Fluorouracil

Antineoplastic, Antimetabolite (pyrimidine analog)

Fluorouracil (5-FU)

Efudex (topical), Carac (topical), Fluoroplex (topical); generic IV

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Summary

Classes

Antineoplastic, Antimetabolite (pyrimidine analog)

Common uses

Actinic keratosis (topical)▲0▼, Superficial basal cell carcinoma (topical)▲0▼, Colorectal and other GI malignancies (IV systemic, in regimens)▲0▼, Breast cancer (IV, in regimens)▲0▼

Pharmacy

Starting dose

Topical: 0.5-5% cream/solution to lesions BID × 2-4 weeks; systemic IV: regimen-specific in cancer chemotherapy

Preparations

0.5% (Carac), 1% (Fluoroplex), 5% (Efudex) topical creams/solutions; 50 mg/mL IV

US FDA Max

Topical: nightly; systemic: regimen-specific

Pharmacology

Routes

Topical, IV

Onset

Topical: inflammation, erythema, crusting at 2 weeks; complete response weeks to months after course

Duration

N/A

Half-life

~10-20 minutes systemically (rapid hepatic and erythrocyte dihydropyrimidine dehydrogenase clearance)

Bioavailability

Topical: minimal systemic absorption (oral systemic 5-FU not used due to poor and variable absorption)

Pregnancy

Topical: avoid; systemic: contraindicated in pregnancy.^{[citation needed]}

Legal status

Rx-only in US

Purported mechanism

Fluorouracil is a fluorinated pyrimidine analog incorporated into RNA and converted to fluorodeoxyuridine monophosphate (FdUMP), which covalently inhibits thymidylate synthase and blocks de novo dTMP synthesis; the resulting "thymineless death" is most potent against rapidly dividing cells.▲0▼ Severe systemic toxicity (myelosuppression, mucositis, diarrhea, hand-foot syndrome, neurotoxicity in 5-10%) is amplified in patients with dihydropyrimidine dehydrogenase (DPYD) deficiency; CPIC-supported pre-treatment DPYD genotyping is standard in many oncology centers. Topical actions reproduce the same antimetabolite effect locally with minimal systemic absorption.