Antidotes

An antidote is a substance that counteracts the effects of a poison or toxin. Antidotes may act by binding the toxin, inhibiting its action, reversing pathophysiological effects, or restoring normal metabolism. They are categorized as specific antidotes, which target particular poisons, and nonspecific or supportive measures that reduce harm or buy time for elimination.

Common specific antidotes include naloxone for opioid overdose; N-acetylcysteine for acetaminophen toxicity; fomepizole or ethanol for methanol or ethylene glycol poisoning; pralidoxime with atropine for organophosphate poisoning; protamine for heparin overdose; and antivenoms for venomous bites or stings. Chelating agents such as dimercaprol, edetate calcium disodium (CaNa2-EDTA), or deferoxamine are used for certain heavy metal poisonings. Reversal agents like flumazenil may reverse benzodiazepine effects in controlled settings, but their use is limited by the risk of seizures and withdrawal in some patients.

In some cases, antidotes are used with other therapies, such as glucagon for certain beta-blocker toxicities or calcium for calcium channel blocker overdose, though these must be used with care.

Mechanisms differ: receptor antagonism (naloxone), substrate competition or enzyme inhibition (fomepizole), chelation (dimercaprol, EDTA, deferoxamine), or restoration of critical molecules (N-acetylcysteine replenishing glutathione). Availability and timing are critical; antidotes may have narrow windows and potential adverse effects, and not all poisons have antidotes. When antidotes exist, they are used within guidelines or poison-control protocols, often alongside decontamination and supportive care.