Aspirin and related salicylates are the primary treatment for mild to moderate pain, such as that associated with headache, joint and muscle pain, and dysmenor-rhea. At higher doses aspirin is an effective analgesic in rheumatoid arthritis (see Chapter 36). The analgesic effects of salicylates are thought to be due to the inhibition of prostaglandin synthesis in the periphery and to a less well documented mechanism at cortical areas.
The salicylates are also potent antipyretic agents, with the exception of diflunisal, which is only weakly active. Aspirin acts at two distinct but related sites. It decreases prostaglandin-induced fever in response to pyrogens and induces a decrease in interleukin-1 modulation of the hypothalamic control of body temperature. Thus, the hypothalamic control of body temperature returns, vasodilation occurs, heat dissipates, and fever decreases. Other uses of aspirin include inhibition of platelet aggregation via inhibition of throm-boxanes, which has been shown to decrease the incidence of blood clots, myocardial infarction, and transient ischemic attacks.
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