Pain and aspirin

3 The aspirin story

As long ago as 400 BC the physician Hippocrates, from the island of Kos (now a popular Greek holiday destination) prescribed a concoction made from willow leaves to help relieve the pain of childbirth. Ever since then (and probably even before) herbal remedies based on the leaves or bark of willow trees have been used for the alleviation of pain and fever. In the 1840s the chemists of the day were able to extract the substance salicin from the bark of willow trees by treating it with boiling water. They isolated and identified salicin and found that it was the active ingredient in the pharmacological action of willow bark. This, then, became the lead compound from which other pain-reducing drugs have been developed, including aspirin, of which millions of tablets are taken annually throughout the world.

In 1870 van Nencki, working at the University of Basle, showed that in the body salicin is converted to salicylic acid. As natural products such as salicin usually only occur in small amounts and are often difficult to synthesise, a common strategy is to find a related compound that can easily be made in large amounts in the laboratory. In this case, salicylic acid looked promising, but treating patients with salicylic acid instead of salicin, whilst affording the same reduction in symptoms, also had the marked disadvantage of causing severe irritation to the mouth, the gullet and the stomach lining – an early example of undesirable side-effects. So this modification of the lead compound salicin was not an improvement. (Salicylic acid can be used to remove warts from the skin, e.g. the preparation sold as ‘Compound W®’ – a solution of salicylic acid in acetic acid. Its ability to destroy tissue is then of use!). Note that the symbol ® means that the name is a registered trade mark.

A further modification was to convert the salicylic acid into sodium salicylate and see what effect this had. This resulted in a compound that still had the same pharmacological properties as salicylic acid but had the advantage of reduced irritation. A new disadvantage appeared, though – it tasted awful!

The German chemist, Felix Hofmann, then set about modifying the structure of salicylic acid. He made one small change at a time and tested each new product on his father who had rheumatism, until in 1898 he arrived at a product that was as effective as salicylic acid, but lacked the severe irritation and taste problems. This new material was given the name aspirin and, after further clinical trials was manufactured and marketed by the company Bayer, as the first medicinal drug to be available in tablet form.