Aqueous Humor Flow in Normal Human Eyes Treated with Brimonidine and Dorzolamide, Alone and in Combination

CLINICAL SCIENCES Aqueous Humor Flow in Normal Human Eyes Treated With Brimonidine and Dorzolamide, Alone and in Combination

Hidetoshi Tsukamoto, MD; Lill-Inger Larsson, MD, PhD

Objectives: To measure the effectiveness of topical 0.2% 28.2%±18.0% (PϽ.001), dorzolamide by 19.3%±22.0% brimonidine tartrate as a suppressor of aqueous humor (P=.007), and the combination of brimonidine and dor- flow in the human eye compared with the effectiveness zolamide by 37.2%±20.6% (PϽ.001). The combination of 2% dorzolamide hydrochloride, and to measure the of both drugs statistically significantly suppressed aque- additivity of the effects of the 2 drugs. ous humor flow compared with dorzolamide alone (PϽ.001) and brimonidine alone (P=.04). The IOP was Design: A randomized, double-masked, placebo- reduced by a mean±SD of 11.6%±10.1% (PϽ.001) by controlled study was performed in 20 healthy human sub- brimonidine, 8.5%±14.1% (P=.02) by dorzolamide, and jects. The topical drugs were instilled twice daily the day 17.9%±16.5% (PϽ.001) by the combination. The com- before and again in the morning on the day of the mea- bination of drugs reduced IOP better than dorzolamide surements. The rate of aqueous humor flow was mea- (PϽ.001), but not more than brimonidine (P=.06). sured from 8 AM to 4 PM by clearance of topically applied fluorescein using a fluorophotometer, after Conclusions: The combination of brimonidine and dor- administration of doses of each drug singly and both drugs zolamide caused a further reduction of aqueous humor flow together. Intraocular pressure (IOP) was measured with compared with each drug applied alone. The IOP was fur- applanation tonometry. ther reduced by the combination compared with dorzolamide alone, but not compared with brimonidine alone. Results: Compared with placebo, brimonidine reduced the aqueous humor flow by a mean±SD of Arch Ophthalmol. 2004;122:190-193

␣ HE ADRENERGIC 2-RECEP- cause there are many ocular hypotensive tor agonist brimonidine tar- drugs commercially available, different trate1-7 is a topically ap- therapeutic regimens exist. Brimonidine plied ocular hypotensive added to treatment with ␤-adrenergic an- agent. Studies of brimon- tagonists has been shown to lead to a sig- idine have demonstrated that the ocular nificant additive lowering of the IOP and T 24 hypotensive effect primarily is caused by of the aqueous humor production. Bri- reduction of aqueous humor produc- monidine and dorzolamide are used in tion,7-15 but increased uveoscleral out- clinical practice not only as monothera- flow has also been reported in rabbits16 and pies but also in different combination treat- in humans.11 ments.12-15,25-29 The purpose of the pres- Dorzolamide hydrochloride is a car- ent study was to measure aqueous humor bonic anhydrase inhibitor that is used for flow and IOP after topical administration treatment of glaucoma. This topically ap- of brimonidine, alone and in combina- plied drug lowers the intraocular pres- tion with dorzolamide, to determine sure (IOP) by suppressing the aqueous hu- whether the effects of the 2 drugs are ad- mor production.17-23 Compared with a ditive on aqueous flow and IOP. systemically administered drug of the same class, it has fewer systemic adverse ef- METHODS fects, but its ability to reduce the aque- From the Department of 17,20 The study was carried out at the Department Ophthalmology, Uppsala ous humor formation is weaker. of Ophthalmology, Uppsala University Hospi- University Hospital, Uppsala, Monotherapy is not always suffi- tal. Twenty healthy volunteers were enrolled Sweden. The authors have no cient for an adequate control of the IOP into the study. There were 10 women and 10 relevant financial interest in in patients with glaucoma, and addi- men (mean age, 29.2 years; range, 24-49 years). this article. tional treatment may be prescribed. Be- All subjects underwent an eligibility examina-

