Technical Field:
The present invention relates to a stable gel forming solution with low preservative content. More particularly, the present invention relates to a stable solution comprising Timolol or its pharmaceutically acceptable salt, which forms gel on contact with tear fluid. The invention further relates to process for preparation of stable gel forming solution. The present invention relates to an ophthalmic gel forming solution comprising low concentration of preservative.
Background & Prior Art:
Ocular drug delivery has been a major challenge to pharmacologists and drug delivery scientists due to its unique anatomy and physiology. The physiological constraints imposed by the protective mechanisms of the eye lead to low absorption of drugs, resulting in short duration of therapeutic effect. Poor bioavailability of ophthalmic solutions is caused partly by the rapid decrease of drug concentration in the precorneal tear fluid. The rapid precorneal elimination of drugs given in the eye drops is mainly due to conjunctival absorption and drainage of drug induced by lachrymation and normal tear turnover. The limited permeability of the cornea also contributes to the low absorption of ocular drugs. Due to poor ocular bioavailability, many ophthalmic drugs are applied frequently and in high concentrations, which cause both ocular and systemic side effects.
Several other compositions, like viscous solutions, gels, eye ointments or solid eye implants or inserts, have been developed for ocular drug delivery to prolong contact time of the vehicle and slow down the elimination of the drug. However, these compositions pose problems of patient noncompliance. From this viewpoint, liquid dosage form is preferred in ophthalmic drug delivery, in spite of poor bioavailability problems associated with it.
Gel forming solutions are liquid compositions which gels on contact with physiological fluids i.e. tear fluids, saliva, etc. The gel formation is dependent on factors like changes

in physiological stimuli like temperature and pH, solvent exchange and swelling and chemical reactions like enzymatic, chemical or photo-initiated, or the combinations of two or more factors. These systems promote ease and convenience of administration, deliverance of accurate dose as well as prolong residence time of drug in contact with mucosa. Gel forming systems have improved bioavailability profile over liquid compositions.
Preservatives are an important component of ophthalmic preparations, providing antimicrobial activity in the bottle and preventing microbial spoilage of the product and / or decomposition of active drug. The US Food and Drug Administration and the US Pharmacopoeia mandate that all multi-dose ophthalmic preparations should contain preservative to ensure a nonhazardous degree of contamination. Often under recognized, however there are significant cytotoxic effects of preservatives associated with long-term therapy and especially use of multiple preserved drugs.
High concentration of preservatives can damage and irritate ocular tissue and cause problems like eye irritation, redness, itching, dry eye symptoms, etc. Preservative-free products may prevent the toxic side effects, but they are expensive and the small unit-dose containers can be difficult to use, hindering compliance. Use of more than one multi-dose ocular drug products in therapy increases the exposure of preservatives to eye tissue along with possibility of adverse events related to it. Physicians should consider treatment with effective agents that contain preservatives with minimal effects on ocular tissue.
Chronic topical therapies may induce ocular surface damage through allergic reactions, dry eye-like reactions, and direct epithelial damage through epithelial barrier disruption. Preservatives used to avoid contamination of topical ophthalmic compounds or to enhance their permeability remain the main causative agents of these detrimental effects.

