Once--daily versus T wice--daily Levobunolol (0.5 0/0) Therapy A Crossover Study Robert J. Derick, MD/,2 Alan L. Robin, MD,1,2 James Tielsch, PhD,3 Jeffrey L. Wexler, MD,2 Elaine P. Kelley,4 Jack F. Stoecker,4 Gary D. Novack, PhD,4 Anne L. Coleman, MD 1,2
T
he authors executed a two-period, randomized, double-masked, crossover study comparing once-daily to twice-daily levobunolol hydrochloride (0.5%) in 20 patients with elevated intraocular pressure (lOP). Modified diurnal curves were performed at four times for each study arm: baseline, day 1, day 14, and day 28. The mean diurnal corrected decrease in lOP from baseline ranged from 16% ± 11 % to 22% ± 9% when the subjects were treated twice daily, and from 14% ± 1 0% to 18% ± 8% when the same subjects were treated once daily. At day 1, patients had a significantly greater lOP lowering after twice-daily therapy than after once-daily therapy (P < 0.05). At 14 and 28 days, there was no clinically significant difference between the two treatment regimens. The results of our crossover study suggest that once-daily treatment with levobunolol (0.5%) is as effective as twice-daily treatment. Ophthalmology 1992; 99:424-429
Levobunolol is a nonselective (3,-(32 adrenoceptor antagonist that effectively lowers intraocular pressure (lOP) in subjects with glaucoma and ocular hypertension. '-6 Levobunolol, like other ophthalmic (3-blockers, is usually applied twice daily. The rationale for twice-daily dosing Originally received: July 25. 1991. Revision accepted: October 22. 1991. I Glaucoma Service. Wilmer Institute. Johns Hopkins Hospital. Baltimore. 2 Krieger Eye Institute. Sinai Hospital, Baltimore. 3 Dana Center. Wilmer Institute, Johns Hopkins Hospital. Baltimore. 4AIlergan Pharmaceuticals, Irvine. Presented in part at the Association for Research in Vision and Ophthalmology Annual Meeting, Sarasota. April 1990. Supported in part by a grant from the Zanvyl Krieger Foundation and Allergan. Inc. Irvine. California. Dr. Coleman is currently affiliated with the Department of Ophthalmology. UCLA School of Medicine. Los Angeles. Dr. Novack is currently affiliated with Pharmalogic, Inc. Irvine. Drs. Derick. Rohin. Tielsch. Wexler. and Coleman have no proprietary interests in Allergan. Inc, or levobunolol. Reprint requests to Alan 1.. Robin. MD. 6115 Falls Rd. Third Floor, Baltimore. MD 21209-2226.
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of ophthalmic (3-blockers is, in part, based on the original dose-response studies oftimolol. 7 However, there is recent evidence suggesting that less frequent application may be as effective. Once-daily dosing may be all that is required to obtain the maximum effect of a (3-blocker. Schlecht and Brubaker8 demonstrated that aqueous humor production does not recover to a normal level for at least 14 days, and lOP does not increase for at least 2 to 4 weeks after discontinuation of medication in patients on long-term timolol therapy. Nonselective (3-blocker therapy may require a less frequent dosing interval. Perhaps after a patient has achieved a new steady state of aqueous production while taking levobunolol, once-daily dosing or perhaps even less frequent dosing may be adequate to achieve maximum lOP reduction from (3-blocker therapy. There are several potential advantages of once-daily dosing. Nonselective (3,-(32 adrenoceptor antagonists can cause many adverse reactions, including bradycardia, systemic hypotension, bronchoconstriction, and central nervous system side effects. 9,10 The amount of levobunolol gaining access to the systemic circulation theoretically would be decreased by using a less frequent dosing schedule. Once-daily therapy would also reduce the cost of
Derick et al . Levobunolol Therapy glaucoma therapy and possibly improve patient compliance. Several investigators have shown that once-daily therapy with levobunolol 0.5% is effective, and compares favorably with timolol 0.5% used once daily.11,12 In addition, the issue of once-daily versus twice-daily dosing of levobunolol (0.5%) has been examined by Rakofsky and coworkers 13 using a parallel study design. They found oncedaily therapy with levobunolol to be as effective as twicedaily therapy in decreasing mean lOPs. However, there are limitations to these parallel studies. A parallel design uses two separate, randomly assigned, and what are hoped to be similar groups of patients. No previous studies have been conducted to evaluate whether an equivalent ocular hypotensive effect can be achieved by comparing once-daily therapy with twice-daily therapy in the same individuals. Studies using a parallel design cannot entirely address this issue. In a crossover design, no assumption about the effectiveness of the randomization process or similarity of the patients is required, as each patient serves as his own control. Since the issues of once-daily versus twice-daily dosing of topical .a-blockers have important medical and economic ramifications, we chose to evaluate this issue using a crossover design in which all patients received both once-daily and twice-daily levobunolol 0.5% in two separate I-month study periods.
Patients and Methods This study used a single-centered, two-period, randomized, double-masked, crossover design. We enrolled 21 chronic open-angle glaucoma or ocular hypertensive patients with symmetrical untreated lOP readings of at least 22 mmHg in both eyes. Neither eye had marked optic nerve damage or visual field loss by automated perimetry. Before study entry, patients were required to cease all ocular hypotensive medications for a minimum of 30 days. We excluded subjects from study participation whose elevated lOP was not controlled by 2 medications or who had glaucoma laser or filtration surgery within the past 3 months; women of childbearing potential or nursing mothers; patients with cardiovascular or pulmonary contraindications to .a-blockers, uncontrolled systemic disease, or hypersensitivity to the study medication ingredients; patients using systemic .B-blockers, corticosteroids, or a-agonist agents; patients with corticosteroid-induced,
Table 1. Examination Protocol Observation or Measurement
SAM
12 noon
History Visual acuity Biomicroscopy Intraocular pressure Pulse rate Blood pressure
x x x x x x
x x x
4:30
x x
x
PM
Table 2. Study Design Month
Group A
Group B
1 2 3
Washout" Levobunolol 0.5% QD Washout" Levobunolol 0.5% BID
Washout" Levobunolo1 0.5% BID Washout" Levobuno101 0.5% QD
4
• Patients discontinued all medications for glaucoma during this month. QD
=
once daily; BID
=
twice daily.
