A classic example of activation in toxicology is the metabolism of acetaminophen. In therapeutic doses, acetaminophen is safely metabolized through conjugation pathways. However, in overdose situations, a significant portion is converted by cytochrome P450 enzymes into a highly reactive metabolite, N-acetyl-p-benzoquinone imine (NAPQI), which can cause severe liver damage if not adequately detoxified by glutathione. Another example is the bioactivation of herbicides and pesticides, such as parathion. Parathion itself is relatively non-toxic but is converted in the body to paraoxon, a potent inhibitor of acetylcholinesterase, leading to neurotoxic effects.
