Comparative acute effects of brimonidine 0.2% versus dorzolamide 2% combined with beta-blockers in glaucoma

Fixed combination of topical brimonidine 0.2% and timolol 0.5% for glaucoma and uncontrolled intraocular pressure

Lowering IOP is the most readily modifiable risk factor to delay the development and progression of glaucoma (POAG). The fixed combination of brimonidine tartrate 0.2% and timolol maleate 0.5% (FCBT) combines a highly selective α2-adrenergic agonist (brimonidine) with a non-selective β-blocker (timolol). FCBT reduces aqueous production and enhances uveoscleral outflow. Concomitant brimonidine and timolol have additive effects on reducing intraocular pressure (IOP). Multi-center randomized control trials have documented superiority of FCBT twice daily on IOP control compared with monotherapy with the individual components, and equal efficacy compared with concomitant therapy. IOP reduction with FCBT versus fixed combination dorzolamide 2% and timolol 0.5% (FCDT) was similar in a small study. Other studies (n > 293) evaluating concomitant brimonidine and timolol have shown that it is not inferior to FCDT. However, concomitant brimonidine and timolol administered twice daily was significantly less efficacious in IOP reduction than fixed combination latanoprost 0.005% and timolol 0.5% (FCLT). There are no published studies comparing FCBT with FCLT. The side effect profile for FCBT reflects that of its individual components. FCBT was generally well tolerated, with less ocular side effects than brimondine alone, but more than timolol alone. Documented systemic effects were few, although this could be confounded by selection bias. FCBT is a safe and effective IOP lowering agent for POAG and ocular hypertension.

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.

Ocular pharmacokinetic/pharmacodynamic modeling for multiple anti-glaucoma drugs

We have constructed a new ocular pharmacokinetic pharmacodynamic (PK/PD) model for anti-glaucoma drugs to describe ocular hypotensive effects on intraocular pressure (IOP) after instillation of a combination of an alpha(1)-adrenergic antagonist, bunazosin, and a beta-adrenergic antagonist, timolol, into rabbits. This model was constructed by the combination of two ocular PK/PD models for bunazosin and timolol by including aqueous humor dynamics based on both action mechanisms. We also verified the reliability of this model by confirming the drug concentrations in aqueous humor and ocular hypotensive effects after instillation of the drug combination. The aqueous humor concentrations of timolol and bunazosin were determined by an HPLC, and ocular hypotensive effect-time profiles were measured using a telemetry system, which was able to record automatically detailed effects. The combined model could simulate the aqueous humor concentrations of both drugs and the additive IOP-lowering effect after instillation of the combination using the MULTI (RUNGE) program and PK/PD parameters which were obtained from ocular hypotensive effects after instillation of bunazosin alone or timolol alone. The theoretical concentration curves of both drugs in the aqueous humor and the theoretical ocular hypotensive effect curves almost agreed with both the observed concentrations and ocular hypotensive effects after instillation of the drug combination. These results indicate the reliability and usefulness of PK/PD modeling considering aqueous humor dynamics to predict IOP in multidrug therapy. This is the first study to develop a PK/PD model for multidrug therapy for the eye.

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.

Dorzolamide/Timolol Fixed Combination Versus Concomitant Administration of Brimonidine and Timolol in Patients with Elevated Intraocular Pressure

BACKGROUND

To compare the intraocular pressure (IOP) lowering effect, tolerability, and patient-reported measures of the dorzolamide/timolol fixed combination and the concomitant administration of brimonidine and timolol after 3 months.

METHODS

Four hundred ninety-two patients with ocular hypertension, primary open-angle glaucoma, exfoliative glaucoma, or pigmentary glaucoma participated in this randomized, observer-masked, multicenter study. Following 3 weeks of timolol monotherapy, patients with a peak IOP of > or = 2 mm Hg were randomized to receive either fixed combination dorzolamide/timolol twice daily or concomitant brimonidine plus timolol twice daily for 3 months. The IOP-lowering effects at peak and trough, tolerability, and patient-reported convenience and satisfaction were measured at months 1 and 3.

RESULTS

At month 3 peak, the dorzolamide/timolol group had an adjusted mean (SE) change from baseline IOP of -4.30 (0.24) mm Hg versus -5.27 (0.23) mm Hg in the brimonidine-plus-timolol group, with a treatment difference of 0.97 mm Hg (95% CI: 0.40, 1.53). At the month 3 trough timepoint and both month 1 timepoints, the 95% CIs of the treatment differences were within the prespecified comparability boundary of +/- 1.5 mm Hg. The incidence of drug-related adverse experiences was similar between treatment groups. Patient-reported assessments of convenience and satisfaction showed no statistically significant differences between treatment groups.

CONCLUSIONS

The IOP-lowering effect of the dorzolamide/timolol fixed combination and concomitant brimonidine plus timolol were comparable at 3 of the 4 timepoints measured. Patient-reported measures and the incidence of adverse experiences in both treatment groups were similar.

Dorzolamide/timolol combination versus concomitant administration of brimonidine and timolol: six-month comparison of efficacy and tolerability

PURPOSE

To compare the efficacy and tolerability of the 2% dorzolamide/0.5% timolol combination ophthalmic solution twice daily to the concomitant administration of 0.2% brimonidine ophthalmic solution twice daily and 0.5% timolol ophthalmic solution twice daily.

DESIGN

Randomized, multicenter, observer-masked, parallel-group study.

PARTICIPANTS

Two hundred ninety-three patients with ocular hypertension or primary open-angle glaucoma participated.

