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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Specific antidotes

Medicines that reverse or neutralise one poison or a small group of poisons. They support, but never replace, airway, breathing and circulation care.

Updated 2026-11-01

## What they are

A mixed group defined by use, not by chemistry: receptor antagonists (flumazenil, naloxone), enzyme reactivators or inhibitors (pralidoxime, fomepizole), substrates that rebuild a detoxifying pathway (acetylcysteine, sodium thiosulfate), antibodies that bind the drug (digoxin Fab), agents that fix oxygen transport (methylene blue, sodium nitrite) and gut decontaminants (activated charcoal). Many are scarce, so hospitals and poison lines plan their stock.

## Mechanism of action

Each antidote acts at the step where its poison causes harm: it competes at the receptor, frees or blocks the enzyme, supplies a missing substrate, binds the poison in blood or gut, or converts the haemoglobin. Timing matters: several work only before the damage is fixed (liver necrosis, aged acetylcholinesterase, toxic acids already formed).

Target: Varies with the poison: receptors, enzymes, the poison itself or haemoglobin

## Key points

- Classic pairs: paracetamol → acetylcysteine; organophosphates → atropine + pralidoxime; benzodiazepines → flumazenil; opioids → naloxone; methanol/ethylene glycol → fomepizole or ethanol.
- More pairs: cyanide → hydroxocobalamin or sodium nitrite then sodium thiosulfate; digoxin → digoxin Fab; methaemoglobinaemia → methylene blue; iron → deferoxamine; lead → succimer, dimercaprol + edetate.
- Antidotes come after decontamination and support of airway, breathing and circulation.
- In Colombia, pesticides caused about a third of the suicidal poisonings reported in 2015; the national toxicology line advises on antidote use.
- Several antidotes are hard to obtain in Colombia and Latin America (for example sodium nitrite; methylene blue is registered as a diagnostic, not as an antidote).

## Drugs in this class

- [**Acetylcysteine** The antidote for paracetamol (acetaminophen) overdose: it refills the liver's glutathione so the toxic metabolite is… Hepatic glutathione and the toxic metabolite NAPQI](https://durgical.com/en/pharmacology/acetylcysteine/)
- [**Activated charcoal** A fine black powder that binds many poisons in the gut so less is absorbed. Most useful early after ingestion and only… Adsorption of the poison in the gut lumen](https://durgical.com/en/pharmacology/activated-charcoal/)
- [**Pralidoxime** An oxime that reactivates acetylcholinesterase blocked by organophosphate pesticides. It is always given with… Acetylcholinesterase inhibited by an organophosphate](https://durgical.com/en/pharmacology/pralidoxime/)
- [**Flumazenil** A competitive antagonist at the benzodiazepine site of the GABA-A receptor. It reverses benzodiazepine sedation but… GABA-A receptor, benzodiazepine site (α1/γ2 interface)](https://durgical.com/en/pharmacology/flumazenil/)
- [**Fomepizole** Blocks alcohol dehydrogenase so methanol and ethylene glycol are not turned into their toxic acids. Ethanol is the… Alcohol dehydrogenase](https://durgical.com/en/pharmacology/fomepizole/)
- [**Digoxin immune Fab** Antibody fragments made in sheep that bind digoxin in the blood and pull it off the sodium pump. The specific antidote… Digoxin itself (and other cardiac glycosides)](https://durgical.com/en/pharmacology/digoxin-immune-fab/)
- [**Methylthioninium chloride (methylene blue)** A blue dye that turns methaemoglobin back into normal haemoglobin. It is avoided in G6PD deficiency and with… Methaemoglobin, through NADPH-dependent reduction](https://durgical.com/en/pharmacology/methylthioninium-chloride/)
- [**Sodium nitrite** A cyanide antidote that turns some haemoglobin into methaemoglobin, which pulls cyanide off mitochondria. It is… Haemoglobin (converted to methaemoglobin)](https://durgical.com/en/pharmacology/sodium-nitrite/)
- [**Sodium thiosulfate** A sulfur donor that lets the enzyme rhodanese turn cyanide into thiocyanate, which the kidneys excrete. Given after… Rhodanese (thiosulfate sulfurtransferase)](https://durgical.com/en/pharmacology/sodium-thiosulfate/)

## Others in the class

- Atropine (organophosphates)
- Hydroxocobalamin (cyanide)
- Physostigmine (anticholinergic delirium)
- Ethanol (methanol, ethylene glycol)
- Calcium gluconate
- Prussian blue (thallium, caesium)
- Lipid emulsion (local anaesthetics)

## Test yourself

Think of the answer, then tap the question to see it.

## Which antidote is used for paracetamol overdose, and what does it restore?

Acetylcysteine, which restores hepatic glutathione.

## Which two antidotes are given together in organophosphate poisoning?

Atropine (muscarinic effects) and pralidoxime (reactivates acetylcholinesterase).

## Why does an antidote never replace supportive care?

Most poisonings are managed mainly with airway, breathing, circulation and decontamination; antidotes act on one step and may be short-acting or unavailable.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Guía para el Manejo de Emergencias Toxicológicas](https://minsalud.gov.co/sites/rid/Lists/BibliotecaDigital/RIDE/DE/GT/guias-manejo-emergencias-toxicologicas-outpout.pdf) (Ministerio de Salud y Protección Social; Organización Panamericana de la Salud, 2017); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025).

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