Acetaminophen, plasma or serum

Acetaminophen is one of the most widely used analgesics on the market today. It is available in many formulations including liquid, tablets, capsules and suppositories. The chemical name is N-acetyl-p-aminophenol (APAP). Acetaminophen has an excellent safety profile in therapeutic doses, but hepatotoxicty can develop in overdose situations. Metabolism is primarily hepatic with the half life being 2 to 4 hours. The parent compound, acetaminophen is non-toxic, but the metabolite N-acetyl-benzoquinoneimine (NAPQI) is toxic. Normally, glutathione will bind the NAPQI and form a non-toxic conjugate which is excreted. In overdose situations, as glutatione stores are depleted, the NAPQI binds to the lipid bilayer of the hepatocytes resulting in necrosis. N-acetylcysteine (NAC) is an effective antidote.