Fluorouracil with salicylic acid

How it works

Fluorouracil inhibits thymidylate synthase to disrupt DNA synthesis in rapidly dividing atypical keratinocytes, while salicylic acid softens and removes hyperkeratotic surface scale to enhance penetration.

Prescribing in practice

• Expect an intended local inflammatory reaction (erythema, erosion, crusting) at treated lesions; apply only to the keratoses themselves, protecting surrounding healthy skin, and avoid eyes, mucous membranes and broken skin.
• It is contraindicated in pregnancy and breast-feeding because of the cytotoxic fluorouracil component.
• Avoid use in patients with known dihydropyrimidine dehydrogenase deficiency, in whom systemic toxicity risk is increased.

Monitoring

Review treated lesions for the expected reaction and for healing after the course, and reassess any lesion that fails to resolve to exclude malignancy.

Counselling the patient

• A localised reaction with redness and soreness is expected and indicates the treatment is working.
• Apply precisely to the rough patches only and keep it away from the eyes, lips and normal skin.
• Protect treated areas from sunlight during and after the course.

Evidence & guidelines

Topical field therapies including fluorouracil are recommended options for actinic keratosis in line with established dermatology guidance.