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Purpose: The aim of this study was to determine the vitreous brimonidine concentration of topically applied brimonidine-Purite 0.15%., Methods: Patients scheduled for a pars plana vitrectomy were invited to participate in this study after institutional review board (IRB) approval was obtained. Each patient was asked to apply brimonidine-Purite (0.15%) drops in the designated eye either every 12 h (b.i.d.; 9 patients) or every 8 h (t.i.d.; 10 patients) for the 2 weeks proceeding scheduled surgery. The importance of the last topical dose being 12 h (b.i.d. group) or 8 h (t.i.d. group) before the scheduled surgery, was emphasized. Four (4) patients served as controls and did not receive any drops. Vitreous (approximately 0.5-1.0 mL) was aspirated prior to opening the infusion line. Specimens were frozen at -68 degrees C until analyzed., Results: In the b.i.d. group, the mean concentration of brimonidine was 16.74 nM+/-10.33 standard deviation (range, 0.42-34.68 nM; median, 16.38); in the t.i.d. group, the mean concentration of brimonidine was 19.16 nM+/-15.40 standard deviation (range, 0.22-39.48 nM; median, 16.98). A significant difference was observed between the (no drug) control vitreous brimonidine levels and b.i.d. or t.i.d. vitreous levels (P<0.01, <0.01, respectively; n=4, 9, and 10, respectively); and in brimonidine levels between t.i.d. phakic patients and t.i.d. patients with posterior chamber lens (P=0.04; n=4 and 6, respectively)., Conclusions: Brimonidine-Purite 0.15%, topically applied b.i.d. or t.i.d. for 2 weeks prior to collection, acquired vitreous levels of brimonidine at or above the 2-nM concentration known to activate the neuroprotective alpha-2 receptor in animals.

Purpose: Adenosine receptors modulate several ocular responses; however, our understanding of factors that influence ocular extracellular adenosine levels is limited. The objective of this study was to evaluate how changes in intraocular pressure (IOP) influence endogenous levels of the purines adenosine and inosine, in the aqueous humor of normal and ocular-hypertensive patients., Patients and Methods: Informed consent was obtained from 51 individuals undergoing cataract extraction or glaucoma surgical procedures. IOP was measured immediately prior to surgery. At the start of the surgical procedure, an aqueous sample of 75-100 microL was obtained. Purine levels were determined by reverse-phase HPLC., Results: In normotensive individuals, mean aqueous adenosine and inosine levels were 5.2 +/- 1.1 and 19.4 +/- 2.2 ng/100 microL, respectively. No significant correlation between IOP and purine concentration was measured in this group. In ocular hypertensive individuals, the mean aqueous adenosine and inosine concentration was significantly elevated when compared to normotensive individuals. In the ocular hypertensive individual, this elevation in adenosine level was significantly correlated with IOP (r(2) = 0.42)., Conclusions: These results demonstrate that in ocular hypertensive individuals, aqueous adenosine concentration is correlated with IOP. As the activation of adenosine receptors can modulate IOP and retinal blood flow, adenosine release during periods of ocular hypertension may play an important role in the physiological responses to elevated IOP.