Effects of topical brimonidine-timolol on injection intervals in patients receiving combination therapy for retinal vein occlusions

Abstract

Purpose : Combination therapy with anti-VEGF agents and dexamethasone implants for retinal vein occlusions (RVOs) is administered approximately every 4 months. Brimonidine-timolol drops primarily decrease the production of aqueous humor, potentially increasing medication retention and decreasing the frequency of combination therapy needed. This study assessed whether patients who used topical brimonidine-timolol had increased time intervals between injections than those who did not.

Methods : This retrospective review studied patients receiving combination therapy to treat RVOs between 2009 and 2016. Duration in days between combination therapy treatments was recorded for patients who were on topical brimonidine-timolol and those who were not. The groups were then divided based on which anti-VEGF agent they received (bevacizumab, ranibizumab, or aflibercept). Independent 2-sample t-tests were used for statistical analysis.

Results : Twenty-nine eyes with 146 injection intervals were assessed in the brimonidine-timolol group, versus 66 eyes with 242 injection intervals in the control group. There was no statistically significant difference in the days between cycles of combination therapy for those using the drops (136.52±70.40 days) and control (137.10±61.22 days) (p=0.93). Subgroup analysis based on the anti-VEGF agent used showed no significant difference in number of days between injections for those with (139.26±90.54) and without (137.55±53.91) drops in the bevacizumab group (p=0.90), and for those with (126.40±54.94) and without drops (137.13±60.42) in the ranibizumab group (p=0.20). Aflibercept was the only group with significantly more days between injections (p=0.04) in those who used drops (175.61±63.75) and those who did not (136.32±74.27).

Conclusions : The use of topical brimonidine-timolol in patients who received combination therapy for RVOs only significantly increased the time interval between injections in patients who received aflibercept. Aflibercept is the only anti-VEGF that also binds placental growth factor (PIGF), and PIGF blockage can decrease diffusion capacity across membranes. This, in combination with the effect of brimonidine-timolol as a primary aqueous suppressant (despite the outflow facilitation of brimonidine), may explain why patients who received aflibercept had longer injection intervals.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.