Dorzolamide with timolol

How it works

Dorzolamide decreases aqueous humour secretion via inhibition of ciliary carbonic anhydrase, and timolol reduces aqueous production through beta-adrenergic blockade, giving additive intraocular pressure reduction.

Prescribing in practice

• Because the timolol component is systemically absorbed, the combination is contraindicated in reactive airways disease (asthma, severe COPD), sinus bradycardia, heart block and uncontrolled heart failure.
• Avoid in patients with sulphonamide hypersensitivity, as dorzolamide is a sulphonamide derivative.
• Use cautiously in severe renal impairment, where systemic dorzolamide accumulation and metabolic acidosis are more likely.

Monitoring

Check intraocular pressure to confirm response and remain alert to systemic beta-blockade, including bradycardia, bronchospasm and blunting of hypoglycaemic warning signs.

Counselling the patient

• Apply gentle pressure to the inner corner of the eye after instilling to minimise systemic absorption.
• Separate this from any other eye drops by a few minutes and instil this preparation last if it is a gel-forming product.
• Seek advice if you develop breathing difficulty, a slow pulse or marked tiredness.

Evidence & guidelines

NICE glaucoma guidance (NG81) supports combination topical therapy when a single intraocular-pressure-lowering agent fails to achieve target pressures.