Rx CARE

New glaucoma drug offers convenient once-daily dosing

Data compiled by NDC Health indicate that U.S. ophthalmic beta-blocker sales currently exceed $170 million per year, with more than 4.4 million prescriptions written annually. Clinicians will soon be able to offer those with glaucoma a nonselective beta-blocker with the convenience of once-daily dosing.

The Food & Drug Administration recently approved timolol (Istalol, ISTA Pharmaceuticals) ophthalmic solution 0.5% for the treatment of elevated intraocular pressure in patients with ocular hypertension or open-angle glaucoma. The product will be available within the next several months.

Until now, topically applied, ophthalmic beta-blockers were dosed twice daily, said Thomas Mundorf, M.D., an ophthalmologist in private practice in Charlotte, N.C., who was a clinical investigator for the Istalol clinical trials in the United States. This particular formulation of timolol, which contains potassium sorbate, enhances the bioavailability of the drug, he explained.

The twice-daily formulations of timolol, such as Timoptic (Merck) and timolol gel-forming/drops (Falcon Pharmaceuticals), are thicker than Istalol, Mundorf said. He went on to say that Istalol was formulated so that the product could be dosed once daily.

The labeling for Istalol contains a bold-faced warning that, like other topically applied ophthalmic drugs, it is absorbed systemically. The manufacturer cautions that the same adverse reactions associated with systemic beta-blockers may occur with topical administration. The company advises that Istalol is contraindicated in those with bronchial asthma, severe chronic obstructive pulmonary disease, sinus bradycardia, second- or third-degree atrioventricular block, overt cardiac failure, cardiogenic shock, or hypersensitivity to any component of the product.

According to ISTA Pharmaceuticals, Istalol should not be used alone in the treatment of angle-closure glaucoma. The company does not recommend the concomitant use of two topical beta-blockers and advises close observation of those receiving both an oral beta-blocker and Istalol. ISTA added that caution should be used in the coadministration of beta-blockers and oral or intravenous calcium antagonists.

Beta-blockers should be used with caution in those with cerebrovascular insufficiency, ISTA said. They should also be used with caution in persons who have diabetes or are subject to hypoglycemia.

Close observation of those taking a beta-blocker concomitantly with a catecholamine-depleting drug such as reserpine is recommended.

ISTA said that, in clinical trials, the most frequently reported adverse event associated with Istalol use was burning or stinging upon instillation. Other adverse events included blurred vision, the development of cataracts, conjunctival infection, headache, hypertension, infection, itching, and decreased visual acuity.

Pharmacists can remind patients to use Istalol regularly as prescribed, said Mundorf. Patients should be careful not to use more of the product per dose than recommended, because it may have systemic side effects, he added.

Pharmacists should instruct those who are using multiple eyedrops that are dosed at similar times to separate the instillation of each agent by at least five minutes, Mundorf cautioned. He also said that patients should close their eyes for two minutes following the instillation of eyedrops.

"Because glaucoma is a serious chronic condition, it is important to offer patients therapeutic alternatives," said Mundorf. "Istalol gives patients an effective therapeutic option with the convenience of a once-daily formulation," he concluded.

Charlotte LoBuono

TIPS TO REMEMBER: Istalol

• Patients should be instructed not to allow the tip of the dispensing container to contact the eye or surrounding area.
• Contact lenses should be removed prior to the administration of Istalol. Lenses may be reinserted 15 minutes following administration.
• Istalol is classified as Pregnancy Category C. It should be used during pregnancy and lactation only if the therapeutic benefits outweigh potential risk to the fetus.

 

Charlotte LoBuono. New glaucoma drug offers convenient once-daily dosing. Drug Topics Jul. 12, 2004;148:22.