uveitic, or neovascular glaucoma; and patients with active ocular disease, corneal abnormalities, or patients who wore contact lenses. Our institutional review board approved the study and written informed consent was obtained from all subjects. On the first day, we obtained a medical and ophthalmic history. Initial examination included Snellen visual acuity measurement, slit-lamp evaluation of the anterior segment, ophthalmoscopic examination of the optic nerve, and a visual field if one had not been performed within the last 3 months. Intraocular pressure, resting heart rate, and blood pressure were measured in each patient at 8:00 AM, 12:00 noon, and 4:30 PM. After this baseline examination, we randomized patients into two treatment groups: group A began the study with once-daily levobunolol 0.5%, and group B began with twice-daily levobunolol 0.5%. This sequence was masked to both the investigator and the patient. All patients received different color-coded bottles for both morning and evening medications. The evening bottle always contained levobunolol 0.5%, while the morning bottle contained levobunolol 0.5% in group B and vehicle in group A. Patients were instructed to use their morning bottle in both eyes between 5:00 and 7:00 AM and their evening bottle in both eyes between 5:00 and 7:00 PM beginning the evening of the baseline examination. Patients then administered their drops for 1 month and returned for follow-up examinations 1 day, 14 days, and 28 days after the baseline examination (Tables 1 and 2). Follow-up examinations were identical to the baseline examinations, including diurnal lOP measurements, except ophthalmoscopy and visual fields were not performed. Thus, patients receiving once-daily levobunolol had lOP determinations during the final 12 hours oftheir 24-hour dosing interval while patients receiving twicedaily levobunolol had lOP measurements during the entire 12 hours between each twice-daily dose. After completion of the first period, all subjects underwent a I-month washout without receiving any ocular hypotensive medication. Another baseline examination was performed, including diurnal lOP measurements, on no ocular medications, at 8:00 AM , 12:00 noon, and 4:30 PM. Each subject then underwent the crossover to the alternate dosing schedule and received new bottles of test medications that evening (patients in group A started twice-daily treatment and patients in group B started oncedaily treatment). Follow-up examinations were again per-
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formed 1 day, 14 days, and 28 days later, in a method identical to the first study arm. In designing the study, sample size calculations were based on a clinically significant difference of 2 mmHg in mean lOP between the treatment regimens. The values of lOP on each examination day were calculated by averaging the values of the right and left eye for all three diurnal measurements (a total of 6 lOP values were averaged). Intraocular pressure changes from baseline at each examination were analyzed by a two-way analysis ofvariance model for crossover studies. 14 We also analyzed our data to insure that there was an adequate washout between the two treatment arms. An analysis of variance model for crossover studies was used to account for any carryover effect at baseline and at each follow-up period. There was not considered to be a significant carryover effect unless P .:S 0.10.
Results patients were selected for the study, and 20 patlents completed both arms of the crossover. One patient elected not to complete the second arm of the crossover because of time considerations. We did not include her. data because data from both study arms for every subject are needed to perform the crossover analysis. Demographic characteristics of the subjects are included in Table 3. The diurnal mean lOP was similar at baseline for the subjects before either once-daily or twice-daily treatment with levobunolol 0.5% (23.14 ± 2.70 mmHg versus 23.27 ± 1.96 mmHg, respectively). As expected, both once-daily and twice-daily treatment significantly lowered mean lOP at all follow-up intervals (P < 0.0001) (Fig 1, Tables 4 and 5). In the once-daily group, the mean lOP decline from baseline ranged from 14% to 18%. Declines from baseline lOP for the twice-daily study arm ranged from 16% to 22%. The only noteworthy difference between the
24.0 23.0 22.0 21.0 C) J: 20.0 E 19.0 E D.. 18.0 Q 17.0 16.0 15.0 14.0
II Once-daily
•
Baseline
1
Day
Twice-daily
14
28
Figure 1. Mean diurnal corrected intraocular pressure (± standard error) of open-angle glaucoma or ocular hypertensive subjects during the crossover study. Both treatment regimens showed significant decreases of intraocular pressure from baseline at all time periods (P < 0.001). There was a significant difference between the two treatments on day 1 (P < 0.05), but not on days 14 or 28 (P > 0.17, P > 0.91, respectively).
Tw~nty-one
Table 3. Demographic Information Variable Age (yrs) Mean ± standard deviation Range Sex Male Female Race White Black Iris color Brown Green Blue Diagnosis Open-angle glaucoma Ocular hypertension
426
Subjects (n
=
20)
two treatment schedules (when all 6 lOP values for each patient were averaged, Table 4) was on day 1 when the lOP decrease from baseline in the twice-daily group was greater than the once-daily group (P < 0.05). On days 14 and 28, there was no difference in the mean ocular hypotensive effect between once-daily and twice-daily treatment with 0.5% levobunolol. We found similar results when evaluating each treatment period. There were only significant differences in diurnal variation (Table 5) on day 1 (8:00 AM and 12:00 noon) and day 14 (8:00 AM). There was no difference in diurnal variation at any later time period throughout the study. By day 28, the diurnal mean lOP values for both treatment groups were within 0.5 mmHg of each other at each time point (Table 5). At 8:00 AM, lOP measurements were performed 1 to 3 hours after instillation in the twice-daily group and 13 to 15 hours after instillation in the once-daily group. The 12:00 noon measurements were made 5 to 7 hours after instillation oflevobunolol in the once-daily group and 17 Table
55.55 ± 13.17 31-74
Day
12 (60%)
Baseline Day 1 Day 14 Day 28
8(40%)
10 (50%) 4(20%) 6 (30%) 6(30%) 14 (70%)
Mean Intraocular Pressures and Mean Changes from Baseline Levobunolol (0.5%)"
8(40%)
12 (60%)
4.
Once Daily 23.2 20.0 18.9 19.5
± 2.7 ± 2.3 (14%) ± 1.9 (18%) ± 2.9 (16%)
Twice Daily 23.2 18.1 18.1 19.6
± 2.0 ± 2.2 (22%) ± 1.7 (22%) ± 2.6 (16%)
• n = 20. All data represent mean intraocular pressure ± standard deviation in mmHg averaged from both eyes at three times on each examination day (6 intraocular pressure measurements were used to calculate each data point listed above). Numbers in parentheses represent percent reduction from baseline. Once daily versus twice daily difference is Significant on day 1 (P < 0.05).
