AU2006225278B2 - Combination of brimonidine and timolol for topical ophthalmic use - Google Patents

Description

Our Ref: 12720731 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): Address for Service: Invention Title: Allergan, Inc.

2525 Dupont Drive Irvine California 92612 United States of America DAVIES COLLISON CAVE Patent Trade Mark Attorneys 255 Elizabeth Street Sydney, New South Wales, Australia, 2000 Combination of brimonidine and timolol for topical ophthalmic use The following statement is a full description of this invention, including the best method of performing it known to me:- 5951

O-I

O COMBINATION OF BRIMONIDINE AND TIMOLOL FOR STOPICAL OPHTHALMIC USE BACKGROUND OF THE INVENTION 00 This invention relates to the topical ophthalmic use ofbrimonidine in Scombination with timolol when indicated for treatment of glaucoma or ocular Shypertension. Such combinations or formulations are available for separate use in Sthe ophthalmic art and have been combined in serial application during the course of treatment of glaucoma. However, there are concerns and expressed reservations in the ophthalmic community about patient compliance when the patient is required to administer separate medications to treat a single disease or condition such as glaucoma. There is, moreover, a long felt need for an effective and safe topical ophthalmic pharmaceutical composition including brimonidine and timolol which has increased stability and requires a lower effective concentration of preservative as compared to the individual agents taken alone. Finally, there is a need to increase the efficacy of many topical ophthalmic agents, without increasing the systemic concentration of such topical agents, since it is well known that many of such topically-applied ophthalmic agents cause systemic side effects, e.g. drowsiness, heart effects, etc. Unexpectedly it has been discovered that brimonidine in combination with timolol meets these criteria.

Brimonidine is disclosed in U.S. Patent 3,890,319. The use ofbrimonidine for providing neuroprotection to the eye is disclosed in U.S. Patents 5,856,329; 6,194,415 and 6,248,741.

Timolol, as an ophthalmic drug, is disclosed in U.S. Patents 4,195,085 and 4,861,760.

Summary of the invention As now claimed, according to one aspect the present invention provides a method of treating glaucoma which comprises administering a therapeutically effective amount of a composition comprising an effective amount of brimonidine and an effective amount of timolol in a pharmaceutically acceptable carrier topically to the affected eye.

OD

00

O

0 i 0.

t", 0t' 00, 1^,

(N

in

(N,

-2- As now claimed, according to another aspect the present invention also provides a method of lowering intraocular pressure which comprises administering a therapeutically effective amount of a composition comprising an effective amount of brimonidine and an effective amount of timolol in a pharmaceutically acceptable carrier to the affected eye.

DESCRIPTION OF THE INVENTION Brimonidine is an alpha adrenergic agonist represented by the following formula: HN NIH

N

COOH

I

H-C-OH

HO-C-H

COOH

The chemical name for brimonidine is 5-Bromo-6-(2imidazolidinylideneamino)quinoxaline L-tanrate.

Timolol is a beta adrenergic agent represented by the following formula:

H

3

C

CH

3

OH

O HO

O

S3 0 Brimonidine is available from Allergan, Inc., Irvine, California as an ophthalmic pharmaceutical product having the name Alphagan®.

00 r- Timolol is available from various sources, including Merck Co., Rahway, New n s Jersey.

The compositions of the present invention are administered topically. The Sdosage is 0.001 to 1.0, e.g. mg/per eye BID; wherein the cited mass figures represent the sum of the two components, brimonidine and timolol. The compositions of the present invention can be administered as solutions in a suitable ophthalmic vehicle.

In forming compositions for topical administration, the mixtures are preferably formulated as 0.01 to 0.5 percent by weight brimonidine and 0.1 to percent by weight timolol solution in water at a pH of 4.5 to 8.0, e.g. about 6.9.

While the precise regimen is left to the discretion of the clinician, it is recommended that the solution be topically applied by placing one drop in each eye two times a day. Other ingredients which may be desirable to use in the ophthalmic preparations of the present invention include preservatives, co-solvents and viscosity building agents.

