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Topical antifungal (ophthalmic — polyene) Pregnancy: US labelling: animal reproduction studies have not been conducted with natamycin. It is also not known whether natamycin can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. It should be given to a pregnant woman only if clearly needed.

Natamycin 5% Eye Drops

Brand names: Natacyn

Natamycin 5% eye drops are a topical polyene antifungal suspension used to treat fungal keratitis and other fungal infections of the ocular surface, and are a first-line agent for filamentous fungal corneal infection such as Fusarium.

Adult dose

Dose: Fungal keratitis (preferred initial dosage): one drop instilled in the conjunctival sac at hourly or two-hourly intervals; usually reduced to one drop 6 to 8 times daily after the first 3 to 4 days
Route: Topical ophthalmic (instil in the conjunctival sac); shake well before using
Frequency: Hourly or two-hourly initially; usually reduced to 6 to 8 times daily after the first 3 to 4 days
Therapy should generally be continued for 14 to 21 days or until there is resolution of active fungal keratitis. In many cases it may be helpful to reduce the dosage gradually at 4 to 7 day intervals to assure that the replicating organism has been eliminated. Less frequent initial dosage (4 to 6 daily applications) may be sufficient in fungal blepharitis and conjunctivitis. Initial and sustained therapy of fungal keratitis should be determined by the clinical diagnosis, laboratory diagnosis by smear and culture of corneal scrapings, and drug response; whenever possible the in vitro activity of natamycin against the responsible fungus should be determined. The effectiveness of natamycin as a single agent in fungal endophthalmitis has not been established. Safety and effectiveness in paediatric patients have not been established and no paediatric regimen is printed - for children use a children's formulary. No UK SPC for natamycin eye drops is listed on eMC — this dose is from US prescribing information (Natacyn, Eyevance Pharmaceuticals, LLC) and must be verified against UK practice.

Dose adjustments

Renal

Not addressed in the US labelling retrieved for this page.

Hepatic

Not addressed in the US labelling retrieved for this page.

Dose independently re-sourced from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • History of hypersensitivity to any of its components

Side effects

  • Postmarketing events (frequency cannot be estimated): allergic reaction, change in vision, chest pain, corneal opacity, dyspnoea, eye discomfort, eye oedema, eye hyperaemia, eye irritation, eye pain, foreign body sensation, paraesthesia and tearing

Monitoring

  • Clinical response and drug response guide initial and sustained therapy of fungal keratitis
  • Laboratory diagnosis by smear and culture of corneal scrapings; determine the in vitro activity of natamycin against the responsible fungus whenever possible

Clinical monograph

How it works

Natamycin binds ergosterol in the fungal cell membrane, disrupting membrane integrity and causing leakage of cellular contents and fungal cell death.

Prescribing in practice

  • Suspected microbial keratitis is a sight-threatening emergency that should be managed under specialist ophthalmology supervision with corneal scrapes for microscopy and culture before or alongside starting treatment.
  • Penetration into the cornea is limited and poor for deep or intraocular fungal disease, so it is most effective for surface and anterior corneal infection and may need to be combined with or switched to systemic or other antifungals.
  • Shake the suspension well and continue for the full course directed, as fungal keratitis typically requires prolonged treatment with frequent early dosing.

Monitoring

Monitor by repeated slit-lamp examination of the corneal infiltrate and epithelial healing to confirm clinical response.

Counselling the patient

  • Use the drops exactly as frequently as directed, including overnight if instructed early in treatment.
  • Do not wear contact lenses while you have the infection or are using the drops.
  • Attend all follow-up appointments, as fungal eye infections heal slowly and need close review.

Evidence & guidelines

Natamycin is an established first-line topical antifungal for filamentous fungal keratitis, supported by comparative trial evidence (the MUTT studies) favouring it for Fusarium keratitis.

Reference: RCOphth Microbial Keratitis Guidelines; Natacyn SPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Pathways