Derick et al . Levobunolol Therapy Table 5. Diurnal Variation in Intraocular Pressure (mmHg) Visit Day
Time of Day
Day 0
SAM 12 Noon 4:30 PM SAM 12 Noon 4:30 PM SAM 12 Noon 4:30 PM SAM 12 Noon 4:30 PM
Day 1
Day 14
Day 2S
Once Daily (Mean ± Standard Deviation) 25.1 23.0 21.5 20.S 20.3 19.1 19.6 19.0 lS.5 19.1 19.4 lS.6
± ± ± ± ± ± ± ± ± ± ± ±
3.0 3.2 3.0 3.9 3.0 3.2 2.5 2.S 2.S 2.S 3.0 2.6
Pvalues
Twice Daily (Mean ± Standard Deviation)
Drug
Carry Over
± ± ± ± ± ± ± ± ± ± ± ±
0.206 0.302 0.313 0.0070.0010.234 0.0200.17S 0.412 0.7S0 0.495 0.362
0.162 0.137 0.109 0.530 0.261 0.111 0.497 0.561 0.400 0.606 O.S11 0.515
23.9 23.7 22.3 lS.3 lS.0 lS.2 lS.2 lS.5 lS.0 19.3 19.0 19.0
2.9 2.1 2.2 1.S 1.S 2.4 1.9 1.9 2.0
1.7
2.1 1.S
• Significant (P < 0.05) between-group intraocular pressure difference. This was only seen at 2 time intervals on day 1, and 1 time interval on day 14. There was no significant (P < 0.10) carryover effect seen at any time interval.
to 19 hours after instillation of levobunolol in the oncedaily group. The 4:30 PM measurements represent the point that was most distant from dosing in the once-daily levobunolol group, approximately 21.5 to 23.5 hours versus 9.5 to 11.5 hours after instillation in the twice-daily group. Assuming a minimum clinically meaningful difference of 2 mmHg, the power to detect this difference at the (\' = 0.05 probability level was 78% and 86% on days 14 and 28, respectively. In addition, there was no indication of a treatment order effect at any of the follow-up times. The carryover (Table 5) was never significant. We were unable to detect a difference in the ocular hypotensive response to 0.5% levobunolol, once-daily versus twice-daily, related to race, sex, or iris color. No changes of note occurred in visual acuity, biomicroscopic, or ophthalmoscopic findings during the study. Significant decreases in mean resting heart rate occurred
-
85
CI)
-
tU a: 80 ....
~
Once-daily
•
Twice-daily
tU
CI)
J:
75
Cl
s::
-=
U)
CI)
a:
70 65 Baseline
14
28
Day Figure 2. Mean resting heart rate (± standard error) of patients during the crossover study. There was a significant between-group difference on day 1 (P < 0.02), but not on days 14 or 28.
with each of the treatment regimens (Fig 2). Reductions in mean resting heart rate from baseline were significantly greater with twice-daily therapy on day 1 (10.4 ± 7.7 versus 5.0 ± 8.9, P < 0.02), but not on days 14 or 28 (P> 0.1). However, no patient was dropped from the study because of symptoms related to a reduction in heart rate. No significant between-group changes in mean systolic or diastolic blood pressure were observed during the study. Regardless of the frequency of instillation, the most common patient complaint was ocular burning or stinging. These complaints were infrequent.
Discussion This report confirms the results of prior parallel studies, which found once-daily levobunolol 0.5% to be effective in lowering elevated lOP. An important feature of our study is its crossover design, in which each subject received both once-daily and twice-daily treatment. There are, however, disadvantages to a crossover design. The time commitment for each patient is twice as long as that required in a similar parallel design. In our study, each patient required two drug washout periods rather than the one washout period required in a parallel design. Withholding medication for 2 months could potentially jeopardize a glaucoma patient with advanced disease. For this reason, an additional placebo arm was not included in the current study. The completion of both study arms by each patient is required for the analysis. In this regard, we were fortunate not to have incurred a higher dropout rate. Despite these difficulties, a crossover design enables the clinician to evaluate whether an equivalent ocular hypotensive effect can be achieved by comparing once-daily and twice-daily dosing within the same group of individuals. Indeed, we were unable to demonstrate any difference in mean lOP change from baseline when we com-
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Volume 99, Number 3, March 1992
pared the two dosing regimens after the first day of each period. We conclude, therefore, that the patients in our sample responded in a clinically identical manner to the two treatment regimens after the first day oftherapy. Although our sample size was relatively small, the 78% to 86% power of our design to find a 2 mmHg lOP difference compares favorably with the parallel study reported previously.13 Another important feature of our study design was the monitoring ofIOP over many hours on every examination day. Each patient underwent a baseline diurnal lOP determination and three follow-up diurnal lOP determinations while on each dosing schedule. This type of design will partially eliminate nondrug-related influences on lOP by considering an individual's diurnal variation. The mean reduction in lOP ranged from 14% to 22% in our patients, which is slightly lower than the 18% to 27% reported in other series of patients. 4 - 6 However, differing study designs in which diurnal variation is not considered make direct comparisons difficult. In this study, patients in the once-daily group were given levobunolol 0.5% in the evening rather than in the morning. While this is not standard practice, it was done in this case to allow diurnal measurements to be performed during office hours. With this regimen, the 12:00 noon lOP measurements were taken 17 to 19 hours after instillation of drug. If the conventional morning instillation had been used, the points corresponding to 17 to 19 hours after instillation would occur while patients were asleep (approximately 12:00 AM to 2:00 AM). Henkind and co-workers l5 showed that lOP is lowest during these hours and is normally at its highest point in the morning hours. Topper and Brubaker l6 demonstrated that aqueous humor flow is decreased during sleep and that timolol does not suppress aqueous formation during sleep. In actual practice, patients instilling levobunolol 0.5% in the morning may theoretically be providing greater protection against morning lOP elevations since the peak ocular hypotensive effect oflevobunolol has been demonstrated to occur 2 to 4 hours after instillation. I Only on the first day after the initiation of treatment was there a difference in the ocular hypotensive effect of levobunolol 0.5%. This difference favored twice-daily treatment. Subjects on the once-daily regimen would only have received a single dose of drug before the day 1 examination. Therefore, the observed difference between once-daily and twice-daily therapy on day 1 may reflect that a steady state drug level had not yet been achieved. Few data have been published about the pharmacokinetics of topically applied levobunolol. The major breakdown product of levobunolol, dihydrolevobunolol, has a halflife of 7 hours in the systemic circulation and is similar in efficacy and potency to levobunolol. 17 Using basic pharmacokinetics, a drug reaches a systemic steady state level after approximately 4 halflives. 18 Perhaps a similar situation exists for intraocular levels of ophthalmic medications after topical instillation, rendering single-drop dose-response studies of ,a-blockers somewhat misleading. Alternatively, binding of drug in the anterior segment may create a depot after several days explaining comparable
428
effects of once-daily to twice-daily therapy at weeks 2 and 4. Timolol has been shown to bind to melanin in the iris and ciliary body in vitro and in animal models and this may also hold true for other ,a-blockers such as levobunolo1. 19 ,20 Perhaps an intraocular drug depot develops in chronic users oftimolol, which could explain the persistent reduction in aqueous flow and significant lowering ofIOP for more than 2 weeks after withdrawal of the medication in these patients. 8,2 I Although the present study shows that once-daily administration is as effective as twice-daily administration, perhaps less frequent administration will have similar effects. Topical ,a-blockers can cause myriad systemic side effects, including bradycardia, hypotension, central nervous system effects, bronchoconstriction, and adverse changes of blood cholesterol levels. 22 All of these side effects can theoretically be reduced by lowering systemic absorption through a less frequent dosing regimen. Our study was not designed to establish a substantial difference in systemic side effects between the two regimens. Other investigators, however, have demonstrated trends toward less systemic effects with once-daily dosing.1 3 Another method to decrease the frequency of systemic side effects might possibly be through use of a lower concentration of a drug. Although not evaluated in our study, previous dose-response studies as well as clinical parallel studies have shown levobunolol 0.25% to be effective in treating ocular hypertension. 23 ,24 Kass et al 25 have shown that medication compliance is better in patients using timolol twice daily than in patients using pilocarpine four times daily. There are no published reports to our knowledge comparing compliance between once-daily and twice-daily regimens of topical ophthalmic medications. Eisen and co-workers26 have shown that compliance improves as the prescribed dose frequency is changed from three times daily to once daily in patients receiving therapy for systemic hypertension. Patient compliance was not objectively determined in the current study; however, this may be an advantage of oncedaily treatment. The cost of glaucoma medication to the patient has not been formally studied, however, this factor should be considered in any treatment plan, and especially when the medication is for long-term use. Assuming a 50% reduction of refills for once-daily treatment, a patient could save hundreds of dollars per year for an equivalent ocular hypotensive response. The results of this study suggest that levobunolol 0.5% used once daily is as effective in lowering lOP as twicedaily therapy in selected patients with elevated lOP.
