Effect of brimonidine tartrate on ocular hemodynamics in healthy volunteers

Brimonidine tartrate ophthalmic solution 0.025% for redness relief: an overview of safety and efficacy

INTRODUCTION

Ocular redness, or conjunctival hyperemia, is a common ophthalmic sign associated with reduced quality of life. For redness without apparent underlying pathology, topical ophthalmic decongestants have been widely used.

AREAS COVERED

Brimonidine tartrate was approved in 2017 as a topical vasoconstrictor at a 0.025% concentration for relief of ocular redness. Since then, investigators have reported on efficacy and safety findings from studies evaluating low-dose brimonidine for reducing ocular redness.

EXPERT OPINION

Brimonidine is highly selective for α₂-adrenergic receptors. Clinical trials have so far shown that the drug in low doses significantly reduces ocular redness in comparison to vehicle for up to 8 hours. Brimonidine-treated eyes did not present side effects of other vasoconstrictors, such as hypotension, cardiac arrhythmia or drowsiness. Ocular adverse events such as allergic reactions and redness rebound were also minimal. In this review, we examine in detail published literature on the mechanism of brimonidine tartrate and its efficacy and safety in relieving conjunctival hyperemia.

Comparative Assessment of Retinal Blood Flow Velocity Changes Following Brimonidine and Brinzolamide Administration Using Retinal Function Imaging

Purpose

Impaired ocular blood flow has been associated with the etiopathogenesis of glaucoma. Topical brimonidine lowers intraocular pressure, a major glaucoma risk factor. However, brimonidine's influence on retinal blood flow remains to be fully elucidated. Our aim was to compare the effect of topical brimonidine and brinzolamide administration on retinal blood flow velocity in second and third order vessels in healthy adults using the retinal function imager.

Methods

In 10 healthy probands between 23 and 32 years of age, one eye was randomly selected to receive 2 treatment rounds with 3 single doses of brimonidine 2 mg/mL and brinzolamide 10 mg/mL at 12-hour intervals each. The fellow eyes served as intra-individual controls. Immediately before the first drop and 2 hours after the last drop of each treatment round, all subjects were examined, including Goldmann tonometry, Pascal tonometry, assessment of retinal blood flow velocity using the retinal function imager, as well as blood pressure and pulse measurements.

Results

Intraocular pressure decreased significantly in treated eyes while remaining stable in control eyes, indicating reliable application of brimonidine and brinzolamide drops. In contrast, retinal blood flow velocities did not demonstrate any significant differences between groups after both treatment rounds.

Conclusions

Neither brimonidine nor brinzolamide appear to alter retinal blood flow velocity in a clinically relevant manner. The slight velocity changes detected in our study are likely physiologic fluctuations. Our findings do not support the rationale of a detrimental effect of topical brimonidine on ocular blood flow and hence brimonidine may be further administered for lowering intraocular pressure with the appropriate caution. However, our study is strongly limited by the small sample size and, thus, further research with larger cohorts of healthy volunteers and patients with glaucoma is needed to confirm the results.

Translational Relevance

The study provides information about the effect of the topically administered antiglaucoma medications brimonidine and brinzolamide on the ocular blood flow and its regulation. The findings indicate that beside the lowering of IOP there is no evidence for an additional effect on the development of glaucoma.

Effects of a Single Dose of Topical Brimonidine 0.15% on Anterior Segment Morphology, Pupil Characteristics, and Choroidal Thickness in Healthy Subjects

PURPOSE

To investigate the effects of a single dose of brimonidine 0.15% on anterior segment morphology, pupil characteristics, and choroidal blood flow in treated and untreated eyes of healthy subjects and to compare the results obtained with those in another healthy volunteer group.

METHODS

Participants were classified as study and control groups. The eyes in the study group were randomized. Only one eye received one drop of brimonidine (treated eyes), and the contralateral eye received single dose of sodium hyaluronate (untreated eyes). In addition, only right eyes of control subjects, who had single dose of sodium hyaluronate to both eyes, were analyzed (control eyes). Anterior segment parameters including central corneal thickness (CCT), aqueous depth, anterior chamber volume, iridocorneal angle (ICA), horizontal anterior chamber diameter, and pupil measurements including scotopic, mesopic, photopic, and dynamic pupil diameters (PDs) were performed with Sirius Scheimpflug camera. Choroidal thickness (CT) measurements were taken with optical coherence tomography. These measurements were taken at baseline and repeated 1 hour after the dosing.

RESULTS

Only the treated eyes had significantly thicker CCT and wider ICA values after instillation of brimonidine. Static and dynamic PD values of treated eyes and even untreated eyes significantly decreased after brimonidine. However, brimonidine has no significant effect on CT measurements.

CONCLUSION

A single dose of brimonidine causes thickening in CCT and widening in ICA values in treated eyes. In addition, it has significant effect to decrease the scotopic, mesopic, photopic, and dynamic PD values in treated and even contralateral eyes while has no effect on choroidal blood flow.

Effects of the Glaucoma Drugs Latanoprost and Brimonidine on Corneal Temperature

Purpose

The aim of this study was to investigate the effects of the glaucoma drugs latanoprost, brimonidine, and the combination of both on the central corneal temperature (CT) of healthy subjects by means of infrared thermography. Changes of the central CT may reflect changes of ocular blood flow.

Methods

Before application and during 2 hours after the application of latanoprost, brimonidine, or the combination of both in one eye, the CT in both eyes of 40 healthy subjects was measured repeatedly.

Results

Brimonidine reduced CT by approximately 0.5°C. This effect was statistically significant (P < 0.0001). Latanoprost, however, had a very small and insignificant influence (P = 0.47). Accordingly, the combination of brimonidine and latanoprost also reduced CT up to 0.5°C, and this effect was statistically significant (P < 0.0001).

Conclusions

Brimonidine, but not latanoprost, had a significant effect on central CT. This cooling effect of brimonidine is most probably due to a drug-induced reduction of blood circulation in the ciliary body and iris and to a certain extent also to a reduction of blood flow in the fundus of the eye.

Translational Relevance

This study shows evidence that thermography of the cornea provides indirect information on the influence of drugs on the blood flow to the anterior segment of the patient's eye.

Neuroprotection in Glaucoma

Glaucoma is a degenerative optic neuropathy characterized by retinal ganglion cell (RGC) loss and visual field defects. It is known that in some glaucoma patients, death of RGCs continues despite intraocular pressure (IOP) reduction. Neuroprotection in the field of glaucoma is defined as any treatment, independent of IOP reduction, which prevents RGC death. Glutamate antagonists, ginkgo biloba extract, neurotrophic factors, antioxidants, calcium channel blockers, brimonidine, glaucoma medications with blood regulatory effect and nitric oxide synthase inhibitors are among compounds with possible neuroprotective activity in preclinical studies. A few agents (such as brimonidine or memantine) with neuroprotective effects in experimental studies have advanced to clinical trials; however the results of clinical trials for these agents have not been conclusive. Nevertheless, lack of compelling clinical evidence has not prevented the off-label use of some of these compounds in glaucoma practice. Stem cell transplantation has been reported to halt experimental neurodegenerative disease processes in the absence of cell replacement. It has been hypothesized that transplantation of some types of stem cells activates multiple neuroprotective pathways via secretion of various factors. The advantage of this approach is a prolonged and targeted effect. Important concerns in this field include the secretion of unwanted harmful mediators, graft survival issues and tumorigenesis. Neuroprotection in glaucoma, pharmacologically or by stem cell transplantation, is an interesting subject waiting for broad and multidisciplinary collaborative studies to better clarify its role in clinical practice.

Effect of brimonidine on retinal vascular autoregulation and short-term visual function in normal tension glaucoma

PURPOSE

To assess whether brimonidine 0.15% alters retinal vascular autoregulation and short-term visual function in normal tension glaucoma patients who demonstrate retinal vascular dysregulation.

DESIGN

Nonrandomized clinical trial.

METHODS

In this prospective study, 46 normal tension glaucoma patients not previously treated with brimonidine underwent retinal vascular autoregulation testing and visual function assessment using frequency doubling technology perimetry and equivalent noise motion sensitivity testing. We measured blood flow in a major temporal retinal artery with subjects seated and then while reclined for 30 minutes. Patients having a change in retinal blood flow with posture change outside the range previously found in healthy subjects were classified as having retinal vascular dysregulation. They were treated with brimonidine 0.15% for 8 weeks and designated for retesting.

RESULTS

Twenty-three patients demonstrated retinal vascular dysregulation at the initial visit. Younger age (P = .050) and diabetes (P = .055) were marginally significant risk factors for retinal vascular dysregulation. After the 8-week course with brimonidine, 14 of the 17 patients who completed the study showed a return of posture-induced retinal blood flow changes to levels consistent with normal retinal vascular autoregulation (P < .0001). We found no significant changes in frequency doubling technology perimetry or in motion detection parameters following treatment with brimondine (P > .09 for all tests performed).

CONCLUSIONS

Brimonidine significantly improved impaired retinal vascular autoregulation in normal tension glaucoma patients, but short-term alteration in visual function could not be demonstrated.

Effects of dorzolamide-timolol and brimonidine-timolol on retinal vascular autoregulation and ocular perfusion pressure in primary open angle glaucoma

PURPOSE

To assess whether dorzolamide 2%-timolol 0.5% (D/T) and/or brimonidine 0.2%-timolol 0.5% (B/T) alters retinal vascular autoregulation (RVA) and seated ocular perfusion pressure (sOPP) in primary open angle glaucoma (POAG) patients who demonstrate retinal vascular dysregulation (RVD) on timolol 0.5% alone.

METHODS

In this prospective, observer-masked, crossover study, 21 POAG patients with untreated intraocular pressure (IOP) >21 mmHg were treated for 6 weeks with timolol 0.5%. Subsequently, we measured inferior temporal retinal artery blood flow in the left eye with subjects seated and then while reclined for 30 min using the Canon Laser Blood Flowmeter. Subjects with a change in retinal blood flow in response to posture change outside of the range previously found in healthy subjects were designated as having RVD and randomized to either D/T or B/T for 6 weeks and re-tested. This was followed by treatment with the opposite medication.

RESULTS

Seven of the 21 subjects demonstrated RVD in response to posture change following timolol 0.5%. Multiple linear regression analysis indicated that lower sOPP was the main determinant of RVD (P=0.033). After treatment with D/T, all 7 converted from RVD to normal RVA status (P=0.001). Four of 6 subjects showed a similar return to normal RVA following B/T (P=0.066). Mid-morning sOPP was 41.1±5.5 mmHg post-timolol, 46.3±6.5 mmHg post-D/T, and 38.6±6.0 mmHg post-B/T (D/T vs. B/T, P=0.026).

CONCLUSIONS

D/T significantly improved RVA in POAG patients exhibiting RVD while on timolol 0.5% alone. D/T also increased sOPP compared to B/T. There was no significant difference (P=0.37) between D/T and B/T in improving RVA.

Effect of brimonidine on retinal blood flow autoregulation in primary open-angle glaucoma

PURPOSE

To determine whether topically applied brimonidine affects the retinal hemodynamic autoregulatory response to posture change in patients with normal tension glaucoma.

METHODS

Six patients with normal tension glaucoma (primary open-angle glaucoma and maximum untreated intraocular pressure <22 mmHg) in each eye were studied. We retrospectively reviewed retinal hemodynamic data acquired when the patients were off and on treatment with brimonidine 0.15% (twice a day, both eyes) during the course of their care. At each testing session, vessel diameter and blood speed at the same site along the inferior temporal retinal artery of 1 eye were measured while sitting, while reclining for 30 min, and again while sitting using a retinal laser Doppler instrument. Blood flow was computed automatically. Brachial artery blood pressure and heart rate were also measured. The Wilcoxon signed rank test was used to assess the statistical significance of the differences in each measured parameter while subjects were on and off brimonidine.

RESULTS

Off brimonidine, the mean blood flow rate increased by 68.0%±34.3% (range: +17% to +108%) after 30 min in reclined posture compared to baseline-seated measures. On brimonidine, the mean blood flow rate increased by 8.9%±16.8% (range: -9.7 to +28.0%) after 30 min in reclined posture compared to baseline-seated measures. The difference in the posture-induced changes for blood flow rate while on brimonidine compared to off brimonidine was statistically significant (P=0.027).

CONCLUSIONS

Off brimonidine, the patients exhibited marked increases in retinal blood flow while reclining. On brimonidine, the hemodynamic changes were consistent with normal autoregulatory control of retinal blood flow.

