Peripherally, Aspirin acts by inhibiting the synthesis and release of prostaglandins. Acting centrally it appears to produce analgesia at a hypothalamic site in the brain. The mode of action is not known. Aspirin also acts on the hypothalamus to produce antipyresis.
Heat dissipation is increased as a result of vasodilation and increased peripheral blood flow.
The antipyretic activity may also be related to inhibition of synthesis and release of prostaglandins. Mild to moderate pain or fever, including arthritis , thromboembolic disorders, transient ischemic attacks, rheumatic fever, and post myocardial infarction. 1- 2 hours As a result of rapid hydrolysis, plasma concentrations of aspirin are always low and rarely exceed 20 mg q per ml at ordinary therapeutic doses. Effective analgesia is usually achieved at plasma levels of 15 to 30 mg per 100 ml. 1- 3.5 hrs.