Gimeracil (CAS: 103766-25-2)

The combination drug tegafur/gimeracil/oteracil (trade name Teysuno) is used

for the treatment of advanced gastric cancer. It is also being developed for the

treatment of hepatocellular carcinoma.

Mechanism of action

Tegafur is the actual chemotherapeutic agent. It is a prodrug of the active

substance fluorouracil (5-FU).

Gimeracil inhibits the degradation of fluorouracil by reversibly blocking a

 dehydrogenase enzyme. This results in higher 5-FU levels and a prolonged

half-life of the substance.

Oteracil mainly stays in the gut because of its low permeability, where it reduces

the production of 5-FU by blocking the enzyme orotate phosphoribosyltransferase.

Lower 5-FU levels in the gut result in a lower gastrointestinal toxicity.