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Aspirin (USAN), also known as acetylsalicylic acid, is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as antipyretic to reduce fever, and as an anti-inflammatory medication.
Aspirin is an acetyl derivative of salicylic acid that is a white, crystalline, weakly acidic substance, with a melting point of 135 °C (275 °F). Acetylsalicylic acid decomposes rapidly in solutions of ammonium acetate or of the acetates, carbonates, citrates or hydroxides of the alkali metals. Acetylsalicylic acid is stable in dry air, but gradually hydrolyses in contact with moisture to acetic and salicylic acids. In solution with alkalis, the hydrolysis proceeds rapidly and the clear solutions formed may consist entirely of acetate and salicylate.
The synthesis of aspirin is classified as an esterification reaction. Salicylic acid is treated with acetic anhydride, an acid derivative, causing a chemical reaction that turns salicylic acid's hydroxyl group into an acetyl group, (R-OH -> R-OCOCH3). This process yields aspirin and acetic acid, which is considered a byproduct of this reaction. Small amounts of sulfuric acid (and occasionally phosphoric acid) are almost always used as a catalyst. This method is commonly employed in undergraduate teaching labs.
Formulations containing high concentrations of aspirin often smell like vinegar. This is because aspirin can decompose through hydrolysis in moist conditions, yielding salicylic acid and acetic acid.
Aspirin was the first discovered member of the class of drugs known as nonsteroidal anti-flammatory drugs (NSAIDs), not all of which are salicylates, although they all have similar effects and most have inhibition of the enzyme cyclooxygenase as their mechanism of action. Today, aspirin is one of the most widely used medications in the world, with an estimated 40,000 tonnes it being consumed each year. In countries where Aspirin is a registered trademark owned by Bayer, the generic term is acetylsalicylic acid (ASA).
Aspirin is one of the first-line drugs used in the treatment of migraine, bringing relief in 50-60% of the cases. In general, aspirin works well for dull, throbbing pain; it is ineffective for pain caused by most muscle cramps, bloating, gastric distension and acute skin irritation. Aspirin did not ease pain during cycling exercise, while caffeine, surprisingly, was very effective. Similarly, aspirin, codeine or paracetamol (acetaminophen) were not better than placebo for muscle soreness after exercise.
Aspirin has an antiplatelet effect by inhibiting the production of thromboxane, which under normal circumstances binds platelet molecules together to create a patch over damage of the walls within blood vessels. Aspirin is also used long-term, at low doses, to help prevent heart attacks, strokes, and blood clot formation in people at high risk for developing blood clots. It has also been established that low doses of aspirin may be given immediately after a heart attack to reduce the risk of another heart attack or of the death of cardiac tissue.
The main undesirable side effects of aspirin are gastrointestinal ulcers, stomach bleeding especially in higher doses. In children and adolescents, aspirin is no longer used to control flu-like symptoms or the symptoms of chickenpox or other viral illnesses, because of the risk of Reye’s syndrome.
Aspirin overdose can be acute or chronic. In acute poisoning, a single large dose is taken; in chronic poisoning, higher than normal doses are taken over a period of time. Acute overdose has a mortality rate of 2%. Chronic overdose is more commonly lethal with a mortality rate of 25%; chronic overdose may be especially severe in children. Toxicity is managed with a number of potential treatments including: activated charcoal, intravenous dextrose and normal saline, sodium bicarbonate, and dialysis.