Oteracil

Oteracil's main role within Teysuno is to reduce the activity of 5-FU within normal gastrointestinal mucosa, and therefore reduce's gastrointestinal toxicity. It functions by blocking the enzyme orotate phosphoribosyltransferase (OPRT), which is involved in the production of 5-FU.

Based on the results of in vitro studies, a part of oteracil is non-enzymatically degraded to 5-azauracil (5-AZU) by gastric fluid, and is then converted to cyanuric acid (CA) in the digestive tract. Only a small amount of oteracil is metabolised in the liver because of its low permeability.

After administration of a single dose of 50 mg Teysuno (expressed as tegafur content), median Tmax for Teysuno components tegafur, gimeracil, and oteracil was 0.5, 1.0, and 2.0 hours, respectively.

Following a single dose of Teysuno, approximately 3.8% to 4.2% of administered tegafur, 65% to 72% of administered gimeracil, and 3.5% to 3.9% of administered oteracil were excreted unchanged in the urine.

Although no intravenous data are available for Teysuno in humans, the volume of distribution could be roughly estimated from the apparent volume of distribution and urinary excretion data as 16 l/m2, 17 l/m2, and 23 l/m2 for tegafur, gimeracil and oteracil, respectively.