(REPRINTED) ARCH OPHTHALMOL / VOL 122, FEB 2004 WWW.ARCHOPHTHALMOL.COM 190

% Difference (P Value) Aqueous Humor Flow, vs Dorzolamide vs Brimonidine Drug Applied No. of Eyes µL/min vs Placebo Hydrochloride Tartrate Placebo 20 3.04 ± 0.86 ...... Dorzolamide 20 2.45 ± 0.56 19.3 ± 22.0 (.007) ...... Brimonidine 20 2.18 ± 0.54 28.2 ± 18.0 (Ͻ.001) 11.0 ± 20.5 (Ͻ.09) . . . Brimonidine and dorzolamide 20 1.91 ± 0.50 37.2 ± 20.6 (Ͻ.001) 22.1 ± 18.7 (Ͻ.001) 12.5 ± 22.1 (.04)

*Data are given as mean ± SD.

tion consisting of a medical and ophthalmic history, visual acu- IOP was then recorded as the mean of the 3 measurements. Di- ity measurement, slitlamp examination, applanation tonom- lute milk rather than fluorescein was used as the disclosing agent etry, and ophthalmoscopy. Exclusion criteria were ocular disease, to avoid the introduction of more fluorescein to the cornea and systemic disease requiring long-term medical treatment, preg- mismeasurement of aqueous humor flow. nancy or lactation, inability to comply with tonometry or fluo- Aqueous humor flow was calculated from the clearance rophotometry, an IOP difference between the 2 eyes greater than of fluorescein at each 2-hour interval by using the following ⌬ ⌬ ⌬ 3 mm Hg, and known drug hypersensitivity. The research pro- equation: clearance= M/(Ca t), where M is the loss of mass tocol followed the tenets of the Declaration of Helsinki and was of fluorescein in the combined cornea and anterior chamber ⌬ approved by the Ethical Committee of Uppsala University. An during t interval, and Ca is the mean concentration in the an- informed consent was obtained from all participants. The study terior chamber during the interval, estimated from the initial consisted of 2 parts. At least 4 weeks elapsed between the parts and final fluorescence and assuming a single exponential de- to ensure complete elimination of the drugs. In part 1, the effect cay. Aqueous humor flow was calculated from the rate of clear- of 0.2% brimonidine–treated eyes vs placebo-treated eyes was ance of fluorescein after subtracting the presumed rate of dif- studied. In part 2, topical application of 2% dorzolamide was fusional clearance (0.25 µL/min).30 added to both eyes. Four treatment regimens were thus com- After completion of the study and tabulation of the data, the pared, with 20 eyes in each treatment group: (1) placebo- code was broken and the data stratified by drug. The statistical treated eyes, (2) brimonidine-treated eyes, (3) dorzolamide- analysis was carried out using a 2-sided t test for paired samples. treated eyes, and (4) brimonidine and dorzolamide–treated eyes. PϽ.05 was considered statistically significant. The coefficient of The study was randomized, double-masked, and placebo- variation of measurements of aqueous humor flow under condi- controlled. The brimonidine, dorzolamide, and placebo eye- tions similar to those in this experiment is approximately 23%.31 drops were given by random assignment and were adminis- The mean±SD aqueous humor flow in daytime is 2.75±0.63 µL/ tered from identical-appearing dropper bottles labeled by subject min.30 A sample size of 20 in each group provided a power of 