US Patent No. 5492937 describes a liquid carrier composition which forms a highly viscous layer or gel at body temperature using water soluble nonionic cellulose ether, a charged surfactant and optional additives in water. The optional additives are selected from the group consisting of flavoring agents, colorants, preservatives, isotonic agents and their mixtures.
US Patent No. 5403841 demonstrates a method of delivering drug to the eye comprising drug and carageenan capable of gelation upon exposure to sodium ions at concentrations found in lachrymal fluid. The other components of the composition include ophthalmically acceptable buffers, preservatives, and tonicity agents.
US Patent No. 5422116 describes a method of providing a slow and sustained release of an ophthalmic treating agent and chitosan as the release rate controlling agent in a formulation administrable in drop form, upon contact with higher pH of the ocular fluid, is converted into a stiff gel that releases ophthalmic treating agent over a prolonged period of time. The suitable preservative used is selected from benzalkonium chloride, thimerosal, phenethyl alcohol, methylparaben, propylparaben, chlorhexidine, sorbic acid and the like.
US Patent No. 5599534 demonstrates a reversibly gelling composition for sustained delivery of a therapeutic or diagnostic agent, which comprises an aqueous solution including a pH responsive gelling polymer and thermally nonresponsive polymer. The said composition contains suitable water soluble preservatives.
The above mentioned prior art demonstrates use of various polymers used for preparation of gel forming solutions, which form stiff gel on contact with tear fluid. They comprise of preservatives, present at their conventional concentrations, are likely to prove to be toxic in case of multi-dose therapy and multiple drug therapy.

Hence, there is a need in the art for a stable gel forming ophthalmic preparation with low preservative content, which solves the problems of low bioavailability and patient compliance.
The inventors of the present invention have found a novel ophthalmic solution that can conveniently gel on contact with tear fluid, which is stabilized with lower preservative content than conventional ophthalmic compositions.
Brief Description of the Drawing:
Fig I: Process Flowchart for Preparation of Gel Forming Solution containing Active agent.
Object of the Invention:
The present invention relates to a stable gel forming composition comprising of low concentration of preservative.
An object of the present invention is to provide a stable solution comprising Timolol or its pharmaceutically acceptable salt which forms gel on contact with tear fluid.
Another object of the present invention is to provide a method for preparation of a stable gel forming solution, which comprises of following steps - A) Preparation of slurry of excipients, followed by sterilization, B) Preparation solution of active agent, followed by sterilization, C) Mixing of slurry of excipients and solution of API, under slow stirring, with pH adjustment, followed by making up of volume, in sterile atmosphere.
Another object of the invention is to provide an ophthalmic gel forming solution comprising low concentration of preservative.

Summary of the Invention:
The present invention relates to a stable gel forming solution with low preservative content.
The present invention relates to a stable solution comprising Timolol or pharmaceutically acceptable salts, which forms gel on contact with tear fluid.
Also the present invention relates to a process for preparation of a stable gel forming solution, comprising of the following steps - A) Preparation of slurry of excipients, followed by sterilization, B) Preparation solution of active agent, followed by sterilization, C) Mixing of slurry of excipients and solution of API, under slow stirring, with pH adjustment, followed by making up of volume.
The present invention also relates to an ophthalmic gel forming solution comprising low concentration of preservative.
Description of the Invention:
The gel forming solution of present invention gels in contact with tear fluid, which increases the precorneal residence time. The prolonged precorneal residence improves the ocular bioavailablity of the drug.
The gel forming solution of the present invention comprises of low preservative content as compared to conventional compositions. The low preservative content of the present invention is particularly useful for patient population suffering from toxicity due to over exposure of preservatives.
The gel forming solution of the present invention is in liquid form before application to the eye and gels only on contact with the tear fluid. These solutions conveniently provide advantages of both the liquid composition and gel based drug delivery. The composition is in the form of a liquid before instillation into the eye which then undergoes a liquid-gel phase transition, and changes from the liquid phase to the gel

phase. This is brought about by the ionic strength of the physiological fluid which is in this case is the tear fluid.
The present invention relates to a stable gel forming solution comprising of low content of preservative.
The present invention provides a stable gel forming solution comprising timolol maleate or its acceptable salts, preservative and pharmaceutically acceptable excipients.
According to one embodiment, the concentration of preservative used is in the range of 0.003-0.01%.
According to one embodiment, the concentration of preservative used is in the range of 0.025 to 0.075%.
According to one embodiment, the concentration of preservative used is in the range of 0.025 to 0.005%.
According to preferred embodiment, the concentration of preservative used is 0.005%.
According to one embodiment, the concentration of preservative used is 0.025%.
According to one embodiment, the concentration of preservative used is 0.075%.
According to one embodiment, the preservative used is benzalkonium chloride, either as a solid material or readymade 50% w/v solution in equivalent amounts.
According to one embodiment, the present invention provides a stable gel forming solution comprising timolol maleate or its acceptable salts and at least one pharmaceutical excipient.

