This phenomenon is known as chemical antagonism, e.g., Chelation of heavy metals by dimercaprol. The exposure of a chemical to an organism may thus reduce the toxicity of another and the chemical reaction thus produces a less toxic product. For example, Isopropanol has no effect on the liver, but it can considerably increase the hepatotoxicity in presence of CCl 4. The term ‘potentiation’ is used to describe the situation in which the toxicity of substances on an organ is markedly increased by another substance which itself has no effect on that organ. If the combined effect is greater than the sum, the interaction is considered to be synergistic, e.g., CCl 4 and ethanol on the liver. If this combined effect is equal to the sum of the effect of each substance given alone, the interaction is considered to be additive, e.g., combinations of most organphosphorus pesticides on cholinesterase activity. Toxicity of a chemical in an animal may also be either increased or decreased by simultaneous or consecutive exposure to another chemical.
An antidote is strictly defined as ‘a remedy for counteracting a poison’ or substances which prevent action of poisons are called ‘antidotes’, and procedures applied to reduce toxicity in acute poisoning are termed antidotal procedures.
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