Brimonidine eye drops (Alphagan): uses, side effects and cautions

Brimonidine tartrate is an alpha-2 adrenergic agonist. Applied to the eye it lowers intraocular pressure, which is raised in open-angle glaucoma and ocular hypertension. The emc entry for Alphagan 0.2% eye drops states two roles: as the only pressure-lowering drop in people who cannot use a topical beta blocker, and as an extra drug when the target pressure is not reached with one agent.

The recommended adult dose, including older people, is 1 drop in the affected eye or eyes twice daily, about 12 hours apart. To reduce how much is absorbed into the body, press the inner corner of the eye for one minute after each drop. This can reduce body-wide side effects and increase local activity. Avoid touching the dropper tip to any surface.

If you use more than one eye medicine, leave 5 to 15 minutes between them. The preservative, benzalkonium chloride, can discolour soft contact lenses and irritate the eye, so remove lenses before the drop and wait at least 15 minutes before putting them back. It has not been studied in people with liver or kidney impairment, who need caution.

The most commonly reported effects are dry mouth, redness of the eye and burning or stinging, each occurring in about a quarter to a third of patients and usually transient. Headache and fatigue or drowsiness are very common, and blurred vision, itching, a sensation of grit and conjunctival follicles are also common in the eye. Dizziness, abnormal taste, eyelid swelling and redness, tearing, light sensitivity and dry eye are also listed.

An allergic reaction affecting the eye, such as allergic conjunctivitis or swollen, itchy eyelids, occurred in 12.7% of trial participants, with most starting between 3 and 9 months and 11.5% stopping treatment because of it. If an allergic reaction appears, treatment should be stopped, and delayed reactions have been linked with a rise in eye pressure in some cases. Seek medical advice if your eyes become red, swollen or itchy after months of use.

Uncommon effects include depression, palpitations or irregular heartbeat and nasal dryness; very rare ones include insomnia, low or high blood pressure and inflammation inside the eye. Suspected side effects can be reported through the Yellow Card scheme.

Brimonidine must not be used by people allergic to it or its ingredients, by neonates and infants under 2 years, or by people taking monoamine oxidase inhibitors or antidepressants that act on noradrenaline, such as tricyclics and mianserin.

Take care in severe, unstable or uncontrolled cardiovascular disease, depression, poor blood supply to the brain or heart, Raynaud's phenomenon, low blood pressure on standing, and thromboangiitis obliterans. Use caution in dry eye or damaged corneas. Children aged 2 and over, especially ages 2 to 7 or weighing 20 kg or less, need close monitoring because sleepiness is frequent and can be severe.

Alcohol, barbiturates, opioids, sedatives and anaesthetics may add to the sedative effect. Care is advised with medicines that affect how the body handles circulating amines, such as chlorpromazine, methylphenidate and reserpine, and with antihypertensives and heart glycosides, because small falls in blood pressure have been seen. Be cautious when starting or changing medicines that act on adrenergic receptors, such as isoprenaline or prazosin.

Safety in human pregnancy has not been established. Animal studies showed no malformations but at higher exposures showed pre-implantation loss and reduced postnatal growth, so Alphagan should be used in pregnancy only if the benefit to the mother outweighs the risk to the foetus. It is not known whether brimonidine reaches human milk, and the entry says it should not be used by women nursing infants.

Brimonidine can cause tiredness or drowsiness and blurred or abnormal vision, especially at night or in dim light. Wait until these clear before driving or using machinery.