According to one embodiment of the present invention, the gel forming solution is a clear, colorless solution without any particulate matter, with pH between the range of 5.5 to 7.5 and osmolarity in the range of 250 to 350 msOs/kg.
In further embodiment, the gel forming solution forms a clear transparent gel on contact with the tear fluid, about 5 minutes after instillation of solution into the eye. The viscosity of the gel formed is such that it will not cause inconvenience upon instillation in the eye. The viscosity of the gel formed is in the range of 200 to 400 cPs, preferably 270 to 350 cPs.
According to another embodiment, the present invention provides a method for preparation of gel forming solution.
According to an embodiment, the present invention relates to an ophthalmic gel forming solution comprising of Timolol or its pharmaceutically acceptable salts. Other than timolol, active ingredient selected from group comprising of brimonidine, azelastine, bromfenac, olopatadine, tobramycin, dexamethasone or its pharmaceutically acceptable salts and combinations thereof can be used in the present invention.
In accordance with the present invention, stable ophthalmic solution comprises of active agent and one or more of surfactants, osmolality agents, gelling agents, chelating agents, preservatives, pH adjusting agents and isotonicity modifying agents.
Surfactant used in the present invention may be selected from the group comprising polysorbate 80, polysorbate 20, tyloxapol, tromethamine, triton X-100, poloxamer, ethoxylated alcohol, propoxylated alcohol and combinations thereof.
Osmolality agent used in the present invention may be selected from a group comprising mannitol, dextrose, glycerin, potassium chloride, sodium chloride, glycerin, boric acid, sorbitol, propylene glycol and combinations thereof.

Gelling agent used in the present invention may be selected from the group comprising natural water soluble polysaccharides, carbopol, poloxamers, pluronics, semi-synthetic celluloses and combinations thereof. Representative examples of gelling agent which can be used in the present invention may be selected from group comprising of gellan gum, xanthan gum, guar gum, hydroxypropyl cellulose, ethyl methyl cellulose, hydroxy ethyl cellulose, various grades of carbopol and combinations thereof.
Chelating agent used in the present invention may be selected from the group comprising disodium edetate, trisodium edetate, ethylene diamine tetraacetic acid and combinations thereof.
Preservative used in the present invention may be selected from the group comprising benzalkonium chloride (BKC), benzyl alcohol, methyl paraben, propyl paraben, thimerosal, chlorobutanol, benzethonium chloride, cetyl pyridinium chloride, phenyl ethanol, phenyl propanol, phenyl mercuric acetate, phenyl mercuric nitrate, phenyl mercuric borate, chlorhexidine acetate or gluconate, cetrimide, chlorocresol and combinations thereof.
pH adjusting agent may be selected from the group comprising sodium hydroxide, hydrochloric acid, potassium hydroxide, sodium carbonate, citric acid, phosphoric acid, acetic acid, tartaric acid, sodium hydrogen carbonate, boric acid, borax and combinations thereof.
Isotonicity modifying agent may be selected from group comprising of lactose, sucrose, glycerol and combinations thereof.
According to one embodiment of the present invention, the stable ophthalmic solution comprising 0.1 to 1% of active agent, 0.1 to 2 % of gelling agent, 0.5 to 6% of osmolality agent, 0.1 to 3 % of surfactant and 0.003 to 0.01 % of preservative agent.

