GB2189045A

GB2189045A - Disinfecting contact lenses using sulphur dioxide and/or benzoic acid

Info

Publication number: GB2189045A
Application number: GB08706823A
Authority: GB
Inventors: David John Drain; John Gordon Bernard Howes; Derek Andrew Hollingsbee
Original assignee: Smith and Nephew Associated Companies PLC
Current assignee: Smith and Nephew PLC
Priority date: 1986-03-22
Filing date: 1987-03-23
Publication date: 1987-10-14
Anticipated expiration: 2007-03-23
Also published as: GB8908923D0; GB2214328B; GB2214328A; GB2189045B; GB8706823D0

Abstract

A contact lens is disinfected with an aqueous solution containing sulphur dioxide and/or benzoic acid, optionally under acidic conditions, for a period of time sufficient to disinfect the lens. The sulphur dioxide may be released from a metabisulphite or dithionite. The pH of the solution may be adjusted to the range 6 to 8 so that when the disinfected lens is removed from the solution and replaced in the eye, it is substantially non-irritant to the eye. The pH adjustment is preferable carried out employing the delayed release of a material which has an alkaline reaction with water whereby all the components of the system may be present at the beginning of the disinfection cycle. Compositions and packs for use in the disinfection are also described.

Description

SPECIFICATION Disinfecting composition The present invention relates to the disinfection of contact lenses and more particularly to disinfection processes which involve contacting the lens to be disinfected with an aqueous solution containing sulphur dioxide and/or benzoic acid and more particularly to the use of an aqueous solution containing sulphur dioxide generated from a sulphur dioxide-liberating compound and benzoic acid; to compositions used in such disinfection processes and to packs to enable the processes to be carried out.

Contact lenses when worn daily can become contaminated with dirt, cosmetics, tear debris, proteins, microorganisms and the like which if they are not removed from the lens can cause irritation when the lens is replaced in the eye. It is advisable, therefore, that contact lenses, and soft contact lenses in particular, are cleaned and disinfected on a regular basis, preferably daily.

It has long been recognised that the disinfection of contact lenses and soft contact lenses in particular, is beset with problems. Chemical methods have been considered. These methods reduce the propensity to cause a protein build-up on the lens caused by heat disinfection methods but may instead suffer from the disadvantage that the chemical agent may concentrate in the lens. When the lens is replaced in the eye, the chemical agent may be released from the lens and damage the cornea. Certain chemical disinfectants, for example those containing halogen or halogen oxyacids, have been found to damage certain lens polymers.It would be advantageous therefore to have a cold disinfecting process for contact lenses which was especially suitable for use with soft contact lenses, in which the disinfecting means did not cause protein deposition, did not concentrate in the lens, did not affect lens polymers and could be made safe to allow direct replacement of the lens into the eye after the disinfecting process. It has been found that these criteria are met if the disinfecting process employs as the disinfecting medium an aqueous solution of sulphur dioxide and/or benzoic acid and preferably of a synergistic mixture of sulphur dioxide and benzoic acid.

This process is suitable for disinfecting hard, hydrophilic (soft) and gas permeable contact lenses but is particularly suitable for disinfecting soft contact lenses.

Accordingly the present invention provides a method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with an aqueous solution containing sulphur dioxide and/or benzoic acid.

Aptly the present invention provides a method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with an aqueous solution containing sulphur dioxide. Preferably the sulphur dioxide will be generated from a sulphur dioxide-liberating compound.

In one favoured aspect the present invention provides a method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with an aqueous solution containing a sulphur dioxide-liberating compound.

In a more favoured aspect thereof the present invention provides a method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with a solution containing sulphur dioxide and then adjusting the pH of the solution so that when the disinfected lens is removed from the solution and replaced in the eye it is non-irritant to the eye. Suitably the pH of the solution will be adjusted to the range 6 to 8.

Accordingly in a particularly favoured aspect the present invention provides a method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with a solution containing a sulphur dioxide-liberating compound and then adjusting the pH of the solution so that when the disinfected lens is removed from the solution the solution has a pH of from 6 to 8.