References 1. Duzman E, Ober M, Scharrer A, Leopold IR. A clinical evaluation of the effects of topically applied levobunolol and timolol on increased intraocular pressure. Am J Ophthalmol 1982; 94:318-27. 2. Partamian LG, Kass MA, Gordon M. A dose-response study of the effect of levobunolol on ocular hypertension. Am J Ophthalmol 1983; 95:229-32.
Derick et al . Levobunolol Therapy 3. Cinotti A, Cinotti D, Grant W, et al. Levobunolol vs timolol for open-angle glaucoma and ocular hypertension. Am J Ophthalmol 1985; 99:11-7. 4. Ober M, Scharrer A, David R, et al. Long-term ocular hypotensive effect oflevobunolol: results of a one-year study. Br J Ophthalmol 1985; 69:593-9. 5. Berson FG, Cohen HB, Foerster RJ, et al. Levobunolol compared with timolol for the long-term control of elevated intraocular pressure. Arch Ophthalmol 1985; 103:379-82. 6. The Levobunolol Study Group. Levobunolol: a beta-adrenoceptor antagonist effective in the long-term treatment of glaucoma. Ophthalmology 1985; 92:1271-6. 7. Zimmerman TJ, Kass MA, Yablonski ME, Becker B. Timolol maleate: efficacy and safety. Arch Ophthalmol1979; 97:656-8. 8. Schlecht LP, Brubaker RF. The effects of withdrawal of timolol in chronically treated glaucoma patients. Ophthalmology 1988; 95:1212-6. 9. Novack GO, Tang-Liu DD-S, Kelley EP, et al. Plasma levobunolol levels following topical administration with reference to systemic side effects. Ophthalmologica 1987; 194: 194-200. 10. Leren P, Foss PO, Nordvik B, Fossbalkk B. The effect of enalapril and timolol on blood lipids. A randomized multicenter hypertension study in general practice in Norway. Acta Med Scand 1988; 223:321-6. 11. Wandel T, Charap AD, Lewis RA, et al. Glaucoma treatment with once-daily levobunolol. Am J Ophthalmol 1986; 101 :298-304. 12. David R, Foerster RJ, Ober M, et al. Glaucoma treatment with once-daily levobunolol [letter]. Am J Ophthalmol 1987; 104:442-3. 13. Rakofsky SI, Melamed S, Cohen JS, et al. A comparison of the ocular hypotensive efficacy of once-daily and twice-daily levobunolol treatment. Ophthalmology 1989; 96:8-11. 14. Cochran WG, Cox GM. Experimental Designs, 2nd ed. New York: John Wiley and Sons, 1957; 117-21.
15. Henkind P, Leitman M, Weitzman E. The diurnal curve in man: new observations. Invest Ophthalmol 1973; 12: 705-7. 16. Topper JE, Brubaker RF. Effects of timolol, epinephrine, and acetazolamide on aqueous flow during sleep. Invest Ophthalmol Vis Sci 1985; 26:1315-9. 17. DiCarlo FJ, Leinweber F-J, Szpiech JM, Davidson IWF. Metabolism of L-bunolol. Clin Phannacol Ther 1977; 22: 858-63. 18. Gilman AG, Goodman LS, Gilman A. Goodman and Gillman's The Pharmacologic Basis of Therapeutics, 6th ed. New York: MacMillan, 1980; 23. 19. Menon lA, Trope GE, Basu PK, et al. Binding of timolol to iris-ciliary body and melanin: an in vitro model for assessing the kinetics and efficacy oflong-acting antiglaucoma drugs. J Ocul Pharmacol 1989; 5:313-24. 20. Abrahamsson T, Bostrom S, Brautigam J, et al. Binding of the {3-blockers timolol and H 216/44 to ocular melanin. Exp Eye Res 1988; 47:565-77. 21. Steinert RF, Thomas JV, Boger WP Ill. Long-term drift and continued efficacy after multiyear timolol therapy. Arch Ophthalmol 1981; 99:100-3. 22. Coleman AL, Diehl DLC, Jampel HD, et al. Topical timolol decreases plasma high-density lipoprotein cholesterol level. Arch Ophthalmol 1990; 108:1260-3. 23. Boozman FW III, Carriker R, Foerster R, et al. Long-term evaluation of 0.25% levobunolol and timolol for therapy for elevated intraocular pressure. Arch Ophthalmol 1988; 106:614-8. 24. Wandel T, Fishman 0, Novack GO, et al. Ocular hypotensive efficacy of 0.25% levobunolol instilled once daily. Ophthalmology 1988; 95:252-5. 25. Kass MA, Gordon M, Morley RE Jr, et al. Compliance with topical timolol treatment. Am J Ophthalmol 1987; 103: 18893. 26. Eisen SA, Miller OK, Woodward RS, et al. The effect of prescribed daily dose frequency on patient medication compliance. Arch Intern Med 1990; 150: 1881-4.
