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Antimetabolite — Intralesional Scar Treatment Pregnancy: Contraindicated

5-Fluorouracil (Intralesional — Keloid/Scar)

Brand names: Efudix (topical), 5-FU Injection (off-label intralesional use)

Adult dose

Dose: 50 mg/mL solution: 0.1–0.5 mL per cm of scar; combination with triamcinolone: 0.1 mL 5-FU + 0.9 mL triamcinolone 40 mg/mL
Route: Intralesional injection
Frequency: Every 2–4 weeks for 6–12 sessions
Max: 2 mL of 50 mg/mL per session
Off-label use for keloid and hypertrophic scar treatment. Inhibits fibroblast proliferation — reduces collagen overproduction in scars. Most effective in combination with triamcinolone (reduces recurrence rates vs. triamcinolone alone). Standard combination: 0.1 mL 5-FU (50 mg/mL) + 0.9 mL triamcinolone (40 mg/mL).

Paediatric dose

Route:
Seek specialist opinion — limited paediatric data for intralesional use. Cytotoxic agent — use with caution.

Dose adjustments

Renal

Use with caution in renal impairment — systemic absorption from large injections possible.

Hepatic

Use with caution in hepatic impairment — 5-FU hepatically metabolised.

Clinical pearls

  • DPD deficiency testing: MHRA 2020 mandates DPD testing before systemic 5-FU — for intralesional use, risk is much lower but document informed consent
  • Combination therapy superiority: triamcinolone + 5-FU achieves ~70% response vs ~50% for triamcinolone alone in keloids (meta-analysis data)
  • Use cytotoxic handling precautions — wear gloves; dispose of sharps as cytotoxic waste

Contraindications

  • Pregnancy
  • Breastfeeding
  • Bone marrow suppression
  • Dihydropyrimidine dehydrogenase (DPD) deficiency — life-threatening toxicity

Side effects

  • Pain during injection
  • Tissue necrosis at injection site (if extravasated)
  • Hyperpigmentation at injection site
  • Systemic toxicity (rare from intralesional doses — myelosuppression, mucositis if large volumes)

Interactions

  • Warfarin (increases INR — monitor if repeated sessions)
  • Metronidazole (increases 5-FU toxicity)

Monitoring

  • Scar response at each session
  • FBC if multiple large-volume injections
  • INR if on warfarin

Reference: BNFc; BNF 90; MHRA 5-FU DPD Testing Guidance 2020; BAPRAS Keloid Guidelines; Naeini et al. Dermatol Surg 2006. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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