Cosopt can help reduce dosing frequency for glaucoma patients

Issue: November 1998

Cosopt (Merck) is the first combination medication approved in this country for treating glaucoma and ocular hypertension in more than 25 years - since epinephrine was bottled with pilocarpine. Cosopt is a combination of timolol maleate 0.5% (a nonselective beta-blocker) and dorzolamide HCl 2% (a topical carbonic anhydrase inhibitor). Cosopt may offer some significant advantages in managing glaucoma and ocular hypertension.

One of the most difficult problems with managing any chronic condition is achieving compliance with the prescribed therapy. With glaucoma and ocular hypertension, patients have a difficult time understanding why they should compromise their lifestyle with multiple medications administered at various times when their eyes feel fine and they have no problems with their vision.

Patient confusion

Patients are often confused when they are prescribed multiple medications with different dosing schedules. The potential for inappropriate use is very real. Multiple medications and the need for drop spacing also can cause loss of effectiveness. In many cases, patients use drops without spacing, washing out the previous drop and reducing its effectiveness.

Noncompliance is even more of a problem when patients take their drops on the day they visit you for follow-up. Although the intraocular pressure (IOP) appears to be controlled, it is, in fact, inadequate most of the time. Because glaucoma is slowly progressive, and progression is difficult to detect, patients may have years of continued optic nerve damage despite having acceptable IOP when checked in your office.

These issues are particularly frustrating to the clinician who has to keep adding medications to the therapeutic regimen of those patients who fail to achieve an adequate target pressure or demonstrate progressive glaucomatous damage. Despite our best efforts at pa tient education, studies reveal a high level of noncompliance in glaucoma patients.

Cosopt is an alternative that may help with patient compliance by combining two very effective and well-tested glaucoma medications in one bottle. The ability to prescribe one drop that contains both medications should help patients maintain a better level of IOP than if each were prescribed separately, because of improved patient compliance. Cosopt will also help prevent patient confusion regarding their eye drops, because only one bottle must be used.

Equally effective

In terms of effectiveness, Cosopt twice daily is about equally effective as using Timoptic (timolol maleate 0.5%, Merck) twice daily and Trusopt (dorzolamide HCl 2.0%, Merck) three times daily. The side effects of Cosopt are similar to those experienced by patients who use these medications separately and most commonly include burning and stinging upon instillation and a bitter or unusual taste following administration, both well-known effects of Trusopt.

Although these side effects may not seem significant, they can result in patient noncompliance to avoid these unpleasant effects. Cosopt is contraindicated in patients who otherwise have contraindications to either a nonselective beta-blocker or a carbonic anhydrase inhibitor. Those contraindications include congestive heart failure, sinus bradycardia, asthma or chronic obstructive pulmonary disease, or hypersensitivity to either of the component drugs.

Treatment with Cosopt will produce a significantly lower IOP than that which can be achieved with Timoptic alone. An additional 10% to 20% IOP reduction can be achieved by adding the topical carbonic anhydrase inhibitor to patients who are already taking a topical nonselective beta-blocker but have inadequate or marginal IOP control.

Dorzolamide and corneal function

Although carbonic anhydrase is an essential enzyme in corneal endothelial function, several studies have shown no effect of topical Trusopt on corneal function. The best study showed no significant effect of topically applied dorzolamide on corneal deswelling after hy po xic stress compared to placebo. (Egan CA, Hodge DO, McLaren JW, Bourne WM. Effect of dorzolamide on cor neal endothelial function in normal hu man eyes. Invest Ophthalmol Vis Sci, 1998; 39:23-29.) Another study found no significant change in corneal thickness or endothelial cell count with topical dorzolamide use over a period of 90 days. (Kaminski S, Hommer A, Koyuncu D. In fluence of dorzolamide on corneal thick ness, endothelial cell count and corneal sen sibility. Acta Ophthalmol, 1998;76:78-79.)

I have not had any patient experience a significant increase in corneal edema with the use of topical dorzolamide. Practitioners may wish to consider the potential effect on the corneal endothelium, particularly in patients who have advanced endothelial cell loss from either previous intraocular surgery or corneal dystrophy.

Cosopt monotherapy may prove to be an excellent substitute for those patients who currently take both Timoptic and Trusopt and in patients who otherwise have inadequate IOP on a beta-blocker alone. It may also be useful in patients with compliance problems or in patients who might otherwise have difficulty using more than one drop.

Cosopt, one drop twice a day, combined with latanoprost once a day offers patients a great combination of medications that can achieve dramatic IOP reductions with only three drops a day in each eye. This is a far cry from the days when patients used up to eight drops a day (per eye) and four pills a day with the same level of effectiveness.

For Your Information:

Cosopt is available from Merck, P.O. Box 4, West Point, PA 19486; (215) 652-5000.