Aspirin will be 100 years old this October! Aspirin was developed in Germany by a chemical process described by research chemist Felix Hoffman on October 10, 1897. The active ingredient in aspirin, acetyl salicylic acid, is a synthetic derivative of a compound, salicin, which occurs naturally in plants, notably the willow tree. Extracts of willow were traditionally used in folk medicine and as early as 400 BC the Greek physician Hippocrates recommended a brew made from willow leaves to treat labour pains. Later in 1763 an English clergyman, Reverend Edward Stone carried out the first proper scientific study of the herbal medicine when he described the benefits he observed after giving ground up willow bark to 50 parishioners suffering from rheumatic fever.
How aspirin works was a mystery until relatively recently. During the 1970s the British scientist Professor John Vane discovered that it blocked an enzyme needed for the production of natural hormones called prostaglandins involved in many body processes including pain and tissue injury. In 1982 Professor Vane, now Sir John Vane, won the Nobel Prize for Medicine for this work.
The liver appears to be the principal site for salicylate metabolism, although other tissues may also be involved.. The half-life of aspirin in the circulation is from 13 to 19 minutes so that the blood level drops quickly after absorption is complete. However, the half-life of the salicylate ranges between 3.5 and 4.5 hours, which means that 50% of the ingested dose leaves the circulation within that time. [The affect on platelets can be "felt" up to 10 days, which is why patients are asked not to take aspirin for 2 weeks prior to surgery.] Excretion of salicylates occurs principally via the kidneys. Salicylate can be detected in the urine shortly after its ingestion but the full dose requires up to 48 hours for complete elimination.