Fluorouracil (5-FU)

Fluorouracil (5-FU): Uses, Dosage and Side Effects

Overview

• Fluorouracil’s metabolites stop the production of pyrimidine, which blocks DNA from being synthesised and stops it from functioning.

Uses of Fluorouracil (5-FU)

• Treatment of basal cell and squamous cell carcinoma (topically), and systemically in a number of canine carcinomas.
•  Rarely used in small animal practice.

Dose of Fluorouracil (5-FU) in Dogs and Cats

Dogs:

• All uses: 150 mg/m2 i.v. once weekly for 6 weeks or once every 3 weeks when combined with carboplatin.
• In patients that have liver, renal or bone marrow impairment, reduce dose by half.
• Topical use: Apply to affected area q24h.

Cats:

• Do not use.

Side Effects of Fluorouracil (5-FU) in Dogs and Cats

• Leucopenia with a nadir between 7 and 14 days.
• Thrombocytopenia, anaemia, alopecia, hyperpigmentation, dermatitis, cerebellar ataxia, and convulsions.

Contraindications of Fluorouracil (5-FU) in Dogs and Cats

• It can induce potentially fatal neurotoxicity in cats in any form (including topically), so it should not be administered in any way.

Some Notes:

• Cimetidine inhibits the 5-FU metabolism.
• Synergism exists between 5-FU and carboplatin in human oncology, but this combination has not been extensively used in small animals and may be more toxic.
• When administered prior to 5-FU, methotrexate is synergistic, but antagonistic when administered subsequently.
• Vincristine increases 5-FU’s cytotoxicity.