Compounds which will liberate sulphur dioxide in the presence of water are well known.

Metabisulphites and dithionites, for example, will decompose in the presence of water with the liberation of sulphur dioxide and these compounds have been found to be suitable for use as sulphur dioxide liberating compounds for use in the process of the invention. They are conventionally used in the form of their ammonium or alkali metal salts of which sodium salts are preferred and particularly favoured is the use of sodium metabisulphite. This compound has been used as an antioxidant in adrenaline eye drops and is known to be non-irritant when instilled in the eye, however its use as a disinfecting agent in ophthalmic applications has not been disclosed or suggested.

The amount of sulphur dioxide-liberating compound may be such as to provide a concentration of sulphur dioxide in solution of aptly 40 to 5000 ppm, and suitably 50 to 500 ppm, more suitably 75 to 400ppm and preferably 100 to 250 ppm of sulphur dioxide.

The disinfecting agent may therefore be presented either in a preformed solution or as a solid form for dissolving in water or in a solution of tonicity agent for example sodium chloride and/or buffering agent and the like. Suitable water may include distilled water, deionised water or tap water. Since sulphur dioxide-liberating compounds do so under acidic conditions the tablet or water it is dissolved in should contain an acidic component to provide the initial solution with a pH of from 1.8 to 5.5, more suitably 1.8 to 4.0 and preferably 1.8 to 3.2 for example 2.0 and 3.0.

Suitable acidifying agents may include sorbic, benzoic, tartaric ascorbic, lactic, acetic fumaric, citric, maleic, adipic and malic acid, or inorganic mineral acids such as hydrochloric or phosphoric acid.

In another aspect the present invention provides a method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with an aqueous solution containing an effective amount of benzoic acid.

In this favoured aspect the present invention provides a method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with a solution containing an effective amount of benzoic acid and then adjusting the pH of the solution so that when the disinfected lens is removed from the solution and replaced in the eye it is non-irritant to the eye. Suitably the pH of the solution will be adjusted to the range 6 to 8.

Suitably the compositions used in the previous invention will contain from 0.01 to 0.25% benzoic acid, more suitably 0.05 to 0.225% and preferably from 0.1 to 0.2%. The skilled worker will appreciate that an disinfecting effective amount of benzoic acid will vary according to the pH value of the solutions which contains it, however, the compositions used in the present invention will generally contain the amounts given above. Since benzoic acid is antimicrobial only under acidic conditions the tablet or water it is dissolved in may contain an additional acidic component to provide the initial solution with a pH of from 1.8 to 5.5, more suitably 2.5 to 5.0 and preferably 2.5 to 4.5 for example 3.0 or 4.0.

Suitable acidifying agents may include sorbic, ascorbic, tartaric, lactic, acetic, fumaric, citric, maleic, adipic and malic acid or inorganic mineral acids such as hydrochloric or phosphoric acid.

Surprisingly it has been found that sulphur dioxide and benzoic acid exhibit synergistic antibacterial activity against several important organisms and especially Candida albicans when they are employed in an aqueous solution at a pH of from 1.8 to 3.2.

Accordingly in a preferred aspect the present invention provides a method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with an aqueous solution containing an effective amount of a synergistic mixture of sulphur dioxide and benzoic acid.

Accordingly in another aspect thereof the present invention provides a method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with a solution containing an effective amount of a synergistic mixture of sulphur dioxide and benzoic acid and then adjusting the pH of the solution so that when the disinfected lens is removed from the solution and replaced in the eye it is non-irritant to the eye. Suitably the pH of the solution will be adjusted to the range of 6 to 8.

Suitably the compositions used in this aspect of the present invention will contain from 0.01 to 0.25% by weight of benzoic acid, more suitably 0.05 to 0.225% and preferably from 0.1 to 0.2%.

(When used herein the term % refers to % by weight).

The amount of sulphur dioxide-liberating compound which is to be used with benzoic acid may suitably be such as to provide a concentration of sulphur dioxide in solution of aptly 10 to 5000 ppm and suitably 10 to 500 ppm, more suitably 15 to 200 ppm and preferably 20 to 100 ppm of sulphur dioxide, for example 25 ppm.