95% number, sequence, and right and left eyes. These sterile eye- for detecting a true difference of 20% between the eyes.32 dropper bottles contained 0.2% brimonidine tartrate (Alpha- gan; Allergan, Inc, Irvine, Calif), 2% dorzolamide hydrochlo- RESULTS ride (Trusopt; Merck Sharp and Dohme/Isotopes, St Louis, Mo), or placebo (Isopto-Plain; Alcon Laboratories, Fort Worth, Tex). The effects of the different drugs on aqueous humor flow Each part of the study was performed on 2 sequential days, are presented in Table 1. Brimonidine reduced aque- day 1 and day 2. On day 1, the subjects reported to the re- Ͻ search area at 8 AM, and they were given 1 drop of 0.2% bri- ous humor flow by a mean±SD of 28.2%±18.0% (P .001) monidine in one eye and 1 drop of placebo in the other eye. and dorzolamide by 19.3%±22.0% (P=.007) compared The procedure was repeated at 5 PM. On day 2, when flow was with placebo, while there was no statistically significant measured, eyedrops were again instilled at 8 AM. As a precau- difference between brimonidine and dorzolamide (P=.09). tion to prevent cross-contamination between the eyes, sub- Brimonidine and dorzolamide applied in combination sup- jects were given separate tissues for each eye and were asked pressed the flow by a mean±SD of 37.2%±20.6% com- to blot only one eye with each tissue. In part 2, brimonidine pared with placebo (PϽ.001). The aqueous humor flow and placebo eyedrops were administered according to the same was statistically significantly reduced by the combina- schedule as in part 1, but at every time point for eyedrop in- tion of both drugs compared with dorzolamide alone stillation, 1 drop of 2% dorzolamide was also administered to Ͻ both eyes 5 minutes after the other eyedrops (ie, dorzolamide (P .001) and brimonidine alone (P=.04). was administered twice daily). The research personnel admin- The IOP (Table 2) was statistically significantly re- istered all eyedrops, except fluorescein, because of the risk of duced by a mean±SD of 11.6%±10.1% by brimonidine error with eyedrop self-administration. alone (PϽ.001) and 8.5%±14.1% by dorzolamide alone The subjects were instructed to awaken at 2 AM on day 2 (P=.02) compared with placebo, but there was no dif- and instill 1 drop of 2% fluorescein into each eye 3 to 5 times, ference between the effects of the 2 drugs in reducing IOP according to age, at 5-minute intervals, and then they returned (P=.35). The combination of both drugs statistically sig- to sleep. The subjects reported to the test area at 8 AM and un- nificantly reduced IOP compared with dorzolamide derwent measurements of the fluorescence of the cornea and the (PϽ.001), but not compared with brimonidine (P=.06). anterior chamber with a fluorophotometer (Fluorotron Master; Coherent Radiation, Palo Alto, Calif). The procedure was repeated every other hour until 4 PM. Immediately after each mea- COMMENT surement of fluorescence, the IOP was measured with a Gold- mann tonometer. Tonometry was started in the right eye, The results of this study confirm previous results that 0.2% alternating between the eyes for a total of 3 readings per eye. The brimonidine tartrate and 2% dorzolamide hydrochlo-

