Acute versus chronic effects of brimonidine on aqueous humor dynamics in ocular hypertensive patients

Brimonidine blocks glutamate excitotoxicity-induced oxidative stress and preserves mitochondrial transcription factor a in ischemic retinal injury

Glutamate excitotoxicity-induced oxidative stress have been linked to mitochondrial dysfunction in retinal ischemia and optic neuropathies including glaucoma. Brimonindine (BMD), an alpha 2-adrenergic receptor agonist, contributes to the neuroprotection of retinal ganglion cells (RGCs) against glutamate excitotoxicity or oxidative stress. However, the molecular mechanisms of BMD-associated mitochondrial preservation in RGC protection against glutamate excitotoxicity-induced oxidative stress following retinal ischemic injury remain largely unknown. Here, we tested whether activation of alpha 2 adrenergic receptor by systemic BMD treatment blocks glutamate excitotoxicity-induced oxidative stress, and preserves the expression of mitochondrial transcription factor A (Tfam) and oxidative phosphorylation (OXPHOS) complex in ischemic retina. Sprague-Dawley rats received BMD (1 mg/kg/day) or vehicle (0.9% saline) systemically and then transient ischemia was induced by acute intraocular pressure elevation. Systemic BMD treatment significantly increased RGC survival at 4 weeks after ischemia. At 24 hours, BMD significantly decreased Bax expression but increased Bcl-xL and phosphorylated Bad protein expression in ischemic retina. Importantly. BMD significantly blocked the upregulations of N-methyl-D-aspartate receptors 1 and 2A protein expression, as well as of SOD2 protein expression in ischemic retina at 24 hours. During the early neurodegeneration following ischemic injury (12–72 hours), Tfam and OXPHOS complex protein expression were significantly increased in vehicle-treated retina. At 24 hours after ischemia, Tfam immunoreactivity was increased in the outer plexiform layer, inner nuclear layer, inner plexiform layer and ganglion cell layer. Further, Tfam protein was expressed predominantly in RGCs. Finally, BMD preserved Tfam immunoreactivity in RGCs as well as Tfam/OXPHOS complex protein expression in the retinal extracts against ischemic injury. Our findings suggest that systemic BMD treatment protects RGCs by blockade of glutamate excitotoxicity-induced oxidative stress and subsequent preservation of Tfam/OXPHOS complex expression in ischemic retina.

Fixed-combination brimonidine-timolol versus latanoprost in glaucoma and ocular hypertension: a 12-week, randomized, comparison study

OBJECTIVE

To evaluate the intraocular pressure (IOP)-lowering efficacy and safety of fixed-combination brimonidine 0.2%-timolol 0.5% compared with latanoprost 0.005% in patients with glaucoma or ocular hypertension.

RESEARCH DESIGN AND METHODS

This was a prospective, randomized, multicenter, investigator-masked clinical trial. After washout of any previous IOP-lowering medications, patients with IOP of 24 mmHg or higher were randomized to twice-daily fixed-combination brimonidine 0.2%-timolol 0.5% (n = 73) or once-daily latanoprost 0.005% (n = 75, dosed in the evening, with vehicle control in the morning to maintain masking) for 12 weeks. IOP was measured at 8 a.m. (before dosing), 10 a.m., and 3 p.m. at baseline, week 6, and week 12.

CLINICAL TRIAL REGISTRATION

The trial is registered with the identifier 00811564 at http://www.clinicaltrials.gov .

MAIN OUTCOME MEASURES

The primary efficacy endpoint was diurnal IOP (averaged over 8 a.m., 10 a.m., and 3 p.m.) at week 12. Safety measures included biomicroscopy.

RESULTS

There was no statistically significant difference between the treatment groups in mean diurnal IOP at baseline (p = 0.118). At week 12, the mean (SD) diurnal IOP was 17.8 (2.9) mmHg with brimonidine-timolol and 17.9 (3.9) mmHg with latanoprost (p = 0.794). The percentage of patients achieving at least a 20% decrease from baseline diurnal IOP at week 12 was 87.7% in the brimonidine-timolol group and 77.3% in the latanoprost group (p = 0.131). Measured biomicroscopic changes from baseline to week 12 were infrequent in both groups.

CONCLUSIONS

Fixed-combination brimonidine-timolol was as effective as latanoprost in reducing IOP in patients with glaucoma or ocular hypertension. Both treatments demonstrated favorable ocular tolerability. The duration of the study was 12 weeks, and additional studies will be needed to compare the efficacy and safety of fixed-combination brimonidine-timolol and latanoprost during long-term treatment.

Brimonidine tartrate-eudragit long-acting nanoparticles: formulation, optimization, in vitro and in vivo evaluation

In the present study, an effort was made to design prolonged release Eudragit nanoparticles of brimonidine tartrate by double emulsion-solvent evaporation technique for the treatment of open-angle glaucoma. The effect of various formulation variables like initial drug amount, lecithin proportion, phase volume and pH, secondary emulsifier and polymer proportion were studied. Various process variables like energy and duration of emulsification, lyophilization on the characteristics of nanoparticles and in vitro drug release profile were studied. The selected formulations were subjected to in vivo intraocular pressure-lowering efficacy studies by administering aqueous dispersion of nanoparticles into the lower cul de sac of glaucomatous rabbits. The prepared Eudragit-based nanoparticles were found to have narrow particle size range and improved drug loading. The investigated process and formulation variables found to have significant effect on the particle size, drug loading and entrapment efficiency, and in vitro drug release profile of nanoparticles. The selected formulations upon in vivo ocular irritability and tolerability tests were found to be well tolerated with no signs of irritation. In vivo pharmacodynamic efficacy studies revealed that the selected nanoparticle formulations significantly improved the therapy as area under the ∆IOP vs. time curve [AUC((∆IOP vs. t))] showed several fold increase in intensity and duration of intraocular pressure (IOP) decrease. All the selected nanoparticle formulations were found to prolong the drug release in vitro and prolong IOP reduction efficacy in vivo, thus rendering them as a potential carrier in developing improved drug delivery systems for the treatment of glaucoma.

Brimonidine in the treatment of glaucoma and ocular hypertension

Treatment in glaucoma aims to lower intraocular pressure (IOP) to reduce the risk of progression and vision loss. The alpha2-adrenergic receptor agonist brimonidine effectively lowers IOP and is useful as monotherapy, adjunctive therapy, and replacement therapy in open-angle glaucoma and ocular hypertension. A fixed combination of brimonidine and timolol, available in some countries, reduces IOP as effectively as concomitant therapy with brimonidine and timolol and offers the convenience of 2 drugs in a single eyedrop. Brimonidine is safe and well tolerated. Its most common side-effects are conjunctival hyperemia, allergic conjunctivitis, and ocular pruritus. The newest formulation of brimonidine, brimonidine-Purite 0.1%, has a higher pH to improve the ocular bioavailability of brimonidine. This formulation contains the lowest effective concentration of brimonidine and is preserved with Purite(R) to enhance ocular tolerability. Brimonidine-Purite 0.1% is as effective in reducing IOP as the original brimonidine 0.2% solution preserved with benzalkonium chloride. Recent results from preclinical and clinical studies suggest that brimonidine may protect retinal ganglion cells and their projections from damage and death independently of its effects on IOP. The potential for neuroprotection with brimonidine is an added benefit of its use in glaucoma and ocular hypertension.

