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Alpha Adrenergic Receptor Agonist (Alpha Agonist)

Brimonidine

Brimonidine is now available in two forms: Alphagan 0.2% ophthalmic solution and Alphagan-P 0.15% ophthalmic solution. Very simply, Allergan has replaced the BAK preservative with a much less toxic proprietary preservative, Purite. This is the same non-toxic preservative that is used in their Refresh Tears artificial tear. The 0.15% solution is equally effective to the 0.2% traditional solution.

Generic brimonidine is markedly less expensive than Alphagan-P, and performs equally as well. The FDA made the following key conclusions:

• "The risk/benefit ratio of AlphaganR vs AlphaganR P is essentially the same"
  
• "The differences in adverse events and IOP lowering ability are not clinically significant"
  
• "We find any differences in study results between the two products to be typical of the variability seen in clinical trials and do not find the difference in this case to be clinically significant"

Brimonidine is approved for tid therapy. There is some debate on whether tid or bid dosing is better. While tid administration will give maximum and more uniform IOP reduction, most studies have found that bid administration will adequately reduce IOP in most patients. Because of a distinct “trough” effect at about eight hours, we do dose brimonidine tid when using this drug as monotherapy; however, its use for monotherapy is rarely employed.

We tell the patient to instill the first drop within the first hour upon awakening, and the second drop near bedtime. This does leave a relative gap in coverage in the afternoon hours (when IOP is generally physiologically lower anyway), but hopefully keeps enough drug on-board to suppress the common surge in IOP during the early morning (pre-waking) hours.

We occasionally recommend three minutes of gentle eyelid closure to maximize ocular absorption and effectiveness, and minimize systemic absorption. (We employ this technique in patients on multiple po medications and/or who have poorer health when prescribing adrenergic acting medications, i.e., the beta-blockers and the alpha adrenergic receptor agonists.)

Brimonidine reduces IOP by approximately 20 to 25%. Because of its rapid onset of action, it can be useful in treating acute rises in IOP, such as post-laser spikes and angle closure. Its most commonly-discussed systemic side effects are dry mouth and fatigue. Uveitis was reported in the September 2000 American Journal of Ophthalmology to be a potential late side effect, so be aware of this association. This granulomatous uveitis was seen after about one year of brimonidine therapy, and subsided upon cessation of the drug.

Dr. Louis Pasquale, quoted earlier in this chapter, made another interesting observation in the March/April 2002 issue of Vision and Aging: “The systemic side effects of brimonidine don’t get a lot of attention. A strikingly high number of patients have a great deal of central nervous system-type side effects with this drug, increasing headache, fatigue, inability to sleep at night, dry eye and mouth.”