Flucytosine is an antifungal medication. It's commonly used to treat candida and cryptococcus infections. It can be administered orally or intravenously. In almost all cases, it's used together with another antifungal as it's of limited effectiveness on its own.
It has some serious side effects, including suppression of bone marrow, anorexia, diarrhea, nausea, and psychosis. It's contraindicated for pregnant women, although its toxicity is not confirmed. Its effectiveness in children is also questionable.
Although flucytosine is not on patent, the cost of the medication varies greatly in the developed world as there are usually national manufacturing monopolies on the drug. A day's supply in Europe costs about $20 U.S., while a similar supply in the U.S. costs about 100 times that. It's rarely available in the developing world, but where it's available it sells for as little as $2 per dose.
When administered, flucytosine breaks down into other molecules which interfere with the ability of the fungus to build necessary proteins.
Flucytosine is eventually removed by the kidneys. About half the drug in the bloodstream will be eliminated every 3-6 hours, depending on the patient.