Uridine triacetate

Uridine triacetate, formerly known as vistonuridine, is an orally active prodrug of the naturally occurring nucleoside uridine. It is used for the treatment of hereditary orotic aciduria (Xuriden), or for the emergency treatment of fluorouracil or capecitabine overdose or toxicity (Vistogard). It is provided in the prodrug form as uridine triacetate as this form delivers 4- to 6-fold more uridine into the systemic circulation compared to equimolar doses of uridine itself.

When used for the treatment or prevention of toxicity associated with fluorouracil and other antimetabolites, uridine triacetate is utilized for its ability to compete with 5-fluorouracil (5-FU) metabolites for incorporation into the genetic material of non-cancerous cells. It reduces toxicity and cell-death associated with two cytotoxic intermediates: 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP) and 5-fluorouridine triphosphate (FUTP). Normally, FdUMP inhibits thymidylate synthase required for thymidine synthesis and DNA replication and repair while FUTP incorporates into RNA resulting in defective strands. As a result, these metabolites are associated with various unpleasant side effects such as neutropenia, mucositis, diarrhea, and hand–foot syndrome. Like many other neoplastic agents, these side effects limit the doses of 5-FU that can be administered, which also affects the efficacy for treatment. By pre-administering with uridine (as the prodrug uridine triacetate), higher doses of 5-FU can be given allowing for improved efficacy and a reduction in toxic side effects ^A18578. It can also be used as a rescue therapy if severe side effects present within 96 hours after initiation of therapy.

Uridine triacetate is also used for the treatment of hereditary orotic aciduria, also known as uridine monophosphate synthase deficiency. This rare congenital autosomal recessive disorder of pyrimidine metabolism is caused by a defect in uridine monophosphate synthase (UMPS), a bifunctional enzyme that catalyzes the final two steps of the de novo pyrimidine biosynthetic pathway. As a result of UMPS deficiency, patients experience a systemic deficiency of pyrimidine nucleotides, accounting for most symptoms of the disease. Additionally, orotic acid from the de novo pyrimidine pathway that cannot be converted to UMP is excreted in the urine, accounting for the common name of the disorder, orotic aciduria. Furthermore, orotic acid crystals in the urine can cause episodes of obstructive uropathy. When administered as the prodrug uridine triacetate, uridine can be used by essentially all cells to make uridine nucleotides, which compensates for the genetic deficiency in synthesis in patients with hereditary orotic aciduria. When intracellular uridine nucleotides are restored into the normal range, overproduction of orotic acid is reduced by feedback inhibition, so that urinary excretion of orotic acid is also reduced.