Update on the role of alpha-agonists in glaucoma management

Glaucoma is the second most common cause of world blindness (following cataract) with estimated cases reaching 79.6 million by 2020. Although the etiology of glaucoma is multi-factorial, intraocular pressure (IOP) is the only modifiable factor in glaucoma management proven to alter the natural course of the disease. Among various classes of IOP-lowering medications currently available, alpha-adrenergic receptor agonists are used either as monotherapy, as second-line therapy, or in fixed combination with beta-blockers. Non-selective adrenergic agonists such as epinephrine and dipivefrin are infrequently used today for the treatment of glaucoma or ocular hypertension, and have been replaced by the alpha-2-selective agonists. The use of apraclonidine for IOP reduction in glaucoma or OHT is limited due to a high rate of follicular conjunctivitis. The alpha-2-selective agonist in use today is brimonidine. The brimonidine-purite formulations are preferred to brimonidine-benzalkonium chloride (BAC) formulations due better tolerability while maintaining similar efficacy. Brimonidine is also effective when used in combination with a beta-blocker. Using brimonidine-timolol fixed combination (BTFC) as first-line therapy has an added potential for neuroprotection. This would be a valuable strategy for glaucoma treatment, for patients who are intolerant of prostaglandin analogs, or for patients where prostaglandin analogues are contraindicated as first-line therapy, such as in patients with inflammatory glaucoma.

[Effect on ocular blood flow of Combigan® versus placebo in patients with ocular hypertension]

PURPOSE

This study was undertaken to compare the ocular haemodynamic effects of Combigan(®) versus placebo in patients with ocular hypertension (OHT).

METHODS

Thirty patients with OHT were included in a controlled, randomised, double blind study in two parallel groups; 15 were randomised to receive Combigan(®) and 15 to receive placebo for a period of 3 months. At baseline and at 3 months retrobulbar blood flowmeasurements of the ophthalmic artery (OA) and central retinal artery (CRA) were taken using colour Doppler imaging(CDI) ultrasound, concurrently with intraocular pressure (IOP).

RESULTS

Combigan(®) significantly reduced IOP after 3 months of treatment (P = 0.001), whereas placebo showed no significant change in IOP. The baseline haemodynamic parameters were similar between treatment and placebo groups. Patients treated with Combigan® showed a statistically significant decrease in CRA resistive index (P = 0.007).

CONCLUSIONS

Patients treated for 3 months with Combigan(®) showed a significant decrease of CRA resistive index that could be explained by the decrease in IOP.

Comparative analysis of the effects of brimonidine and dorzolamide on ocular blood flow velocity in patients with newly diagnosed primary open-angle glaucoma

The aim of this study was to evaluate the effects of brimonidine 0.2% and dorzolamide 2% on the ocular blood flow velocity in patients with newly diagnosed primary open-angle glaucoma (POAG). Forty-four (44) patients with newly diagnosed POAG were included in a prospective, comparative, randomized clinical study. Twenty-six (26) healthy volunteers, whose age and gender matched, were recruited to compare the baseline hemodynamic characteristics of the patients. After a complete eye examination, baseline blood flow velocity measurements of the retrobulbar vessels were made with color Doppler ultrasonography. Patients were randomly assigned to receive either brimonidine 0.2% or dorzolamide 2% for a 3-month period. Blood flow velocity measurements were repeated after 3 months. Both brimonidine and dorzolamide significantly reduced the intraocular pressure. The baseline ophthalmic artery pulsatility index was higher in patients with POAG than control subjects. Whereas there was a significant increase in peak systolic velocity of the central retinal artery, no significant change was observed in the other vessels with brimonidine and dorzolamide treatment. There was little difference, in terms of ocular blood flow velocity, between newly diagnosed glaucoma patients and control subjects. Both topical brimonidine and dorzolamide significantly reduced the intraocular pressure without altering ocular blood flow velocity in patients with newly diagnosed POAG.

Brimonidine evokes heterogeneous vasomotor response of retinal arterioles: diminished nitric oxide-mediated vasodilation when size goes small

