Absorption of Brimonidine 0.1% and 0.15% Ophthalmic Solutions in the Aqueous Humor of Cataract Patients

Purpose: To determine and compare the human aqueous humor (AH) concentrations of 2 formulations of brimonidine ophthalmic solution [0.1% brimonidine Purite (BP) (average pH 7.4 to 8.0) and 0.15% BP (average pH 6.6 to 7.4)]. Patients and Methods: Single-center, randomized, controlled, double-masked, prospective study. Twenty-two patients were randomized to receive one 30-mu L drop of 0.1%, (n = 11) or 0.15% BP (n = 11) into the eye requiring routine cataract surgery. Solutions were administered approximately 40 to 55 minutes before surgery and AH samples (100 mu L) were withdrawn from treated eyes at surgery initiation. Times from instillation to sampling were recorded. Brimonidine AH concentrations were assayed by high performance liquid chromatography-tandem mass spectrometry. Results: Mean brimonidine AH concentrations sampled 52 +/- 9 and 54 +/- 8 minutes (P = 0.57) after instillation of 0.1% and 0.15% BP solutions were 59.4 +/- 42.7 and 95.5 +/- 87.5 ng/mL, respectively (P = 0.23). When normalized for concentration differences between the 2 formulations, AH concentrations were similar (P = 0.85). Both solutions were well tolerated with no adverse events observed. Conclusions: Brimonidine AH concentrations in human eyes after single doses of 0.1% or 0.15% BP ophthalmic solutions were proportional to the respective concentrations of the brimonidine formulation instilled. The pH difference between these 2 formulations seemed to exert no effect on brimonidine bioavailability or the tolerability of the solution.