(REPRINTED) ARCH OPHTHALMOL / VOL 122, FEB 2004 WWW.ARCHOPHTHALMOL.COM 191

% Difference (P Value)

Intraocular vs Dorzolamide vs Brimonidine Drug Applied No. of Eyes Pressure, mm Hg vs Placebo Hydrochloride Tartrate Placebo 20 11.5 ± 2.5 ...... Dorzolamide 20 10.6 ± 2.6 8.5 ± 14.1 (.02) ...... Brimonidine 20 10.2 ± 2.3 11.6 ± 10.1 (Ͻ.001) 3.4 ± 17.0 (.35) . . . Brimonidine and dorzolamide 20 9.5 ± 2.5 17.9 ± 16.5 (Ͻ.001) 10.3 ± 11.0 (Ͻ.001) 7.2 ± 15.5 (.06)

*Data are given as mean ± SD.

second part of the present study, when the combination Table 3. Previous Studies of Aqueous Humor Flow of brimonidine and dorzolamide was administered to one eye and dorzolamide was instilled in the other eye. The Inhibition of flow measured in the dorzolamide-treated eye could thus Drug and Source Aqueous Flow, % reflect a crossover effect of brimonidine. Brimonidine tartrate In the present study, the IOP was further reduced 11 Toris et al, 1995 20 by the combination of brimonidine and dorzolamide com- Maus et al,33 1999 22 Larsson,24 2001 33 pared with dorzolamide alone, but not with bri- Present study 28 monidine. This finding was inconsistent with the re- Dorzolamide hydrochloride sults from the flow measurements. Only healthy Maus et al,17 1997 17 volunteers were included in the study, and the mean±SD Wayman et al,18 1997 18 baseline IOP of 11.5±2.5 mm Hg was low. A deviation 20 Larsson and Alm, 1998 17 of 1 to 2 mm Hg from the true IOP is inherent in the tech- Vanlandingham and Brubaker,21 1998 13 Vanlandingham et al,22 1998 13 nique, and the discrepancy between the results from the Ingram and Brubaker,23 1999 14 IOP measurements and the flow measurements could be Present study 19 explained by this. Brimonidine and timolol Traditionally, the medical treatment of glaucoma has Larsson,24 2001 59 consisted of empirical trials of single drugs or combina- Dorzolamide and timolol 18 tions of drugs in individual patients, a process that is ef- Wayman et al, 1997 55 ficient when few effective choices are available. With the Brubaker et al,34 2000 51 Brimonidine and dorzolamide increasing number of effective ocular hypotensive drugs Present study 37 for glaucoma treatment, the number of potential trial se- quences or combinations rapidly increases. Clinicians need a management strategy based on pharmacological mecha- nisms and relative efficacy. Previous investigations sug- ride suppress the aqueous humor formation. There was gest that the efficacy of combining different aqueous flow no statistically significant difference in the flow reduc- suppressants would be less than the combined effect of each tion when brimonidine or dorzolamide was given sepa- given as monotherapy,27 and the present study supports rately. When they were applied in combination, a fur- this. Studies of the effects of combinations of drugs are thus ther reduction of flow was seen. important as a basis for predicting the most efficient strat- Table 3 lists the aqueous humor flow rates in this egy in the medical management of glaucoma. study along with those in other studies involving bri- In conclusion, the effect of short-term administra- monidine and dorzolamide. The studies used the fluo- tion of dorzolamide was partly additive to the effect of bri- rophotometric technique for determining flow, and there monidine. The combination of brimonidine and dorzol- is good consistency between the studies in the effects of amide caused a further reduction of aqueous humor flow the different drugs. compared with each drug applied alone. The IOP was fur- The effect on aqueous humor flow of short-term ad- ther reduced by the combination compared with dorzol- ministration of apraclonidine hydrochloride and bri- amide alone, but not compared with brimonidine alone. monidine in healthy volunteers was measured by Schadlu and coworkers.8 The reduction of aqueous humor flow Submitted for publication June 21, 2002; final revision re- by each drug could explain the reduction of IOP. In ad- ceived August 17, 2003; accepted September 10, 2003. dition, a consensual effect on aqueous humor flow in the This study was supported in part by grants from the fellow eye was noted: 16% for apraclonidine and 17% for Glaucoma Research Foundation, Uppsala University, and brimonidine. The total effect of brimonidine on reduc- from Kronprinsessans Arbetsna¨mnd fo¨r de Synskadade, ing the aqueous humor flow was 44% to 48% in their Stockholm, Sweden. study. Considering the consensual effect, the reduction Corresponding author and reprints: Lill-Inger Lars- of 28% by brimonidine alone that was found in the pres- son, MD, PhD, Department of Ophthalmology, Uppsala Uni- ent study corresponds well with their findings. The con- versity Hospital, S-75185 Uppsala, Sweden (e-mail: sensual effect of brimonidine could also have affected the [email protected]).

