2.9 : Antidotes

Antidotes are medicinal substances used to counteract the harmful effects of toxins or drugs in the body. They function in various ways, each uniquely designed to combat specific toxic compounds.

Specific antidotes operate by inhibiting the enzymes that control biochemical pathways, reducing the production of harmful metabolites.

An example of an antidote is atropine, which counteracts the detrimental effects of cholinesterase inhibitors. It achieves this by deactivating muscarinic receptors, thereby preventing an overload of acetylcholine from reaching the receptor site.

Antidotes can also reactivate altered enzymes, enhancing their functionality and reducing toxicity. Furthermore, some antidotes can directly neutralize toxic drug metabolites by binding to them. They may also transform these toxic metabolites into less harmful substances. For example, sodium thiosulfate is employed as an antidote in cyanide poisoning cases. It expedites the conversion of cyanide into thiocyanate, a less toxic metabolite that is more easily eliminated from the body. In situations of heavy metal poisoning, chelators serve as effective antidotes. They form complexes with the heavy metals, which are excreted through the urine, reducing the toxic load on the body.