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T
he authors executed a two-period, randomized, double-masked, crossover study comparing once-daily to twice-daily levobunolol hydrochloride (0.5%) in 20 patients with elevated intraocular pressure (lOP). Modified diurnal curves were performed at four times for each study arm: baseline, day 1, day 14, and day 28. The mean diurnal corrected decrease in lOP from baseline ranged from 16% ± 11 % to 22% ± 9% when the subjects were treated twice daily, and from 14% ± 1 0% to 18% ± 8% when the same subjects were treated once daily. At day 1, patients had a significantly greater lOP lowering after twice-daily therapy than after once-daily therapy (P < 0.05). At 14 and 28 days, there was no clinically significant difference between the two treatment regimens. The results of our crossover study suggest that once-daily treatment with levobunolol (0.5%) is as effective as twice-daily treatment. Ophthalmology 1992; 99:424-429
Levobunolol is a nonselective (3,-(32 adrenoceptor antagonist that effectively lowers intraocular pressure (lOP) in subjects with glaucoma and ocular hypertension. '-6 Levobunolol, like other ophthalmic (3-blockers, is usually applied twice daily. The rationale for twice-daily dosing Originally received: July 25. 1991. Revision accepted: October 22. 1991. I Glaucoma Service. Wilmer Institute. Johns Hopkins Hospital. Baltimore. 2 Krieger Eye Institute. Sinai Hospital, Baltimore. 3 Dana Center. Wilmer Institute, Johns Hopkins Hospital. Baltimore. 4AIlergan Pharmaceuticals, Irvine. Presented in part at the Association for Research in Vision and Ophthalmology Annual Meeting, Sarasota. April 1990. Supported in part by a grant from the Zanvyl Krieger Foundation and Allergan. Inc. Irvine. California. Dr. Coleman is currently affiliated with the Department of Ophthalmology. UCLA School of Medicine. Los Angeles. Dr. Novack is currently affiliated with Pharmalogic, Inc. Irvine. Drs. Derick. Rohin. Tielsch. Wexler. and Coleman have no proprietary interests in Allergan. Inc, or levobunolol. Reprint requests to Alan 1.. Robin. MD. 6115 Falls Rd. Third Floor, Baltimore. MD 21209-2226.
424
of ophthalmic (3-blockers is, in part, based on the original dose-response studies oftimolol. 7 However, there is recent evidence suggesting that less frequent application may be as effective. Once-daily dosing may be all that is required to obtain the maximum effect of a (3-blocker. Schlecht and Brubaker8 demonstrated that aqueous humor production does not recover to a normal level for at least 14 days, and lOP does not increase for at least 2 to 4 weeks after discontinuation of medication in patients on long-term timolol therapy. Nonselective (3-blocker therapy may require a less frequent dosing interval. Perhaps after a patient has achieved a new steady state of aqueous production while taking levobunolol, once-daily dosing or perhaps even less frequent dosing may be adequate to achieve maximum lOP reduction from (3-blocker therapy. There are several potential advantages of once-daily dosing. Nonselective (3,-(32 adrenoceptor antagonists can cause many adverse reactions, including bradycardia, systemic hypotension, bronchoconstriction, and central nervous system side effects. 9,10 The amount of levobunolol gaining access to the systemic circulation theoretically would be decreased by using a less frequent dosing schedule. Once-daily therapy would also reduce the cost of
Derick et al . Levobunolol Therapy glaucoma therapy and possibly improve patient compliance. Several investigators have shown that once-daily therapy with levobunolol 0.5% is effective, and compares favorably with timolol 0.5% used once daily.11,12 In addition, the issue of once-daily versus twice-daily dosing of levobunolol (0.5%) has been examined by Rakofsky and coworkers 13 using a parallel study design. They found oncedaily therapy with levobunolol to be as effective as twicedaily therapy in decreasing mean lOPs. However, there are limitations to these parallel studies. A parallel design uses two separate, randomly assigned, and what are hoped to be similar groups of patients. No previous studies have been conducted to evaluate whether an equivalent ocular hypotensive effect can be achieved by comparing once-daily therapy with twice-daily therapy in the same individuals. Studies using a parallel design cannot entirely address this issue. In a crossover design, no assumption about the effectiveness of the randomization process or similarity of the patients is required, as each patient serves as his own control. Since the issues of once-daily versus twice-daily dosing of topical .a-blockers have important medical and economic ramifications, we chose to evaluate this issue using a crossover design in which all patients received both once-daily and twice-daily levobunolol 0.5% in two separate I-month study periods.
Patients and Methods This study used a single-centered, two-period, randomized, double-masked, crossover design. We enrolled 21 chronic open-angle glaucoma or ocular hypertensive patients with symmetrical untreated lOP readings of at least 22 mmHg in both eyes. Neither eye had marked optic nerve damage or visual field loss by automated perimetry. Before study entry, patients were required to cease all ocular hypotensive medications for a minimum of 30 days. We excluded subjects from study participation whose elevated lOP was not controlled by 2 medications or who had glaucoma laser or filtration surgery within the past 3 months; women of childbearing potential or nursing mothers; patients with cardiovascular or pulmonary contraindications to .a-blockers, uncontrolled systemic disease, or hypersensitivity to the study medication ingredients; patients using systemic .B-blockers, corticosteroids, or a-agonist agents; patients with corticosteroid-induced,
Table 1. Examination Protocol Observation or Measurement
SAM
12 noon
History Visual acuity Biomicroscopy Intraocular pressure Pulse rate Blood pressure
x x x x x x
x x x
4:30
x x
x
PM
Table 2. Study Design Month
Group A
Group B
1 2 3
Washout" Levobunolol 0.5% QD Washout" Levobunolol 0.5% BID
Washout" Levobunolo1 0.5% BID Washout" Levobuno101 0.5% QD
4
• Patients discontinued all medications for glaucoma during this month. QD
=
once daily; BID
=
twice daily.
