NAPQI

NAPQI (N-acetyl-p-benzoquinone imine) is a toxic byproduct produced during the xenobiotic metabolism of the analgesic paracetamol (acetaminophen). It is normally produced only in small amounts, and then almost immediately detoxified in the liver.

However, under some conditions in which NAPQI is not effectively detoxified (usually in case of paracetamol overdose), it causes severe damage to the liver. This becomes apparent after 3–4 days after ingestion and may result in death from fulminant liver failure several days after the overdose.