Dorzolamide

Mechanism of action

✂Carbonic anhydrase IIDorzolamide

ⓘ The figure shows dorzolamide bound to the zinc ion in the active site of human carbonic anhydrase II.

Dorzolamide inhibits carbonic anhydrase II in the ciliary processes. Less bicarbonate is formed, and because aqueous humour secretion depends on it, less fluid is made and intraocular pressure falls. Given as an eye drop it avoids most of the systemic acidosis of oral acetazolamide, but it is still a sulfonamide.

1. Dorzolamide blocks carbonic anhydrase II in the ciliary body
2. Less bicarbonate is formed
3. Less aqueous humour is secreted; pressure falls

Indications

• Open-angle glaucoma Open-angle glaucoma →
• Ocular hypertension

Adverse effects

Common

• Burning or stinging right after the drop
• Bitter taste
• Superficial punctate keratitis
• Allergic eye reactions: conjunctivitis, eyelid reactions
• Blurred vision, tearing, dryness, light sensitivity

Contraindications

• Hypersensitivity to any component
• Not recommended in severe kidney impairment (drug and metabolite leave by the kidney)

Key interactions

Oral carbonic anhydrase inhibitors (acetazolamide)

Additive systemic effects; the combination is not recommended

High-dose salicylates

Acid–base and electrolyte changes may lead to salicylate toxicity, as seen with oral inhibitors

What is monitored

• Intraocular pressure
• Skin rash or signs of a blood disorder (fever, sore throat, bleeding)
• Cornea in patients with low endothelial counts

Administration and safety

• Soft contact lenses come out before the drop and go back in 15 minutes later (benzalkonium chloride).
• Other eye drops are spaced at least 5 minutes apart.
• The dropper tip must not touch the eye, to avoid contaminating the bottle.

Pregnancy and breastfeeding

There are no adequate studies in pregnant women; high oral doses caused vertebral malformations in rabbits, so it is used only if clearly needed.

Nursing care

• Ask about sulfonamide allergy before starting.
• Explain that a bitter taste is common and harmless.
• Teach the patient to report rash, eyelid swelling or red, sticky eyes; the drop is stopped and the eye reviewed.
• Remember that acute angle-closure glaucoma needs more than pressure-lowering drops.

Pharmacokinetics

Absorption

Reaches the systemic circulation after eye drops; plasma levels are usually too low to measure

Distribution

Accumulates in red blood cells bound to carbonic anhydrase II; its metabolite binds carbonic anhydrase I

Elimination

Mostly unchanged in the urine

Half-life

Very long washout from red blood cells (terminal half-life of about four months)

Test yourself

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Connections

← Back to the class: Antiglaucoma agents

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - DORZOLAMIDE HYDROCHLORIDE OPHTHALMIC SOLUTION- dorzolamide hydrochloride solution/ drops (DailyMed (U.S. National Library of Medicine), 2026); Dorzolamide and Timolol Ophthalmic: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); RCSB PDB - 4M2U: Carbonic Anhydrase II in complex with Dorzolamide (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.