Antidotes
Antidotes are agents used to counteract the toxic effects of poisons or overdoses.
They may work by:
- Neutralizing the poison
- Preventing absorption
- Promoting elimination
- Reversing or blocking physiological effects
Common Antidotes and Their Mechanisms
1. Acetaminophen (Paracetamol)
- Antidote: N-acetylcysteine (NAC)
- Administration: Oral or IV; most effective within 8–10 hours of overdose.
Mechanism:
- Replenishes hepatic glutathione.
- Detoxifies NAPQI, the toxic metabolite of acetaminophen.
2. Opioids (e.g., Morphine, Heroin)
- Antidote: Naloxone
- Administration: Intranasal, IM, SC, or IV
Mechanism:
- Competitive antagonist at μ-opioid receptors.
- Rapidly reverses CNS and respiratory depression.
3. Benzodiazepines (e.g., Diazepam, Lorazepam)
- Antidote: Flumazenil
- Administration: IV
Use with caution: Can trigger withdrawal seizures in dependent patients.
Mechanism:
- Competitive antagonist at GABA-A benzodiazepine receptor site.
- Reverses sedation and respiratory depression.
4. Methanol and Ethylene Glycol
- Antidote: Fomepizole (preferred) or Ethanol
- Administration: IV
Mechanism:
- Inhibits alcohol dehydrogenase.
- Prevents conversion into toxic metabolites (e.g., formic acid, oxalic acid).
5. Organophosphates (e.g., insecticides)
- Antidote: Atropine + Pralidoxime
- Administration: IV
Mechanism:
- Atropine: Blocks muscarinic receptors to reduce secretions and bradycardia.
- Pralidoxime: Reactivates acetylcholinesterase enzyme inhibited by the toxin.
6. Warfarin
- Antidote: Vitamin K1 (Phytonadione)
- Administration: Oral or IV depending on INR and bleeding severity.
Mechanism:
- Promotes synthesis of clotting factors II, VII, IX, X.
- Reverses anticoagulant effects of warfarin.
7. Anticholinergics (e.g., Atropine, Diphenhydramine)
- Antidote: Physostigmine
- Administration: IV (use with caution)
Mechanism:
- Acetylcholinesterase inhibitor.
- Increases synaptic acetylcholine to counteract anticholinergic symptoms.
- Caution: Can cause seizures or bradycardia.
8. Beta-blockers
- Antidote: Glucagon
- Administration: IV
Mechanism:
- Activates adenylate cyclase independently of beta-receptors.
- Increases cAMP → enhances cardiac contractility and heart rate.