Fluorouracil
A pyrimidine analog that blocks thymidylate synthase, used for colorectal, breast, stomach and pancreatic cancer.
Also called 5-fluorouracil (common name) or 5-FU (abbreviation).
Drug card
- Class
- Antimetabolite
- How it works
- Inhibiting thymidylate synthase so cells run short of thymidine for DNA
- Used for
- Colorectal cancer
- Breast cancer
- Stomach cancer
- Pancreatic cancer
- Known for
- Bone marrow suppression
- Severe mucositis and mouth sores
- Hand-foot syndrome
- Its name
- -uracil means an uracil derivative (anticancer or antithyroid)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does fluorouracil work?
A uracil analog that cells turn into three active nucleotides: FdUMP inhibits thymidylate synthase, starving the cell of thymidine for DNA, while FUTP and FdUTP are built into RNA and DNA. Dihydropyrimidine dehydrogenase (DPD) breaks it down, so people lacking DPD get severe or fatal toxicity.
Like other antimetabolites: Antimetabolites resemble natural molecules that cells use to build DNA and RNA, such as folate or the pyrimidine bases, closely enough to enter the same pathways. There they block a key enzyme or are built into the nucleic acid, so DNA synthesis fails. Actively dividing tissues feel it most: the tumor, bone marrow, the mouth and gut lining, and a developing fetus.
Uses
What is fluorouracil used for?
- Colorectal cancer
- Breast cancer
- Stomach cancer
- Pancreatic cancer
- Actinic keratoses (as a skin cream)
Side effects
Side effects of fluorouracil
- Bone marrow suppressionKnown forSerious
- Severe mucositis and mouth soresKnown forSerious
- Hand-foot syndromeKnown for
- Severe diarrheaSerious
- Angina and myocardial ischemiaSerious
- Heart failure and arrhythmiasSerious
- Confusion from high ammonia (encephalopathy)Serious
- Cerebellar ataxia and other nerve toxicitySerious
- Nausea and vomiting
- Photosensitivity and darkened skin over veins
- Tear duct narrowing and vision changes
- AnaphylaxisSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Test for DPYD variants before starting unless treatment is urgent; avoid it in complete DPD deficiency.
- It raises the INR with warfarin: monitor INR and prothrombin time closely.
- Withhold it for heart toxicity, severe diarrhea or mucositis, severe hand-foot syndrome, or confusion with high ammonia.
- Uridine triacetate is the antidote for overdose.
Good to know: A cream form treats actinic keratoses and some superficial basal cell carcinomas.
Remember it
A way to remember it
Antimetabolites are counterfeit parts on the DNA production line.
Methotrexate imitates folate and blocks DHFR; fluorouracil imitates uracil and blocks thymidylate synthase. Either way, dividing cells cannot make DNA.
Written for biofideX
Its name
-uracil means uracil derivative (anticancer or antithyroid)
Fluorouracil, an anticancer antimetabolite, and propylthiouracil, an antithyroid drug, share the ending. WHO splits them into -racil and -thiouracil.
- Every drug name stem
Its class
Antimetabolites
Other antimetabolites with a card:
Easily mixed up with alkylating agents, antibacterial folate antagonists and antiproliferative immunosuppressants.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Fluorouracil injection: label (DailyMed)
- Fluorouracil (NCI Thesaurus)
- Fluorouracil Injection (NCI)
- Fluorouracil (Topical) (NCI)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Cancer chemotherapy
Fluorouracil is one of 9 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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