 | Glaucoma: What Every Patient Should Know |  |
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Just as blocking beta adrenergic receptors helps by cutting down aqueous formation, stimulating the other type, alpha receptors, with an agonist helps by speeding water flow out through the uveoscleral pathway, as well as to decrease inflow of aqueous, both combining to lower pressure. There are 3 drugs in this class, only one of which is most commonly used for chronic glaucoma therapy, brimonidine (Alphagan P). Brimonidine both generically and as the brand name Alphagan is available as 0.1%, 0.15% and 0.2% strengths, all seemingly similar in potency. The companies have tried marketing the lower strengths in the hope that the side effects will be lessened without losing the power to lower pressure. Patients should pay attention to which strength they are getting to keep it consistent, though even experts can’t tell any difference in the effects. Generic brimonidine appears a reasonable alternative to the brand.
The drug apraclonidine (Iopidine) was originally approved for very short-term use, but is still occasionally used in the same role as brimonidine. Both have as their biggest possible side effect a frequency of allergic reaction that is significantly higher than all other glaucoma drugs. If a patient is taking 4 kinds of drops and develops an allergy, we always stop the alpha agonist first to see if it clears up and 9 times out of 10 that is the drop causing it. Doctors see this reaction as lumps called follicles on the white part of the eye’s surface covering, the conjunctiva. This was also characteristic of an older alpha drug, dipivefrin (Propine) and all the prior epinephrine group of eye drops in this class used back in the 1960s. Brimonidine rarely causes people to feel like they have to fall asleep even during the daytime, and it is should never be used in, infants or young children. It should also be used carefully in those with dementia. General body reactions that occur with some frequency with brimonidine are a feeling of dryness in the mouth and feeling tired. Theoretically, it could increase heart rate or blood pressure, but this was not found in formal research studies.
There is some possible data that brimonidine has protective effects in glaucoma in addition to its lowering of eye pressure. Unfortunately, the small number of patients studied and the dropout of more than half the brimonidine patients from side effects makes the study less than powerful as proof that this is true. By law, companies can only claim that a drug works for the reasons shown in experiments that they give to the FDA. Thus, it is not correct to say at this time that brimonidine or any other eye drop protects the eye by any mechanism other than lowering the pressure. The law has not prevented drug salespersons from making unfounded claims for their drugs. They know that if they say something often enough, it becomes what you could call “marketing truth.” Say it enough, and people believe it is true, even if the evidence isn’t there. That is to be different from scientific truth, which requires that objective research be done and show that the claimed benefit is real.
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