uveitic, or neovascular glaucoma; and patients with active ocular disease, corneal abnormalities, or patients who wore contact lenses. Our institutional review board approved the study and written informed consent was obtained from all subjects. On the first day, we obtained a medical and ophthalmic history. Initial examination included Snellen visual acuity measurement, slit-lamp evaluation of the anterior segment, ophthalmoscopic examination of the optic nerve, and a visual field if one had not been performed within the last 3 months. Intraocular pressure, resting heart rate, and blood pressure were measured in each patient at 8:00 AM, 12:00 noon, and 4:30 PM. After this baseline examination, we randomized patients into two treatment groups: group A began the study with once-daily levobunolol 0.5%, and group B began with twice-daily levobunolol 0.5%. This sequence was masked to both the investigator and the patient. All patients received different color-coded bottles for both morning and evening medications. The evening bottle always contained levobunolol 0.5%, while the morning bottle contained levobunolol 0.5% in group B and vehicle in group A. Patients were instructed to use their morning bottle in both eyes between 5:00 and 7:00 AM and their evening bottle in both eyes between 5:00 and 7:00 PM beginning the evening of the baseline examination. Patients then administered their drops for 1 month and returned for follow-up examinations 1 day, 14 days, and 28 days after the baseline examination (Tables 1 and 2). Follow-up examinations were identical to the baseline examinations, including diurnal lOP measurements, except ophthalmoscopy and visual fields were not performed. Thus, patients receiving once-daily levobunolol had lOP determinations during the final 12 hours oftheir 24-hour dosing interval while patients receiving twicedaily levobunolol had lOP measurements during the entire 12 hours between each twice-daily dose. After completion of the first period, all subjects underwent a I-month washout without receiving any ocular hypotensive medication. Another baseline examination was performed, including diurnal lOP measurements, on no ocular medications, at 8:00 AM , 12:00 noon, and 4:30 PM. Each subject then underwent the crossover to the alternate dosing schedule and received new bottles of test medications that evening (patients in group A started twice-daily treatment and patients in group B started oncedaily treatment). Follow-up examinations were again per-
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Ophthalmology
formed 1 day, 14 days, and 28 days later, in a method identical to the first study arm. In designing the study, sample size calculations were based on a clinically significant difference of 2 mmHg in mean lOP between the treatment regimens. The values of lOP on each examination day were calculated by averaging the values of the right and left eye for all three diurnal measurements (a total of 6 lOP values were averaged). Intraocular pressure changes from baseline at each examination were analyzed by a two-way analysis ofvariance model for crossover studies. 14 We also analyzed our data to insure that there was an adequate washout between the two treatment arms. An analysis of variance model for crossover studies was used to account for any carryover effect at baseline and at each follow-up period. There was not considered to be a significant carryover effect unless P .:S 0.10.
Results patients were selected for the study, and 20 patlents completed both arms of the crossover. One patient elected not to complete the second arm of the crossover because of time considerations. We did not include her. data because data from both study arms for every subject are needed to perform the crossover analysis. Demographic characteristics of the subjects are included in Table 3. The diurnal mean lOP was similar at baseline for the subjects before either once-daily or twice-daily treatment with levobunolol 0.5% (23.14 ± 2.70 mmHg versus 23.27 ± 1.96 mmHg, respectively). As expected, both once-daily and twice-daily treatment significantly lowered mean lOP at all follow-up intervals (P < 0.0001) (Fig 1, Tables 4 and 5). In the once-daily group, the mean lOP decline from baseline ranged from 14% to 18%. Declines from baseline lOP for the twice-daily study arm ranged from 16% to 22%. The only noteworthy difference between the
24.0 23.0 22.0 21.0 C) J: 20.0 E 19.0 E D.. 18.0 Q 17.0 16.0 15.0 14.0
II Once-daily
•
Baseline
1
Day
Twice-daily
14
28
Figure 1. Mean diurnal corrected intraocular pressure (± standard error) of open-angle glaucoma or ocular hypertensive subjects during the crossover study. Both treatment regimens showed significant decreases of intraocular pressure from baseline at all time periods (P < 0.001). There was a significant difference between the two treatments on day 1 (P < 0.05), but not on days 14 or 28 (P > 0.17, P > 0.91, respectively).
Tw~nty-one
Table 3. Demographic Information Variable Age (yrs) Mean ± standard deviation Range Sex Male Female Race White Black Iris color Brown Green Blue Diagnosis Open-angle glaucoma Ocular hypertension
426
Subjects (n
=
20)
two treatment schedules (when all 6 lOP values for each patient were averaged, Table 4) was on day 1 when the lOP decrease from baseline in the twice-daily group was greater than the once-daily group (P < 0.05). On days 14 and 28, there was no difference in the mean ocular hypotensive effect between once-daily and twice-daily treatment with 0.5% levobunolol. We found similar results when evaluating each treatment period. There were only significant differences in diurnal variation (Table 5) on day 1 (8:00 AM and 12:00 noon) and day 14 (8:00 AM). There was no difference in diurnal variation at any later time period throughout the study. By day 28, the diurnal mean lOP values for both treatment groups were within 0.5 mmHg of each other at each time point (Table 5). At 8:00 AM, lOP measurements were performed 1 to 3 hours after instillation in the twice-daily group and 13 to 15 hours after instillation in the once-daily group. The 12:00 noon measurements were made 5 to 7 hours after instillation oflevobunolol in the once-daily group and 17 Table
55.55 ± 13.17 31-74
Day
12 (60%)
Baseline Day 1 Day 14 Day 28
8(40%)
10 (50%) 4(20%) 6 (30%) 6(30%) 14 (70%)
Mean Intraocular Pressures and Mean Changes from Baseline Levobunolol (0.5%)"
8(40%)
12 (60%)
4.
Once Daily 23.2 20.0 18.9 19.5
± 2.7 ± 2.3 (14%) ± 1.9 (18%) ± 2.9 (16%)
Twice Daily 23.2 18.1 18.1 19.6
± 2.0 ± 2.2 (22%) ± 1.7 (22%) ± 2.6 (16%)
• n = 20. All data represent mean intraocular pressure ± standard deviation in mmHg averaged from both eyes at three times on each examination day (6 intraocular pressure measurements were used to calculate each data point listed above). Numbers in parentheses represent percent reduction from baseline. Once daily versus twice daily difference is Significant on day 1 (P < 0.05).