Antimicrobial Preservative: Ophthalmic products are typically packaged in multidose form. Preservatives are thus required to prevent microbial contamination during use. Suitable preservatives include: benzalkonium chloride, thimerosal, chlorobutanol, methyl paraben, propyl paraben, phenylethyl alcohol, edetate disodium, sorbic acid, Onamer M, or other agents known to those skilled in the art. In the prior art ophthalmic products, typically such preservatives are employed at a level of from 0.004% to 0.02%. In the compositions of the present application the preservative, preferably benzalkonium chloride, may be employed at a level of from 0.001% to less than

(O

4

O

0.01%, e.g. from 0.001% to 0.008%, preferably about 0.005% by weight. It has 0 been found that a concentration of benzalkonium chloride of 0.005% is sufficient to 0preserve the compositions of the present invention from microbial attack. This concentration may be advantageously compared to the requirement of 0.01% benzalkonium chloride to preserve timolol in the individual, \NO commercially-available ophthalmic products. Moreover, it has been found that 0adequate lowering of intraocular pressure has been obtained when administering the compositions of this invention twice a day as compared to the FDA-approved regimen wherein brimonidine ophthalmic solution, i.e. Alphagan® ophthalmic solution is administered three times a day and timolol ophthalmic solution, i.e.

Timoptic® ophthalmic solution is administered twice a day. This results in the exposure of the patient to 67% and 50% of benzalkonium chloride, with the compositions of this invention, as compared to the administration of Alphagan® and Timoptic®, respectively. In FDA-approved adjunctive therapy, wherein Alphagan® and Timoptic® are serially administered, the patient is exposed to almost three times the concentration ofbenzalkonium chloride as compared to the administration of the compositions of this invention twice a day. (It is noted that it is known that benzalkonium chloride at high concentrations is cytotoxic.

Therefore, minimizing the patient's exposure to benzalkonium chloride, while providing the preservative effects afforded by benzalkonium chloride, is clearly desirable.) Co-Solvents: The solubility of the components of the present compositions may be enhanced by a surfactant or other appropriate co-solvent in the composition. Such cosolvents include polysorbate 20, 60, and 80, Pluronic F68, F-84 and P-103, cyclodextrin, or other agents known to those skilled in the art. Typically such co-solvents are employed at a level of from 0.01% to 2% by weight.

IO

O

Viscosity Agents: 00 t Viscosity increased above that of simple aqueous solutions may be desirable s to increase ocular absorption of the active compound, to decrease variability in IO0 dispensing the formulation, to decrease physical separation of components of a

O

Ssuspension or emulsion of the formulation and/or to otherwise improve the ophthalmic formulation. Such viscosity building agents include as examples polyvinyl alcohol, polyvinyl pyrrolidone, methyl cellulose, hydroxy propyl methylcellulose, hydroxyethyl cellulose, carboxymethyl cellulose, hydroxy propyl cellulose or other agents known to those skilled in the art. Such agents are typically employed at a level of from 0.01% to 2% by weight.

The present invention further comprises an article of manufacture comprising packaging material and a pharmaceutical agent contained within said is packaging material, wherein the pharmaceutical agent is therapeutically effective for lowering intraocular pressure and wherein the packaging material comprises a label which indicates the pharmaceutical agent can be used for lowering intraocular pressure and wherein said pharmaceutical agent comprises an effective amount of brimonidine and an effective amount of timolol.

The following example is a representative pharmaceutical composition of the invention for topical use when indicated for treating glaucoma.

EXAMPLE I The combination of active pharmaceutical ingredients is as follows: Brimonidine Tartrate 0.20 and Timolol Maleate 0.68 (Equivalent to 0.50 timolol) The Brimonidine-Timolol combination formulation presented in the Table, below, is a sterile, preserved, aqueous solution. The formulation vehicle is based upon a timolol ophthalmic solution which contains an isotonic phosphate buffer

O

0 system at pH 6.9. The formulation preservative is benzalalkonium chloride (BAK) O at a concentration of 0.005 (50 ppm). The formulation passes regulatory

O

required preservative efficacy testing (PET) criteria for USP (United States SPharmacopoeia) and EP (European Pharmacopoeia-A and -B over 24 months.

00 Table F' Brimonidine Tartrate Active 0.2 C Timolol Maleate, EP Active 0.681 Benzalkonium Chloride, NF, EP Preservative 0.005 Sodium Phosphate, monobasic monohydrate, USP Buffer 0.43 Sodium Phosphate, dibasic heptahydrate, USP Buffer 2.15 Sodium Hydroxide, NF pH adjust Adjust pH to 6.9 Hydrochloric Acid, NF pH adjust Adjust pH to 6.9 Purified Water, USP, EP Solvent q.s. ad Equivalent to 0.5 Timolol, free base The pharmaceutical composition of Example I is used in the clinical study reported below.

