Uridine triacetate is used to treat an overdose of capecitabine or fluorouracil. In addition, it is used as a pyrimidine analog for uridine replacement indicated for the treatment of hereditary orotic aciduria. Following oral administration, uridine triacetate is deacetylated by nonspecific esterases present throughout the body, yielding uridine in the circulation. Uridine competitively inhibits cell damage and cell death caused by fluorouracil. Uridine can be used by essentially all cells to make uridine nucleotides, compensating 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. Adverse reactions occurring in >2% of patients receiving uridine triacetate included vomiting, nausea, and diarrhea. In vitro data showed that uridine triacetate was a weak substrate for P-glycoprotein. Due to the potential for high local (gut) concentrations of the drug after dosing, the interaction of uridine triacetate with orally administered P-gp substrate drugs cannot be ruled out.

Cytarabine is a pyrimidine nucleoside analog. Cytarabine or cytosine arabinoside (Cytosar-U or Depocyt) is a chemotherapy agent used mainly in the treatment of cancers of white blood cells such as acute myeloid leukemia (AML) and non-Hodgkin lymphoma. It also has antiviral and immunosuppressant properties. Cytarabine is an antimetabolite antineoplastic agent that inhibits the synthesis of DNA. It is a cell cycle phase-specific, affecting cells only during the S phase of cell division. Intracellularly, cytarabine is converted into cytarabine-5-triphosphate (ara-CTP), which is the active metabolite. The mechanism of action is not completely understood, but it appears that ara-CTP acts primarily through inhibition of DNA polymerase. Incorporation into DNA and RNA may also contribute to cytarabine cytotoxicity. Cytarabine is cytotoxic to a wide variety of proliferating mammalian cells in culture.The drug has a short plasma half-life, low stability and limited bioavailability. Overdosing of patients with continuous infusions may lead to side effects. Thus, various prodrug strategies and delivery systems have been explored extensively to enhance the half-life, stability and delivery of cytarabine. Alternative, delivery systems of cytarabine have emerged for the treatment of different cancers. The liposomal-cytarabine formulation has been approved for the treatment of lymphomatous meningitis.

Elacytarabine (CP-4055 or araC-5'elaidic acid ester) is a lipid-conjugated derivative of the nucleoside analog cytarabine. Elacytarabine blocks cell division and may kill cancer cells. It is a type of antimetabolite. It was studied in clinical trials for the treatment of solid tumors. In preclinical and clinical studies, elacytarabine has demonstrated both safety and efficacy in acute myeloid leukemia (AML), with noteworthy activity among the cytarabine-refractory AML population. Elacytarabine was granted orphan drug designation status from the European Commission in 2007 and from the US FDA in 2008, with a fast-track approval designation from the FDA in 2010. Elacytarabine development has been discontinued.

Cytosine is a pyrimidine nucleobase, one of the five main bases of nucleic acids. In DNA and RNA cytosine is paired with guanine. Only small amounts of cytosine administered with food are incorporated in DNA. The majority of cytosine is synthesized de-novo starting from carbamoyl phosphate.

Uracil is a common and naturally occurring pyrimidine derivative, one of the four nucleobases in the nucleic acid of RNA In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by it’s methylated form -- thymine. Originally discovered in 1900 by Alberto Ascoli, it was isolated by hydrolysis of yeast nuclein;[4] it was also found in bovine thymus and spleen, herring sperm, and wheat germ. It is a planar, unsaturated compound that has the ability to absorb light. Uracil readily undergoes regular reactions including oxidation, nitration, and alkylation. While in the presence of phenol (PhOH) and sodium hypochlorite (NaOCl), uracil can be visualized in ultraviolet light. Uracil also has the capability to react with elemental halogens because of the presence of more than one strongly electron donating group. Uracil readily undergoes addition to ribose sugars and phosphates to partake in synthesis and further reactions in the body. Uracil becomes uridine, uridine monophosphate (UMP), uridine diphosphate (UDP), uridine triphosphate (UTP), and uridine diphosphate glucose (UDP-glucose). Each one of these molecules is synthesized in the body and has specific functions. Uracil's use in the body is to help carry out the synthesis of many enzymes necessary for cell function through bonding with riboses and phosphates. Uracil serves as allosteric regulator and coenzyme for reactions in the human body and in plants. Uracil can be used for drug delivery and as a pharmaceutical. When elemental fluorine is reacted with uracil, 5-fluorouracil is produced. 5-Fluorouracil is an anticancer drug (antimetabolite) used to masquerade as uracil during the nucleic acid replication process. In combination with Tegafur, uracil used as a chemotherapy drug (called UFT or UFUR) used in the treatment of cancer, primarily bowel cancer. UFT is an anticancer medication composed of a fixed molar ratio (1:4) of tegafur and uracil to be administered with calcium folinate.

Cytarabine is a pyrimidine nucleoside analog. Cytarabine or cytosine arabinoside (Cytosar-U or Depocyt) is a chemotherapy agent used mainly in the treatment of cancers of white blood cells such as acute myeloid leukemia (AML) and non-Hodgkin lymphoma. It also has antiviral and immunosuppressant properties. Cytarabine is an antimetabolite antineoplastic agent that inhibits the synthesis of DNA. It is a cell cycle phase-specific, affecting cells only during the S phase of cell division. Intracellularly, cytarabine is converted into cytarabine-5-triphosphate (ara-CTP), which is the active metabolite. The mechanism of action is not completely understood, but it appears that ara-CTP acts primarily through inhibition of DNA polymerase. Incorporation into DNA and RNA may also contribute to cytarabine cytotoxicity. Cytarabine is cytotoxic to a wide variety of proliferating mammalian cells in culture.The drug has a short plasma half-life, low stability and limited bioavailability. Overdosing of patients with continuous infusions may lead to side effects. Thus, various prodrug strategies and delivery systems have been explored extensively to enhance the half-life, stability and delivery of cytarabine. Alternative, delivery systems of cytarabine have emerged for the treatment of different cancers. The liposomal-cytarabine formulation has been approved for the treatment of lymphomatous meningitis.

Cytarabine ocfosfate (commercial name: Starasid) is a prodrug having stearyl group attached to phosphoric acid at 5' position of arabinose moiety of cytosine arabinoside (Ara-C). This drug is given orally. The mode of action is in the inhibition of DNA synthesis after conversion to Ara-CTP as in Ara-C. The drug is metabolized in the liver, producing the intermediate metabolite, C-C3PCA which is converted to Ara-C gradually. This property results in the maintenance of relatively long time the blood Ara-C levels. This was proved to be active clinically against acute leukemia and MDS.

Cytarabine ocfosfate (commercial name: Starasid) is a prodrug having stearyl group attached to phosphoric acid at 5' position of arabinose moiety of cytosine arabinoside (Ara-C). This drug is given orally. The mode of action is in the inhibition of DNA synthesis after conversion to Ara-CTP as in Ara-C. The drug is metabolized in the liver, producing the intermediate metabolite, C-C3PCA which is converted to Ara-C gradually. This property results in the maintenance of relatively long time the blood Ara-C levels. This was proved to be active clinically against acute leukemia and MDS.