MEDICAL TREATMENT OF GLAUCOMA 185

The a-adrenergic compounds are characterized by a high allergic-reaction rate. Epinephrine is said to have an allergic rate of 50% by 5 years, and apraclonidine has an allergic rate of approximately 20% by 1 year. Because of its high allergy rate, apraclonidine is used almost exclusively for acute pressure control or to prevent pressure rise after laser procedures. Brimonidine is less likely to cause an allergy, but many patients develop one often months after starting the drug. Yet brimonidine can often be used successfully in

patients that have had a previous allergic reaction to apraclonidine. The newer 0.15% and 0.1% formulation of brimonidine is packaged with a less-allergy-provoking preservative and has a reduced allergic rate.

Due to their high allergy rate and poor pressure lowering effect, epinephrine and dipivefrin are rarely used today. Brimonidine has become an important drug for treating glaucoma. It works as well as a nonselective b-blocker at peak effect, although less well at trough 6–12 hours later, and almost all patients have some reduction in pressure. Aside from allergy, it is well tolerated by the eye. Systemically, it can cause dry mouth and fatigue, which can be debilitating. Brimonidine is contraindicated in infants because it causes CNS depression and apnea. There is also some evidence from animal models of glaucoma that brimonidine may protect ganglion cells from death. There is no evidence of this property in humans, but this drug has sparked interest in treating glaucoma by mechanisms other than pressure reduction.

9.Any tips on prescribing carbonic anhydrase inhibitors (CAIs)?

Topical CAIs took more than 40 years to develop, and were particularly welcome as oral CAIs cause a myriad of side effects. The most common complaints with oral CAIs

are lack of energy and lethargy, lack of appetite and weight loss, nausea and/or an upset stomach, and a metallic taste to foods. The most dangerous side effect is hypokalemia, especially when a CAI is combined with a potassium-reducing diuretic. This combination is dangerous in patients taking digitalis. Depression and aplastic anemia are other serious side effects. The same sort of side effects can be seen with the topical medications, but they are extremely rare. Because complaints are frequent with oral CAIs, most ophthalmologists rarely use them unless there is a need for acute pressure control, or if topical CAIs are not effective. There is no additional benefit to using topical CAIs concurrently with oral CAIs in the same patient. Dorzolamide allows IOP fluctuation when used twice daily. However, twice-daily usage gives an adequate response when combined with a topical b-blocker, which diminishes the wash-out effect of aqueous production. Brimonidine can often be used 2x/day when combined with another aqueous suppressant.

The two topical CAIs are equally effective, but brinzolamide might be a bit less irritating to the eye. Dorzolamide has been reported to augment blood flow to the optic nerve. This may help reduce the impact of free radicals that have been postulated to be a cause of glaucoma.

KEY POINTS: GLAUCOMA TOPICAL MEDICATIONS

1.Allow 5 minutes between drops to prevent one drug from washing the other out of the eye.

2.Punctal occlusion can dramatically reduce systemic side effects of glaucoma drugs.

3.A patient on glaucoma drugs with dry or irritated eyes may be developing a medication allergy. Check the conjunctiva of the lower lid for a follicular reaction.

4.Noncompliance is the most common cause of ineffective medication.