The Effects of Cosopt® Vs Xalacom® on Ocular Hemodynamics and Intraocular Pressure (IOP) in Primary Open-angle Glaucoma (POAG) (Xal-Cos)
|Open-Angle Glaucoma Ocular Hypertension||Drug: Dorzolamide+Timolol Maleate0.5% Drug: Latanoprost+Timolol Maleate0.5%+Lytears|
|Study Design:||Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Double Blind (Participant, Care Provider, Investigator, Outcomes Assessor)
|Official Title:||A Comparative Analysis of the Effects of Cosopt® Versus Xalacom® on Ocular Hemodynamics and Intraocular Pressure in Patients With Primary Open-angle Glaucoma|
- Ocular hemodynamics as measured by Color Doppler imaging [ Time Frame: 3 years ]
- Intraocular pressure as measured by Goldmann applanation tonometry [ Time Frame: 3 Years ]
|Study Start Date:||December 2008|
|Estimated Study Completion Date:||June 2012|
|Estimated Primary Completion Date:||December 2011 (Final data collection date for primary outcome measure)|
Active Comparator: 1
Cosopt* b. i. d. (dosed morning and bedtime) will be administered topically
Drug: Dorzolamide+Timolol Maleate0.5%
Cosopt* b. i. d.
Other Name: Cosopt
Active Comparator: 2
Xalacom* q.d.(dosed bedtime) and placebo vehicle q.d. (dosed morning) topically in the other group
Drug: Latanoprost+Timolol Maleate0.5%+Lytears
Other Name: Xalacom* QHS
Background and Rationale
Apoptosis of retinal ganglion cell has been considered as the most plausible pathogenic mechanism of glaucoma. Apoptosis can be caused by neurotrophic factor withdrawal or glutamate release and both of them are triggered by elevated intraocular pressure (IOP) and ischemia simultaneously or separately.
The topical carbonic anhydrase inhibitor, Dorzolamide (Trusopt*), has recently been approved for chronic use in the treatment of glaucoma. The ocular hypotensive effects of this topical carbonic anhydrase inhibitor seem likely to produce the same results as *-adrenergic antagonists. Systemic carbonic anhydrase inhibitors are known to have vasodilatory effects (Maren,1987). Rassam S.M.B., Patel V. and Kohner E.M. (1993) have concluded that acetazolamide causes an increase in retinal blood flow in the human retinal circulation. It has also been demonstrated that Trusopt* increases retinal circulation as measured by scanning laser ophthalmoscopy (SLO) (Harris, Arend, Martin, 1996). Furthermore, Trusopt increases arteriovenous passage (AVP) time and improves contrast sensitivity in normal tension glaucoma patients (Harris, 1999).
Cosopt* (dorzolamide hydrochloride-timolol maleate ophthalmic solution) is combination of a topical carbonic anhydrase inhibitor and a topical beta-adrenergic receptor blocking agent. Each of these two components reduces intraocular pressure. The IOP-reducing effect of Cosopt b.i.d. was greater (1-3 mm Hg) than that of monotherapy with either 2.0 % dorzolamide t.i.d. or 0.5 % timolol b.i.d. The IOP-lowering effect of Cosopt* b.i.d. was approximately 1 mm Hg less than that of concomitant therapy with 2.0% dorzolamide t.i.d. and 0.5 % timolol b.i.d. A previous study showed that the retinal circulation (AVP time) was significantly accelerated after replacing Timoptic* with Cosopt* in glaucoma patients (Harris, 1999).
Latanoprost (Xalatan*) is a prostaglandin F2* analogue which is believed to reduce IOP by increasing the outflow of aqueous humor. The retinal vascular effects of Latanoprost, however, remain unclear. While some studies have shown PGF2* to induce constriction in bovine isolated aqueous veins (Nielsen 1996), other studies have been unable to demonstrate an effect on retrobulbar flow velocities (Drance 1996). It is possible that vasoconstrictive properties of the drug may produce a negative impact on previously ischemic retinal tissue or at best no change.
In a recent study comparing Trusopt® with Xalatan® some very encouraging results emerged, AVP time was significantly reduced with Trusopt®, but not with Xalatan® despite the fact that Xalatan® increases perfusion pressure (due to IOP) more than Trusopt®. This is the strongest evidence so far of a pressure independent effect of Trusopt® on ocular blood flow.
- To compare the IOP efficacy of Cosopt® and Xalacom® on IOP.
- To determine the perfusion pressure effect of Cosopt® and Xalacom®.
- To determine the blood flow effect of the two drugs on the ophthalmic, central retinal and short posterior ciliary arteries, using Color Doppler Imaging (CDI).
Please refer to this study by its ClinicalTrials.gov identifier: NCT00815373
|Meir Medical Center|
|Kfar Saba, Israel|
|Principal Investigator:||Adi Abulafia, MD||Meir Medical Center, Tel Aviv University|