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H1 antihistamine + mast cell stabiliser Pregnancy: Pregnancy: there are no adequate data from the use of ketotifen eye drops in pregnant women. Animal studies using maternally toxic oral doses showed increased pre- and postnatal mortality, but no teratogenicity; systemic levels after ocular administration are much lower than after oral use. Caution should be exercised when prescribing to pregnant women. Breast-feeding: although animal data following oral administration show excretion into breast milk, topical administration to humans is unlikely to produce detectable quantities in breast milk — Zaditen eye drops can be used during lactation. Fertility: there are no data available on the effect of ketotifen fumarate on fertility in humans.

Ketotifen

Brand names: Zaditen

Ketotifen is an antihistamine with mast cell stabilising properties used as eye drops for the treatment of seasonal allergic conjunctivitis.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: SCOPE — this dose is for KETOTIFEN 0.25 mg/ml EYE DROPS (topical ophthalmic use), which is this page's route and brand (Zaditen). Oral ketotifen formulations are different products with their own SPCs and are NOT covered by this source. Topical ocular antihistamine / mast-cell stabiliser treatment — adults, elderly and children aged 3 years and older: one drop of Zaditen into the conjunctival sac twice a day.
Route: Ophthalmic — instilled into the conjunctival sac
Frequency: Twice a day
Max: One drop into the conjunctival sac twice a day — this SPC states no higher dose, no dose escalation and no titration step.
The contents and dispenser remain sterile until the original closure is broken; to avoid contamination do not touch any surface with the dropper tip. If Zaditen is used concomitantly with other eye medications there must be an interval of at least 5 minutes between the two medications. This medicine contains 2.6 micrograms benzalkonium chloride in each drop — benzalkonium chloride may be absorbed by soft contact lenses and may change their colour, so remove contact lenses prior to application and wait at least 15 minutes before reinsertion; it may also cause eye irritation, especially in dry eyes or disorders of the cornea. The use of oral dosage forms of ketotifen may potentiate the effect of CNS depressants, antihistamines and alcohol; although this has not been observed with Zaditen eye drops, the possibility of such effects cannot be excluded. SOURCE COMPLETENESS: the §4.2 posology and §4.3, §4.4/§4.5, §4.6 and §4.8 sections in this bundle were all captured without truncation. The §4.1 indications section was not fetched, so no licensed-indication wording is quoted here beyond the product's pharmacological class.

Paediatric dose

Route: Ophthalmic — instilled into the conjunctival sac
Frequency: Twice a day
Max: One drop twice a day
FIXED DROP DOSE, NOT WEIGHT-BASED — dosePerKg is deliberately null because this SPC expresses the paediatric dose in drops, not per kilogram. Do not derive a per-kg or per-ml figure. CHILDREN AGED 3 YEARS AND OLDER, verbatim §4.2: 'Adults, elderly and children (age 3 and older): one drop of Zaditen into the conjunctival sac twice a day.' The paediatric dose is therefore identical to the adult dose from age 3. UNDER 3 YEARS, verbatim §4.2 Paediatric population: 'The safety and efficacy of Zaditen in children aged from birth to 3 years have not yet been established.' No dose is available for that age group from this source. Verify any use under 3 years against a children's formulary and specialist advice.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients listed in Section 6.1

Side effects

  • Common — eye irritation, eye pain, punctate keratitis, punctate corneal epithelial erosion
  • Uncommon — hypersensitivity, headache, vision blurred (during instillation), dry eye, eyelid disorder, conjunctivitis, photophobia, conjunctival haemorrhage, dry mouth, rash, eczema, urticaria, somnolence
  • Post-marketing, frequency not known — hypersensitivity reactions including local allergic reaction (mostly contact dermatitis, eye swelling, eyelid pruritis and oedema)
  • Post-marketing, frequency not known — systemic allergic reactions including facial swelling/oedema (in some cases associated with contact dermatitis)
  • Post-marketing, frequency not known — exacerbation of pre-existing allergic conditions such as asthma and eczema
  • Post-marketing, frequency not known — dizziness

Monitoring

  • No laboratory or systemic monitoring is specified in this SPC for the ophthalmic route
  • Watch for eye irritation, which may be caused by the benzalkonium chloride preservative — especially in dry eyes or disorders of the cornea
  • Check contact lens use: lenses must be removed before instillation and not reinserted for at least 15 minutes
  • Where other eye medications are co-prescribed, confirm an interval of at least 5 minutes between them

Clinical monograph

How it works

It blocks histamine H1 receptors and stabilises mast cells to reduce the release of inflammatory mediators, relieving the itching, redness and watering of allergic conjunctivitis.

Prescribing in practice

  • Preservatives such as benzalkonium chloride in some formulations can be absorbed by soft contact lenses and cause ocular irritation, so lenses should be removed before instillation and reinserted only after a suitable interval.
  • Transient stinging or burning and, rarely, mild drowsiness may occur.
  • Used for symptomatic relief of allergic conjunctivitis and is generally well tolerated for seasonal use.

Monitoring

No systemic monitoring is required; review symptom control clinically and reassess if symptoms persist or worsen.

Counselling the patient

  • Remove soft contact lenses before instilling and wait the recommended interval before reinserting them.
  • Brief blurring or stinging may occur after instillation, so wait until vision clears before driving.

Evidence & guidelines

Topical antihistamine and mast cell stabilising drops are recommended for allergic conjunctivitis in NICE Clinical Knowledge Summaries.

Reference: 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.

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