The skilled worker will appreciate that an effective disinfecting amount of sulphur dioxide and benzoic acid in aqueous solution will vary according to the pH value of the solution which contains them. However, the compositions used in the present invention will generally contain the amounts given above.

The final composition of the disinfectant solution may be selected so as to give a solution which is substantially isotonic that is it will have a tonicity equivalent to a 0.7 to 1.2% solution of sodium chloride. The solutions containing an effective disinfecting amount of benzoic acid and/or sulphur dioxide-liberating compound are normally hypotonic and thus the tonicity of such solutions should be adjusted by the components of the neutralising system as described herein after and/or by a tonicity agent such as sodium chloride.

The period of time envisaged for disinfection of a contact lens is from 10 minutes to 8 hours.

If desired the system can be used for disinfecting a lens by allowing it to stand overnight in contact with the disinfecting solution.

Since replacement of a lens into the eye from a solution of low pH value for example 1.8 to 3.2 would be irritant, it is necessary to adjust the pH of the solution containing it for example to the range 6 to 8 before the lens can be removed and replaced safely directly into the eye. This adjustment may be achieved by adding agent such as a sterile alkali solution or a tablet containing material which has an alkaline reaction with water to the solution containing the lens at the end of the disinfection cycle. There is a risk that this step may be omitted and a lens from a non-neutralised solution may be replaced in the eye.It is preferred instead to add at the beginning of the disinfection process a neutralising system which will slowly release or provide delayed release of agent which will adjust the pH of the solution so that when the disinfected lens is removed from the disinfecting solution, the solution has a pH from 6 to 8. The adjustment of the pH of the solution may be facilitated by manually mixing the contents from time to time and especially just prior to removing the lens.

In a further aspect therefore the present invention provides an aqueous solution suitable for the disinfection of a contact lens which solution contains an effecting disinfecting amount of sulphur dioxide and/or benzoic acid.

In a further aspect thereof the present invention provides an aqueous solution suitable for the disinfection of a contact lens which solution contains an effective disinfecting amount of sulphur dioxide.

In a further aspect thereof the present invention provides an aqueous solution suitable for the disinfection of a contact lens which solution contains an effective disinfecting amount of benzoic acid.

Suitably the aqueous solutions may additionally contain an acidic component as hereinbefore described. Preferably the acidic component is tartaric acid or citric acid.

The aqueous solution will aptly contain the proportions of sulphur dioxide and benzoic acid as hereinbefore described.

Thus in a preferred aspect the invention provides an aqueous solution suitable for the disinfection of a contact lens which solution contains from 0.1 to 0.25% benzoic acid and from 10 to 500 ppm of sulphur dioxide and which solution has a pH of from 1.8 to 3.2.

Conventionally a contact lens is disinfected by contacting it in a container, which may be closed by a screw cap, with an aqueous solution containing the disinfecting agent. The disinfecting agent may therefore be presented either in a preformed solution or as a solid form for dissolving in water. Suitable water may include distilled water, deionised water or tap water.

Since benzoic acid and sulphur dioxide are antimicrobial only under acidic conditions the tablet or water they are dissolved in may, contain an additional acidic component to provide the initial solution with a pH of from 1.8 to 3.2, and preferably provide a pH of 2.0 to 3.0 for example 2.0, 2.5 or 3.0.

Thus the presentation of the system with which to carry out the method of the invention may include (a) an aqueous solution into which is added a tablet of the benzoic acid and/or sulphur dioxide liberating compound and a tablet adapted to slowly release or delayed release a material having an alkaline reaction with water.

(b) a two layer tablet which has a rapidly dissolving layer which contains benzoic acid and/or sulphur dioxide-liberating compound and optionally an acidifying agent and a slowly dissolving or delayed release layer containing the neutralising agent. Such a tablet may be added to water in which the lens is immersed or if the acidifying agent is not present in the tablet, the tabet may be added to acidified water.

