How does Aspirin Work?
Explaining the chemistry and biochemistry of Acetylsalicylic Acid
Mar 17, 2007
Aspirin is probably one of the best known medicines known in the world. Whenever we have a headache or other pain, it is likely that we will reach for the aspirin. What is this miracle drug? How does it work?
History
The story of Aspirin begins hundred of years ago. It was common knowledge among normal people that chewing the bark of the willow tree eased aches and pains. The father of modern medicine, Hippocrates, wrote about it in the fifth century BC. Through the eighteenth and nineteenth centuries AD, scientists were able to isolate the chemical which had the pain relieving effect. It was called Salicin and a derivative, Salicylic Acid was discovered to have the same properties. This chemical is based on a hexagonal “benzene ring” with two groups added. One is a hydroxyl group (formula –OH) and the other is a carboxylic acid group (-COOH). See introductory article on organic chemistry. The problem with these chemicals was that they caused horrendous digestive problems, so it was necessary to look for a way to make it less harmful.
Acetylsalicylic Acid
Eventually it was discovered that if salicylic acid was reacted with another chemical to change the hydroxyl group on the benzene ring to an acetyl group (-OCOOH), the resulting chemical was less harmful. The chemical is called acetylsalicylic acid (ASA) and it was given the name Aspirin by the company that first made it commercially (Bayer Pharmaceutical)
How does ASA reduce pain and inflammation?
Despite being used since the turn of the century, it wasn’t until the early seventies that it was discovered how aspirin works. ASA binds to an enzyme called cylooxygenase-2 in cells. This is produced in large quantities in cells which are damaged and so cause pain. Without the presence of ASA this enzyme makes chemicals called prostaglandins which send messages to the brain that part of the body is in pain. They also cause the area that has been damaged to release fluid from the blood so that it will swell up or inflame. This protects the damaged cells from further damage by creating a cushion. When aspirin is taken the enzyme is no longer able to make prostaglandins and some of the pain messages don’t get sent to the brain, so we feel less pain. Also the areas don’t inflame as much and inflammation is reduced.
What about the blood?
Recently a new effect of ASA has been discovered. ASA goes into the blood stream and blocks the production of prostaglandins wherever they are formed. This is mainly in areas of damaged cells, but they are also formed in other parts of the body. In the blood stream prostaglandins cause clotting. This is useful when we have a cut or a nose bleed for example, but blood clots also cause heart attacks. This is the reason why many older people take aspirin continually, to prevent blood clots in their blood stream and so reduce the risk of heart attacks.
This is the journey of one chemical from willow bark to wonder drug!
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