Inflammatory glaucoma

Glaucoma is seen in about 20% of the patients with uveitis. Anterior uveitis may be acute, subacute, or chronic. The mechanisms by which iridocyclitis leads to obstruction of aqueous outflow include acute, usually reversible forms (e.g., accumulation of inflammatory elements in the intertrabecular spaces, edema of the trabecular lamellae, or angle closure due to ciliary body swelling) and chronic forms (e.g., scar formation or membrane overgrowth in the anterior chamber angle). Careful history and follow-up helps distinguish steroid-induced glaucoma from uveitic glaucoma. Treatment of combined iridocyclitis and glaucoma involves steroidal and nonsteroidal antiinflammatory agents and antiglaucoma drugs. However, glaucoma drugs can often have an unpredictable effect on intraocular pressure (IOP) in the setting of uveitis. Surgical intervention is required in case of medical failure.

Method of Literature Search:

Literature on the Medline database was searched using the PubMed interface.

Brimonidine prevents axonal and somatic degeneration of retinal ganglion cell neurons

BACKGROUND

Brimonidine is a common drug for lowering ocular pressure and may directly protect retinal ganglion cells in glaucoma. The disease involves early loss of retinal ganglion cell transport to brain targets followed by axonal and somatic degeneration. We examined whether brimonidine preserves ganglion cell axonal transport and abates degeneration in rats with elevated ocular pressure induced by laser cauterization of the episcleral veins.

RESULTS

Ocular pressure was elevated unilaterally by 90% for a period of 8 weeks post- cauterization. During this time, brimonidine (1mg/kg/day) or vehicle (phosphate-buffered saline) was delivered systemically and continuously via subcutaneous pump. Animals received bilateral intravitreal injections of fluorescent cholera toxin subunit β (CTB) two days before sacrifice to assess anterograde transport. In retinas from the vehicle group, elevated pressure induced a 44% decrease in the fraction of ganglion cells with intact uptake of CTB and a 14-42% reduction in the number of immuno-labelled ganglion cell bodies, with the worst loss occurring nasally. Elevated pressure also caused a 33% loss of ganglion cell axons in vehicle optic nerves and a 70% decrease in CTB transport to the superior colliculus. Each of these components of ganglion cell degeneration was either prevented or significantly reduced in the brimonidine treatment group.

CONCLUSIONS

Continuous and systemic treatment with brimonidine by subcutaneous injection significantly improved retinal ganglion cell survival with exposure to elevated ocular pressure. This effect was most striking in the nasal region of the retina. Brimonidine treatment also preserved ganglion cell axon morphology, sampling density and total number in the optic nerve with elevated pressure. Consistent with improved outcome in the optic projection, brimonidine also significantly reduced the deficits in axonal transport to the superior colliculus associated with elevated ocular pressure. As transport deficits to and from retinal ganglion cell projection targets in the brain are relevant to the progression of glaucoma, the ability of brimonidine to preserve optic nerve axons and active transport suggests its neuroprotective effects are relevant not only at the cell body, but throughout the entire optic projection.

Efficacy of brimonidine in preventing intraocular pressure spikes following phacoemulsification in glaucoma patients

PURPOSE

To measure intraocular pressure (IOP) elevation 6 and 24 hours after phacoemulsification in patients with glaucoma and to investigate the efficacy of brimonidine tartrate 0.2% in preventing IOP rise on the first postoperative day following cataract surgery.

METHODS

In this prospective randomized single-masked study, 86 eyes of 78 patients with well-controlled open-angle glaucoma were scheduled for phacoemulsification surgery. Patients were randomly assigned into 2 groups. Group A received 1 drop of brimonidine tartrate 0.2% and group B, which served as a control group, received 1 drop of artificial tears. Intraocular pressure was measured at baseline, before surgery, and 6 and 24 hours postoperatively.

RESULTS

Within each group, we found a statistically significant difference in IOP between baseline and 6 hours postoperatively (p<0.01) and between 6 and 24 hours (p<0.01). There was no statistically significant difference between baseline IOP and 24-hour values. Comparing the 2 groups, there was no statistically significant difference in preoperative and 24-hour postoperative IOP. Six hours after surgery, the mean IOP in the brimonidine group was 18.52±4.58 mmHg, compared with 20.86±3.79 mmHg in the control group. Treatment with brimonidine tartrate 0.2% significantly reduced postoperative IOP elevation 6 hours following cataract extraction (p=0.009).

CONCLUSIONS

Patients with medically well-controlled glaucoma may experience a substantial increase in IOP shortly after phacoemulsification surgery. Instillation of brimonidine tartrate 0.2%, although it significantly reduced IOP elevation following cataract operation, did not completely prevent IOP spikes.

Fixed combinations of dorzolamide-timolol and brimonidine-timolol in the management of glaucoma

IMPORTANCE OF THE FIELD

The emergence of fixed-combination drugs for the treatment of glaucoma has, to some extent, changed the medical management of glaucoma. The potential benefits of these drugs include a reduction in the total number of drops and preservatives instilled per day and improved patient comfort factors, which may contribute to better compliance. Combination medications may also improve therapeutic efficacy and play an important role in controlling medication cost. However, the fixed dosing may be a disadvantage in some cases.

AREA COVERED IN THIS REVIEW

This review describes the composition, pharmacokinetics, mode of action, efficacy, side effects, and safety profile of fixed-combination dorzolamide-timolol and fixed-combination brimonidine-timolol.

WHAT THE READER WILL GAIN

Understanding of the pros, cons, and safety profile of two FDA approved fixed-combination antiglaucoma medication.

TAKE HOME MESSAGE

Fixed-combination medications may be a reasonable adjunct to prostaglandins if a large drop in the intraocular pressure (IOP) is desired and adding only one medication is unlikely to reach the target IOP range. Both mentioned drugs are effective in reducing the IOP and further clinical studies will help identify differences in efficacy between the two. The clinician must make an individualized assessment of the medication's risk-benefit profile for each patient.

Reduced expression of Pax6 in lens and cornea of mutant mice leads to failure of chamber angle development and juvenile glaucoma

Heterozygous mutations in PAX6 are causative for aniridia, a condition that is frequently associated with juvenile glaucoma. Defects in morphogenesis of the iridocorneal angle, such as lack of trabecular meshwork differentiation, absence of Schlemm's canal and blockage of the angle by iris tissue, have been described as likely causes for glaucoma, and comparable defects have been observed in heterozygous Pax6-deficient mice. Here, we employed Cre/loxP-mediated inactivation of a single Pax6 allele in either the lens/cornea or the distal optic cup to dissect in which tissues both alleles of Pax6 need to be expressed to control the development of the tissues in the iridocorneal angle. Somatic inactivation of one allele of Pax6 exclusively from epithelial cells of lens and cornea resulted in the disruption of trabecular meshwork and Schlemm's canal development as well as in an adhesion between iris periphery and cornea in juvenile eyes, which resulted in the complete closure of the iridocorneal angle in the adult eye. Structural changes in the iridocorneal angle presumably caused a continuous increase in intraocular pressure leading to degenerative changes in optic nerve axons and to glaucoma. In contrast, the inactivation of a single Pax6 allele in the distal optic cup did not cause obvious changes in iridocorneal angle formation. We conclude that the defects in iridocorneal angle formation are caused by non-autonomous mechanisms due to Pax6 haploinsufficiency in lens or corneal epithelial cells. Pax6 probably controls the expression of signaling molecules in lens cells that regulate the morphogenetic processes during iridocorneal angle formation.

