Antiplatelet drugs Acetylsalicylic acid

Most NSAIDs are nonselective inhibitors of cyclooxygenases, acting on both COX 1 and COX 2 isoforms to decrease formation of PGs and thromboxanes. This action is a primary (but not sole) contributor to the pharmacologic actions of NSAIDs. These actions include analgesic, antipyretic, anti-inflammatory, and antiplatelet effects. Acetylsalicylic acid (ASA) is the prototype of the group, which includes more than 20 individual drugs. 

Clinical use Acetylsalicylic acid is the prototype of a nonsteroidal anti-inflammatory drug and is used in a large number of inflammatory and pain indications including musculoskeletal, soft tissue and joint disorders, headache, dysmenorrhoea and fever (Symposium on new perspectives on aspirin therapy 1983, various authors). Furthermore, acetylsalicylic acid is used as an antiplatelet drug in the acute treatment of myocardial infarction in combination with thrombolytics and for the prevention of myocardial infarction and stroke (Patrono, 1994). 

Depending on the assay system, acetylsalicylic acid shows a balanced inhibition of COX-1 and COX-2 or a selectivity towards COX-1. When used in low doses as antiplatelet drug, the main target is COX-1. In addition to a COX inhibition, acetylsalicylic acid modulates the activities of several cellular kinases which may contribute to its antiinflammatory effects (Tegeder et al., 2001). 

Acetylsalicylic acid is usually given by oral administration (0.5-8 g/day) for pain and inflammation and for antiplatelet therapy (75-100 mg/day). It is also available in rectal and topical formulations and as a soluble lysine derivative for intravenous or intramuscular application. Acetylsalicylic acid is often used in multi-drug preparations. The main side-effects are gastrointestinal disorders. Use in children is limited due to the risk of Reye s syndrome (Waldmann et al., 1982). The lithium, magnesium, calcium, and aluminium salts of acetylsalicylic acid are used in some special preparations. 

Mean salicylate concentrations in those who used acetyl-salicylic acid as an analgesic were 8.3 qmol/l in 1985, and 16.5 qmol/l in 1988,1991, and 1998, while salicylate concentrations in subjects who used acetylsalicylic acid as an antiplatelet drug fell from 9.8 pg/ml in 1985 to 7.8 pg/ml in 1988, 3.0 qg/ml in 1991, and 0.8 pg/ml in 1998. This fall in serum salicylate concentrations reflects changes in the usual dose of acetylsalicylic acid. 

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