Carbonic Anhydrase Inhibitor (Topical) Pregnancy: Caution — limited data

Dorzolamide

Brand names: Trusopt, Cosopt (with timolol)

Adult dose

Dose: 1 drop TDS (monotherapy). Cosopt (dorzolamide 2%/timolol 0.5%): 1 drop BD.

Route: Topical ophthalmic

Frequency: TDS or BD (combination)

Max: 1 drop per eye TDS

For raised intraocular pressure (glaucoma, ocular hypertension). Can be used in patients where beta-blocker eye drops contraindicated (asthma). Sulfonamide derivative — avoid if sulfonamide allergy.

Paediatric dose

Route: Ophthalmic

Frequency: TDS

Max: 1 drop TDS

Concentration: 2% solution drop/ml

Children: specialist paediatric ophthalmology only. Off-label use for congenital/paediatric glaucoma.

Dose adjustments

Renal

Avoid if eGFR <30 — systemic carbonic anhydrase inhibition; accumulation

Hepatic

Caution in hepatic impairment

Clinical pearls

Cosopt (dorzolamide/timolol combination): convenient BD dosing — reduces drops needed vs separate preparations
Apply nasolacrimal occlusion after instilling drops: press medial canthus for 1–2 min — reduces systemic absorption and bitter taste
Avoid in sulfonamide allergy — dorzolamide is a sulfonamide derivative

Contraindications

Sulfonamide allergy
Severe renal impairment (eGFR <30)
Corneal endothelial disease

Side effects

Bitter taste (systemic absorption via nasolacrimal duct)
Burning/stinging on instillation
Corneal oedema (rare)
Systemic effects (rare): metabolic acidosis, renal calculi

Interactions

Oral acetazolamide — additive systemic carbonic anhydrase inhibition
High-dose aspirin — increased salicylate toxicity (carbonic anhydrase interaction)

Monitoring

IOP measurement
Visual acuity and fields
Corneal clarity

Reference: BNFc; BNF; Royal College of Ophthalmologists Glaucoma Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways