Combination Eye Drop to Control Intraocular Pressure

Simbrinza^® is an ophthalmic suspension containing brinzolamide (1%) and brimonidine tartrate (0.2%). This fixed-dose combination product is indicated for adults with ocular hypertension or open-angle glaucoma in whom intraocular pressure is not sufficiently controlled by monotherapy.

Intraocular pressure is normally maintained within the range of 10-21 mmHg. Ocular hypertension occurs when the intraocular pressure is elevated beyond this range. Patients with intraocular hypertension frequently do not experience any signs or symptoms. However, if left untreated, the risk of developing glaucoma is increased. Open-angle glaucoma is the most common form of glaucoma, responsible for at least 90% of cases. Open-angle glaucoma is an insidious condition that can cause irreversible damage to the eye before symptoms are noticed by the patient. The term ‘open-angle’ refers to the angle where the iris and cornea meet. In this condition, the angle remains wide which still allows aqueous humour to flow over the drainage canals of the trabecular meshwork. This is in contrast to the rare and more acute form of glaucoma, angle-closure glaucoma, which should not be treated with Simbrinza^®.

Although glaucoma is a significant and preventable cause of visual impairment and blindness, compliance to therapy is a major issue. Numerous studies demonstrate that adherence is improved when the treatment regimen is simple. Simbrinza^® simplifies dosing for patients by reducing the number of drops required to be instilled in each sitting. The cumulative amount of preservatives and excipients administered to the eye is also minimised which may improve patient tolerance to therapy.

Brinzolamide and brimonidine have different mechanisms of action, yet both reduce the production of aqueous humour from the ciliary process in the eye. Brinzolamide is a carbonic anhydrase inhibitor that reduces the formation of bicarbonate ions. This leads to decreased transport of sodium and fluid across the ciliary epithelium and a reduction of intraocular pressure. Brimonidine is a selective α₂ receptor agonist that causes local vasoconstriction and reduced aqueous humour production. It also increases the uveoscleral outflow of aqueous humour, providing a dual mechanism of action.

Clinical trials demonstrate that brinzolamide and brimonidine combination eye drops have similar efficacy, safety, and side effect profiles to the simultaneous use of separate brinzolamide and brimonidine eye drops. The most common adverse effects reported were ocular hyperaemia and ocular allergic-type reactions.

Simbrinza^® is available on the Pharmaceutical Benefits Scheme (PBS) as a restricted benefit. Its inclusion on the PBS was based on a cost-minimisation basis compared with dorzolamide/timolol and the individual components of Simbrinza^®, as well as favourable safety and efficacy outcomes.