INTERVENTION

After an open-label 3-week 0.5% timolol run-in period, patients with an hour 2 intraocular pressure (IOP) of > or = 22 mmHg were randomly assigned to receive either the dorzolamide/timolol combination twice daily or the concomitant use of brimonidine twice daily and timolol twice daily (brimonidine + timolol) for 6 months.

MAIN OUTCOME MEASURES

The IOP-lowering effects at hour 0 and hour 2 were collected at 1, 3, and 6 months. We hypothesized that both treatment regimens would have comparable hour 2 IOP-lowering effects at month 3. The treatments were considered comparable if the two-sided 95% confidence interval of the treatment difference was within +/- 1.5 mmHg. Tolerability data were also collected at 1, 3, and 6 months.

RESULTS

The primary efficacy analysis was based on the modified intent-to-treat population. At month 3, hour 2, the dorzolamide/timolol group had an adjusted mean (standard error) change in IOP of -5.04 (0.30) mmHg versus -5.41 (0.30) mmHg in the brimonidine + timolol group, with a treatment difference of 0.36 (0.40) mmHg (95% confidence interval [CI] of -0.42-1.14 mmHg). At month 3, hour 0, the dorzolamide/timolol group had a change in IOP of -3.66 (0.29) mmHg versus -4.15 (0.28) mmHg in the brimonidine + timolol group, with a treatment difference of 0.49 (0.39) mmHg (95% CI of -0.27-1.25 mmHg). Likewise, at all other observed time points, the 95% confidence interval of the treatment difference was within +/- 1.5 mmHg. Ninety-three patients (64%) in the dorzolamide/timolol group and 88 patients (60%) in the brimonidine + timolol group had adverse experiences that were deemed drug related by the investigator, for which 7 patients (5%) in the dorzolamide/timolol group and 8 patients (5%) in the brimonidine + timolol group were discontinued from the study.

CONCLUSIONS

The efficacy of the dorzolamide/timolol combination and the concomitant administration of brimonidine and timolol were comparable. The incidence of drug-related adverse experiences and the incidence of discontinuations caused by drug-related adverse experiences were similar between groups.

Three-month comparison of brimonidine and latanoprost as adjunctive therapy in glaucoma and ocular hypertension patients uncontrolled on beta-blockers: tolerance and peak intraocular pressure lowering

PURPOSE

To compare the tolerance and peak intraocular pressure (IOP)-lowering efficacy of brimonidine and latanoprost as adjunctive therapy in patients with ocular hypertension or glaucoma uncontrolled on beta-blockers.

DESIGN

A prospective, multicenter, double-masked, parallel-design clinical trial.

PARTICIPANTS

One hundred fifteen patients with IOP inadequately controlled on topical beta-blocker monotherapy.

METHODS

Patients were randomly assigned to receive brimonidine, 0.2%, twice a day or latanoprost, 0.005%, every day as adjunctive therapy for 3 months. After 1 month of adjunctive treatment, patients who failed to meet a target 15% reduction in IOP at peak drug effect were crossed over to the other study medication. The target sample size of 51/group gave a power of 0.80 to detect a difference of 1 mmHg in mean IOP lowering between groups.

MAIN OUTCOME MEASURES

The primary outcome variables were reduction in IOP from baseline at peak drug effect, response rate, and quality of life as measured using the Glaucoma Disability Index.

RESULTS

Mean beta-blocker-treated baseline IOP was comparable between treatment groups (approximately 21.3 mm Hg). After 1 month of adjunctive therapy, brimonidine and latanoprost provided comparable IOP lowering (4.88 mmHg [22.8%] with brimonidine and 5.01 mmHg [23.5%] with latanoprost, P = 0.798). Response rates were similar in both groups, with 44 of 54 brimonidine patients and 43 of 53 latanoprost patients achieving the minimum target 15% IOP reduction at peak drug effect at month 1 (P = 0.963). Among patients who were successful at month 1 and continued on the initial study medication, mean IOP reductions were 4.55 mmHg with brimonidine and 5.49 mmHg with latanoprost (P = 0.149) at month 3. There was no significant difference in the ability of brimonidine and latanoprost to maintain at least a 15% additional reduction in IOP for 3 months (28 of 38 patients on brimonidine vs. 30 of 36 patients on latanoprost achieved > or =15% IOP reduction at month 3; P = 0.314). Patients in the latanoprost group were more likely to report negative quality-of-life variables than patients in the brimonidine group. Significantly more latanoprost patients reported watery or teary eyes (34 of 53, 64.2% vs. 23 of 54, 42.6% with brimonidine; P = 0.025) and hands and feet that became cold easily (24 of 53, 45.3% vs. 12 of 54, 22.2% with brimonidine; P = 0.012).

CONCLUSIONS

As adjunct therapy with beta-blockers, brimonidine twice daily and latanoprost every day were comparable in lowering IOP at peak effect, but brimonidine was better tolerated, with fewer reports of adverse quality-of-life effects.

Update on topical carbonic anhydrase inhibitors

Topical carbonic anhydrase inhibitors are a novel addition to the armamentarium of medical glaucoma treatment; dorzolamide has been available since 1995 and brinzolamide since 1998. They lower intraocular pressure by inhibiting carbonic anhydrase, a key enzyme for aqueous humor formation. Intraocular pressure-lowering activity of the substances appears to be the same and is similar to that of most other agents, but it does not reach the activity of the unselective beta-blocker timolol or the prostaglandin latanoprost. On concomitant treatment, additivity is reached with all other topical agents. A possible improvement of blood flow may offer an additional benefit, but its significance for the long-term outcome for human glaucoma remains to be shown. Side effects are mostly local. A more physiologic pH of brinzolamide appears to be advantageous.