Posted by: Andrew Haynes14 OCT 2014
I like my blog postings to include the occasional piece marking a major anniversary relevant to pharmacy. So, during a recent weekend in Chipping Norton, Oxfordshire, I was miffed to discover that last year I missed a 250th anniversary linked to the development of aspirin. But I’ll tell you about it anyway.
Out for a walk in the water meadows one day, Chipping Norton’s vicar, Edward Stone (1702–68), detached and nibbled a piece of willow bark and was struck by its extreme bitterness. Knowing that cinchona bark, the source of quinine, was bitter, he guessed that willow bark might also have therapeutic properties.
Stone believed in the doctrine of signatures — the idea that God marked everything he created with a sign (signature) indicating the purpose of its creation. For example, from the shape of a plant’s leaves, the colour of its flowers, its habitat, etc, one could supposedly determine its role in God’s plan.
Stone reasoned: “As this tree delights in a moist or wet soil where agues [fevers] chiefly abound, the general maxim that many natural maladies carry their cures along with them, or that their remedies lie not far from their causes, was so very apposite to this particular case that I could not help applying it; and that this might be the intention of Providence here, I must own, had some little weight with me.”
Stone went on to treat 50 ague sufferers with doses of 20 grains (about 1.3g) of powdered willow bark in a little water every four hours. He consistently found it to be “very efficacious in curing agues and intermitting disorders”. And so on 25 April 1763 (250 years ago last year) he wrote to the president of the Royal Society of London, the Earl of Macclesfield, describing the bark’s beneficial effects. His letter still survives.
Edward Stone was by no means the first person to use willow bark medicinally: Hippocrates (440–377BC) prescribed it to reduce fever 2,400 years ago. But Stone is the first person known to have conducted a clinical trial, however rudimentary it may have been.
Willow bark, as pharmacists know, contains salicin, a precursor of aspirin. It was to be another 65 years before a French chemist, Henri Leroux, produced pure salicin from the bark. Ten years later, Raffaele Piria, an italian chemist working in Paris, split salicin into a sugar and an aromatic component, salicylaldehyde. By hydrolysis and oxidation he converted the latter to an acid, which he named salicylic acid.
The problem with salicylic acid as a therapeutic agent is its irritant action on the stomach. In 1853, another French chemist, Charles Frédéric Gerhardt, buffered the acid with sodium and treated the resultant sodium salicylate with acetyl chloride to produce acetylsalicylic acid. He then lost interest, but other chemists went on to establish the compound’s chemical structure and devise more efficient methods of synthesis. By the end of the 19th century the German firm Bayer was selling acetylsalicylic acid around the world under its brand name (now a generic name, of course) Aspirin.