Beta blocker still option as initial or adjunctive IOP-lowering medication, physician says

Baltimore-Beta blockers continue to play an important role as an ocular hypotensive agent for both primary and adjunctive treatment, and when a beta blocker is indicated, the novel formulation of timolol maleate 0.5% ophthalmic solution with potassium sorbate (Istalol, ISTA Pharmaceuticals) is a good choice, said Alan L. Robin, MD.

"Use of beta blockers for IOP-lowering is not a thing of the past. Their place in the treatment algorithm has changed with the advent of the prostaglandin analogues," said Dr. Robin, associate professor of ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore. "However, while beta blockers may no longer be considered the gold standard for initial medical therapy in most patients, they are a viable second-line choice for primary therapy in certain clinical situations and definitely have a major role as an add-on or adjunctive therapy in patients responding insufficiently to prostaglandin analogue monotherapy."

Discussing issues relevant to selection of an add-on agent in patients already on prostaglandin therapy, Dr. Robin noted that the choices aside from a beta blocker include the alpha-agonist brimonidine or the carbonic anhydrase inhibitor dorzolamide. Those agents suffer from several drawbacks, however. Relevant to both is that they involve three times daily administration.

Brimonidine and dorzolamide also have limitations in terms of IOP-lowering activity. Brimonidine has a potent peak effect, but it is relatively short-lived so that IOP can fluctuate significantly throughout the day, leaving patients without good 24-hour IOP control. Used as monotherapy, the topical carbonic anhydrase inhibitor only lowers IOP by about 15% to 18%.

"Timolol affords a potent and consistent IOP-lowering effect, with an average reduction of approximately 25%, and a product that could be administered once daily in the morning, such as [timolol maleate with potassium sorbate], then becomes an excellent adjunctive medication in the patient using a prostaglandin analogue once daily in the evening," he said.

Discussing the role of beta blockers as primary therapy, Dr. Robin identified several situations where a prostaglandin analogue may not be considered the treatment of choice. One such patient subgroup would include blue-eyed individuals who are strongly opposed to experiencing eye color change induced by their topical treatment. Also, due to the risk of hyperemia with a prostaglandin analogue, an alternative agent may be preferred.

An alternative to a prostaglandin analogue also might be sought for women who wish to become pregnant because the topical prostaglandin analogue may cause spontaneous abortion. And cost is an important issue to consider when prescribing treatment for all patients, whether or not these factors exist.

"Prostaglandin analogue treatment may be expensive, and it is important to investigate whether cost will prohibit the patient from filling the prescription, using it as directed, or refilling it when it runs out," Dr. Robin said.

With a proven track record of efficacy during almost 3 decades of use, timolol is an excellent choice as initial IOP-lowering medication in the patient who is not a good candidate for a prostaglandin analogue and has no contraindications to treatment with a non-selective beta blocker. In that situation, [timolol maleate with potassium sorbate] is again an excellent choice because it offers convenient once-daily dosing to promote compliance, he said.

"This formulation of timolol contains potassium sorbate that enhances the lipophilicity of the beta blocker. As a result, there is reported enhanced transcorneal penetration of the active ingredient, attainment of a higher concentration of timolol in the anterior chamber, and potentially more prolonged IOP-lowering activity relative to other timolol solutions," he said.

Gel preparations of timolol also are approved for once-daily dosing, but compared with those products, [timolol maleate with potassium sorbate] may have the advantage of not causing transient blurring of vision, Dr. Robin said.

"Glaucoma patients are very conscious about that blurring effect of gel preparations. As an ophthalmic solution, [timolol maleate with potassium sorbate] is well-tolerated and has good patient acceptance," Dr. Robin said.