Three-month, randomized, parallel-group comparison of brimonidine-timolol versus dorzolamide-timolol fixed-combination therapy

OBJECTIVE

Fixed combinations of 0.2% brimonidine-0.5% timolol and 2% dorzolamide-0.5% timolol are used to lower intraocular pressure (IOP). The objective of this study was to evaluate the IOP-lowering efficacy and ocular tolerability of brimonidine-timolol compared with dorzolamide-timolol when used as monotherapy or as adjunctive therapy to a prostaglandin analog (PGA) in patients with glaucoma or ocular hypertension.

STUDY DESIGN AND METHODS

Pooled data analysis of two randomized, investigator-masked, 3-month, parallel-group studies with identical protocols (ten sites). In all, 180 patients with open-angle glaucoma or ocular hypertension who were in need of lower IOP received topical brimonidine-timolol BID or dorzolamide-timolol BID as monotherapy (n = 101) or as adjunctive therapy to a PGA (latanoprost, bimatoprost, or travoprost) (n = 79).

CLINICAL TRIAL REGISTRATION

The studies are registered with the identifiers NCT00822081 and NCT00822055 at http://www.clinicaltrials.gov.

MAIN OUTCOME MEASURES

IOP was measured at 10 a.m. (peak effect) at baseline and at months 1 and 3. Tolerability/comfort was evaluated using a patient questionnaire.

RESULTS

There were no statistically significant between-group differences in patient demographics. Most patients were Caucasian, and the mean age was 68 years. There were also no statistically significant differences between treatment groups in baseline IOP. At month 3, the mean (SD) reduction from baseline IOP for patients on fixed-combination monotherapy was 7.7 (4.2) mmHg (32.3%) with brimonidine-timolol versus 6.7 (5.0) mmHg (26.1%) with dorzolamide-timolol (p = 0.040). The mean reduction from PGA-treated baseline IOP for patients on fixed-combination adjunctive therapy was 6.9 (4.8) mmHg (29.3%) with brimonidine-timolol versus 5.2 (3.7) mmHg (23.5%) with dorzolamide-timolol (p = 0.213). Patients on brimonidine-timolol reported less burning (p < 0.001), stinging (p < 0.001), and unusual taste (p < 0.001) than patients on dorzolamide-timolol.

CONCLUSIONS

Fixed-combination brimonidine-timolol provided the same or greater IOP lowering compared with fixed-combination dorzolamide-timolol. Both fixed-combination medications were safe and well-tolerated. Brimonidine-timolol received higher ratings of ocular comfort than dorzolamide-timolol. The duration of the studies was 3 months, and additional studies will be needed to compare the efficacy and tolerability of brimonidine-timolol and dorzolamide-timolol during long-term treatment.

Treatment of patients with primary open-angle glaucoma with a fixed combination of brimonidine 0.2%/timolol 0.5%: multicenter, open-label, observational study in Germany

OBJECTIVE

At the introduction of the fixed-combination of brimonidine/timolol in Germany in 2006, a non-interventional, multicenter, observational, open-label study was initiated to evaluate efficacy, tolerability, and safety of this preparation in a broad patient population.

METHODS

The study population comprised patients with bilateral primary open-angle glaucoma or ocular hypertension with insufficient intraocular pressure (IOP) control who participating physicians determined required a change of medication, and who switched to exclusive use of the new fixed-combination brimonidine 0.2%/timolol 0.5%. Patient demographics and information on specific risk factors were collected. IOP readings were recorded for each eye at treated baseline (previous therapy), 4 to 6 weeks, and 12 weeks after changing to twice-daily brimonidine/timolol. Tolerability was measured using a four-step scale ranging from excellent to poor. All adverse events were recorded.

RESULTS

Mean treated baseline IOP (+/-SD) for all patients (N = 861) was 20.8 +/- 3.5 mmHg. Five hundred sixty-five patients switched from monotherapy, 138 patients switched from other fixed combinations, and 158 patients had been using non-fixed combinations of up to four different active agents. The brimonidine/timolol fixed combination provided an additional IOP decrease in most pretreatment subgroups, with an overall reduction to 16.9 +/- 2.6 mmHg after 4 to 6 weeks and to 16.5 +/- 2.7 mmHg after 12 weeks. Both of these values were significantly lower than baseline IOP (p < 0.001). A target pressure of <18 mmHg was achieved in 79.5% of all eyes at week 12. Tolerability of fixed-combination brimonidine/timolol was rated excellent or good by the physicians for 97.1% of patients, and by 93.4% of the patients themselves. Few adverse events occurred during the treatment period.

CONCLUSIONS

Although this study was limited by its observational design, our results show that the fixed combination of brimonidine 0.2%/timolol 0.5% was effective, well tolerated, and safe in a broad POAG patient population.

Non-systemic delivery of topical brimonidine to the brain: A neuro-ocular tissue distribution study

To date, the risks of central nervous system (CNS) side effects of topically administered ophthalmic therapeutic agents are thought to be the consequence of systemic absorption of these drugs. This paper envisions the possibility of drug delivery to the CNS following ocular application through non-systemic routes. After single instillation of 50 microl of 3H-radiolabeled Alphagan solution (0.2%) in the cul de sac of the right eye, three male albino rabbits (2-2.5 kg) were sacrificed at each time point (5, 15, 30 and 60 min). Both sides (eyes) specimens of aqueous humor, cornea, iris, lens, vitreous, conjunctiva, sclera, ciliary body, choroid, retina, optic nerve, optic tract and olfactory bulb were weighed, and blood samples were measured, before combustion in tissue oxidizer and radioactive liquid scintillation counting. Significant 3H-brimonidine levels were found in right and left optic nerves and tracts with extremely low corresponding drug levels in blood. Uveal tract (ciliary body, iris and choroid tissues) brimonidine levels were relatively high in the treated eye, and the highest among contralateral eye tissues. Our data provide the first case of good CNS availability after ocular application of conventional ophthalmic therapeutic agent, through non-systemic routes. Similar neuro-ocular pharmacokinetic studies should be adopted as a routine ocular therapeutics evaluation study.

Brimonidine-purite 0.1% versus brimonidine-purite 0.15% twice daily in glaucoma or ocular hypertension: a 12-month randomized trial

OBJECTIVE

To compare the safety and intraocular pressure (IOP)-lowering effects of brimonidine-purite 0.1% with the marketed formulation of brimonidine-purite 0.15% (Alphagan P 0.15%) when used twice daily (BID) by patients with glaucoma or ocular hypertension previously treated with brimonidine-purite 0.15% for at least 6 weeks.

METHODS

In a 12-month, randomized, double-masked, multicenter, parallel group, non-inferiority study, patients with glaucoma or ocular hypertension who were treated with brimonidine-purite 0.15% BID were randomly assigned to continue brimonidine-purite 0.15% (n=102) or to administer brimonidine-purite 0.1% (n=105) BID for 12 months. IOP was measured at approximately 8 a.m. (hour 0) and 10 a.m. (hour 2).

MAIN OUTCOME MEASURES

Mean change from baseline IOP and adverse events.

