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Fixed Combination Glaucoma Treatment — CAI + Beta-blocker Pregnancy: §4.6, verbatim: 'COSOPT should not be used during pregnancy.' Dorzolamide — no adequate clinical data in exposed pregnancies; teratogenic effect in rabbits at maternotoxic doses. Timolol — no adequate data in pregnant women; 'Timolol should not be used during pregnancy unless clearly necessary.' Epidemiological studies have not revealed malformative effects but show a risk of intrauterine growth retardation when beta-blockers are given orally, and signs of beta-blockade (bradycardia, hypotension, respiratory distress, hypoglycaemia) have been seen in the neonate when beta-blockers were administered until delivery — 'If this medicinal product is administered until delivery, the neonate should be carefully monitored during the first days of life.' Breast-feeding: it is not known whether dorzolamide is excreted in human milk; beta-blockers are excreted in breast milk, though at therapeutic ophthalmic doses of timolol clinical beta-blockade in the infant is unlikely — 'If treatment with COSOPT is required, then lactation is not recommended.'

Dorzolamide / Timolol Fixed Combination (Cosopt)

Brand names: Cosopt, Cosopt PF (preservative-free)

Cosopt is a topical ophthalmic fixed-dose combination of dorzolamide (a carbonic anhydrase inhibitor) and timolol (a non-selective beta-blocker), used to lower intraocular pressure in open-angle glaucoma and ocular hypertension when a single agent is inadequate.

Adult dose

Dose: Elevated intraocular pressure (IOP) in patients with open-angle glaucoma or pseudoexfoliative glaucoma, when topical beta-blocker monotherapy is not sufficient: one drop of COSOPT in the conjunctival sac of the affected eye(s) two times daily. If another topical ophthalmic agent is being used, COSOPT and the other agent should be administered at least ten minutes apart. Sourced from COSOPT 20 mg/ml + 5 mg/ml eye drops, solution; the preservative-free presentation (Cosopt PF) also named on this page is a separate product and is not covered by this source.
Route: Topical (ophthalmic) — one drop instilled into the conjunctival sac of the affected eye(s). After instillation: 'Close your eye and press the inner corner of the eye with your finger for about two minutes. When using nasolacrimal occlusion or closing the eyelids for 2 minutes, the systemic absorption is reduced. This may result in a decrease in systemic side effects and an increase in local activity.' (§4.2)
Frequency: Two times daily.
Max: One drop in the affected eye(s) twice daily — §4.2 states no higher dose for this indication.
LICENSED INDICATION (§4.1, verbatim and complete): 'Indicated in the treatment of elevated intraocular pressure (IOP) in patients with open-angle glaucoma or pseudoexfoliative glaucoma when topical beta-blocker monotherapy is not sufficient.' PRODUCT SWAP SINCE THE PREVIOUS REVIEW: this page was previously held because the bundle carried only a dorzolamide-ONLY SPC, which stated single-agent regimens and none of the timolol contraindications. The bundle now carries the actual fixed-combination SPC that hold asked for, so both the combination regimen and the beta-blocker contraindications below come from the correct product. HANDLING (§4.2, verbatim): 'Patients should be instructed to wash their hands before use and avoid allowing the tip of the container to come into contact with the eye or surrounding structures. Patients should also be instructed that ocular solutions, if handled improperly, can become contaminated by common bacteria known to cause ocular infections. Serious damage to the eye and subsequent loss of vision may result from using contaminated solutions.' SYSTEMIC ABSORPTION (§4.4): 'Like other topically applied ophthalmic agents timolol is absorbed systemically. Due to beta-adrenergic component, timolol, the same types of cardiovascular, pulmonary and other adverse reactions seen with systemic beta-adrenergic blocking agents may occur.' SULFONAMIDE CLASS EFFECT (§4.4): 'Dorzolamide contains a sulfonamido group, which also occurs in sulfonamides. Therefore, the same types of adverse reactions found with systemic administration of sulfonamides may occur with topical administration, including severe reactions such as Stevens-Johnson syndrome and toxic epidermal necrolysis.' CAUTIONS (§4.4): mild/moderate COPD — use only if the potential benefit outweighs the potential risk; first degree heart block — beta-blockers only with caution, due to their negative effect on conduction time; severe peripheral circulatory disturbance (e.g. severe Raynaud's disease or syndrome); hepatic impairment — not studied, use with caution; cardiovascular disease and hypotension — beta-blocker therapy should be critically assessed and other active substances considered. PAEDIATRIC (§4.2, verbatim): 'Efficacy in paediatric patients has not been established. Safety in paediatric patients below the age of 2 years has not been established.' Some sections of the product information we used were incomplete — check the full SPC.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Reactive airway disease, including bronchial asthma or a history of bronchial asthma, or severe chronic obstructive pulmonary disease
  • Sinus bradycardia, sick sinus syndrome, sino-atrial block, second or third degree atrioventricular block not controlled with pacemaker, overt cardiac failure, cardiogenic shock
  • Severe renal impairment (CrCl < 30 ml/min) or hyperchloraemic acidosis
  • Hypersensitivity to one or both active substances or to any of the excipients listed in section 6.1
  • §4.3 notes: 'The above are based on the components and are not unique to the combination.'

