Comparison of latanoprost with fixed-combination dorzolamide and timolol in adult patients with elevated intraocular pressure: an eight-week, randomized, open-label, parallel-group, multicenter study in Latin America

BACKGROUND

The newer ocular hypotensive agents available to treat glaucoma and ocular hypertension (OHT) include latanoprost, a prostaglandin F(2alpha) analogue, and the fixed combination of dorzolamide hydrochloride, a carbonic anhydrase inhibitor, and timolol maleate, a beta-blocker.

OBJECTIVE

The aim of this study was to compare the efficacy and tolerability of latanoprost with that of the fixed combination of dorzolamide and timolol over 8 weeks.

METHODS

This interventional, 8-week, randomized, open-label, parallel-group study was conducted at 18 centers in 6 Latin American countries. Patients with unilateral or bilateral primary open-angle, pigmentary, or exfoliative glaucoma or OHT were randomized to receive latanoprost, 1 drop in the affected eye QD (evening), or fixed-combination dorzolamide/timolol, 1 drop in the affected eye BID (morning and evening). Medications were self-administered, 1 drop per affected eye. At baseline and week 8, intraocular pressure (IOP) was measured 3 times each at 8:30 am, 10:00 am, 2:00 pm, and 5:00 pm and after the water-drinking test, which estimates the IOP peak of diurnal tension curve, performed following the 5:00 pm IOP assessment. The primary efficacy outcome was change in diurnal IOP (the mean of IOP measurements) from baseline to week 8. Adverse effect (AE) data were recorded at each visit.

RESULTS

A total of 229 patients were randomized (latanoprost, n = 112; dorzolamide/timolol, n = 117). Mean baseline diurnal IOP values were similar between the 2 groups. Mean (SD) diurnal IOP reductions at week 8 before the water-drinking test were 6.9 (3.0) mm Hg for the latanoprost group and 6.4 (3.2) mm Hg for the dorzolamide/timolol group. Mean IOP values were similar at all time points except at 5:00 pm, when levels were significantly lower in latanoprost-treated patients (P = 0.025). After the water-drinking test, the increase in IOP values was similar between groups at baseline but lower in latanoprost-treated patients at week 8 (adjusted difference, 1.08 mm Hg; P = 0.012). Fewer patients treated with latanoprost reported ocular or systemic AEs (P = 0.025 and P < 0.001, respectively).

CONCLUSIONS

In this study of patients with unilateral or bilateral primary open-angle, pigmentary, or exfoliative glaucoma or OHT IOP reductions generally were similar between treatment groups, except at 5:00 pm, when the mean IOP level was significantly lower in latanoprost-treated patients. Latanoprost was better tolerated than fixed-combination dorzolamide and timolol.

Assessment of systemic adverse reactions induced by ophthalmic beta-adrenergic receptor antagonists

To assess quantitatively the risks of ophthalmic beta-blocking agents for cardiovascular and respiratory adverse reactions, we analyzed the binding kinetics of beta-blocking agents to the beta-1 and beta-2 adrenoceptors. The relationship between the occupancies for beta-1 and beta-2 adrenoceptors and the effects on the exercise pulse rate or the forced expiratory volume in one second (FEV1) after topical administration of carteolol, befunolol, timolol and betaxolol was analyzed using a ternary complex model. The beta-1 and beta-2 receptor occupancies after ophthalmic administration were calculated to be quite high as well as those after oral administration. The maximum occupancies for beta-1 and beta-2 receptors after ordinary ophthalmic administration were 52% and 88% for carteolol, 52% and 61% for befunolol, 62% and 82% for timolol, and 44% and 3% for betaxolol, respectively. Concave relationships were obtained between a decrease in exercise pulse rate and the beta-1 receptor occupancy and between a decrease in FEV1 and beta-2 receptor occupancy, respectively. Nasolacrimal occlusion was estimated to decrease the exercise pulse rate and FEV1 by 65% and 50%, respectively. The beta-1 and beta-2 adrenoceptor occupancies were proved to be the most appropriate indicators for cardiac and pulmonary adverse reactions evoked by ophthalmic beta-blocking agents.

Antiglaucoma medications: a review of safety and tolerability issues related to their use

BACKGROUND

Much experience has been gained with the use of older classes of antiglaucoma agents--topical beta-adrenergic-receptor antagonists, nonselective adrenergic-receptor agonists, oral carbonic anhydrase inhibitors, and cholinergic agents. In the past decade, new drugs and classes of drugs used to treat glaucoma have become available, including topical carbonic anhydrase inhibitors, prostaglandin analogues, and alpha2-adrenergic-receptor agonists. Extensive community-based use of antiglaucoma medications has led to an increased understanding of the acute and long-term safety and tolerability issues associated with their use.

OBJECTIVE

This paper reviews the side effects associated with the various classes of topical antiglaucoma drugs, with a particular focus on long-term safety issues.

Duration and long-term efficacy of phenylephrine-induced reduction in the systemic absorption of ophthalmic timolol in rabbits

Co-administration of phenylephrine decreases systemic timolol absorption after a single topical ocular dose of timolol in rabbits. This is probably due to vasoconstriction in the conjunctiva of the eye and nasal mucosa. In this study, we evaluated the duration of action and long-term efficacy of phenylephrine in reducing the systemic absorption of ophthalmic timolol in pigmented rabbits. Although co-administered phenylephrine had a short duration of interaction with systemic timolol absorption (20-60 min), its effect on systemic timolol absorption was substantial. The long-term vasoconstrictive effect of phenylephrine was studied by administering timolol-phenylephrine eyedrops into the eyes of rabbits once a day for two months. Systemic peak concentrations of timolol following timolol-phenylephrine eyedrop administration remained unchanged throughout the study. Phenylephrine may be useful additive in decreasing the systemic concentrations of ophthalmic drugs.

Systemic drug interactions with topical glaucoma medications

Topically administered ophthalmic medications are capable of attaining clinically important serum concentrations, as evidenced by the variety of systemic side effects they can produce. These drugs are therefore also capable of interacting with other drugs administered orally and intravenously. This is especially important when medications are administered to an elderly population, who are often receiving multiple medications. The Physician's Desk Reference and the United States Pharmacopeia Drug Information directory contain numerous warnings of potential interactions between topical glaucoma medications and systemically administered drugs. Unfortunately, literature supporting such interactions is limited, both in quantity and quality, being anecdotal in many cases. This report summarizes available information regarding the nonocular interactions between topical ophthalmic glaucoma medications and other systemically administered medications. Clinical evidence of these interactions is lacking in many cases.