RESULTS

Demographics and baseline characteristics were similar between treatment groups. Treated-baseline mean IOPs at both timepoints were similar between groups (p > or = 0.606). Brimonidine-purite 0.1% provided IOP-lowering that was non-inferior to brimonidine-purite 0.15% at each of the 12 follow-up timepoints, and there were no statistically significant between-group differences at any timepoint. The most commonly reported adverse event was conjunctival hyperemia (13.5% for brimonidine-purite 0.1%; 10.8% for brimonidine-purite 0.15%). No significant differences in the incidence of adverse events were noted between the two formulations.

CONCLUSIONS

Brimonidine-purite 0.1% BID is as effective as brimonidine-purite 0.15% BID in lowering IOP in patients with glaucoma or ocular hypertension who were previously treated with brimonidine-purite 0.15%, and both formulations are well tolerated. Limitations of the study include enrollment of only patients who were already on treatment with brimonidine-purite 0.15%. The 0.1% formulation of brimonidine-purite allows for decreased exposure to brimonidine while providing an IOP-lowering effect comparable to that of the 0.15% formulation. Clinical trial registered at clinicaltrials.gov; identifier: NCT00168363.

Effects of central corneal thickness on the efficacy of topical ocular hypotensive medications

PURPOSE

To determine the effect of central corneal thickness (CCT) on the efficacy of intraocular pressure (IOP)-reducing drugs in patients with ocular hypertension (OHT).

METHODS

This retrospective study analyzed research records of 115 OHT patients and 97 ocular normotensive (ONT) volunteers. CCT was measured by slit-lamp pachymetry and IOP by pneumatonometry. The OHT patients were divided into Thick (>540 microm, n=52) and Thin (<or=540 microm, n=63) Cornea groups. Measurements in the OHT group were made after washout of all IOP-lowering drugs and at 1 week of treatment with latanoprost 0.005%, dorzolamide 2%, brimonidine 0.2%, apraclonidine 0.5%, pilocarpine 2%, or unoprostone 0.15% to 1 eye and vehicle contralaterally. ONT volunteers also were divided into Thick (n=34) and Thin (n=63) Cornea groups. Results were compared between groups using unpaired t tests or nonparametric Wilcoxon tests and within groups using linear regression analyses.

RESULTS

Baseline IOPs were not different between CCT groups of OHT patients or of ONT volunteers. After 1 week of drug treatment, IOP was significantly (P=0.02) lower in the OHT Thin Cornea group (16.0+/-3.0 mm Hg, mean+/-SD) than the OHT Thick Cornea group (17.4+/-2.8 mm Hg). There was a positive correlation between IOP and CCT (R=0.06, P=0.007) in OHT drug-treated eyes, but not OHT vehicle-treated or ONT untreated eyes. The final IOP was significantly lower in the Thin than the Thick Cornea group treated with brimonidine (P=0.02) but not with latanoprost (P=0.91).

CONCLUSIONS

When dosed with IOP lowering drugs, eyes with thinner corneas had lower IOPs than eyes with thicker corneas. This suggests a reduced efficacy of some glaucoma medications in ocular hypertensive patients with thick corneas.

Mechanism of action of bimatoprost, latanoprost, and travoprost in healthy subjects. A crossover study

PURPOSE

To study the effects of 3 prostaglandin analogs, bimatoprost, latanoprost, and travoprost, on aqueous dynamics in the same subjects and to compare techniques of assessing outflow facility.

DESIGN

Experimental study (double-masked, placebo-controlled, randomized paired comparison, 4-period crossover).

PARTICIPANTS

Thirty healthy adult subjects.

METHODS

Bimatoprost, latanoprost, travoprost, or a placebo was administered to the left eye once a day in the evening for 7 days, after a minimum 4-week washout period between each session. Tonographic outflow facility was measured by Schiøtz tonography and pneumatonography on day 7. On day 8, the aqueous humor flow rate and fluorophotometric outflow facility were measured by fluorophotometry. Uveoscleral outflow was calculated from the aqueous humor flow rate and outflow facility using the Goldmann equation.

MAIN OUTCOME MEASURES

Facility of outflow, aqueous humor flow rate, intraocular pressure (IOP), and calculation of uveoscleral outflow.

RESULTS

All medications lowered IOP relative to a placebo. None of the drugs affected aqueous humor production. All medications increased outflow facility compared with placebo when measured by Schiøtz and 2-minute pneumatonography (P< or =0.02); the apparent increase of outflow facility measured with fluorophotometry and 4-minute pneumatonography did not reach statistical significance. In contrast, uveoscleral outflow was significantly increased by all medications when calculated from 4-minute pneumatonography data, and fluorophotometry and Schiøtz data at higher episcleral venous pressures. The apparent increase found with 2-minute pneumatonography did not reach statistical significance. These differing results in the same patients indicate that differences in measurement techniques, and not differences in mechanism of action, explain previous conflicting published reports on the mechanism of action of the prostaglandins.

CONCLUSIONS

Bimatoprost, latanoprost, and travoprost have similar mechanisms of action. All 3 drugs reduce IOP without significantly affecting the aqueous production rate. All drugs increase aqueous humor outflow, either by enhancing the pressure-sensitive (presumed trabecular) outflow pathway or by increasing the pressure-insensitive (uveoscleral) outflow, but the assessment of the amount of flow through each pathway depends upon the measurement technique.

Efficacy and safety of brimonidine and dorzolamide for intraocular pressure lowering in glaucoma and ocular hypertension

BACKGROUND

Brimonidine and dorzolamide are intraocular pressure (IOP)-lowering medications most commonly used in second-line treatment of glaucoma and ocular hypertension.

SCOPE

An evidence-based review of comparative clinical trials of brimonidine and dorzolamide was undertaken to determine the relative efficacy and safety of these drugs in reducing IOP. Using the keywords 'brimonidine' and 'dorzolamide', all articles describing such trials from September 1966 to July 2007 were found in MEDLINE and EMBASE.

FINDINGS

In all identified studies, brimonidine and dorzolamide were both found to provide significant IOP reduction from treated or untreated baseline levels. Results of eight trials reported to date indicate that brimonidine produced either a lower treated IOP or greater pressure reduction from baseline than dorzolamide at one or more measured timepoints, and provided comparable IOP lowering over all other measurements. Differences between the IOP reductions provided by brimonidine and dorzolamide were more pronounced when the medications were used adjunctively with other classes of drugs. Six other trials showed similar efficacy, and one additional monotherapy study showed lower IOP with dorzolamide treatment. Ocular burning was noted with dorzolamide more than any other adverse event with either drug. Trials ranged widely in duration of therapy and the time of day IOP measurements were taken, and many were too small for sufficient statistical power.

CONCLUSION

Brimonidine and dorzolamide are both efficacious and reasonably well tolerated. Possible overall distinctions in efficacy were obscured by differences in study designs and treatment regimens, but adjunctive therapy with brimonidine may reduce IOP as effectively or more effectively than adjunctive or fixed combination dorzolamide therapy. In certain patients with glaucoma and ocular hypertension brimonidine may be a better choice than dorzolamide for second-line treatment.