Preservative Efficacy Test data of the selected concentration of preservative confirms the concentration of preservative in selected range is appropriate for preservation.
In another embodiment, the gel forming solution comprises of natural water soluble polysaccharide as the gelling agent.
According to an embodiment, the present invention also provides a process for preparation of a stable ophthalmic solution, comprising of the following steps -
A) Preparation of slurry of excipients, followed by sterilization and pH adjustment,
B) Preparation solution of active agent, followed by sterilization,
C) Mixing of slurry of excipients and solution of API, under slow stirring, with pH adjustment, followed by making up of volume using water, in a sterile environment.
According to an embodiment, the present invention also provides a process for preparation of a stable ophthalmic solution, comprising of the following steps -
A) Preparation of slurry of excipients, followed by sterilization and pH adjustment,
B) Preparation solution of Timolol maleate, followed by sterilization,
C) Mixing of slurry of excipients and solution of Timolol maleate, under slow stirring, with pH adjustment, followed by making up of volume using water.
The ophthalmic gel forming solution of the present invention has completed stability studies stored as 5ml white LDPE vial with white HDPE cap with clear nozzle upto duration of 6 months. Study of physical characteristics and chemical assays for finished product and gel formed after contact with tear fluid are determined. Gel diffusion studies for the formulations of the present invention are further carried out. Data of the said studies will illustrate various aspects of the present invention.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to person skilled in the art upon reference to the description. It is

therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined.
The invention is further exemplified with following example and is not intended to limit the scope of the invention.
Example 1.

Sr. No. Ingredient % w/v
1. Timolol (as maleate) 0.5
2. Gellan gum 0.4
3. Mannitol 3.0
4. Tromethamine 0.5
5. Benzalkonium Chloride 0.005
6. Hydrochloric Acid 0.1N q.s to adjust pH to 7
7. Water for Injection q.stolOO
Manufacturing Process:
1. In a clean S.S.Vessel, Mannitol and Gellan gum were dissolved in water under slow stirring.
2. Tromethamine was added to step 1 under stirring.
3. Benzalkonium chloride was dissolved in water and transferred to step 2 under slow stirring.
4. The slurry from step 3 was sterilized by autoclave at 121°C for 30 min.
5. The slurry from step 4 was cooled to room temperature.
6. pH was checked and adjusted to 7 using 0. IN Hydrochloric acid
7. Timolol maleate was dissolved in water and filtered through 0.2(x membrane filter. The timolol maleate solution was transferred to slurry from step 5 under slow stirring.
8. pH was checked and adjusted to 7 using 0. IN Hydrochloric acid.
9. The volume was made up using water and the solution was stirred for 15 min.

Example 2.

Sr. No. Ingredient % w/v
1. Timolol (as maleate) 0.5
2. Gellan gum 0.1
3. Mannitol 3.0
4. Tromethamine 0.5
5. Benzalkonium Chloride 0.005
6. Hydrochloric Acid 0.1N q.s to adjust pH to 7
7. Water for Injection q.sto 100
Manufacturing Process:
1. In a clean S.S.Vessel, Gellan gum was dissolved in water under slow stirring.
2. Tromethamine was added to step 1 under stirring.

3. Benzalkonium chloride was dissolved in water and was transferred to step 2 under slow stirring.
4. The slurry from step 3 was sterilized using autoclave at 121°C for 30min.
5. The slurry from step 4 was cooled to room temperature.
6. Timolol maleate was dissolved in water and Mannitol, filtered through 0.2jx membrane filter and added to slurry from step 5.
7. pH was checked and adjusted to 7 using 0.1N Hydrochloric acid.
8. The volume was made up using water and the solution was stirred for 15min.
Example 3.

Sr. No. Ingredient % w/v
1. Timolol (as maleate) 0.5
2, Xanthan gum 0.1
3. Mannitol 1.0
4. Tromethamine 0.2
5. Benzalkonium Chloride 0.005
6. Hydrochloric Acid 0.1N q.s to adjust pH to 7

7. Water for Injection q.sto 100
Manufacturing Process:
1. In a clean S.S.Vessel, Xanthan gum was dissolved in water under stirring.
2. Mannitol and Tromethamine were added to step 1 under stirring.
3. Benzalkonium chloride was dissolved in water and was transferred to step 2 under slow stirring.
4. The slurry from step 3 was sterilized using autoclave at 121°C for 30min.
5. The slurry from step 4 was cooled to room temperature.
6. Timolol maleate was dissolved in water, filtered through 0.2(0, membrane filter and added to slurry from step 5.
7. The pH was checked and adjusted to pH 7 using 0. IN Hydrochloric acid.
8. The volume was made up using water and the solution was stirred for 15min.
Example 4.

