The drug acetaminophen or paracetamol is an analgesic (a pain reliever).
In North America it is sold in generic form or under a number of trade names: for instance Tylenol (McNeil-PPC, Inc), Anacin-3 and Datril while it is known as Panadol in parts of Asia and Australasia. In some formulations acetaminophen is combined with the opiate codeine. It relieves headaches and other minor aches and pains, and lowers fever. Its chemical formula is C8H9NO2.
Compared to other common analgesics such as aspirin and ibuprofen, which belong to a class of drugs known as non-steroidal anti-inflammatory drugs or NSAIDs, acetaminophen has the advantage of not causing stomach problems, though it doesn't reduce inflammation or act as an anticoagulant.
Common dosage is 500mg (up to 1000mg) every 4 hours for adults. Doses above 150mg/kg or 7.5g for an adult is likely to cause hepatotoxicity. Overdoses of acetaminophen can lead to liver failure and a painful death if untreated; because of the wide over-the-counter availability of the drug, it is often used in suicide attempts. Acetaminophen should not be taken after alcohol consumption, because the liver, when engaged in alcohol breakdown, cannot properly dispose of acetaminophen, thus leading to hepatotoxicity.
Treatment for acetaminophen overdose is the use of intravenous N-acetylcysteine.
It was first synthesized in 1873 by Harmon Northrop Morse, but was not used medically until 1893. It did not gain popularity until after WW II when it was found to be a metabolite of phenacetin (this fact was first discovered in 1899 and rediscovered in 1948), offering similar effects but markedly less toxicity.
The US patent on acetaminophen has expired and generic versions of the drug are widely available under the Drug Price Competition and Patent Term Restoration Act of 1984, although certain Tylenol preparations are protected until 2007. US patent 6,126,967 filed September 3, 1998 was granted for "Extended release acetaminophen particles".
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Method of action
Acetaminophen, like the other drugs mentioned above, works by reducing the activity of the cyclo-oxygenase 2 (COX) enzyme which produces prostaglandins. While the other drugs operate as competitive inhibitors and directly block the active site of COX, acetaminophen blocks COX indirectly; this indirect blockage is effective in brain and endothelial cells but not in platelets and immune cells which have high levels of peroxides. This is the reason that aspirin fights inflammation and acts as an anticoagulant.
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