Antidotes and Specific Therapies

General Principles & Common Antidotes - Antidote Arsenal

• Antidotes counteract poison effects by:
  • Receptor antagonism (e.g., Naloxone)
  • Chelating toxins (e.g., Deferoxamine)
  • Replenishing depleted substrates (e.g., N-acetylcysteine)
  • Enzyme reactivation (e.g., Pralidoxime)
• Key Poison-Antidote Pairs:
  • Paracetamol: N-acetylcysteine (NAC). Dose by nomogram.
  • Opioids: Naloxone. Titrate to respiration. 📌 "Wake up, breathe!"
  • Benzodiazepines: Flumazenil. ⚠️ Caution: seizures in chronic users/co-ingestants.
  • Organophosphates/Carbamates: Atropine (muscarinic symptoms), Pralidoxime (AChE regeneration, for OPs).
  • Methanol/Ethylene Glycol: Fomepizole (preferred) or Ethanol. Inhibits alcohol dehydrogenase.
  • Iron: Deferoxamine. IV. "Vin rosé" urine.
  • Cyanide: Hydroxocobalamin or Sodium thiosulfate + Sodium nitrite.
  • Digoxin: Digoxin-specific antibody (Fab) fragments.
  • Beta-blockers: Glucagon, High-dose insulin euglycemic therapy (HIET).
  • Calcium Channel Blockers: Calcium salts, Glucagon, HIET.
  • Heavy Metals (Pb, As, Hg): Chelators (e.g., Dimercaprol, Succimer, EDTA).

⭐ N-acetylcysteine for paracetamol poisoning is most effective if given within 8-10 hours post-ingestion.

Cholinergic & Anticholinergic Poisoning - Toxidrome Tango

Cholinergic (Wet): ↑ACh.

• 📌 DUMBBELLS: Diarrhea, Urination, Miosis, Bronchorrhea/Bradycardia, Emesis, Lacrimation, Salivation/Sweating.
• Causes: Organophosphates (OPs), carbamates, mushrooms.
• Rx:
  • Atropine: ACh antagonist. Adults: 2-5 mg IV; Peds: 0.02-0.05 mg/kg. Titrate: dry secretions, HR >80.
  • Pralidoxime (2-PAM): OPs. Reactivates AChE. 1-2 g IV. Use before "aging".
  • Diazepam for seizures.

Anticholinergic (Dry): ↓ACh.

• 📌 "Red as beet, dry as bone, blind as bat, mad as hatter, hot as hare, full as flask."
• Causes: Datura, belladonna, TCAs, antihistamines.
• Rx:
  • Supportive: Cooling, hydration.
  • Physostigmine: AChE inhibitor. 0.5-2 mg IV slowly. For severe symptoms.
  • ⚠️ Contra: TCA (QRS >100ms), bradycardia.
  • Benzodiazepines for agitation.

⭐ Physostigmine is contraindicated in TCA overdose with QRS prolongation (>100 ms) due to the risk of precipitating asystole or complete heart block.

Heavy Metals, Toxic Alcohols, Cyanide - Detox Diversions

• Heavy Metals:
  • Lead: Paint, batteries. Features: Abdominal colic, anemia (basophilic stippling), encephalopathy, wrist/foot drop. Burton's line. Antidotes: Dimercaprol (BAL), CaNa2EDTA, Succimer (DMSA). 📌 Mnemonic "LEAD": Lines, Encephalopathy/Erythrocyte stippling, Abdominal colic/Anemia, Drop.
  • Arsenic: Garlic breath, rice-water stools, Mee's lines. Antidotes: BAL, DMSA.
  • Mercury: Neurotoxicity (Minamata), erethism, renal damage. Antidotes: BAL, DMSA, DMPS.
  • Iron: GI upset, shock, metabolic acidosis. Serum Fe > 350-500 mcg/dL. Antidote: Deferoxamine (vin rosé urine).
• Toxic Alcohols:
  • Methanol (→ Formic Acid): ↑ Osmolar & Anion gap, "snowstorm" vision. Antidote: Fomepizole/Ethanol, Folate, Hemodialysis.
  • Ethylene Glycol (→ Oxalic Acid): ↑ Osmolar & Anion gap, AKI (calcium oxalate crystals), hypocalcemia. Antidote: Fomepizole/Ethanol, Thiamine, Pyridoxine, Hemodialysis.
• Cyanide:
  • Inhibits cytochrome oxidase → cellular hypoxia.
  • Features: Bitter almond breath, seizures, lactic acidosis.
  • Antidotes: Hydroxocobalamin (preferred); Nitrites + Sodium Thiosulfate.

  ⭐ Ethylene glycol poisoning: envelope-shaped calcium oxalate crystals in urine are key for diagnosing AKI.

High‑Yield Points - ⚡ Biggest Takeaways

• N-acetylcysteine is crucial for paracetamol poisoning, by replenishing glutathione stores.
• Naloxone rapidly reverses opioid overdose effects by antagonizing μ-receptors.
• Flumazenil antagonizes benzodiazepines; use with caution due to seizure precipitation risk.
• Organophosphate poisoning requires atropine (muscarinic effects) and pralidoxime (enzyme reactivation).
• Sodium bicarbonate alkalinizes for TCA cardiotoxicity and enhances salicylate elimination.
• Deferoxamine is the specific chelator for acute iron poisoning.
• Fomepizole or ethanol inhibits alcohol dehydrogenase in methanol/ethylene glycol toxicity.