Sr. No. Ingredient % w/v
1. Timolol (as maleate) 0.5
2. Carbopol 0.1
3. Mannitol 1.5
4. Tromethamine 2.0
5. Benzalkonium Chloride 0.005
6. Hydrochloric Acid 0.1N q.s to adjust pH to 7
7. Water for Injection q.s to 100
Manufacturing Process:
1. In a clean S.S.Vessel, Carbopol was dissolved in water under stirring.
2. Mannitol was added to step 1 under stirring.
3. Benzalkonium chloride was dissolved in water and transferred to step 2 under slow stirring.
4. The slurry from step 3 was sterilized using autoclave at 121°C for 30min.
5. The slurry from step 4 was cooled to room temperature.

6. Timolol maleate was dissolved in water, filtered using 0.2μ membrane filter and added to slurry from step 5.
7. The pH was checked and adjusted to 7 using 0.1N Hydrochloric acid.
8. The volume was made up using water and the solution was stirred for 15min.
Example 5.

Sr. No. Ingredient % w/v
1. Timolol (as maleate) 0.5
2. Carbopol 0.1
3. Mannitol 1.5
4. Tromethamine 2.5
5. Benzalkonium Chloride 0.005
6. Hydrochloric Acid 0.1N q.s to adjust pH to 7
7. Water for Injection q.sto 100
Manufacturing Process:
1. In a clean S.S.Vessel Carbopol was dissolved in water under stirring.
2. Mannitol and Tromethamine were added to step 1 under stirring.
3. Benzalkonium chloride was dissolved in water and transferred to step 2 under slow stirring.
4. The slurry from step 3 was sterilized using autoclave at 121°C for 30min.
5. The slurry from step 4 was cooled to room temperature.
6. Timolol maleate was dissolved in water, filtered through 0.2μ membrane filter and added to slurry from step 5.
7. The pH was checked and adjusted to 7 using 0. 1N Hydrochloric acid.
8. The volume was made up using water and the solution was stirred for 15min

Table 1 to 3 represents the stability data of example 5. Stability Data
Table 1.
Product Name : Timolol Gel
Strength : 5 ml
Batch No : TML/D/06
Storage Condition : 25° C± 2° C/40%± 5% RH

TESTS SPECIFICATION 25° C ± 2° C / 40% ± 5% RH

Initial 1 Month 2 Month 3 Month 6 Month
Description Clear solution Complies Complies Complies Complies Complies
Assay *■
1 .Timolol 95-105% 100.4 NA NA 99.4 96.0
2.Benzalkonium chloride 95-105% 99.2 NA NA 97.4 97.0
2. pH Between 8.1 to 9 6.2 NA NA 5.9 5.7
Conclusion: From the above data shows that the product is stable at 25° C / 40% RH for the period of 3 months in the recommended storage condition.
Table 2.
Product Name : Timolol Gel
Strength : 5 ml
Batch No : TML/D/06
Storage Condition : 30° C ± 2° C / 65% ± 5% RH

TESTS SPECIFICATION 30° C ± 2° C / 65% ± 5% RH

Initial 1 Month 2 Month 3 Month 6 Month
Description Clear solution Complies Complies Complies Complies Complies
Assay
1.Timolol 95-105% 100.4 NA NA 96.8 96.4
2.Benzalkonium chloride 95-105% 99.2 NA NA 99.9 97.0
2.pH Between 8.1 to 9 6.2 NA NA 6.0 5.71

Conclusion: From the above data shows that the product is stable at 30° C / 65% RH for the period of 3 months in the recommended storage condition.