(REPRINTED) ARCH OPHTHALMOL / VOL 122, FEB 2004 WWW.ARCHOPHTHALMOL.COM 192

©2004 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/30/2021 and acetazolamide as suppressors of aqueous humor flow in humans. Arch Oph- REFERENCES thalmol. 1997;115:45-49. 18. Wayman L, Larsson LI, Maus T, Alm A, Brubaker RF. Comparison of dorzol- 1. Greenfield DS, Liebmann JM, Ritch R. Brimonidine: a new ␣2-receptor agonist amide and timolol as suppressors of aqueous humor flow in humans. Arch Oph- for glaucoma treatment. J Glaucoma. 1997;6:250-258. thalmol. 1997;115:1368-1371. 2. Schuman JS, Horwitz B, Choplin NT, et al, Chronic Brimonidine Study Group. A 19. Wayman L, Larsson LI, Maus T, Brubaker RF. Additive effect of dorzolamide on 1-year study of brimonidine twice daily in glaucoma and ocular hypertension: a aqueous humor flow in patients receiving long-term treatment with timolol. Arch controlled, randomized, multicenter clinical trial. Arch Ophthalmol. 1997;115: Ophthalmol. 1998;116:1438-1440. 847-852. 20. Larsson LI, Alm A. Aqueous humor flow in human eyes treated with dorzol- 3. Derick RJ, Robin AL, Walters TR, et al. Brimonidine tartrate: a one-month dose amide and different doses of acetazolamide. Arch Ophthalmol. 1998;116:19-24. response study. Ophthalmology. 1997;104:131-136. 21. Vanlandingham BD, Brubaker RF. Combined effect of dorzolamide and latano- 4. Serle JB, Brimonidine Study Group III. A comparison of the safety and efficacy prost on the rate of aqueous humor flow. Am J Ophthalmol. 1998;126:191-196. of twice daily brimonidine 0.2% versus betaxolol 0.25% in subjects with el- 22. Vanlandingham BD, Maus TL, Brubaker RF. The effect of dorzolamide on aque- evated intraocular pressure. Surv Ophthalmol. 1996;41(suppl 1):S39-S47. ous humor dynamics in normal human subjects during sleep. Ophthalmology. 5. Schuman JS. Clinical experience with brimonidine 0.2% and timolol 0.5% in glau- 1998;105:1537-1540. coma and ocular hypertension. Surv Ophthalmol. 1996;41(suppl 1):S27-S37. 23. Ingram CJ, Brubaker RF. Effect of brinzolamide and dorzolamide on aqueous hu- 6. Walters TR. Development and use of brimonidine in treating acute and chronic mor flow in human eyes. Am J Ophthalmol. 1999;128:292-296. elevations of intraocular pressure: a review of safety, efficacy, dose response, 24. Larsson LI. Aqueous humor flow in normal human eyes treated with bri- and dosing studies. Surv Ophthalmol. 1996;41(suppl 1):S19-S26. monidine and timolol, alone and in combination. Arch Ophthalmol. 2001;119: 7. Burke J, Schwartz M. Preclinical evaluation of brimonidine. Surv Ophthalmol. 492-495. 1996;41(suppl 1):S9-S18. 25. Boyle JE, Ghosh K, Gieser DK, Adamsons IA, Dorzolamide-Timolol Study Group. 8. Schadlu R, Maus TL, Nau CB, Brubaker RF. Comparison of the efficacy of apra- A randomized trial comparing the dorzolamide-timolol combination given twice clonidine and brimonidine as aqueous suppressants in humans. Arch Ophthal- daily to monotherapy with timolol and dorzolamide. Ophthalmology. 1998;105: mol. 1998;116:1441-1444. 1945-1951. 