(c) an aqueous solution containing benzoic acid and an acidic component, a tablet which contains a sulphur dioxide-liberating compound and a slowly dissolving or delayed release tablet containing a material which has an alkaline reaction with water.

Aptly the material which has an alkaline reaction with water may be added as a tablet and preferably one which has been adapted to provide slow or delayed release of the material, for example by encapsulation either as particles or as a tablet in a water soluble or water permeable polymer coating, in a solid matrix or in a hard slowly dissolving tablet. Suitable materials include sodium borate, carbonates and bicarbonates such as sodium carbonate or bicarbonate and disodium hydrogen phosphate or other salts which give an alkaline reaction on dissolution in water.

Preferably the alkaline material is present in a tablet which is encapsulated in a water soluble polymer coating. Apt coatings may be formed from materials which include water soluble cellulosic materials such as hydroxypropyl cellulose, hydroxypropyl methyl cellulose, water soluble polymers such as polyvinyl alcohol, polyacrylic acids such as those known as Carbopols (trade mark) Eudragits (trade mark). The coatings may additionally contain a more water soluble material such as lactose to facilitate the solubilisation of the coating. In a particularly preferred form the encapsulated tablet may be effervescent on exposure to water. This has the effect that as the coating dissolves from the tablet and it is exposed to water it begins to effervesce thereby mixing the contents of the container and disrupting any remaining coating so providing rapid release of the alkaline material.The skilled worker will appreciate that the thickness of the coating and its solubility will dictate the time of the delayed release of the alkaline material.

Aptly the effervescence may be provided by an alkaline compound if this compound is for example a carbonate or bicarbonate such as sodium or potassium carbonate or bicarbonate.

Aptly an acidic compound is also present in the tablet also to help to generate the effervescent gas. Suitable acidic agents include citric, tartaric or malic acids. Naturally the alkaline material will be in excess so that the pH of the solution is adjusted to pH 6 to 8.

The delayed release coating to the tablet may be applied by many processes including the following, placing the tablet within a water soluble or water permeable envelope; coating the tablet by spraying or fluidised bed; dip coating by immersing the tablet in a solution of the polymer and drying in warm air, suitable polymer solutions include hydroxypropyl cellulose in ethyl alcohol, hydroxypropyl methyl cellulose in aqueous alcohol; compression coating a tablet centred in a dry polymer powder. Apt processes are dip coating and compression coating.

Typically a 4" tablet containing the neutralising agent and/or tonicity adjusting agent may be coated by compressing in a 3/8" tablet press surrounded by a dry polymer powder. The coating so formed is about 1/,6" thick and may dissolve in 2-3 hours releasing the contents of the tablet the contents of which then dissolve.

In a further aspect the present invention comprises a three part pack for producing a contact lens disinfecting solution, said three part pack comprising one part an aqueous solution of an effective disinfecting amount of benzoic acid, a second part containing a predetermined quantity of a sulphur dioxide liberating compound and another part comprising a predetermined quantity of a tablet adapted to slowly release or delay the release of a material having an alkaline reaction with water.

In a further aspect the present invention comprises a two part pack for producing a contact lens disinfecting solution, said two part pack comprising a predetermined quantity of a tablet containing an effective disinfecting amount of benzoic acid and/or sulphur dioxide-liberating compound and a slowly dissolving or delayed release neutralising agent and another part comprising a predetermined quantity of an aqueous vehicle.

The disinfecting system or the neutralising system or both may also contain a metal ion chelating agent. The chelating agent may be any compound which will chelate at least calcium and magnesium ions from tap water and which is compatible with the other components and with ophthalmic use, that is the chelating agent must be non-irritant to the eye at the concentrations used in the solution. Suitable chelating agents will include ethylene diamine tetra-acetic acid and salts thereof for example with disodium salt and complex polyphosphate for example sodium hexametaphosphate, sodium pyrophosphate or sodium tripolyphosphate.