Table 3.
Product Name Strength Batch No Storage Condition

: Timolol Gel
: 5 ml
: TML/D/06
: 40° C ± 2° C / 25% ± 5% RH

TESTS SPECIFICATION 40° C ± 2° C / 25% ± 5% RH

Initial 1 Month 2 Month 3 Month 6 Month
Description Clear solution Complie
s Complies Complies Complies Complies
Assay
1.Timolol 95-105% 100.4 98.0 96.2 95.8 95.4
2.Benzalkonium chloride 95-105% 99.2 97.1 100.4 101.4 95.5
2. pH Between 6.0-7.0 6.2 6.0 6.1 5.81 5.70
Conclusion: From the above data shows that the product is stable at 40° C / 25% RH for the period of 3 months in the recommended storage condition.
The composition of example 5 was put to Preservative Efficacy Test (PET). Form the
data of PET it is observed that viable microbial count on 'zero' day of the PET study do
not increase during 28 day study cycle.
Table 4 represents result of Preservative efficacy Test for the concentration 0.025
mg/ml.
Table 5 represents result of Preservative efficacy Test for the concentration 0.05 mg/ml.
Table 6 represents result of Preservative efficacy Test for the concentration 0.075
mg/ml.

Preservative Efficacy Test (PET) Table 4.

B.No: TML/D/08 ( Preservative 0.025mg/mL)
Label Claim: Each
mL Contains
Timolol
maleate 5 nig Observation Incubation Period

Incubation Period OHour 7 days 14 days 21 days 28 days Remarks
Name of Microbial Culture \ Limits NA No
increase from Log of Initial Calculated viable Count at "0"Hour Log
reduction in viable count at 14 days from the initial calculated Viable count at "0" Hour. Log of viable count at 21 days ( Limit No
increase from Log of Viable Count at 14 days) Log of viable count at 28 days ( Limit:N
0
increase from Log of Viable Count at 21 days)

Observation

Bacteria E.Coli vial microbial count per mL of inoculated preparation 7.74x10 s 1.30x102 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.8887 2.1139 0.0 0.0 0.0

Pseudo
monas
aerugino
sa vial microbial count per mL of inoculated preparation 8.04x10 s 4.73x102 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.9052 2.6749 0.0 0.0 0.0

Stapg aureus vial microbial count per mL of inoculated preparation 8.58x10 s 1.7xl02 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.9334 2.2304 0.0 0.0 0.0

Yeast and Moulds Candida albicans vial microbial count per mL of inoculated preparation 7.80x10 5 lxlO2 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.8921 2 0.0 0.0 0.0

Aspergil lus niger vial microbial count per mL of inoculated preparation 8.10x10s 1.4x10 2 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.9085 2.1461 0.0 0.0 0.0

Table 5.

B.No: TML/D/07 ( Preservative 0.05mg/mL)
Label Claim: Each
mL Contains
Timolol
maleate 5mg Observation Incubation Period

Incubation Period OHour 7 days 14 days 21 days 28 days Remarks
Name of Microbial Culture \ Limits NA No
increase from Log of Initial Calculated viable Count at "0"Hour Log
reduction in viable count at 14 days from the initial calculated Viable count at "0"
Hour.(Lim it NLT 3) Log of viable count at 21 days( Limit No
increase from Log of Viable Count at 14 days) Log of viable count at 28 days ( Limit:N
0
increase from Log of Viable Count at 21 days)

Observation

Bacteria E.Coli vial microbial count per mL of inoculated preparation 7.74x10 5 1.60x102 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.8887 2.2041 0.0 0.0 0.0

Pseudo
monas
aerugino
sa vial microbial count per mL of inoculated preparation 8.04x10 5 2.30xl02 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.9052 2.3617 0.0 0.0 0.0

Stapg aureus vial microbial count per mL of inoculated preparation 8.58x10 5 1.25xl02 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.9334 2.0969 0.0 0.0 0.0

Yeast and Moulds Candida albicans vial microbial count per mL of inoculated preparation 7.80x105 1.55x102 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.892 2.1903 0.0 0.0 0.0

Aspergil lus niger vial microbial count per mL of inoculated preparation 8.10xl05 0.95x102 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.9085 1.9777 0.0 0.0 0.0

Table 6.