9. Ogodigben M, Chu TC, Potter DE. Alpha-2 adrenoreceptor mediated changes in 26. Clineschmidt CM, Williams RD, Snyder E, Adamsons IA, Dorzolamide-Timolol aqueous dynamics: effect of pertussis toxin. Exp Eye Res. 1994;58:729-736. Combination Study Group. A randomized trial in patients inadequately con- 10. Gabelt BT, Robinson JC, Hubbard WC, et al. Apraclonidine and brimonidine ef- trolled with timolol alone comparing the dorzolamide-timolol combination to mono- fects on anterior ocular and cardiovascular physiology in normal and sympa- therapy with timolol or dorzolamide. Ophthalmology. 1998;105:1952-1959. thectomized monkeys. Exp Eye Res. 1994;59:633-644. 27. Adamsons IA, Polis A, Ostrov CS, Boyle JE, Dorzolamide Safety Study Group. 11. Toris CB, Gleason ML, Camras CB, Yablonski ME. Effects of brimonidine on aque- Two-year safety study of dorzolamide as monotherapy and with timolol and pi- ous humor dynamics in human eyes. Arch Ophthalmol. 1995;113:1514-1517. locarpine. J Glaucoma. 1998;7:395-401. 12. Centofanti M, Manni G, Gregori D, Cocco F, Lorenzano D, Bucci MG. Compara- 28. Le HH, Chang MR, Cheng Q, Lee DA, Hartenbaum D. The effectiveness and safety tive acute effects of brimonidine 0.2% versus dorzolamide 2% combined with of dorzolamide 2% in addition to multiple topical antiglaucoma medications. ␤-blockers in glaucoma. Graefes Arch Clin Exp Ophthalmol. 2000;238:302-305. J Ocul Pharmacol Ther. 1999;15:305-312. 13. Lee DA, Gornbein J, Abrams C, Glaucoma Trial Study Group. The effectiveness 29. Emmerich KH. Comparison of latanoprost monotherapy to dorzolamide com- and safety of brimonidine as mono-, combination, or replacement therapy for pa- bined with timolol in patients with glaucoma and ocular hypertension: a 3-month tients with primary open-angle glaucoma or ocular hypertension: a post hoc analy- randomised study. Graefes Arch Clin Exp Ophthalmol. 2000;238:19-23. sis of an open-label community trial. J Ocul Pharmacol Ther. 2000;16:3-18. 30. Brubaker RF. Measurement of aqueous flow by fluorophotometry. In: Ritch R, 14. Stewart WC, Sharpe ED, Day DG, et al. Comparison of the efficacy and safety of Shields MB, Krupin T, eds. The Glaucomas. Vol 1. St Louis, Mo: CV Mosby Co; latanoprost 0.005% compared to brimonidine 0.2% or dorzolamide 2% when 1989:337-344. added to a topical ␤-adrenergic blocker in patients with primary open-angle glau- 31. Brubaker RF. Flow of aqueous humor in humans: the Friedenwald Lecture. In- coma or ocular hypertension. J Ocul Pharmacol Ther. 2000;16:251-259. vest Ophthalmol Vis Sci. 1991;32:3145-3166. 15. Strahlman ER, Vogel R, Tipping R, Clineschmidt CM, Dorzolamide Additivity Study 32. Dixon WJ, Massey JF Jr. Introduction to Statistical Analysis. New York, NY: Group. The use of dorzolamide and pilocarpine as adjunctive therapy to timolol McGraw-Hill Book Co; 1969:516. in patients with elevated intraocular pressure. Ophthalmology. 1996;103:1283- 33. Maus TL, Nau C, Brubaker RF. Comparison of the early effects of brimonidine 1293. and apraclonidine as topical ocular hypotensive agents. Arch Ophthalmol. 1999; 16. Serle JB, Podos SM, Lee P-Y, Camras CB, Severin CH. Effect of ␣2-adrenergic 117:586-591. agonists on uveoscleral outflow in rabbits. Invest Ophthalmol Vis Sci. 1991;32 34. Brubaker RF, Ingram CJ, Schoff EO, Nau CB. Comparison of the efficacy of be- (suppl):867. taxolol-brinzolamide and timolol-dorzolamide as suppressors of aqueous hu- 17. Maus TL, Larsson LI, McLaren JW, Brubaker RF. Comparison of dorzolamide mor flow in human subjects. Ophthalmology. 2000;107:283-287.

(REPRINTED) ARCH OPHTHALMOL / VOL 122, FEB 2004 WWW.ARCHOPHTHALMOL.COM 193