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.
Alphagan (Allergan)
2 mg/mL eye drops in 5 mL dropper bottles
Approved indication: glaucoma
Australian Medicines Handbook Section 11.2.2
A variety of drugs are available to treat raised intraocularpressure.1 The options include alpha adrenergic agonists which affect the flow of aqueous humour. Brimonidine is an alpha2 adrenergic agonist. As brimonidine has a selective action, the mydrias is seen with other agonists does not occur.
The drops are instilled twice a day. While the half-life of brimonidine is 3 hours, its effect lasts for at least 12 hours. The absorbed drug is metabolised by the liver and then excreted in the urine.
Clinical studies reveal that brimonidine reduces intraocular pressure by 4-6mmHg. Although this effect has been observed for up to a year of treatment, approximately 8% of patients discontinued brimonidine because their glaucoma was not controlled.
Compared with beta blocking eye drops, adrenergic agonists have more adverse effects. Patients using brimonidine may complain that their eyes are red, burning or stinging and that their vision is blurred. In addition to other ocular adverse effects, including allergic reactions, the patients can have systemic adverse effects such as dry mouth and dizziness. Blood pressure may be reduced and palpitations have been reported.
The product information advises that, because of the preservative used, brimonidine should not be instilled within 10 minutes of other eye drops; however, there are no data to support its use in combination with other treatments for glaucoma. Patients with soft contact lenses should not put them in until at least 15 minutes after using brimonidine because the preservative may be absorbed into the lens.
In view of the comparisons, brimonidine should only be prescribed as monotherapy for patients who cannot take beta blockers for their chronic open angle glaucoma.