Combination Products Today: An Update on a New Fixed Combination

Combigan® is a fixed combination made up of brimonidine tartrate (0.2%) and timolol (0.5%, as maleate), two commonly used intraocular pressure (IOP)-lowering agents with complementary mechanisms of action. This paper describes Combigan safety and efficacy studies undertaken for US and European regulatory approval. The studies show that Combigan produces no unexpected adverse effects and that the fixed combination has non-inferiority to the unfixed combination of the same two agents. Phase III trials in the United States and Europe have demonstrated that Combigan lowers IOP more effectively than either of the two agents alone. Allergic conjunctivitis seems to occur less frequently (half the incidence) with Combigan than with brimonidine (Alphagan®) alone. Overall, Combigan shows similar efficacy and safety to concomitant brimonidine and timolol, and superior efficacy to either agent alone, with a favorable benefit-to-risk ratio.

Fixed-combination and emerging glaucoma therapies

Ocular hypotensive agents are the only approved pharmacotherapy for glaucoma. Despite significant advances during the past two decades, a large proportion of glaucoma patients require more than one drug. The most recent additions to the armamentarium of antiglaucoma drugs are fixed-combination products for the glaucoma patient who is insufficiently responsive to monotherapy. Fixed-combination products have the combined efficacy of two ocular hypotensive drugs, and the convenience of a two-drug treatment regimen in a single container, which may aid patient adherence to treatment. Available fixed-combination products consist of timolol 0.5% as an invariant with brimonidine 0.2%, dorzolamide 2%, travoprost 0.004%, latanoprost 0.005% or bimatoprost 0.03%. Research on more advanced antiglaucoma medications continues. Promising new directions appear to be the Rho-kinase inhibitors, microtubule-disrupting agents, serotonergics and cannabimimetics. Efforts continue to improve existing antiglaucoma drugs in an attempt to design second-generation cholinomimetics, adrenergics, prostaglandins and prostamides.

Intravenous administration of clonidine reduces intraocular pressure and alters ocular blood flow

AIM

To evaluate the effect of intravenously administered clonidine on ocular blood flow in healthy volunteers.

METHODS

A randomised, double-masked, placebo-controlled, two-way crossover study was performed in 12 healthy young volunteers. Clonidine (0.2 microg/kg/min) or placebo was administered intravenously over 10 minutes. The effects of clonidine were studied at baseline and up to 150 minutes after infusion. Ocular haemodynamics were measured using laser Doppler flowmetry, laser Doppler velocimetry and a retinal vessel analyser.

RESULTS

Clonidine significantly decreased mean arterial pressure (MAP) and intraocular pressure (IOP). Calculated ocular perfusion pressure decreased significantly by -8.7+/-8.7% after infusion of clonidine (p<0.01 vs placebo). Retinal arterial diameters increased by +4.4+/-2.7% (p = 0.012 vs placebo), whereas no significant change was observed in retinal veins. Red blood cell velocity decreased by -16+/-14% (p<0.01 vs placebo) after infusion of clonidine. Hence, calculated retinal blood flow decreased by -14+/-12% (p = 0.033 vs placebo). Choroidal blood flow increased by +18+/-19% (p<0.01 vs placebo) and optic nerve head blood flow increased by +16+/-23% (p = 0.046 vs placebo) 30 minutes after administration of clonidine but both returned to baseline thereafter.

CONCLUSION

The short-time increase in choroidal and optic nerve head blood flow indicates a transient vasodilatory effect of clonidine due to an unknown mechanism. The decrease in retinal blood flow indicates clonidine-induced vasoconstriction in the retinal microvasculature.

Ocular hypotensive efficacy of brimonidine 0.15% as adjunctive therapy with latanoprost 0.005% in patients with open-angle glaucoma or ocular hypertension

This study was undertaken to evaluate the ocular hypotensive efficacy of brimonidine Purite 0.15% (Alphagan P 0.15%; Allergan, Inc., Irvine, Calif) given as adjunctive therapy with latanoprost 0.005% (Xalatan; Pfizer Inc., New York, NY( to patients with open-angle glaucoma or ocular hypertension. In this multicenter, open-label, prospective evaluation, the intraocular pressure (IOP) of the 43 enrolled patients was > or =18 mm Hg after at least 6 wk of latanoprost monotherapy. The primary outcome measure was IOP at peak drug effect )10 AM, or approximately 2 h after the morning dose of brimonidine 0.15%(. IOP at trough drug effect (8 AM, or approximately 12 h after the evening dose of brimonidine) was also measured. Baseline IOP was 21.9 (+/-2.3) mm Hg. After 1 mo of treatment, additional mean IOP reductions from latanoprost-treated baseline values were 5.8 mm Hg (26%) at peak drug effect (P<.001) and 3.3 mm Hg (15%) at trough (P<.001). At the month 2 visit, additional mean IOP reductions from latanoprost-treated baseline values were 5.1 mm Hg (23%) at peak drug effect (P<.001) and 2.0 mm Hg (9%) at trough (P=.002). Brimonidine Purite 0.15% provided statistically significant additional reductions in IOP from latanoprost-treated baseline values. These findings suggest that brimonidine Purite 0.15% is an efficacious adjunctive therapy in patients given latanoprost who require additional lowering of IOP.

AL-34662: A Potent, Selective, And Efficacious Ocular Hypotensive Serotonin-2 Receptor Agonist

PURPOSE AND METHODS

The aim of this study was to determine the ocular pharmacological characteristics of AL-34662 (1-((S)-2-aminopropyl)-1H-indazole-6-ol), a new synthetic serotonin-2 (5-HT2) receptor-agonist ocular hypotensive agent. A variety of well-documented in vitro and in vivo procedures were utilized to study the pharmacological attributes of AL-34662.

RESULTS

AL-34662 exhibited a high affinity for the rat and human 5-HT2 receptor (IC50=0.8-1.5 nM) and for cloned human 5-HT2A-C receptors (IC50=3-14.5 nM). AL-34662 stimulated phosphoinositide turnover in human ciliary muscle (h-CM; EC50=289+/-80 nM) and in human trabecular meshwork (h-TM; EC50=254+/-50 nM) cells. AL-34662 also mobilized intracellular Ca2+ ([Ca2+]i) in h-CM (EC50=140+/-23 nM) and h-TM (EC50=38+/-8 nM) cells, being a full agonist like 5-HT itself. AL-34662's effects in the h-CM (and h-TM) cells were potently antagonized by 5-HT2A-antagonist M-100907 (IC50=1.8+/-0.7 nM), but weakly by 5-HT2B-antagonist (RS-127445 IC50>10 microM), 5-HT2B/C- antagonist (SB-242084 IC50=2.08 microM) and 5-HT2C antagonist (RS-102221 IC50>1 microM). AL-34662 caused relatively minimal ocular discomfort and hyperemia in rabbit and guinea pig eyes. It efficaciously lowered intraocular pressure (IOP) in the conscious ocular hypertensive monkey eyes (33% at 300 microg). The (R)-enantiomer (AL-34707) and the racemate (AL-34497) were less potent and/or efficacious than AL-34662 in all of these assays.

CONCLUSIONS

AL-34662 is a high-affinity 5-HT2 receptor agonist that potently mobilizes [Ca2+]i in h-CM and h-TM cells, and which efficaciously lowers IOP in conscious ocular hypertensive cynomolgus monkey eyes through a local effect with minimal side-effects.

