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.

Azopt (Alcon)
10 mg/mL in 5 mL dispensers
Approved indication: raised intraocular pressure
Australian Medicines Handbook Section 11.2.7

Conditions such as open-angle glaucoma cause increases in intraocular pressure which can result in blindness. The intraocular pressure can be reduced by drugs which decrease the production, or increase the outflow, of aqueous humour. Carbonic anhydrase inhibitors reduce the production of aqueous humour and can be given topically. Dorzolamide was the first topical member of the class to be approved in Australia.

Brinzolamide is structurally similar to dorzolamide. It has a high affinity for carbonic anhydrase-II, the predominant form of the enzyme in the eye. After brinzolamide is instilled into the eye, some drug is absorbed into the circulation. It is mainly distributed to the red blood cells. As the half-life of brinzolamidein whole blood is 111 days, it takes 6-9 months for the drug concentrations to reach a steady state. These concentrations are not great enough to interfere with the normal functions of carbonic anhydrase in the body.

During short-term clinical trials a twice-daily dose of brinzolamide 1% has reduced intraocular pressure by approximately 3-5 mmHg. In an 18-month study the mean reductions in intraocular pressure were 2.7-3.9 mmHg with brinzolamide and 4.7-5.6 mmHg with timolol 0.5% (a topical beta blocker).1 Another study compared brinzolamide 1% with dorzolamide 2%, and timolol 0.5% for three months. All three drugs had similar effects on intraocular pressure and there were no significant differences in the efficacy of the two carbonic anhydrase inhibitors.2 Adding brinzolamide to treatment with timolol can produce further reductions in intraocular pressure.

Most of the adverse effects of brinzolamide are related to the instillation of the drops. Patients may develop blurring of vision, and sore or painful eyes. They may also complain of a bitter taste.

Although brinzolamide has been used as monotherapy, the carbonic anhydrase inhibitors are second-line drugs. A three-times daily dose was used in some clinical trials, but 76% of patients will respond adequately to a twice-daily dose of brinzolamide.2 This may give the drug an advantage over dorzolamide which is instilled three times a day. Another advantage is that brinzolamide instillation causes significantly less discomfort.2