paraoxon

Paraoxon is an organophosphate insecticide and the active oxon metabolite of the organophosphate pesticide parathion. It is more potent at inhibiting acetylcholinesterase than parathion because of the P=O phosphylation form. Paraoxon is formed in the body by oxidative desulfuration of parathion via liver enzymes, converting the thiono form to the oxon form.

The primary mechanism of action of paraoxon is inhibition of acetylcholinesterase, the enzyme that breaks down acetylcholine at cholinergic synapses. By phosphorylating the active site serine in acetylcholinesterase, paraoxon causes accumulation of acetylcholine, leading to continuous stimulation of muscarinic, nicotinic, and central cholinergic receptors. Clinically, this can manifest as a cholinergic crisis with salivation, lacrimation, urination, defecation, bronchorrhea, bronchospasm, muscle fasciculations, weakness, and altered mental status or seizures.

Exposure to paraoxon can occur via inhalation, dermal contact, or ingestion. Acute toxicity requires rapid decontamination to limit further absorption. Treatment typically includes atropine to counter muscarinic effects and an oxime, such as pralidoxime, to reactivate acetylcholinesterase if administered before aging of the enzyme-bound complex. Supportive care, including respiratory support, may be necessary.

Uses and regulation: Paraoxon has historically been used as a pesticide, but due to its high toxicity to humans and non-target species, many jurisdictions have restricted or phased out its use. Safety considerations, handling controls, and disposal regulations are typically enforced where it remains in use.