EXAMPLE II Objectives: To compare the safety and efficacy of twice-daily dosed brimonidine tartrate 0.2%/timolol 0.5% ophthalmic solution combination (henceforth referred to as Combination) with that of twice-daily dosed timolol ophthalmic solution (henceforth referred to as Timolol) and three-times-daily dosed ALPHAGAN® (brimonidine tartrate ophthalmic solution) 0.2% (henceforth referred to as Brimonidine) administered for three months (plus 9-month masked extension) in patients with glaucoma or ocular hypertension.

(O

7 0 IO Methodology: Structure: multicenter, double-masked, randomized, parallel-group, active control Randomization: patients were randomized to one of the 3 masked treatment groups (Combination, Brimonidine or Timolol) based on an even allocation at each site s Visit Schedule: prestudy, baseline (day week 2, week 6, month 3, month 6, \O month 9, and month 12 0 Number of Patients (Planned and Analyzed): 560 planned to enroll; 586 enrolled (Combination 193, Brimonidine 196, Timolol 197); 502 completed. Mean (range) age: 62.4 (23 to 87) years; 46.1% (270/586) males, 53.9% (316/586) females.

Diagnosis and Main Criteria for Inclusion: Diagnosis: ocular hypertension, chronic open-angle glaucoma, chronic angleclosure glaucoma with patent iridotomy, pseudoexfoliative glaucoma or pigmentary glaucoma and requiring bilateral treatment.

is Key Inclusion Criteria: 2 18 years, day 0 (post-washout) intraocular pressure (IOP) 22 mm Hg and 5 34 mm Hg in each eye and asymmetry of IOP 5 5 mm Hg, bestcorrected Early Treatment of Diabetic Retinopathy Study (ETDRS) visual acuity equivalent to a Snellen score of 20/100 or better in each eye.

Key Exclusion Criteria: uncontrolled systemic disease, abnormally low or high blood pressure or pulse rate for age or contraindication to beta-adrenoceptor antagonist therapy, anticipated alteration of existing chronic therapy with agents which could have a substantial effect on IOP, contraindication to brimonidine therapy, allergy or sensitivity to any of the study medication ingredients, anticipated wearing of contact lenses during the study, laser surgery, intraocular filtering surgery or any other ocular surgery within the past 3 months, or required chronic use of other ocular medications during the study (intermittent use of artificial tear product was allowed).

Test Product, Dose and Mode of Administration, Batch Number: Brimonidine tartrate 0.2%/timolol 0.5% combination ophthalmic solution one drop

(O

O8 ,0

O

D (-35 p.L) instilled in each eye BID in the morning and evening; and vehicle of the Combination ophthalmic solution, one drop (-35 pL) instilled in each eye once oo daily (QD) in the afternoon (for masking purposes).

r-- C Duration of Treatment: 3 months (with a 9-month masked extension) s Reference Therapy, Dose and Mode of Administration, Batch Number: Active control ALPHAGAN® (brimonidine tartrate ophthalmic solution) one drop (-35 pL) instilled in each eye TID in the morning, afternoon, and evening.

Active control timolol ophthalmic solution one drop (-35 JpL) instilled in each eye BID in the morning and evening; and vehicle of the Combination ophthalmic solution, one drop (-35 p.L) instilled in each eye once daily (QD) in the afternoon (for masking purposes).

Criteria for Evaluation: Efficacy: IOP (hours 0, 2, 7, and patient satisfaction questionnaire, patient comfort of study medication questionnaire, pharmacoeconomic evaluation by investigator Safety: Adverse events biomicroscopy, visual acuity visual field, ophthalmoscopy, cup/disc ratio, heart rate, blood pressure, hematology, serum chemistry, urinalysis and pregnancy test.

Other: Quantitation of plasma brimonidine and timolol concentrations (at selected sites), resource utilization (to be reported upon completion of the 1 year study).

Statistical Methods: All data were summarized with descriptive statistics, frequency tables, and/or data listings. Safety analyses included all patients who received at least 1 dose of study medication. Analyses were performed for the primary efficacy variable IOP using

\O

O

the intent-to-treat (ITT) population with last observation carried forward (LOCF), O and the per protocol population with observed cases.

