Abstract and Introduction
Abstract
Purpose: We investigated the intraocular pressure (IOP) variations after switching from 0.005% latanoprost to 0.01% bimatoprost in open-angle glaucoma patients who experienced IOP elevation during treatment.
Patients and Methods: Retrospective, interventional cohort study. Of the 625 patients with open-angle glaucoma, we included 41 patients on latanoprost who showed a peak IOP increase of at least 15% [assessed during the water drinking test (WDT)2] relative to the peak IOP measured during the previous WDT (WDT1).
Main Outcome Measure: Baseline, peak, and IOP measurements at each timepoint (15, 30, and 45 min) during all 3 WDT sessions (WDT1, WDT2, and WDT3) were measured.
Results: The mean peak IOP was 15.6 mm Hg (SE, 0.73) during WDT1; 21.1 mm Hg (SE, 0.73) during WDT2; and 16.1 mm Hg (SE, 0.73) during WDT3 (P<0.001, repeated-measures analysis of variance). Comparing WDT1 versus WDT2, the mean peak IOP difference was 5.5 mm Hg (P<0.001); for WDT1 versus WDT3, the difference was 0.5 mm Hg (P=0.312); for WDT2 versus WDT3, the mean difference was -5.0 mm Hg (P<0.001). The mean IOP at each timepoint during the WDT sessions was significantly different between WDT1 and WDT2 and between WDT2 and WDT3.
Conclusions: Our study suggests that glaucoma patients on latanoprost who experienced IOP elevation during the course of therapy may benefit from switching to bimatoprost. This alternative can potentially postpone more costly or invasive treatment options.
Introduction
Glaucoma is a progressive optic neuropathy characterized by loss of retinal ganglion cells and their axons resulting in a characteristic and distinctive appearance of the optic disc, concomitant loss of visual function, in addition to being the second leading cause of irreversible blindness in the world.[1,2] The mechanism by which glaucoma damages the optic nerve is probably multifactorial but elevated intraocular pressure (IOP) is the main risk factor[3–8] and the only one that can be modified using currently available resources.
Latanoprost (Xalatan) is a F2-alpha prostaglandin analog designed to reduce the IOP in patients with glaucoma and ocular hypertension. It reduces the IOP by increasing the uveoescleral outflow through the ciliary muscle into the suprachoroidal space and episcleral veins. The effect is apparently mediated by an interaction with prostaglandin F receptors.[9–13]
Bimatoprost is an ocular hypotensive drug that belongs to a family of fatty acid amides called prostamides. Prostamides exist naturally in the environment, demonstrate potent activity in reducing IOP, and are biosynthesized from anandamide, a substrate of cyclooxygenase-2.[14] Unlike prostaglandin analogs, bimatoprost does not require conversion to an active metabolite to exert its pharmacological activity.[15] Its mechanism of action includes the reduction of tonographic resistance to aqueous humor outflow and an increase of the outflow rate through the uveoescleral pathway.[16,17]
Some studies have shown that, 2 years after treatment initiation with latanoprost, a significant IOP reduction was sustained, without evidence of reduced effectiveness over that period.[18,19] Also, the differences between diurnal and nocturnal IOP levels were not statistically significant, which suggests a relatively homogeneous hypotensive effect around-the-clock, contrary to what has been described with other ocular hypotensive medications.[20]
When comparing these 2 drugs, IOP reduction tended to be greater with bimatoprost in both short-term[21–24] and long-term studies.[25] In the per-protocol analyses of the XLT Trial, IOP levels tended to be lower in bimatoprost-treated patients although it did not reach statistical significance.[26] Moreover, that study used bimatoprost at 0.03%, as opposed to the concentration of 0.01% widely used today. Noecker et al[25] described a significantly greater IOP reduction during all tonometric measurements in the group of patients treated with bimatoprost compared with latanoprost, although another study did not show a statistically significant advantage.[27]
It has been suggested that the peak IOP may be an important risk factor for progression;[28–31] therefore, glaucoma management should focus not only on reducing IOP but also maintaining its stability over the 24-hour period. The mean IOP has also been shown to strongly correlate with glaucoma progression, unlike IOP fluctuation, the importance of which remains questionable.[32,33]
Although the detection of IOP peaks greatly depends on appropriate IOP monitoring during and outside office hours, IOP mean calculation requires the collection of longitudinal IOP data and may be affected by the interval between visits. Therefore, establishing a target peak IOP is clinically easier than seeking to establish a target mean IOP, as it has been done in clinical trials.[4–6]
An appropriate evaluation of the effectiveness of ocular hypotensive medications often requires the assessment of multiple IOP measurements throughout the day (eg, diurnal tension curves) and in different days. To overcome the limited feasibility of performing diurnal tension curves in large scale, studies have shown that the water drinking test (WDT), a stress test that indirectly assesses the outflow capacity, could be used to detect IOP peaks not identified during office hours with single IOP measurements.[34,35] Different study groups have shown that the WDT can replicate IOP peaks occurring during[36] and outside office hours[37] and between different days.[38] Moreover, the test-retest variability of the WDT has been reported to be excellent among treated[39] and untreated[40] glaucomatous eyes. Because of its validity[36–38] and reproducibility,[39,40] this stress has been used in studies aiming to compare the effectiveness of different medical[41,42] and surgical[43,44] options to lower IOP in glaucoma. In the present study, we used the WDT to assess the peak IOP variations following modifications of medical treatment in glaucoma patients.
The purpose of this study was to investigate IOP variations after switching from 0.005% latanoprost (Xalatan) to 0.01% bimatoprost (Lumigan RC) in patients with open-angle glaucoma (OAG) who experienced a reduction of the hypotensive effect during treatment with latanoprost used alone or in conjunction with other topical hypotensive drugs.
J Glaucoma. 2016;25(4):E359-E366. © 2016 Lippincott Williams & Wilkins