The chelating agent is used in an amount sufficient to remove calcium and magnesium ions from the tap water used to form the disinfecting solution. The skilled worker will appreciate that the minimum amount required will vary depending upon the hardness of the tap water, a minimum amount of at least 0.01% by weight will be generally used. Suitably the amount of chelating agent used will from 0.01 to 1% by weight, more suitably 0.02 to 0.50% and preferably 0.05 to 0.1%.

The use of the term tap water refers to water which has not been de-ionised or specially purified but is sufficiently uncontaminated to be of a potable standard.

Conventionally such water is supplied as drinking water from treatment plants to a tap. This term also includes water of equivalent quality from other sources such as spring water.

Tap water may also have been chlorinated and therefore the disinfecting system may also include a dechlorinating agent. The disinfecting compositions of the present invention may use as dechlorinating agent a metabisulphite especially sodium metabisulphite.

An indicator can be included in the system so that the user may visually determine that the pH value of the disinfecting solution has been adjusted to the range 6 to 8.

The compositions employed in the method of the invention may also contain a surface active agent to assist in the cleaning and/or wetting of the lenses by the disinfecting composition. This is particularly useful when the lenses being treated are hard or gas permeable lenses. Suitable surface active agents include non ionic surface active agents such as polyoxyethylene-polyoxypropylene diol block copolymers, sorbitan fatty acid esters, polyoxyethylated sorbitan fatty acid esters and the like. Suitably the composition may contain from 0.01 to 1% of non-ionic surface active agent and preferable 0.05 to 0.5%.

Example 1 A tablet containing the following ingredients Sodium metabisulphite 7.2mg Citric acid 20mg is prepared by mixing the powdered ingredients together and compressing in a tablet press. The finished tablets may be packaged in a blister pack formed from a material which is a moisture barrier in a conventional manner.

In use a tablet is removed from the pack and dissolved in 10 ml of water and the lens is immersed in the liquid. The solution has a pH of 3.0. The lens may be disinfected by leaving it in the solution overnight. Prior to removing the lens from the solution a tablet comprising Disodium hydrogen phosphate 1 Omg Sodium carbonate 38mg Sodium chloride 45mg.

was added to the solution and dissolved with stirring to adjust the pH to 7.1.

Example 2 A tablet containing the following the following ingredient Sodium metabisulphite 7.2mg is prepared by compressing the powdered ingredient. The tablets may be packaged in a moisture proof blister pack in a conventional manner.

In use the tablet is removed from the pack and dissolved in 5ml of water acidified by the presence of citric acid at a concentration of 2g/litre. The lens is immersed in this solution and allowed to stand overnight. A powder containing the ingredients of the tablet of Example 1 is dissolved in the disinfecting solution to adjust the pH to 7.0.

Example 3 A solution is prepared by dissolved distilled water, Sodium metabisulphite 0.299 Citric acid 0.969 Distilled water to 240g.

The solution is then sterilised by filtration or by treatment and filled into pre-sterilised bottles.

In use the solution (10 ml) is placed in a container having a closing means usually by filling to a predetermined mark. The lens is then immersed in the liquid and allowed to stand overnight.

A tablet containing disodium hydrogen phosphate 10mg sodium carbonate 38mg sodium chloride 45mg is dissolved in the disinfecting solution to give a pH value of 7.2. The lens is removed from the solution and replaced in the eye.

Example 4 A solution of benzoic acid (20mg) in distilled water (10ml) is sterilised by filtration through a 0.22lem polyester filter. The final solution has a pH of 3.0 (approx). A lens is immersed in this solution in a closed container for 4 hours. At the end of this period the contents of a sachet containing anhydrous disodium hydrogen phosphate (116mg) and sodium cloride (25mg), which are previously sterilised by gamma irradiation, are added to the solution containing the lens and the container shaken to dissolve the powder. The resultant solution has a pH value of 7.4 and is approximately isotonic. The lens now disinfected is removed from the solution and is replaced in the eye.

Example 5 A sterile solution of benzoic acid in distilled water is prepared as described in Example 1. A lens is immersed in the solution in a closed container for 6 hours. At the end of this period a compressed tablet containing anhydrous disodium hydrogen phosphate (116mg) and sodium chloride (25mg) is added to the closed container and the container and contents shaken to dissolve the tablet. The final solution has a pH of 7.4 and is approximately isotonic. The disinfected lens may be removed from the solution and replaced in the eye.