00 Ordinal categorical variables were analyzed by the Wilcoxon rank-sum test.

C1 Nominal categorical variables were analyzed using Fisher's exact or Pearson's CN s chi-square tests. Within-group changes from baseline for categorical variables were IN analyzed using the Wilcoxon signed-rank test. Continuous variables (eg, IOP) were Sanalyzed using analysis of variance (ANOVA). Within-group changes from baseline for continuous variables were analyzed using paired t-tests.

A 2-way ANOVA model with factors for treatment and investigator was used for the analysis of IOP. Comparisons were made between the Combination and each of the 2 monotherapies in a pairwise fashion using contrasts from the ANOVA model, with the same error term. A separate ANOVA model was employed at each hour/visit measurement of IOP. Each of the 2 null hypotheses (Combination versus Timolol and Combination versus Brimonidine) was tested at the 0.05 significance s1 level. Point estimates of the mean treatment differences, as well as 2-sided confidence intervals (CI) of the difference, were provided at each timepoint.

Summary Conclusions: Efficacy: At baseline, mean values of diurnal IOP ranged from 22.2 mm Hg to 24.9 mm Hg in the Combination group, 22.5 mm Hg to 25.0 mm Hg in the Brimonidine group, and 22.3 mm Hg to 24.8 mm Hg in the Timolol group. There were no statistically significant differences between treatment groups.

Mean changes from baseline diurnal IOP at week 2, week 6 and month 3 ranged from: -5.2 to -7.9 mm Hg in the Combination group to -5.7 mm Hg in the Brimonidine group to -6.4 mm Hg in the Timolol group

O

0 The mean decreases from baseline diurnal IOP were statistically significant within O each treatment group at each follow-up timepoint (p 0.001).

00 The mean decrease from baseline diurnal IOP was statistically significantly greater with Combination than with Brimonidine at hours 0, 2, and 7 at all follow-up visits (p 0.001). In addition, clinically significant differences of more than 1.5 mm Hg N in mean change from baseline IOP favoring Combination over Brimonidine were seen at hours 0, 2, and 7 at all follow-up visits. At hour 9, the decreases from baseline diurnal IOP were greater for the Combination group than the Brimonidine group at all follow-up visits, although the differences were not statistically significant (p 2 0.104).

The mean decrease from baseline diurnal IOP was statistically significantly greater with Combination than with Timolol at hours 0, 2, 7 and 9 at all follow-up visits (p 0.041). In addition, clinically significant differences of more than 1.5 mm Hg in mean change from baseline IOP favoring Combination over Timolol were seen at week 2 (hours 0, 2, and week 6 (hours 2 and and month 3 (hours 0 and 2).

Mean values of diurnal IOP at week 2, week 6 and month 3 ranged from: 15.9 to 18.1 mm Hg in the Combination group 17.4 to 21.5 mm Hg in the Brimonidine group 17.5 to 18.9 mm Hg in the Timolol group

O

DII

0 IN Mean values of diurnal IOP were statistically significantly less with Combination O than with Brimonidine at hours 0, 2, and 7 at all follow-up visits (p 0.001) and at 00 hour 9 at week 6 and month 3 (p 5 0.011). The mean values of IOP at hour 9 at week 2 were lower for the Combination group than the Brimonidine group, s although the difference was not statistically significant (p 0.205). In addition, o0 clinically significant differences of more than 1.5 mm Hg in mean IOP favoring SCombination over Brimonidine were seen at hours 0, 2, and 7 at all follow-up visits and at hour 9 at month 3.

Mean values of diurnal IOP were statistically significantly less with Combination than with Timolol at hour 0 at week 2 and month 3; and at hours 2, 7 and 9 at all follow-up visits (p 0.050). The mean values of IOP at hour 0, week 6, were lower for the Combination group than the Timolol group, although the difference was not statistically significant (p 0.102). In addition, clinically significant differences of more than 1.5 mm Hg in mean IOP favoring Combination over Timolol were seen at week 2 (hours 0, 2, and week 6 (hours 2, 7, and and month 3 (hours 2 and 9).

At the month 3 or exit visit, a statistically significantly greater "yes" response to the Investigator Pharmacoeconomic Evaluation was recorded for patients receiving Combination 173/190) than for patients receiving Brimonidine 141/192, p <0.001). A "yes" response was recorded for 92.7% (179/193) of patients receiving Timolol. There were no statistically significant differences in the change from baseline in treatment comfort between Combination and each of the monotherapy groups.

