5-Fluorouracil: Topical Use in Dermatology

Overview / Definition5-Fluorouracil (5-FU) is a synthetic pyrimidine analog that serves as a topical chemotherapeutic agent in dermatology. It primarily targets rapidly dividing cells, making it effective against conditions like actinic keratosis and superficial basal cell carcinoma (BCC). 5-FU inhibits the enzyme thymidylate synthase, thereby disrupting DNA synthesis and leading to cell death.Epidemiology5-FU is commonly used in dermatology and is particularly important in populations with high rates of sun exposure, such as individuals with fair skin and those living in sunny climates. The incidence of actinic keratosis is high in older adults, with estimates suggesting that up to 58% of individuals over 40 years may have at least one lesion.Pathophysiology / MechanismThe therapeutic action of 5-FU is primarily through its mechanism as a antimetabolite. It is converted to active metabolites that interfere with RNA and DNA synthesis by:Inhibiting thymidylate synthase.Disrupting RNA processing and function.Causing cellular apoptosis in rapidly dividing cells.This selectivity for proliferating cells makes it effective for treating premalignant and malignant skin lesions.Clinical PresentationPatients treated with 5-FU may present with:Redness and irritation at the application site.Crusting, scaling, and ulceration of the treated areas.Potential for pain or burning during treatment.These local reactions are part of the intended pharmacologic response, indicating that the medication is acting on abnormal skin cells.Diagnosis / WorkupDiagnosis of conditions treated with 5-FU is primarily clinical, based on the appearance of lesions. However, a biopsy may be warranted in cases of:Uncertain diagnosis.Suspected invasive carcinoma.Lack of response to treatment.Dermatoscopy can also assist in characterizing lesions and guiding treatment decisions.Treatment / Management5-FU is typically applied topically in a cream or solution form. The management regimen includes:Application