NAPQI is a metabolite produced in small amounts and detoxified in the liver; under conditions such as acetaminophen poisoning when detoxification is insufficient, it causes severe liver damage. What does NAPQI stand for?

• A. N-acetyl-ρ-quinone imine
• B. N-acetoacetyl-ρ-quinone imine
• C. N-acetyl-ρ-benzoquinone imine
• D. N-acetoacetyl-ρ-benzoquinone imine

Answer: (C)

NAPQI stands for N-acetyl-p-benzoquinone imine. Here, N-acetyl means an acetyl group is attached to nitrogen, and p-benzoquinone refers to the para-substituted benzoquinone ring derived from benzene. The imine part indicates the C=N linkage in this quinone-imine metabolite. This reactive metabolite is formed in small amounts during acetaminophen metabolism and is normally detoxified by glutathione conjugation; when detoxification is overwhelmed, NAPQI can bind to liver proteins and cause damage.