Derick et al . Levobunolol Therapy Table 5. Diurnal Variation in Intraocular Pressure (mmHg) Visit Day
Time of Day
Day 0
SAM 12 Noon 4:30 PM SAM 12 Noon 4:30 PM SAM 12 Noon 4:30 PM SAM 12 Noon 4:30 PM
Day 1
Day 14
Day 2S
Once Daily (Mean ± Standard Deviation) 25.1 23.0 21.5 20.S 20.3 19.1 19.6 19.0 lS.5 19.1 19.4 lS.6
± ± ± ± ± ± ± ± ± ± ± ±
3.0 3.2 3.0 3.9 3.0 3.2 2.5 2.S 2.S 2.S 3.0 2.6
Pvalues
Twice Daily (Mean ± Standard Deviation)
Drug
Carry Over
± ± ± ± ± ± ± ± ± ± ± ±
0.206 0.302 0.313 0.0070.0010.234 0.0200.17S 0.412 0.7S0 0.495 0.362
0.162 0.137 0.109 0.530 0.261 0.111 0.497 0.561 0.400 0.606 O.S11 0.515
23.9 23.7 22.3 lS.3 lS.0 lS.2 lS.2 lS.5 lS.0 19.3 19.0 19.0
2.9 2.1 2.2 1.S 1.S 2.4 1.9 1.9 2.0
1.7
2.1 1.S
• Significant (P < 0.05) between-group intraocular pressure difference. This was only seen at 2 time intervals on day 1, and 1 time interval on day 14. There was no significant (P < 0.10) carryover effect seen at any time interval.
to 19 hours after instillation of levobunolol in the oncedaily group. The 4:30 PM measurements represent the point that was most distant from dosing in the once-daily levobunolol group, approximately 21.5 to 23.5 hours versus 9.5 to 11.5 hours after instillation in the twice-daily group. Assuming a minimum clinically meaningful difference of 2 mmHg, the power to detect this difference at the (\' = 0.05 probability level was 78% and 86% on days 14 and 28, respectively. In addition, there was no indication of a treatment order effect at any of the follow-up times. The carryover (Table 5) was never significant. We were unable to detect a difference in the ocular hypotensive response to 0.5% levobunolol, once-daily versus twice-daily, related to race, sex, or iris color. No changes of note occurred in visual acuity, biomicroscopic, or ophthalmoscopic findings during the study. Significant decreases in mean resting heart rate occurred
-
85
CI)
-
tU a: 80 ....
~
Once-daily
•
Twice-daily
tU
CI)
J:
75
Cl
s::
-=
U)
CI)
a:
70 65 Baseline
14
28
Day Figure 2. Mean resting heart rate (± standard error) of patients during the crossover study. There was a significant between-group difference on day 1 (P < 0.02), but not on days 14 or 28.
with each of the treatment regimens (Fig 2). Reductions in mean resting heart rate from baseline were significantly greater with twice-daily therapy on day 1 (10.4 ± 7.7 versus 5.0 ± 8.9, P < 0.02), but not on days 14 or 28 (P> 0.1). However, no patient was dropped from the study because of symptoms related to a reduction in heart rate. No significant between-group changes in mean systolic or diastolic blood pressure were observed during the study. Regardless of the frequency of instillation, the most common patient complaint was ocular burning or stinging. These complaints were infrequent.
Discussion This report confirms the results of prior parallel studies, which found once-daily levobunolol 0.5% to be effective in lowering elevated lOP. An important feature of our study is its crossover design, in which each subject received both once-daily and twice-daily treatment. There are, however, disadvantages to a crossover design. The time commitment for each patient is twice as long as that required in a similar parallel design. In our study, each patient required two drug washout periods rather than the one washout period required in a parallel design. Withholding medication for 2 months could potentially jeopardize a glaucoma patient with advanced disease. For this reason, an additional placebo arm was not included in the current study. The completion of both study arms by each patient is required for the analysis. In this regard, we were fortunate not to have incurred a higher dropout rate. Despite these difficulties, a crossover design enables the clinician to evaluate whether an equivalent ocular hypotensive effect can be achieved by comparing once-daily and twice-daily dosing within the same group of individuals. Indeed, we were unable to demonstrate any difference in mean lOP change from baseline when we com-
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Volume 99, Number 3, March 1992
pared the two dosing regimens after the first day of each period. We conclude, therefore, that the patients in our sample responded in a clinically identical manner to the two treatment regimens after the first day oftherapy. Although our sample size was relatively small, the 78% to 86% power of our design to find a 2 mmHg lOP difference compares favorably with the parallel study reported previously.13 Another important feature of our study design was the monitoring ofIOP over many hours on every examination day. Each patient underwent a baseline diurnal lOP determination and three follow-up diurnal lOP determinations while on each dosing schedule. This type of design will partially eliminate nondrug-related influences on lOP by considering an individual's diurnal variation. The mean reduction in lOP ranged from 14% to 22% in our patients, which is slightly lower than the 18% to 27% reported in other series of patients. 4 - 6 However, differing study designs in which diurnal variation is not considered make direct comparisons difficult. In this study, patients in the once-daily group were given levobunolol 0.5% in the evening rather than in the morning. While this is not standard practice, it was done in this case to allow diurnal measurements to be performed during office hours. With this regimen, the 12:00 noon lOP measurements were taken 17 to 19 hours after instillation of drug. If the conventional morning instillation had been used, the points corresponding to 17 to 19 hours after instillation would occur while patients were asleep (approximately 12:00 AM to 2:00 AM). Henkind and co-workers l5 showed that lOP is lowest during these hours and is normally at its highest point in the morning hours. Topper and Brubaker l6 demonstrated that aqueous humor flow is decreased during sleep and that timolol does not suppress aqueous formation during sleep. In actual practice, patients instilling levobunolol 0.5% in the morning may theoretically be providing greater protection against morning lOP elevations since the peak ocular hypotensive effect oflevobunolol has been demonstrated to occur 2 to 4 hours after instillation. I Only on the first day after the initiation of treatment was there a difference in the ocular hypotensive effect of levobunolol 0.5%. This difference favored twice-daily treatment. Subjects on the once-daily regimen would only have received a single dose of drug before the day 1 examination. Therefore, the observed difference between once-daily and twice-daily therapy on day 1 may reflect that a steady state drug level had not yet been achieved. Few data have been published about the pharmacokinetics of topically applied levobunolol. The major breakdown product of levobunolol, dihydrolevobunolol, has a halflife of 7 hours in the systemic circulation and is similar in efficacy and potency to levobunolol. 17 Using basic pharmacokinetics, a drug reaches a systemic steady state level after approximately 4 halflives. 18 Perhaps a similar situation exists for intraocular levels of ophthalmic medications after topical instillation, rendering single-drop dose-response studies of ,a-blockers somewhat misleading. Alternatively, binding of drug in the anterior segment may create a depot after several days explaining comparable
428
effects of once-daily to twice-daily therapy at weeks 2 and 4. Timolol has been shown to bind to melanin in the iris and ciliary body in vitro and in animal models and this may also hold true for other ,a-blockers such as levobunolo1. 19 ,20 Perhaps an intraocular drug depot develops in chronic users oftimolol, which could explain the persistent reduction in aqueous flow and significant lowering ofIOP for more than 2 weeks after withdrawal of the medication in these patients. 8,2 I Although the present study shows that once-daily administration is as effective as twice-daily administration, perhaps less frequent administration will have similar effects. Topical ,a-blockers can cause myriad systemic side effects, including bradycardia, hypotension, central nervous system effects, bronchoconstriction, and adverse changes of blood cholesterol levels. 22 All of these side effects can theoretically be reduced by lowering systemic absorption through a less frequent dosing regimen. Our study was not designed to establish a substantial difference in systemic side effects between the two regimens. Other investigators, however, have demonstrated trends toward less systemic effects with once-daily dosing.1 3 Another method to decrease the frequency of systemic side effects might possibly be through use of a lower concentration of a drug. Although not evaluated in our study, previous dose-response studies as well as clinical parallel studies have shown levobunolol 0.25% to be effective in treating ocular hypertension. 23 ,24 Kass et al 25 have shown that medication compliance is better in patients using timolol twice daily than in patients using pilocarpine four times daily. There are no published reports to our knowledge comparing compliance between once-daily and twice-daily regimens of topical ophthalmic medications. Eisen and co-workers26 have shown that compliance improves as the prescribed dose frequency is changed from three times daily to once daily in patients receiving therapy for systemic hypertension. Patient compliance was not objectively determined in the current study; however, this may be an advantage of oncedaily treatment. The cost of glaucoma medication to the patient has not been formally studied, however, this factor should be considered in any treatment plan, and especially when the medication is for long-term use. Assuming a 50% reduction of refills for once-daily treatment, a patient could save hundreds of dollars per year for an equivalent ocular hypotensive response. The results of this study suggest that levobunolol 0.5% used once daily is as effective in lowering lOP as twicedaily therapy in selected patients with elevated lOP.
