Dorzolamide hydrochloride

Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.

Trusopt Eye Drops (Merck Sharp & Dohme)
20 mg/mL in 5 mL bottles

Indication: high intraocular pressure
Systemic carbonic anhydrase inhibitors can be used in the treatment of glaucoma(see 'The medical treatment of glaucoma' Aust Prescr 1993;16:34-7). Theyact on the ciliary processes to reduce the secretion of aqueous humor and therefore intraocular pressure. Dorzolamide is a carbonic anhydrase inhibitorwhich can be used topically for ocular hypertension or open angle glaucoma.Eye drops should avoid the adverse effects, such as acidosis and electrolytedisturbances, associated with systemic carbonic anhydrase inhibitors.

One drop of dorzolamide is given 3 times a day. This lowersthe intraocular pressure by 3-5 mmHg. Most of the drug which reaches the systemiccirculation is excreted unchanged in the urine. The drug accumulates in redblood cells during chronic dosing.

In clinical trials, approximately 7% of patients developedpossible allergic reactions such as conjunctivitis. The most common ocularsymptoms were burning, itching, stinging and blurred vision. Dorzolamide isa sulfonamide, so it may be inappropriate for patients who are hypersensitiveto sulfa drugs.

Although dorzolamide can be used as monotherapy, it will probablybe a second-line therapy. If used as an adjunct to an ophthalmic beta blocker,dorzolamide should only be given twice a day.