Analgesics and Antipyretics

Analgesics are drugs that relieve pain -- the name comes from the Greek word 'algesis', meaning a feeling of pain -- and roughly half of all analgesics work specifically as anti-inflammatory drugs, relieving pain indirectly by reducing the inflammation or swelling that is causing it. A related but distinct category, antipyretics, are drugs used specifically to reduce fever. The chapter traces the historical discovery of this class of drug through a single lineage. For centuries, an extract of the bark of the willow plant (common in Europe) had been known, purely from experience, to relieve pain and reduce fever. In the nineteenth century, chemists isolated and purified the compound actually responsible: salicylic acid, systematically 2-hydroxybenzoic acid -- a benzene ring bearing a -COOH group with a -OH group on the adjacent (ortho) carbon. Salicylic acid itself works, but it also irritates the stomach; chemists found that its acetyl derivative -- aspirin, made by converting the ortho -OH into an ester, -O-CO-CH3 -- retained the pain-relieving and fever-reducing action with markedly fewer side effects, though it still retains some of salicylic acid's stomach-irritating tendency. Because the body metabolises aspirin back toward the active salicylate, it is described in the chapter as a prodrug, and it remains one of the most widely used analgesics even today. A still less problematic pain-killer than aspirin is paracetamol, described in the text simply as 'a phenol': structurally, a benzene ring bearing a -OH group with an -NH-CO-CH3 (acetami …