References 1. Duzman E, Ober M, Scharrer A, Leopold IR. A clinical evaluation of the effects of topically applied levobunolol and timolol on increased intraocular pressure. Am J Ophthalmol 1982; 94:318-27. 2. Partamian LG, Kass MA, Gordon M. A dose-response study of the effect of levobunolol on ocular hypertension. Am J Ophthalmol 1983; 95:229-32.
Derick et al . Levobunolol Therapy 3. Cinotti A, Cinotti D, Grant W, et al. Levobunolol vs timolol for open-angle glaucoma and ocular hypertension. Am J Ophthalmol 1985; 99:11-7. 4. Ober M, Scharrer A, David R, et al. Long-term ocular hypotensive effect oflevobunolol: results of a one-year study. Br J Ophthalmol 1985; 69:593-9. 5. Berson FG, Cohen HB, Foerster RJ, et al. Levobunolol compared with timolol for the long-term control of elevated intraocular pressure. Arch Ophthalmol 1985; 103:379-82. 6. The Levobunolol Study Group. Levobunolol: a beta-adrenoceptor antagonist effective in the long-term treatment of glaucoma. Ophthalmology 1985; 92:1271-6. 7. Zimmerman TJ, Kass MA, Yablonski ME, Becker B. Timolol maleate: efficacy and safety. Arch Ophthalmol1979; 97:656-8. 8. Schlecht LP, Brubaker RF. The effects of withdrawal of timolol in chronically treated glaucoma patients. Ophthalmology 1988; 95:1212-6. 9. Novack GO, Tang-Liu DD-S, Kelley EP, et al. Plasma levobunolol levels following topical administration with reference to systemic side effects. Ophthalmologica 1987; 194: 194-200. 10. Leren P, Foss PO, Nordvik B, Fossbalkk B. The effect of enalapril and timolol on blood lipids. A randomized multicenter hypertension study in general practice in Norway. Acta Med Scand 1988; 223:321-6. 11. Wandel T, Charap AD, Lewis RA, et al. Glaucoma treatment with once-daily levobunolol. Am J Ophthalmol 1986; 101 :298-304. 12. David R, Foerster RJ, Ober M, et al. Glaucoma treatment with once-daily levobunolol [letter]. Am J Ophthalmol 1987; 104:442-3. 13. Rakofsky SI, Melamed S, Cohen JS, et al. A comparison of the ocular hypotensive efficacy of once-daily and twice-daily levobunolol treatment. Ophthalmology 1989; 96:8-11. 14. Cochran WG, Cox GM. Experimental Designs, 2nd ed. New York: John Wiley and Sons, 1957; 117-21.
15. Henkind P, Leitman M, Weitzman E. The diurnal curve in man: new observations. Invest Ophthalmol 1973; 12: 705-7. 16. Topper JE, Brubaker RF. Effects of timolol, epinephrine, and acetazolamide on aqueous flow during sleep. Invest Ophthalmol Vis Sci 1985; 26:1315-9. 17. DiCarlo FJ, Leinweber F-J, Szpiech JM, Davidson IWF. Metabolism of L-bunolol. Clin Phannacol Ther 1977; 22: 858-63. 18. Gilman AG, Goodman LS, Gilman A. Goodman and Gillman's The Pharmacologic Basis of Therapeutics, 6th ed. New York: MacMillan, 1980; 23. 19. Menon lA, Trope GE, Basu PK, et al. Binding of timolol to iris-ciliary body and melanin: an in vitro model for assessing the kinetics and efficacy oflong-acting antiglaucoma drugs. J Ocul Pharmacol 1989; 5:313-24. 20. Abrahamsson T, Bostrom S, Brautigam J, et al. Binding of the {3-blockers timolol and H 216/44 to ocular melanin. Exp Eye Res 1988; 47:565-77. 21. Steinert RF, Thomas JV, Boger WP Ill. Long-term drift and continued efficacy after multiyear timolol therapy. Arch Ophthalmol 1981; 99:100-3. 22. Coleman AL, Diehl DLC, Jampel HD, et al. Topical timolol decreases plasma high-density lipoprotein cholesterol level. Arch Ophthalmol 1990; 108:1260-3. 23. Boozman FW III, Carriker R, Foerster R, et al. Long-term evaluation of 0.25% levobunolol and timolol for therapy for elevated intraocular pressure. Arch Ophthalmol 1988; 106:614-8. 24. Wandel T, Fishman 0, Novack GO, et al. Ocular hypotensive efficacy of 0.25% levobunolol instilled once daily. Ophthalmology 1988; 95:252-5. 25. Kass MA, Gordon M, Morley RE Jr, et al. Compliance with topical timolol treatment. Am J Ophthalmol 1987; 103: 18893. 26. Eisen SA, Miller OK, Woodward RS, et al. The effect of prescribed daily dose frequency on patient medication compliance. Arch Intern Med 1990; 150: 1881-4.
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