Bimatoprost: A Novel Antiglaucoma Agent

The aim of glaucoma therapy is to preserve vision by reducing intraocular pressure (IOP). Following recent National Eye Institute sponsored studies, it is becoming increasingly apparent that every mmHg of extra IOP lowering counts. Bimatoprost is the newest and most effective addition to the physician's armamentarium of ocular hypotensive drugs. Direct clinical comparisons have demonstrated that it is more efficacious than the prostaglandin (PG) FP receptor agonist prodrugs, latanoprost and travoprost, as well as a beta-adrenoceptor antagonist, timolol, alone or in fixed combination with the carbonic anhydrase inhibitor, dorzolamide. Moreover, patients that are refractory to latanoprost therapy may be successfully treated with bimatoprost. Such evidence provides support, at the clinical level, for the contention that bimatoprost is pharmacologically distinct from PG FP receptor agonist prodrugs. Bimatoprost is a structural analog of PGF2alpha-ethanolamide (prostamide F2alpha), which is formed from the endocannabinoid anandamide by a biosynthetic pathway involving cyclooxygenase-2 (COX-2). Their pharmacology is remarkably similar, such that bimatoprost may be regarded as a prostamide mimetic. The target receptor for bimatoprost and the prostamides appears unique and unrelated to PG- and endocannabinoid-sensitive receptors. Extensive ocular distribution/metabolism studies in non-human primates demonstrate that bimatoprost is not a prodrug, it remains essentially intact. Its profound ocular hypotensive effects may, therefore, be attributed to its prostamide-mimetic properties.

Glaucoma Medications

As with many diseases, glaucoma increases in frequency in older populations, and is very often encountered in patients taking multiple medications. While the exact mechanism of glaucomatous optic neuropathy (GON) is not known, intraocular pressure (IOP) is thought to be central to the process, and reducing IOP is the only known effective treatment. The newer definition of glaucoma is an IOP-sensitive optic neuropathy. While large, controlled studies have indicated that reducing IOP will slow the progression of disease, the contributions of other conditions and medications have not been adequately studied. As the adverse effect profiles of medical therapies for glaucoma have improved, use of these agents has increased greatly. This has resulted in a large number of older patients taking glaucoma medications. Since topical medications can easily be overlooked in a medical history, and are for the most part well tolerated, systemic complications from these agents can be missed. In addition to being a common disease requiring treatment, glaucoma is also a model system for other degenerative diseases, and many of the concepts originally developed in relation to neurodegenerative diseases such as Alzheimer's disease are under investigation for glaucoma. These include approaches targeted towards neuroprotection and excitotoxicity.

Development of specific Rho-kinase inhibitors and their clinical application

Hexahydro-1-(isoquinoline-5-sulfonyl)-1H-1,4-diazepine, HA-1077, is a known selective inhibitor of Rho-kinase. Although its IC(50) value against Rho-kinase is more than 10 times lower than those for kinases such as PKA, PKB, PKC, PKG, MLCK, CaMKII and others, the molecule still retains relative potent inhibition activities against these kinases. In order to produce highly specific Rho-kinase inhibitors, several HA-1077 analogs were synthesized and their kinase inhibition properties evaluated. (S)-Hexahydro-1-(4-ethenylisoquinoline-5-sulfonyl)-2-methyl-1H-1,4-diazepine was found to be a potent Rho-kinase inhibitor. The IC50 value against Rho-kinase was 6 nM, while those against other kinases remained at almost the same level as that of HA-1077. Furthermore, we designed HA-1077 analogs on the basis of the complex structure of PKA and HA-1077. Amongst these, (S)-hexahydro-4-glycyl-2-methyl-1-(4-methylisoquinoline-5-sulfonyl)-1H-1,4-diazepine and other glycine derivatives were found to be highly specific Rho-kinase inhibitors. These Rho-kinase specific inhibitors were applied to rabbit ocular hypertensive models and were shown to reduce intraocular pressure. These results demonstrate that the new 5-isoquinolinesulfonylamides are not only potent ROCK selective compounds, but are also useful compounds for clinical applications.

[The effect of brimonidine on the pupillary reflex. A pupillographic study in healthy volunteers]

PURPOSE

The effect of brimonidine in comparison with acetazolamide on pupillary reflex was investigated in 18 volunteers.

METHODS

Infrared pupillography was performed with white diode light of 200 ms duration to measure pupil diameter, constriction latency, reaction time, constriction amplitude, and relative constriction amplitude. The measurements were performed according to a fixed schedule including a phase without medication to determine the baseline level. Data were analyzed by Student's paired t-test.

RESULTS

Application of brimonidine and acetazolamide led to a significantly reduced intraocular pressure as well as static and dynamic differences in the pupillary reflex. The pupil diameter measurements were significantly smaller after both medications in comparison to baseline. The reduction of pupil diameter after brimonidine led to significantly reduced contraction amplitude and prolonged latency.

CONCLUSION

Application of brimonidine leads to significant miosis, which might due to the affinity to alpha(2)-receptors with reduction of noradrenaline release in the synapse. This effect may play a role in a higher decrease of intraocular pressure by increasing aqueous humor outflow in comparison to clonidine and apraclonidine, but further investigations are required.

Effects of a topical alpha2 adrenergic agonist on ciliary blood flow and aqueous production in rabbits

The relationship between ciliary perfusion and aqueous production is poorly understood. It was recently reported that aqueous production decreases when ciliary blood flow is reduced by lowering the ocular perfusion pressure, and hypothesized that drug-induced reduction of ciliary blood flow would also decrease aqueous production. In the present study, we test this hypothesis with an alpha2 adrenergic agonist (brimonidine) formulated for topical application. When used acutely, brimonidine decreases intraocular pressure (IOP) by suppressing aqueous production, although its mechanism of action is unclear. The experiments were performed in four groups of anesthetized rabbits (n=33) in which the following variables were measured: ocular mean arterial pressure (OMAP), IOP, orbital venous pressure (OVP), aqueous flow, ciliary blood flow, ciliary oxygen tension (PO2), episcleral venous pressure (EVP), carotid blood flow and heart rate. The measurements were made before and after brimonidine (0.15%, 40 microl) was applied to the cornea. Brimonidine decreased IOP (-33%, p<0.01), aqueous flow (-39%, p<0.01), ciliary blood flow (-37%, p<0.01), EVP (-42%, p<0.01) and ciliary PO2 (-32%, p<0.05). We conclude that topical brimonidine is a ciliary vasoconstrictor, and that alpha2 adrenergic agonist-induced decreases in ciliary blood flow decrease aqueous production.

Water-drinking test in patients with primary open-angle glaucoma while treated with different topical medications

OBJECTIVE

Reduction and diurnal stabilization of the intra-ocular pressure (IOP) is the mainstay of treatment for glaucoma. Fluctuations of IOP in glaucomatous patients can also be induced by the osmotic variations caused by water ingestion. Such influence can be studied by means of the water-drinking test (WDT). The aim of this study was to perform the WDT in patients with primary open-angle glaucoma (POAG) while they were being treated with different IOP-lowering medications, to test the effect of drugs with different mechanisms of action on the ability to maintain a stable IOP.

METHODS

A total of 280 POAG patients were enrolled, 40 patients per group for each of the tested medications (timolol, dorzolamide, brinzolamide, travoprost,latanoprost, bimatoprost, and brimonidine). After baseline IOP measurement, all patients underwent WDT (1000 mL of water in 10 min). The IOP was measured at 15-min intervals until the return of IOP to baseline values. The main outcomes measured were mean IOP peak, mean IOP percentage increase, and mean time for returning to baseline IOP value.

