Gout results when there's too much uric acid in the bloodstream. Everyone has some uric acid in the bloodstream already; it occurs naturally as the body breaks down purines, which are chemical compounds that also occur naturally during the process of cell death. Purines are also found in abundance in certain foods, including liver, kidney, anchovies, sardines, mussels, bacon and veal, as well as in alcohol. Those purines must also be broken down into uric acid.
Most people are able to get rid of uric acid just by going to the bathroom; kidneys filter uric acid out of the bloodstream and into urine. However, if that process breaks down, either because your body is producing too much uric acid or because your kidneys can't get rid of it fast enough, then the excess uric acid will build up in the bloodstream and crystallize. As the uric acid forms sharp crystals, resembling needles, white blood cells attack the area, which results in a world of pain, inflammation and tenderness at the spot. Doctors don't know exactly why the big toe is particularly susceptible to these attacks; it may be because the toe and the rest of the foot are already subjected to a good deal of physical stress just by walking [sources: Flieger, Los Angeles Times].
Zyloprim doesn't work to cure that pain, which may last a few days or even a few weeks. Rather, it works to cut uric acid off at the pass, so that it's never formed and there's less of it in your bloodstream. Zyloprim inhibits a chemical known as xanthine oxidase, which is the last form a purine takes before it's converted to uric acid.
When purines are broken down, chemicals known as hypoxanthine and xanthine result. Mix in a little xanthine oxidase, and you'll convert those chemicals to uric acid. By blocking xanthine oxidase, Zyloprim still allows the body to break down those purines, but instead of becoming uric acid, the xanthine and hypoxanthine remain in a form that is essentially recyclable and not harmful to the body.
According to some studies, inhibiting xanthine oxidase may have additional benefits. Xanthine oxide may also play a part in ischemia (inadequate blood flow), heart failure and inflammatory disease [source: Pacher et al.]. However, that's not the current indication for Zyloprim. Find out more about that on the next page.