Antimetabolites masquerade as pyrimidine-like molecules which prevents normal pyrimidines from being incorporated into DNA during the S phase of the cell cycle. Fluorouracil (the end-product of catabolism of floxuridine) blocks an enzyme which converts cytosine nucleosides into the deoxy derivative. In addition, DNA synthesis is further inhibited because fluorouracil blocks the incorporation of the thymidine nucleotide into the DNA strand. Mechanism of action
Floxuridine is rapidly catabolized to 5-fluorouracil, which is the active form of the drug. The primary effect is interference with DNA synthesis and to a lesser extent, inhibition of RNA formation through the drugs incorporation into RNA, thus leading to the production of fraudulent RNA. Fluorouracil also inhibits uracil riboside phosphorylase, which prevents the utilization of preformed uracil in RNA synthesis. As well, the monophosphate of floxuridine, 5-fluoro-2-deoxyuridine-5-phosphate (FUDR-MP) inhibits the enzyme thymidylate synthetase. This leads to the inhibition of methylation of deoxyuridylic acid to thymidylic acid, thus interfering with DNA synthesis. Route of elimination
The drug is excreted intact and as urea, fluorouracil, α-fluoro-β-ureidopropionic acid, dihydrofluorouracil, α-fluoro-β-guanidopropionic acid, and α-fluoro-β-alanine in the urine; it is also expired as respiratory carbon dioxide. Side effects
Side effects include:

Common (30% of patients)
Low blood counts. Your white and red blood cells and platelets may temporarily decrease. This can put you at increased risk for infection, anemia and/or bleeding. Mouth sores
Diarrhea (may be severe)

Less common (10–29% of patients)
Poor appetite
Nausea and vomiting
Hair loss
Elevated liver enzymes (temporary increase in alkaline phosphatase, lactate dehydrogenase, transaminase, and bilirubin). This is seen more with the intra-arterial infusion directly into the liver.
Hand-foot syndrome (Palmar-plantar erythrodysesthesia or PPE) -skin rash, swelling, redness, pain and/or peeling of the skin on the palms of hands and soles of feet
Stomach ulcers (This is seen more with the intra-arterial infusion). Contact your health provider immediately
Fever of 100.4 °F (38 °C) or higher, chills (possible signs of infection). Contact your health provider
Diarrhea (2 episodes in a 24-hour period)
Nausea (interferes with ability to eat and unrelieved with prescribed medication)
Vomiting (vomiting more than 4–5 times in a 24-hour period)
Mouth sores (painful redness, swelling or ulcers)
Unusual bleeding or bruising
Black or tarry stools, or blood in your stools
Blood in the urine
Yellowing of the skin or eyes
Tingling or burning, redness, swelling of the palms of the hands or soles of feet

Other
Fertility for both men and women may be affected by floxuridine. Use in research
Apart from its use in chemotherapy, floxuridine is also used in aging research employing a C. elegans model, namely to stop growth and to prevent reproduction. The latter is brought about by treatment of larvae close to maturity with low doses of floxuridine that, even though allowing normal maturation, causes reproducing individuals to lay eggs that are unable to hatch. This limits the population to a single generation allowing quantification of aging processes and measurement of longevity. It has, however, been indicated that floxuridin exposure by itself increases life expectancy potentially leading to flawed data in respective studies. History
Floxuridine first gained FDA approval in December 1970 under the brand name FUDR.