RESULTS

The highest mean IOP peak was found with timolol, whereas no difference was found among the other drugs. The highest mean IOP percentage increase was found with timolol, whereas bimatoprost showed an IOP percentage increase significantly lower than latanoprost, dorzolamide, and brinzolamide. The duration of IOP increase was shortest for bimatoprost and longest for timolol.

CONCLUSION

This study suggests that topical medications that enhance outflow (e.g., bimatoprost, latanoprost, travoprost, and brimonidine) may provide, under stressful conditions such as the WDT, better IOP stabilization than medications that decrease aqueous humor inflow, such as timolol and topical carbonic anhydrase inhibitors.

Current and emerging medical therapies for glaucoma

Glaucoma is a multifactorial optic neuropathy in which there is a characteristic acquired loss of retinal ganglion cells, at levels beyond normal age-related baseline loss, and corresponding atrophy of the optic nerve. Although asymptomatic in its earlier stages, the disease is nevertheless one of the leading global causes of irreversible blindness. Although elevated intraocular pressure (IOP) is one of the most important risk factors and lowering of IOP is the only proven treatment so far, the definition of glaucoma has evolved from a disease caused by increased IOP to one characterised by an IOP-sensitive, progressive optic neuropathy. In recent years, safer and better tolerated topical medications have been developed to control IOP more effectively, thereby limiting the need for surgery. New research has also noted the importance of diurnal IOP variation as a critical risk factor for progression of glaucomatous optic neuropathy (GON) and subsequent visual field loss. Moreover, new discoveries have further elucidated the basic pathophysiological and genetic mechanisms underlying the elevated levels of IOP, as well as the cellular mechanisms of GON. As our understanding of these complex pathways continues to improve, development opportunities for new therapeutic modalities will be enhanced.

Glaucoma medication and aqueous humor dynamics

PURPOSE OF REVIEW

This review evaluates current concepts regarding the effects of glaucoma medication on aqueous humor dynamics and the impact of this on intraocular pressure control and drug selection in clinical practice.

RECENT FINDINGS

Calculations based on the Friedenwald and Goldmann equations have predicted that glaucoma medications that increase pressure-sensitive aqueous outflow will dampen intraocular pressure spikes and therefore may be advantageous over drugs that do not increase outflow facility.

SUMMARY

Further experimental research is required to verify the influence of increased outflow facility on intraocular pressure fluctuation and the effect of this on glaucoma progression.

Latanoprost or Brimonidine as Treatment for Elevated Intraocular Pressure

PURPOSE

To compare the efficacy and tolerability of latanoprost or brimonidine in patients with elevated intraocular pressure (IOP).

MATERIALS AND METHODS

This prospective, randomized, masked-evaluator, parallel-group, multicenter study in the United States included patients with primary open angle glaucoma or ocular hypertension. Patients received latanoprost 0.005% once daily (8:00 AM; n = 152) or brimonidine tartrate 0.2% twice daily (8:00 AM and 8:00 PM; n = 151). Patients underwent evaluation at screening, baseline (randomization), and after 0.5, 3, and 6 months of treatment. IOP was measured at 8:00 AM, 10:00 AM, noon, and 4:00 PM at baseline and the months 3 and 6 visits, and at 8:00 AM only at week 2. The main outcome measure was the difference in diurnal IOP change from baseline to month 6 between treatment groups. Adverse events were recorded at each visit.

RESULTS

Baseline mean diurnal IOP levels were similar between groups. At month 6, the adjusted mean (+/- SEM) diurnal IOP reduction was 5.7 +/- 0.3 mm Hg in the latanoprost group and 3.1 +/- 0.3 mm Hg in patients receiving brimonidine (P < 0.001). The mean difference in diurnal IOP reduction was 2.5 +/- 0.3 mm Hg (95% CI: 1.9, 3.2; P < 0.001). Five times more patients receiving brimonidine than latanoprost were withdrawn from the study due to adverse events.

CONCLUSION

Latanoprost instilled once daily is more effective and better tolerated than brimonidine administered twice daily for the treatment of patients with glaucoma or ocular hypertension. During therapy, the range of daily fluctuation of IOP is less for latanoprost compared with brimonidine.

Advances in glaucoma therapeutics

Glaucoma is a major cause of irreversible blindness in the world. The prevalence of glaucomatous loss in vision will continue to grow as our populations age. Ocular hypertension is a major risk factor for the development of glaucoma and current glaucoma therapy is directed at lowering intraocular pressure. Several new ocular hypotensive agents have been introduced in the past several years providing a variety of treatment options. In addition, various classes of neuroprotective agents demonstrating activity in a wide variety of animal models have been proposed as potential new glaucoma therapeutics. Although these approaches will slow the progression of vision loss, they do not directly intervene in the disease process(es). Advances have been made attempting to understand the pathogenic pathways involved in glaucomatous damage to the eye and in methods to clinically measure glaucoma damage. An increased understanding of the pathophysiology of glaucoma will lead to the development of new therapeutic agents that intervene and perhaps even reverse glaucomatous damage to the eye. There also is a need to develop new methods to clinically measure glaucoma damage because, currently, considerable damage occurs before glaucoma is diagnosed and glaucoma remains underdiagnosed in the general population.

A comparison of the fixed combination of latanoprost and timolol with the unfixed combination of brimonidine and timolol in patients with elevated intraocular pressure. A six month, evaluator masked, multicentre study in Europe

PURPOSE

To compare the intraocular pressure (IOP) reducing effect and safety of fixed combination (FC) latanoprost/timolol with unfixed combination (UFC) brimonidine/timolol in patients with increased IOP.

METHODS

In this 6 month, randomised, evaluator masked, parallel group European study, patients with glaucoma or ocular hypertension and IOP > or =21 mm Hg on monotherapy or >16 mm Hg on dual therapy received either FC latanoprost/timolol at 8:00AM or UFC brimonidine/timolol at 8:00AM and 8:00PM. The primary outcome was the difference from baseline to month 6 in mean diurnal IOP reduction.

RESULTS

325 of 334 randomised patients were included in intent to treat analyses (FC latanoprost/timolol, 163; UFC brimonidine/timolol, 162). Baseline diurnal IOP levels were similar: FC latanoprost/timolol, 26.4 (SD 2.7) mm Hg; UFC brimonidine/timolol, 26.5 (SD 2.8) mm Hg (p = 0.851). At month 6, levels were 16.9 (SD 2.8) mm Hg in FC latanoprost/timolol patients and 18.2 (SD 3.1) mm Hg in UFC brimonidine/timolol patients (p<0.001). No adverse events were reported by 76.4% and 75.5% of patients receiving FC latanoprost/timolol versus UFC brimonidine/timolol, respectively. Larger proportions of brimonidine/timolol treated patients reported study medication related adverse events (18.6% v 7.3%) and discontinued study participation because of this (10.8% v 1.8%).

CONCLUSION

Fixed combination latanoprost/timolol administered once daily is both more effective and better tolerated than twice daily dosing with UFC brimonidine/timolol.

Primary open-angle glaucoma

Primary open-angle glaucoma is a progressive optic neuropathy and, perhaps, the most common form of glaucoma. Because the disease is treatable, and because the visual impairment caused by glaucoma is irreversible, early detection is essential. Early diagnosis depends on examination of the optic disc, retinal nerve fibre layer, and visual field. New imaging and psychophysical tests can improve both detection and monitoring of the progression of the disease. Recently completed long-term clinical trials provide convincing evidence that lowering intraocular pressure prevents progression at both the early and late stages of the disease. The degree of protection is related to the degree to which intraocular pressure is lowered. Improvements in therapy consist of more effective and better-tolerated drugs to lower intraocular pressure, and more effective surgical procedures. New treatments to directly treat and protect the retinal ganglion cells that are damaged in glaucoma are also in development.

