Effects of Ripasudil Hydrochloride Hydrate-Brimonidine Tartrate Fixed-Dose Combination Using Rho Kinase Inhibitor and...

Background/Objectives: Rho-associated protein kinase inhibitors reduce intraocular pressure (IOP) by enhancing aqueous humor outflow through the trabecular meshwork-Schlemm's canal pathway. However, it remains unclear whether the fixed-dose combination of ripasudil hydrochloride hydrate and brimonidine tartrate (GLAALPHA) enhances conventional aqueous outflow in vivo. Methods: This single-center randomized clinical trial included healthy adult volunteers who received GLAALPHA, a brimonidine tartrate-brinzolamide fixed-dose combination (Ailamide), or brimonidine tartrate monotherapy (Aiphagan) in a crossover sequence. The aqueous column width in the episcleral veins was assessed at baseline and at 2 h (primary outcome) and 8 h using hemoglobin video imaging. Results: Among 24 participants, analyses included 23 GLAALPHA-treated eyes, 21 Ailamide-treated eyes, and 22 Aiphagan-treated eyes. Two hours after instillation, the aqueous column width significantly increased from baseline only in the GLAALPHA group (p = 0.002). The percent increase in the aqueous column width at 2 h was significantly greater with GLAALPHA than with Ailamide (p = 0.039) and not significantly different between GLAALPHA and Aiphagan (p = 0.114). At 8 h, the aqueous column width did not differ from the baseline in any groups. Conclusions: In healthy adult eyes, GLAALPHA significantly increased the aqueous column width in the episcleral veins 2 h after instillation, indicating enhanced conventional aqueous outflow. These findings provide evidence that GLAALPHA promotes trabecular outflow beyond the effects of brimonidine tartrate-containing comparators and offer mechanistic insights into its action.