How does aspirin work to bring down a fever?
A fever is one of the body’s mechanisms for fighting infection. Raising the body’s temperature is one way animals have adapted to try to make the environment less hospitable to foreign organisms, like infection-causing bacteria and viruses. Once the body senses an infection, it releases small protein molecules called cytokines, which act as messengers. They travel to a region of the brain called the hypothalamus, which controls the body’s normal temperature “set point.” When the cytokines reach the hypothalamus, they cause an increase in the levels of two enzyme molecules, named cyclooxygenases 1 and 2 (COX1 and COX2). COX1 and COX2 lead to the release of another small protein molecule, prostaglandin E2 (PGE2). When PGE2 is released in the hypothalamus, it causes the body’s temperature set point to increase, leading to a fever.
Aspirin inhibits the activity of COX1 and COX2 and prevents the formation of more PGE2. As the levels of PGE2 in the hypothalamus decrease, the temperature set point returns back toward normal and the fever is resolved.
For more information, please refer to “Antipyretics: Mechanisms of Action and Clinical Use in Fever Suppression” by David M. Aronoff and Eric Neilson, published in The American Journal of Medicine, September 2001, Volume 111, pages 304-315.