Brimonidine, an α2-adrenergic receptor (AR) agonist, has been employed in the treatment of glaucoma due to its beneficial effects on intraocular pressure reduction and neuroprotection. In addition, some studies have implicated that brimonidine might influence ocular blood flow; however, its effect on the retinal microcirculation has not been documented. Herein, we examined the vasomotor action of brimonidine on different branching orders of retinal arterioles in vitro and determined the contribution of the α2-AR subtype and the role of endothelium-derived nitric oxide (NO) in this vasomotor response. First- and second-order retinal arterioles of pigs were isolated, cannulated, and pressurized for functional studies. Videomicroscopic techniques were employed to record diameter changes in response to brimonidine. RT-PCR was performed for detection of α-AR and endothelial NO synthase (eNOS) mRNA in retinal arterioles. All first-order arterioles (82 ± 2 μm ID) dilated dose dependently to brimonidine (0.1 nM to 10 μM) with 10% dilation at the highest concentration. Second-order arterioles (50 ± 1 μm ID) responded heterogeneously with either dilation or constriction. The incidence and magnitude of vasoconstriction were increased with increasing brimonidine concentration. Administration of the NO synthase inhibitor NG-nitro-l-arginine methyl ester abolished the brimonidine-induced vasodilation in first- and second-order arterioles. Regardless of vessel size, vasomotor responses (i.e., vasodilation and vasoconstriction) of retinal arterioles were sensitive to the α2-AR antagonist rauwolscine. Consistent with the functional data, α2A-AR and eNOS mRNAs were detected in retinal arterioles. Collectively, our data demonstrate that brimonidine at clinical doses evokes a consistent NO-dependent vasodilation in first-order retinal arterioles but a heterogeneous response in second-order arterioles. These vasomotor responses are mediated by the activation of α2-AR. It appears that brimonidine, depending on the concentration and vessel size, may alter local retinal blood flow.

The effects of antiglaucoma and systemic medications on ocular blood flow

Based on the body of evidence implicating ocular blood flow disturbances in the pathogenesis of glaucoma, there is great interest in the investigation of the effects of antiglaucoma drugs and systemic medications on the various ocular vascular beds. The primary aim of this article was to review the current data available on the effects of antiglaucoma drugs and systemic medications on ocular blood flow. We performed a literature search in November 2002, which consisted of a textword search in MEDLINE for the years 1968-2002. The results of this review suggest that there is a severe lack of well-designed long-term studies investigating the effects of antiglaucoma and systemic medications on ocular blood flow in glaucomatous patients. However, among the 136 articles dealing with the effect of antiglaucoma drugs on ocular blood flow, only 36 (26.5%) investigated the effects of medications on glaucoma patients. Among these 36 articles, only 3 (8.3%) were long-term studies, and only 16 (44.4%) were double-masked, randomized, prospective trials. Among the 33 articles describing the effects of systemic medications on ocular blood flow, only 11 (33.3%) investigated glaucoma patients, of which only one (9.1%) was a double-masked, randomized, prospective trial. Based on this preliminary data, we would intimate that few antiglaucoma medications have the potential to directly improve ocular blood flow. Unoprostone appears to have a reproducible antiendothelin-1 effect, betaxolol may exert a calcium-channel blocker action, apraclonidine consistently leads to anterior segment vasoconstriction, and carbonic anhydrase inhibitors seem to accelerate the retinal circulation. Longitudinal, prospective, randomized trials are needed to investigate the effects of vasoactive substances with no hypotensive effect on the progression of glaucoma.

The effects of latanoprost and brimonidine on blood flow velocity of the retrobulbar vessels: a 3-month clinical trial

OBJECTIVE

To investigate the effects of topical latanoprost 0.005% and topical brimonidine tartrate 0.2% on retrobulbar blood flow in patients with primary open-angle glaucoma (POAG) and ocular hypertension (OHT).

METHODS

Forty-one consecutive patients with POAG and OHT were enrolled in this prospective, open-label, randomized, parallel study. Patients received either latanoprost 0.005% or brimonidine 0.2% for 3 months. Baseline retrobulbar blood flow measurements of the ophthalmic artery, central retinal artery and temporal short posterior ciliary artery were taken using colour Doppler imaging ultrasound, concurrently with systemic blood pressure, heart rate, ocular perfusion pressure and intraocular pressure (IOP) measurements. These measurements were repeated after 3 months.

RESULTS

Both latanoprost and brimonidine significantly reduced IOP (p < 0.05). While there was a statistically significant increase in peak systolic velocity of the ophthalmic artery, no significant change was observed in the other vessels with latanoprost treatment (p < 0.05). Topical brimonidine did not significantly alter flow velocities or resistive indices in the retrobulbar vessels after 3 months.

CONCLUSION

Topical latanoprost and brimonidine significantly reduced IOP in patients with POAG and OHT without causing significant haemodynamic alterations in the retrobulbar vessels.