Salicylic acid is an aromatic compound with antimicrobial, analgesic, anti-inflammatory, antipyretic, and anticoagulant effects. The compound occurs naturally in numerous plant species, but today it can also be produced synthetically. Salicylic acid is known primarily as the starting substance for the production of aspirin.
What is salicylic acid?
Probably the best-known pharmaceutical application of salicylic acid is aspirin. Salicylic acid is a naturally occurring plant compound. In chemical nomenclature, salicylic acid is also called ortho-hydroxybenzoic acid. It consists of a benzene ring with a carboxy group and a hydroxy group. Since it is extracted from the spar plant, among others, the compound is also known as spiric acid. The product name aspirin is derived from this name.
Medical application, effect and use
Plants produce salicylic acid for their own defense system as an antimicrobial and immunoregulatory agent. In the human organism, salicylic acid has not only antimicrobial but also analgesic, anti-inflammatory, antipyretic and anticoagulant effects. It reduces pain and inflammation by interfering with tissue metabolism: in the event of local tissue damage, cells release arachidonic acid. This is enzymatically converted into prostaglandins – signal molecules that cause fever, inflammatory reactions and pain. Salicylic acid blocks the enzyme for the conversion of arachidonic acid and thus also the further chain of reactions. The British pharmacologist John Robert Vane was awarded the Nobel Prize in Medicine in 1982 for the discovery of this blocking mechanism. Salicylic acid also intervenes in blood clotting via precisely this mechanism of action: In simplified terms, blood vessels must contract and platelets must stick together during blood clotting. These processes are also controlled by prostaglandins and thromboxanes. Salicylic acid also blocks the synthesis of the signaling molecules here, so that platelet aggregation proceeds only inadequately.
Herbal, natural, and pharmaceutical salicylic acid.
The beneficial effects of salicylic acid on humans were discovered by the ancient Greeks and the Native Americans: in both cultures, people brewed an analgesic tea from the bark of willows. Even today, willow extracts are used in homeopathy, most commonly for rheumatism, fatigue, ringing in the ears, and deafness. In addition, there are various chemical forms of administration in traditional medicine: probably the best known pharmaceutical application of salicylic acid is aspirin. To produce aspirin, salicylic acid is esterified with acetic anhydride to form acetylsalicylic acid (ASA). ASA-containing preparations are used, among other things, to relieve pain, reduce fever, as an antirheumatic agent and for thrombosis prophylaxis. Numerous other analgesics also contain salicylic acid or acetylsalicylic acid. Salicylic acid can react with bismuth to form bismuth salts – these relieve gastrointestinal complaints such as diarrhea or heartburn. Another field of application is dermatology: in acne therapy, salicylic acid is used as a 5% solution to combat bacteria and excessive keratinization. As a higher-dose solution, it can also dissolve warts and corns. Studies suggest that salicylic acid also prevents various types of cancer. However, this effect is still insufficiently researched. Salicylic acid is used not only in medicines but also in the cosmetics industry: As colorants and fragrances, salicylic acid esters are added to bath additives, creams, ointments and perfumes, for example. They are also contained as UV filters in sun creams. In the past, salicylic acid was also often used as a preservative in foods. However, this is banned nowadays.
Risks and side effects
In higher doses, salicylic acid has a toxic effect. It irritates the skin and mucous membranes to the point of bleeding. It can also cause allergic reactions, hyperacidity, respiratory problems, and kidney damage. Inner ear damage has also been observed. The anticoagulant effect of salicylic acid, which is used in thrombosis prophylaxis, can be life-threatening in the event of bleeding (e.g. after accidents). Medicines containing ASA must not be taken for several days before operations because of the risk of bleeding. Acetylsalicylic acid is considered the more tolerable form of administration of salicylic acid, but it too frequently causes side effects.Gastrointestinal symptoms are particularly typical after chronic oral ingestion of aspirin or related agents. The gastric mucosa produces prostaglandins to regulate gastric acid secretion. When ASA inhibits prostaglandin synthesis, too much gastric acid is produced. The acid attacks the mucosa, causing inflammation, ulcers and bleeding. In extreme cases, blood loss from severe gastric bleeding can even lead to hypovolemic shock and death. With ongoing ASA therapy, oral acid blockers can prevent such gastric problems.