IO

O

12 STreatment satisfaction was better than baseline for a statistically significantly greater percentage of patients in the Combination group 36/154) than in the oO Brimonidine group 20/151, p 0.005). A total of 19.9% (30/151) of Spatients in the Timolol group reported better treatment satisfaction than baseline.

Safety: °Through month 3 of the study, 53.4% (103/193) of patients in the Combination group, 61.7% (121/196) of the Brimonidine group, and 50.8% (100/197) of the Timolol group experienced one or more adverse events, regardless of causality.

The incidences of oral dryness, eye pruritus, foreign body sensation and conjunctival folliculosis were statistically significantly lower with the Combination than with Brimonidine (p 0.034), while burning and stinging were statistically significantly higher with the Combination than with Brimonidine (p 5 0.028).

There were no statistically significant differences in adverse events between the Combination and Timolol, except for a statistically significantly higher incidence of eye discharge with the Combination 5/193) compared to Timolol 0/197; p 0.029). The most frequently reported adverse events 3% in any treatment group) were as follows, tabulated by descending order in the Combination group: Preferred Term burning sensation in eye conjunctival hyperemia stinging sensation eye infection (body as a whole) visual disturbance epiphora oral dryness eye pruritus allergic conjunctivitis asthenia foreign body sensation conjunctival folliculosis somnolence Combination N= 193 23(11.9%) 16(8.3%) 13(6.7%) 11(5.7%) 6(3.1%) 5 4 3(1.6%) 3 3(1.6%) 2 2 2(1.0%) Brimonidine N= 196 11(5.6%) 23(11.7%) 4 6(3.1%) 11(5.6%) 8(4.1%) 19(9.7%) 13(6.6%) 7(3.6%) 6(3.1%) 10(5.1%) 9 7 Timolol N= 197 25(12.7%) 11(5.6%) 11 8(4.1%) 3 3 1 3 0 1 5 1 0

I

Adverse events led to the discontinuation of 3.6% (7/193) of patients in the Combination group, similar to 3.0% (6/197) of patients in the Timolol group, and statistically significantly less than 14.3% (28/196) of patients in the Brimonidine group (p 0.001). Serious adverse events were reported for 1.0% (2/193) of patients in the Combination group, 2.0% (4/196) of patients in the Brimonidine group, and 2.0% (4/197) of patients in the Timolol group. Two patients receiving Timolol had 4 serious adverse events (emphysema in one patient; nausea, sweating, and tachycardia in the other patient) which were considered possibly related to the

O

S14

O

C study drug. There was 1 death in the Brimonidine group, possibly due to 0 complications from cardiac surgery, and not related to study drug.

oO There were no clinically relevant differences between the Combination and either of the individual components in the mean change from baseline to month 3 for any C 5 hematology, chemistry, or urinalysis parameter. Statistically significant (p 0.048) ,D within-group changes from baseline were found, but were small and not clinically

O

0relevant.

Small but statistically significant (p 0.001) mean reductions in heart rate ranging from -2.1 to -3.7 bpm were seen with the Combination, similar to Timolol. Small but statistically significant (p 0.003) mean reductions in blood pressure at hour 2 (postdose) were seen with the Combination, similar to Brimonidine. These small changes in mean heart rate and blood pressure were associated with clinical symptoms in only a few patients.

Increases from baseline in the severity of conjunctival erythema and conjunctival follicles on biomicroscopy were statistically significantly less with the Combination than with Brimonidine (p 0.011). The majority of patients in each treatment group showed less than a 2-line change from baseline visual acuity. There were no significant between-group differences for changes in visual fields or cup/disc ratio.

Pharmacokinetics: Blood samples were available for 55 patients in the Combination group, 49 patients in the Brimonidine group, and 54 patients in the Timolol group. All samples were assayed for both brimonidine (lower limit of quantitation [LLOQ] 5 pg/mL) and timolol (LLOQ 5 pg/mL). Plasma brimonidine and timolol concentrations were not quantifiable in all but 1 sample on day 0, hour 0 for both Combination and the monotherapy treatment groups.

