Glaucoma medication change less common within drug class

"When a medical regimen fails to control the IOP, clinicians often add medications, but they may choose to switch in some cases," Dr. Netland said.

He added that decisions about whether to switch within a class of glaucoma medication should be evidence-based and individualized for each patient.

The beta-blockers provide several examples of appropriate switches.

"Although the efficacy of betaxolol (Betoptic, Alcon Laboratories) has been found to be slightly less than timolol in clinical trials, the pulmonary side effects of betaxolol are less than those of timolol, and this may provide the rationale for a switch in some patients," Dr. Netland said.

Patients who develop new pulmonary symptoms while using timolol might be candidates for such a change, he added.

A different formulation of the same medication also could have benefits.

"The efficacy and adverse effects of timolol gel-forming solution are essentially identical to those of timolol solution, but it's certainly true that most patients prefer the timolol gel-forming solution with once-a-day dosing as compared with the twice-a-day dosing of timolol solution. This may improve compliance in some patients," Dr. Netland said.

"For the same reasons, the same benefit may be provided by the new formulation of timolol maleate with ascorbic acid, which is also given once a day, versus timolol solution, which is given twice a day," he added.

The only change possible within the category of alpha-2 agonists is between apraclonidine (Iopidine, Alcon Laboratories) and brimonidine.

"The efficacy of these two medications has been equivalent in clinical trials in the short term; the long-term efficacy of apraclonidine after 90 days is not known," Dr. Netland said.

While both medications have a relatively high incidence of allergy, there is little cross-reactive allergic response between them, so a patient who develops an allergy to one of them may have treatment switched to the other.

Few differences in efficacy have been found between the various carbonic anhydrase inhibitors on the market, Dr. Netland said. However, differences in adverse effects may provide a rationale for changing medication.

"The systemic adverse effects of systemic carbonic anhydrase inhibitors are much less than those of topical carbonic anhydrase inhibitors," he said. "This is a well-recognized difference that provides a clear rationale for a switch within a class."

Also, brinzolamide (Azopt, Alcon Laboratories) causes less stinging on instillation than dorzolamide (Trusopt, Merck). While this is a minor adverse effect, it could improve compliance in some patients, Dr. Netland said.

Controversial switching Switches within the prostaglandin analogue class are more controversial, he continued.