The safety and efficacy of unoprostone 0.15% versus brimonidine 0.2%

PURPOSE

To compare the efficacy and safety of unoprostone versus brimonidine both given twice daily in ocular hypertensive or primary open-angle glaucoma subjects.

METHODS

After a 1-month washout period a baseline diurnal curve was measured every 2 hours from 08:00 hours (trough) to 20:00 hours in subjects with a trough intraocular pressure (IOP) and the pressure 24 mmHg. Qualified subjects were randomized to either brimonidine or unoprostone. After 6 weeks of treatment the period 1 diurnal curve was performed. Subjects were then switched to the opposite treatment for 6 weeks and the period 2 diurnal curve was performed.

RESULTS

A total of 33 subjects were included in this study. In the brimonidine-treated group the trough IOP 20.1 +/- 2.8 mmHg was reduced from baseline up to 8 hours after dosing. In the unoprostone-treated group the trough IOP was 19.5 +/- 3.0 mmHg, which was statistically equal to that of brimonidine (p = 0.21), was reduced from baseline for 12 hours after dosing. Brimonidine decreased the IOP statistically more than unoprostone at 10:00 and 12:00 hours (p < 0.0001 and p = 0.02, respectively), while unoprostone reduced the IOP more than brimonidine at 18:00 and 20:00 hours (p = 0.002 and p = 0.05, respectively). Safety levels were similar between groups, but unoprostone caused more ocular stinging than brimonidine (p = 0.008).

CONCLUSION

This study suggests that twice daily brimonidine demonstrates a statistically greater peak reduction in IOP than unoprostone. However, unoprostone, but not brimonidine, decreased IOP over the complete 12-hour daytime dosing cycle.

The inflow and outflow of anti-glaucoma drugs

The treatment of glaucoma by reducing intraocular pressure has relied traditionally on inhibiting aqueous humor secretion (inflow). However, recent therapeutic approaches have targeted aqueous humor outflow. Prostanoid FP receptor agonists selectively increase uveoscleral outflow and the prostamide analog bimatoprost alters trabecular and uveoscleral outflow. An emerging therapeutic strategy is direct neuroprotection of retinal ganglion cells, which are selectively lost in glaucoma.

Short posterior ciliary artery, central retinal artery, and choroidal hemodynamics in brimonidine-treated primary open-angle glaucoma patients

PURPOSE

Malfunction in peripapillary hemodynamics has been suggested to play a major part in the pathogenesis of primary open-angle glaucoma (POAG). The aim of this study was to determine whether topically applied brimonidine can influence blood hemodynamic characteristics associated with the perioptic short posterior ciliary arteries (SPCAs), central retinal artery (CRA), and choroidal vascular system in POAG patients.

DESIGN

Randomized clinical trial. In this prospective, institutional, double-masked, vehicle-controlled, randomized clinical trial, the intraocular pressure (IOP) and vascular dynamics of the SPCAs, CRA, and choroidal vascular system were analyzed in both eyes of 17 POAG patients, before and after treatment with 0.2% brimonidine for 4 weeks.

RESULTS

Mean IOP reduction was significant (18.7%) following treatment with brimonidine. However, no clear changes were recorded with respect to blood perfusion parameters (peak systolic velocity, end-diastolic velocity, pulsatility, and resistance indices) associated with the SPCAs and CRA or the choroidal ocular pulse amplitude.

CONCLUSIONS

Topical treatment of brimonidine to POAG patients causes a significant reduction of IOP, but blood hemodynamic properties associated with the SPCAs, CRA, and choroidal vascular systems appeared unaffected. Topically applied brimonidine, therefore, appears not to constrict or dilate peripapillary blood vessels.

Comparison of prostaglandin F2alpha, bimatoprost (prostamide), and butaprost (EP2 agonist) on Cyr61 and connective tissue growth factor gene expression

Connective tissue growth factor (CTGF) and Cyr61 (cysteine-rich angiogenic protein 61) are members of the CCN gene family that encode multifunctional, extracellular matrix-associated signaling proteins. Because the mechanism of action of certain anti-glaucoma drugs involves extracellular matrix remodeling of ocular ciliary muscle, with a resultant increase in drainage of aqueous humor from the eye, we compared the effects of three pharmacologically distinct ocular hypotensive agents on Cyr61 and CTGF gene expression. Thus, prostaglandin F2alpha (PGF2alpha) (FP receptor agonist), Butaprost (EP2 receptor agonist), and Bimatoprost (a prostamide) were compared. Using Affymetrix gene chip technology, we first identified that PGF2alpha dramatically up-regulated Cyr61 and CTGF mRNA expression in HEK 293/EBNA cells (hFP-HEK 293/EBNA). Northern blot further confirmed the Cyr61 and CTGF up-regulation is in a dose- and time-dependent manner. PGF2alpha-induced up-regulation of Cyr61 appeared to exclusively involve the Rho pathway, and up-regulation of CTGF was via multiple intracellular pathways. Because prostamide receptors are, to date, defined only at the pharmacological level, Bimatoprost effects on Cyr61 and CTGF were studied in the isolated feline iris sphincter preparation, a tissue highly responsive to prostamides. Both PGF2alpha and Bimatoprost up-regulated Cyr61 mRNA expression in the cat iris tissue. Only PGF2alpha up-regulated CTGF mRNA expression in the cat iris. Therefore, PGF2alpha and Bimatoprost appear to interact with different receptors populations in the cat iris, according to their markedly different effects on CTGF. Activation of prostaglandin EP2 receptors (Gs-coupled) also up-regulated Cyr61 but not CTGF mRNA expression in the isolated cat iris. Similar data were observed in human primary ciliary smooth muscle cells. Thus, despite quite different signal transduction pathways, FP receptor stimulation up-regulates CTGF and Cyr61. The prostamide analog Bimatoprost and an EP2-selective agonist affects only Cyr61.

Targeting outflow facility in glaucoma management

Glaucoma is often characterized by decreased pressure-sensitive aqueous outflow through the trabecular meshwork. This defect in pressure-sensitive aqueous outflow is evident from the low tonographic facility of outflow ("C") measured in many patients. The impairment in outflow facility causes the high intraocular pressure (IOP) and large diurnal IOP fluctuations often found in glaucoma. Because large diurnal IOP fluctuations have been shown to be a risk factor for glaucomatous progression, IOP-lowering therapy should aim to achieve a low, stable IOP. Pressure-sensitive aqueous outflow helps prevent and dampen pressure spikes; thus, drugs that enhance outflow facility, in particular, may stabilize as well as lower IOP. Outflow facility is an attractive target for glaucoma treatment because enhancing outflow facility tends to restore the self-regulating tendency of IOP. Older drugs such as the cholinergic pilocarpine and the catecholamine epinephrine act primarily by improving outflow facility. This action is also important for the recently introduced prostamide, bimatoprost, as well as for the prostaglandin prodrug, latanoprost. Realization of the importance of facility of outflow in lowering and stabilizing IOP will stimulate additional research into the mechanism of action of ocular hypotensive agents and will help optimize the medical treatment of glaucoma.