How Does an Antidote Work?
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Antidotes and Their Mode of Action

Published on Dec 12, 2022 and last reviewed on Jul 17, 2023   -  4 min read


Antidotes are substances that can reduce or reverse the toxicity of poisons. In this article, we will discuss antidotes in detail.


Antidotes can counteract or neutralize the effect of toxins and poisons. They can be administered intravenously or through the skin and mouth. Antidotes act by inactivating the poison, blocking its action, preventing its absorption, and neutralizing its effect. Antidotes can also reduce the toxic effects of poisons on different organs in the body. Toxic effects of toxins and poisons on body tissues and organs are reduced by toxic receptor blockage, competitive inhibition of receptors, and opposing its action. Antidotes can significantly reduce mortality and morbidity due to toxic chemical poisoning, but they are not available for all toxic agents.

What Are Antidotes?

An antidote is a chemical, drug, or chelating substance that can neutralize or counteract the effects of poison or a drug in the human body. They can have chemical, pharmacological, or physiological effects inside the body. Antidotes reduce the toxicity of poisons and drugs by neutralizing the poison, reducing its action on organs, and preventing the absorption and conversion of toxins into toxic metabolites.

Based on the mode of action, they can be of three types.

  • Physical Antidote - This type of antidote reduces the toxic effects of poison by physical properties like coating, adsorption, and dissolution.

  • Chemical Antidote - It can reduce the toxic effects by changing the chemical properties of the poison.

  • Pharmacological Antidote - This type of antidote will neutralize and oppose the pharmacological action of the poison.

How Do Antidotes Work?

The harmful effect of poisons and toxic chemicals in the body depends on various factors. It includes dose, route of administration, type of the toxin, and duration of exposure to the toxin. Antidotes can be again classified based on the mechanism of action. Antidotes reduce toxicity based on four basic functions.

It includes:

  • Reducing the Toxin Level - Antidotes act directly on the toxin or drug to reduce its concentration in the body. It includes increased elimination of the toxin and specific and non-specific binding. Specific binding involves immunotherapy, chelation, and bio-scavenger therapy. In specific binding, antidotes bind with the toxic substances and form inert complexes which are least reactive and eventually eliminated from the body. Nonspecific antidotes reduce the toxin levels by preventing its absorption in the gastrointestinal tract. Nonspecific antidotes like activated charcoal will adsorb the toxins and reduce their systemic absorption. Nonspecific antidotes will also interrupt the enterohepatic recirculation of toxic substances and reduce their concentration in the body.

  • Blocking the Action Site of the Toxin - It is achieved by altering the toxin's receptor site or by modifying enzyme activity. Ethyl alcohol, used for methyl alcohol poisoning, competes with methyl alcohol molecules for alcohol dehydrogenase and reduces toxic metabolites. Antidotes like oximes used for organophosphorus poisoning work on the principle of enzyme reactivation.

  • Reducing the Level of Toxic Metabolites- Antidotes can reduce the toxic effects of poisons by neutralizing the toxic metabolites or converting them into less toxic forms. N-Acetyl cysteine used for Paracetamol poisoning converts the toxic metabolites into another form and thus reduces hepatic toxicity. Sodium thiosulphate used for cyanide poisoning converts toxic metabolites to less toxic substances and reduces the toxic effects.

  • Counteracting the Harmful Effects of Toxins - Antidotes can reduce the toxic effects by directly inhibiting or reducing the effect of toxins. Atropine used for organophosphorus poisoning reduces the muscarinic effects of the poison and thus decreases the toxic effects on the body tissues. Vitamin K, used for Warfarin toxicity; folinic acid, used for Methotrexate overdose; and pyridoxine, used for Isoniazid (INH) overdose, work on this principle.

What Are the Commonly Used Antidotes?

  • Activated charcoal is used for the majority of oral toxins.

  • Calcium chloride is used for black widow spider bite poisoning.

  • Acetylcysteine is used for Acetaminophen and Paracetamol poisoning.

  • Flumazenil is used for benzodiazepine overdose.

  • Naloxone is used for opioid poisoning.

  • Atropine is used for carbamate and organophosphate poisoning.

  • Dimercaprol is used for inorganic mercury, gold, and arsenic toxicity.

  • Methylene blue is used for drug-induced methemoglobinemia.

  • Digoxin immune fab is used for Digoxin toxicity.

  • Pralidoxime is used for anti-cholinesterase poisoning.

  • Calcium salts are used for fluoride toxicity.

  • Heparin is used for Ergotamine toxicity.

  • Snake antivenom is used for cobra bites.

  • Sodium thiosulfate for cyanide toxicity.

  • Vitamin C for mercury toxicity.

  • Thiamine (vitamin B1) is used to reduce the toxicity caused by alcohol poisoning.

  • Sodium bicarbonate for poisoning due to chlorine gas inhalation.

  • Protamine sulfate is used for Heparin toxicity.

  • Penicillamine is used for the toxicity of arsenic, gold, lead, zinc, and copper.

  • Mesna is used for Cyclophosphamide toxicity.

  • Deferoxamine is used for toxicity due to iron.