Side effects

  • Approximately 2.4% of patients in clinical studies discontinued because of local ocular adverse reactions, and approximately 1.2% because of local reactions suggestive of allergy or hypersensitivity such as lid inflammation and conjunctivitis
  • Eye disorders with COSOPT — very common: burning and stinging. Common: conjunctival injection, blurred vision, corneal erosion, ocular itching, tearing
  • Eye disorders attributed to the dorzolamide component: eyelid inflammation and eyelid irritation (common); iridocyclitis (uncommon); irritation including redness, pain, eyelid crusting, transient myopia which resolved on discontinuation, corneal oedema, ocular hypotony, choroidal detachment following filtration surgery (rare); foreign body sensation and photophobia (not known)
  • Immune system with COSOPT: signs and symptoms of systemic allergic reactions, including angioedema, urticaria, pruritus, rash and anaphylaxis
  • Nervous system: headache (common with either component); dizziness, syncope, paraesthesia; increase in signs and symptoms of myasthenia gravis, decreased libido, cerebrovascular accident and cerebral ischaemia (attributed to timolol)
  • Psychiatric (timolol component): depression (common); insomnia, nightmares, memory loss (uncommon); hallucination (not known)
  • Metabolism (timolol component): hypoglycaemia
  • Systemic beta-blocker effects: 'Like other topically applied ophthalmic medicines, timolol is absorbed into the systemic circulation. This may cause similar undesirable effects as seen with systemic beta-blocking agents. Incidence of systemic ADRs after topical ophthalmic administration is lower than for systemic administration.'
  • This side-effect list may be incomplete — check the full SPC.

Monitoring

  • Patients with cardiovascular disease should be watched for signs of deterioration of that disease and for adverse reactions (§4.4)
  • Watch for systemic beta-blockade — cardiovascular and pulmonary reactions of the kind seen with systemic beta-blockers may occur; to reduce systemic absorption use nasolacrimal occlusion or eyelid closure for 2 minutes after instillation (§4.2, §4.4)
  • Stop and reassess if signs of serious sulfonamide-type reactions appear, including Stevens-Johnson syndrome and toxic epidermal necrolysis (§4.4)
  • Watch for local ocular allergy or hypersensitivity — lid inflammation and conjunctivitis were the commonest reasons for discontinuation in clinical studies (§4.8)

Clinical monograph

How it works

Dorzolamide reduces aqueous humour production by inhibiting carbonic anhydrase in the ciliary epithelium, while timolol further suppresses aqueous formation through beta-adrenergic blockade; the two complementary mechanisms produce additive pressure lowering.

Prescribing in practice

  • The timolol component carries systemic beta-blockade risk on absorption, so it is contraindicated in asthma, a history of bronchospasm, severe COPD, sinus bradycardia, second- or third-degree AV block and overt heart failure.
  • Dorzolamide is a sulphonamide derivative and may cause hypersensitivity reactions in patients sensitised to sulphonamides.
  • Nasolacrimal occlusion or gentle eyelid closure after instillation reduces systemic absorption of both components.

Monitoring

Monitor intraocular pressure response and review for systemic beta-blocker effects such as bradycardia, bronchospasm and masked hypoglycaemia, particularly in at-risk patients.

Counselling the patient

  • Remove soft contact lenses before instilling and wait before reinserting, as the preservative can be absorbed by lenses.
  • Press gently on the inner corner of the eye for a minute after each drop to limit drug reaching the rest of the body.
  • Report wheeze, breathlessness, a slow heartbeat or unusual fatigue.

Evidence & guidelines

Fixed combinations of dorzolamide and timolol are established second-line options in NICE guidance on glaucoma (NG81) when a single topical agent does not control intraocular pressure.

Reference: NICE NG81 (Glaucoma); MHRA Timolol Safety Warning; SPC Cosopt / Cosopt PF; Confirm identity and dosing against the manufacturer SPC (eMC) and NICE. 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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