs): Irreversible inhibition (covalent bond, "aging").
  • Carbamates: Reversible inhibition.
• Clinical Features (Cholinergic Crisis):
  • Muscarinic: 📌 DUMBELS (Diarrhea, Urination, Miosis, Bronchospasm/Bronchorrhea, Emesis, Lacrimation, Salivation).
  • Nicotinic: Muscle weakness, fasciculations, paralysis, hypertension, tachycardia.
  • CNS: Seizures, coma, respiratory depression.
• Diagnosis: Clinical; ↓ RBC AChE levels. Atropine challenge: 1 mg IV.
• Management:
  • ABCs, Decontamination.
  • Atropine: 2-5 mg IV q 5-15 min until atropinization (target: clear lungs).
  • Pralidoxime (PAM): 1-2 g IV (OPs only, before aging).
  • Diazepam for seizures.
• Complications:
  • Intermediate Syndrome (IMS): 24-96 hrs; muscle weakness.
  • OPIDP (Delayed Polyneuropathy): 2-3 weeks.

⭐ Pralidoxime is generally contraindicated or not useful in pure carbamate poisoning as it may worsen toxicity with certain carbamates (e.g., Sevin/Carbaryl).

Organochlorine Poisoning - Neurotoxic Nightmare

• Mechanism: GABA-A antagonism → CNS hyperexcitability. Also Na⁺/K⁺-ATPase inhibition.

• Examples: DDT, lindane, endosulfan. Lipophilic, fat storage, prolonged effects.

• Key Features:

  • Paresthesias, tremors, ataxia.
  • Myoclonic jerks, generalized seizures (often recurrent/status epilepticus).
  • Respiratory depression.

• Management:

  • Decontamination (skin/GI). ⚠️ Avoid oral fats/oils.
  • Seizure control: Benzodiazepines (e.g., diazepam 5-10 mg IV), phenobarbital.
  • Supportive care. ⚠️ Avoid epinephrine (↑arrhythmia risk).

• ⭐ > Organochlorines sensitize myocardium to catecholamines, risking ventricular arrhythmias.

Aluminium Phosphide Poisoning - Phosphine Peril

• Source: "Celphos", "Phostoxin"; releases $PH_3$ (phosphine) with moisture.
• MOA: Inhibits cytochrome oxidase → cellular hypoxia.
• Clinical:
  • GIT: N/V (garlicky odor), pain.
  • CVS: Refractory shock, arrhythmias, ECG changes.
  • Resp: ARDS, pulm. edema.
  • Severe metabolic acidosis.
• Dx: Clinical; AgNO3 test (gastric/breath → black).
• Rx: No antidote. Supportive care crucial.
  • Gastric lavage (KMnO4 1:10000, coconut oil), charcoal.
  • IV fluids, vasopressors.
  • MgSO4 (IV), NAC.
  • ECMO if refractory shock.

⭐ Profound refractory shock and severe metabolic acidosis are hallmarks.

Paraquat Poisoning - Blue Death Dilemma

• Herbicide causing multi-organ failure, primarily targeting lungs (pulmonary fibrosis).
• Mechanism: Redox cycling → Reactive Oxygen Species (ROS) → oxidative stress.
• Key Features: Oral burns, GI distress, renal failure, "Paraquat Lung".
• Diagnosis: Urine dithionite test (turns blue/green).
• Management:
  • Decontamination: Fuller's earth/activated charcoal.
  • Hemoperfusion (if early).
  • Antioxidants (N-acetylcysteine, Vit C, E).
  • ⚠️ Strict O₂ restriction unless severe hypoxemia.

⭐ Oxygen therapy can worsen lung injury in early paraquat poisoning by enhancing free radical formation due to increased ROS production in the lungs.

Other Pesticides - Brief Bites

• Pyrethroids (e.g., Allethrin, Cypermethrin)
  • Na+ channel modulators → paresthesias (facial tingling), allergic reactions.
  • Tx: Symptomatic; Vitamin E for paresthesias.
• Rodenticides
  • Superwarfarins (e.g., Brodifacoum): Inhibit Vit K epoxide reductase → severe bleeding.
    • Tx: Vitamin K1 (phytonadione), FFP/PCC.
  • Aluminium Phosphide (Celphos): Releases phosphine ($PH_3$) gas.
    • Garlic odor, severe metabolic acidosis, refractory shock, ARDS.
    • Tx: Supportive, MgSO4.

    ⭐ Aluminium phosphide poisoning has very high mortality, often due to refractory cardiogenic shock and arrhythmias.

High‑Yield Points - ⚡ Biggest Takeaways

• Organophosphates (OPs) & Carbamates: Cholinergic crisis (DUMBELS). Treat with Atropine; Pralidoxime for OPs.
• Organochlorines (DDT, Endosulfan): CNS hyperexcitability, seizures. Manage with diazepam.
• Aluminium Phosphide (Celphos): Profound shock, metabolic acidosis. No specific antidote; magnesium sulfate may help.
• Paraquat: Progressive pulmonary fibrosis, multi-organ damage. No specific antidote.
• Garlic odor on breath: Suspect OP or Aluminium Phosphide.
• Atropinization (for OPs/Carbamates): Aim for dry mouth, clear lungs, HR > 80/min.