  • Beta-blockers for Theophylline toxicity.

  • Persian blue can be used for thallium toxicity.

  • Intralipids are used for toxicity due to local anesthetic agents.

  • Hyperbaric oxygen therapy (HBOT) for carbon monoxide and cyanide poisoning.

  • Fresh frozen plasma and vitamin K (phytomenadione) for toxicity due to Warfarin overdose.

  • Chelators like ethylenediaminetetraacetic acid (EDTA) and dimercaptosuccinic acid (DMSA) for toxicity due to heavy metal poisoning.

  • Cyproheptadine for toxicity due to serotonin drugs (serotonin syndrome).

  • Benztropine (INN) and diphenhydramine hydrochloride (DPH) are used to reduce the extrapyramidal reactions caused by antipsychotic drugs.

  • Octreotide for toxicity due to oral hypoglycemic drugs.

  • Calcium gluconate is used for toxicity due to calcium channel blocker drugs and burns due to hydrofluoric acid (hydrogen fluoride and water).

  • Five percent acetic acid (vinegar) for toxicity due to ammonia and urea.

  • Yohimbine or Atipamezole for Amitraz toxicity.

  • Pamidronate sodium or bisphosphonate for cholecalciferol toxicity.

  • 4-Methylpyrazole or ethanol for toxicity due to ethylene glycol.


Antidotes help to prevent and reduce the toxic effects of drugs and poisons. They may act by neutralizing the toxin, decreasing the absorption, preventing the conversion to toxic metabolites, and reducing the effect of toxins on organs. Proper use of antidotes and supportive medical management will reduce the dangerous adverse effects of toxins and help to reduce morbidity and mortality. Proper diagnosis and confirmation of the toxin must be made before using the antidote.

Frequently Asked Questions


What Are the Examples of Antidotes?

An antidote is a substance that counteracts or neutralizes the effects of toxins or drugs in the body. It can be a chemical, medication, or chelating agent. Antidotes that are often administered include activated charcoal, sodium bicarbonate, Acetylcysteine, Naloxone, Atropine, Flumazenil, therapeutic antibodies, and different vitamins.


What Are the Most Commonly Used Antidotes?

Antidotes aid in the prevention and reduction of harmful effects caused by medications and poisons. The most commonly used antidotes are the following:
- Activated Charcoal - For the majority of oral toxins.
- Naloxone - For opioid poisoning.
- Acetylcysteine - For Paracetamol poisoning.
- Thiamine - For alcohol poisoning.
- Vitamin C - For mercury poisoning.
- Calcium Salts - For fluoride toxicity.
- Vitamin K - For Warfarin toxicity.


What Is a Universal Antidote?

For many years, activated charcoal has been administered as a "universal antidote" to most toxins. The universal antidote is a poison antidote that contains activated charcoal as its main constituent. It is a combination of two parts activated charcoal, one part magnesium oxide, and one part tannic acid, given to patients who have swallowed poison. 


What Is the Antidote for Paracetamol Poisoning?

Acetylcysteine has been used as an effective antidote for Paracetamol overdose. It reduces the risk and severity of liver injury after Paracetamol poisoning. If administered within the first eight hours of Paracetamol overdose, Acetylcysteine (N-acetylcysteine) has a nearly 100 percent success rate in avoiding Paracetamol-induced hepatotoxicity. 


What Is the Antidote for Atropine?

Physostigmine is used to counteract the overdose commonly caused by taking Atropine. Physostigmine quickly reverses delirium and coma caused by high doses of Atropine. It is given intravenously in doses ranging from 1 to 4 milligrams (0.5 to 1 milligrams in pediatric patients).


What Is the Antidote for Aspirin?

There is no known antidote for Aspirin toxicity. Acute Aspirin overdose results in mild to moderate symptoms. Early administration of activated charcoal reduces the absorption of Aspirin after overdose. Intravenous bicarbonate administration is also used to increase the excretion of Aspirin and reduce side effects.


What Is the Antidote for a Heparin Overdose?

Protamine sulfate, a cationic polypeptide, is the only therapeutically approved antidote for unfractionated heparin toxicity. Heparin's anticoagulant effects can be quickly reversed with intravenous protamine sulfate.


What Is the Antidote for Warfarin?

Warfarin, commonly known as Coumadin, is an anticoagulant that is taken orally and is used to prevent thrombosis and embolism. Vitamin K, also known as phytonadione, has been used to reverse the effects of Warfarin overdose. It can be taken orally, intravenously, or subcutaneously.


What Is the Antidote for Digoxin Overdose?

Digoxin-specific antibody fragments, also known as Digifab, are a potent antidote that binds Digoxin directly. It treats potentially fatal symptoms associated with Digoxin overdose, like ventricular arrhythmias, hypotension, and symptomatic bradycardia.


What Are Natural Antidotes?

Antidotes are substances that counteract the effects of a toxin or poison. Natural antidotes, like fruits and vegetables, are high in antioxidants and can be used to reduce toxicity. Natural antioxidants have scavenging and chelation activities and can be used instead of synthetic chelating agents.

Last reviewed at:
17 Jul 2023  -  4 min read




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