In the Combination group, mean standard deviation (SD) plasma brimonidine concentrations 1 hour postdose at week 2 and month 3 were 49.7 36.1 and 52.8 46.7 pg/mL, respectively. In the Brimonidine group, mean SD plasma

O

brimonidine concentrations at week 2 and month 3 were 81.0 63.8 and 78.6 48.9 pg/mL, respectively. In the Combination group, mean SD plasma timolol 0 concentrations at week 2 and month 3 were 0.499 0.327 and 0.586 ,I 0.580 ng/mL, respectively. In the Timolol group, mean SD plasma timolol CI 5 concentrations at week 2 and month 3,were 0.950 0.709 and 0.873 ,0 0.516 ng/mL, respectively.

CI Plasma brimonidine and timolol concentrations 1 hour postdose were steady and did not increase over the 3-month study duration. Brimonidine concentrations were 39%, 34% and 39% lower in the Combination group than in the monotherapy group at week 2 (p 0.004), month 3 (p 0.013), and month 12, respectively. Timolol concentrations were 47% and 33% lower in the Combination group than in the monotherapy group at week 2 (p 0.001) and month 3 (p 0.011), respectively.

Timolol concentrations were also significantly lower in the combination treatment group than in the Timolol monotherapy treatment group (p=0.0006). Timolol is concentrations were 49%, 32%, and 21% lower in the combination group than in the monotherapy group at week 2, month 3, and month 12, respectively.

The plasma brimonidine concentration in males was statistically significantly lower than in females for the Brimonidine group (37% lower at week 2 [p 0.034] and 37% lower at month 3 [p 0.017]); the difference was not statistically significant in the Combination group. The plasma timolol concentration in males was statistically significantly lower than in females for both the Combination group (not statistically significant at week 2; 52% lower at month 3 [p 0.012]) and the Timolol group (45% lower at week 2 [p 0.006] and 39% lower at month 3 [p 0.003]).

Plasma brimonidine concentration in the elderly group was not significantly different from in the young group for the combined data from both the combination and Brimonidine treatment groups (p-value=0.1323). However, plasma timolol concentration in the young group was significantly lower than in the elderly group

IO

O

c -16- O for combined data from both the combination and the Timolol treatment groups (p- I value=0.0005).

Conclusions: 00 The Combination treatment (brmonidine tartrate 0.2%/timolol administered tn 5 BID for 3 months was superior to Timolol (timolol BID and Brimonidine C (brimonidine tartrate TID in lowering the elevated IOP of patients with 0 glaucoma or ocular hypertension. The Combination administered BID c demonstrated a favorable safety profile that was comparable to Timolol BID and better than Brimonidine TID with regard to the incidence of adverse events and discontinuations due to adverse events.

The invention has been described herein by reference to certain preferred embodiments. However, as obvious variations thereon will become apparent to those skilled in the art, the invention is not to be considered as limited thereto.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims (1)

17- The Claims defining the invention are as follows: 1. A method of treating glaucoma which comprises administering a therapeutically effective amount of a composition comprising an effective amount of brimonidine and an effective amount of timolol in a pharmaceutically acceptable carrier topically to the affected 00 eye. 1 2. A method of treating glaucoma according to claim 1 wherein the concentration of \O brimonidine is 0.01 to 0.5 percent by weight and the concentration of timolol is 0.1 to percent by weight. 3. A method of treating glaucoma according to claim 1 wherein the concentration of brimonidine is 0.2 percent by weight and the concentration oftimolol is 0.5 percent by weight. 4. A method of lowering intraocular pressure which comprises administering a therapeutically effective amount of a composition comprising an effective amount of brimonidine and an effective amount of timolol in a pharmaceutically acceptable carrier to the affected eye. 5. A method of lowering intraocular pressure according to claim 4 wherein the concentration of brimonidine is 0.01 to 0.5 percent by weight and the concentration of timolol is 0.1 to 1.0 percent by weight. 6. A method of lowering intraocular pressure according to claim 4 wherein the concentration of brimonidine is 0.2 percent by weight and the concentration of timolol is percent by weight. 7. A method of treating glaucoma according to any one of claims 1 to 3 wherein the composition further comprises from 0.001% to less than 0.01% benzalkonium chloride. 8. A method of lowering intraocular pressure according to any one of claims 4 to 6 wherein the composition further comprises from 0.001% to less than 0.01% benzalkonium chloride. 9. A method of treating glaucoma substantially as hereinbefore described. A method of lowering intraocular pressure substantially as hereinbefore described.