B.No: TML/D/09 ( Preservative 0.075mg/mL)
Label Claim: Each
mL Contains
Timolol
maleate Smg Observation Incubation Period

Incubation Period OHour 7 days 14 days 21 days 28 days Remarks
Name of Microbial Culture \ Limits NAx No
increase from Log of Initial Calculated viable Count at "0"Hour Log
reduction in viable count at 14 days from the initial calculated Viable count at "0" Hour. Log of viable count at 21 days ( Limit No
increase from Log of Viable Count at 14 days) Log of viable count at 28 days ( Limit:N
0
increase from Log of Viable Count at 21 days)

Observation

Bacteria E.Coli vial microbial count per mL of inoculated preparation 7.74x10 5 1.75x10 2 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.8887 2.243 0.0 0.0 0.0

Pseudom
onas
aeruginos
a vial microbial count per mL of inoculated preparation 8.04x10 5 1.15xl02 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.9052 2.0606 0.0 0.0 0.0

Stapg aureus vial microbial count per mL of inoculated preparation 8.58x10 s 2.1xl02 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.9334 2.3222 0.0 0.0 0.0

Yeast
and
Moulds Candida albicans vial microbial count per mL of inoculated preparation 7.80x10 5 1.55x10 2 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.892 2.1903 0.0 0.0 0.0

Aspergill us niger vial microbial count per mL of inoculated preparation 8.10xl05 lxlO2 0.0 0.0 0.0 Complies

Log 10 viable microbial count per mL of inoculated preparation 5.9085 2' 0.0 0.0 0.0

Pharmaceutical limit of not less than 3 log reductions is achieved with the preservative system as mentioned in table 4 to 7 indicating the effectiveness of the preservative chosen. Effective log reduction during PET study is indicative of the fact that concentration of preservative used is adequate to impart desired microbial quality to the formulation. This is critical as the product is for ophthalmic application. In short, PET data indicates that the choice and concentration of preservative is appropriate for the product.

We Claim;
1. A stable gel forming solution comprising Timolol maleate and its acceptable salts, preservative and pharmaceutically acceptable excipients.
2. The stable gel forming solution of claim 1, wherein the preservative is selected form the group comprising benzalkonium chloride (BKC), benzyl alcohol, methyl paraben, propyl paraben, thimerosal, chlorobutanol, benzethonium chloride, cetyl pyridinium chloride, phenyl ethanol, phenyl propanol, phenyl mercuric acetate, phenyl mercuric nitrate, phenyl mercuric borate, chlorhexidine acetate or gluconate, cetrimide, chlorocresol and combinations thereof.
3. The stable gel forming solution of claim 1, wherein the concentration of preservative is 0.003% to 0.01%
4. The stable gel forming solution of claim 1, wherein the concentration of preservative is 0.025% to 0.075%
5. The stable gel forming solution of claim, wherein the concentration of preservative is 0.025% to 0.005%.
6. The stable gel forming solution of claim 1, wherein the pharmaceutically acceptable excipients comprises one or more of surfactants, osmolality agents, gelling agents, chelating agents, pH adjusting agents and isotonicity modifying agents.
7. The process to prepare a stable gel forming solution of claim 1, comprising of following steps :-

A) Preparation of slurry of excipients, followed by sterilization and pH adjustment,
B) Preparation of solution of Timolol maleate, followed by sterilization,

C) Mixing of slurry of excipients and solution of Timolol maleate, under slow stirring, with pH adjustment, followed by making up of volume using water.