5-Fluorouracil (Intralesional — Keloid/Scar)

How it works

5-Fluorouracil inhibits thymidylate synthase, disrupting DNA synthesis and selectively suppressing the proliferation of rapidly dividing fibroblasts within the scar.

Prescribing in practice

• It is a cytotoxic agent and must be prepared and administered by trained staff following safe-handling and cytotoxic waste procedures, with avoidance in pregnancy and breastfeeding.
• Often combined with intralesional corticosteroid to improve scar response and reduce injection-site discomfort.
• Local effects include pain, ulceration, hyperpigmentation and tissue necrosis if injected too superficially or at excessive volume.

Monitoring

Monitor the lesion at follow-up for response, ulceration and pigmentary change; systemic monitoring is not usually required given minimal absorption with intralesional use.

Counselling the patient

• Expect some injection-site soreness, redness or temporary skin discolouration.
• Report any open sore, spreading redness or signs of infection at the site.
• Several treatment sessions are usually needed and scars may still recur.

Evidence & guidelines

Intralesional 5-fluorouracil, alone or with corticosteroid, is an established option for refractory keloid and hypertrophic scarring in dermatology and plastic surgery practice.