Example 6 A sterile solution of benzoic acid (8ml of a solution containing 200mg in 100ml distilled water) prepared as described in Example 1 are taken and placed in a closable container. A lens is immersed in the solution in the container for 4 hours.

At the end of this period 2ml of sterile solution of disodium hydrogen phosphate and sodium chloride (5.89 and 1.259 respectively dissolved in 100ml of distilled water and sterilised by filtration) are added to the container. The resultant solution is approximately isotonic and has a pH of 7.2. The disinfected lens may be removed from the solution and replaced in the eye.

Example 7 A solution of benzoic acid (20mg) and sodium metabisulphite (7.2mg) in distilled water (10ml) is sterilised by filtration through a 0.22um polyester filter. The final solution has a pH of 3.0 (approx). A lens is immersed in this solution in a closed container for 4 hours. At the end of this period the contents of a sachet containing anhydrous disodium hydrogen phosphate (160mg) and potassium dihydrogen phosphate (15mg), which are previously sterilised by gamma irradiation, are added to the solution containing the lens and the container shaken to dissolve the powder. The resultant solution has a pH value of 7.0 and is approximately isotonic the lens now disinfected is removed from the solution and is replaced in the eye.

Example 8 A sterile solution of benzoic acid and sodium metabisulphite in distilled water is prepared as described in Example 1. A lens is immersed in the solution in a closed container for 6 hours. At the end of this period a compressed tablet containing anhydrous disodium hydrogen phosphate (160mg) and potassium dihydrogen phosphate (15mg) is added to the closed container and the container and contents shaken to dissolve the tablet. The final solution has a pH of 7.4 and is approximately isotonic. The disinfected lens may be removed from the solution and replaced in the eye.

Example 9 A sterile solution (7 ml) of benzoic acid and sodium metabisulphite (225mg and 60mg in 100ml distilled water) prepared as described in Example 1 are taken and placed in a closable container. A lens is immersed in the solution in the container for 4 hours.

At the end of this period 3ml of sterile solution of disodium hydrogen phosphate and potassium dihydrogen phosphate (8.09 and 0.759 respectively dissolved in 100ml of distilled water and sterilised by filtration) are added to the container. The resultant solution is approximately isotonic and has a pH of 7.2. The disinfected lens may be removed from the solution and replaced in the eye.

Example 10 An aqueous solution of benzoic acid and sodium metabisulphite (10mis containing 20mg and 7.2mg respectively) is placed in a screw-topped container. A tablet comprising Sodium bicarbonate 95mg Tartaric acid 25mg Disodium EDTA 2H20 10mg Disodium hydrogen phosphate lOmg Sodium chloride 15mg Polyethylene glycol 5mg coated with hydroxy propyl cellulose is then added to the container. The tablet is made by compressing together the above ingredients to form a tablet approximately 4" in diameter. A coat of hydroxy propyl cellulose is then compressed around it using a 3/8" tablet punch to give a coated thickness of about 1/its". The lens is then immersed in the solution in the container.After about 2z hours the coating has dissolved sufficiently for the tablet to begin to effervesce. The tablet dissolves into solution so that the final solution is substantially isotonic and has a pH of 7.

Demonstration of Effectiveness 1 A suspension of the following test organisms was prepared at a concentration of 108 organisms/mls Staphylococcus aureus NCTC 10788 Pseudomonas aeruginosa NCTC 0750 Escherichia coli NCTC 86 Candida albicans ATCC 10231 Aspergillus niger ATCC 16404 Serratia marcescens ATCC 14041 Aliquots (20ml) of the test solutions containing 62.5ppm sulphur dioxide buffered to a pH value of 2.0 and containing 125ppm sulphur dioxide buffered to a pH value of 3.0 were innoculated with 200,us of the suspension of the test organism and mixed. The solutions when then sampled immediately and at 3 hours and at 24 hours after mixing by removing 1 ml of solution and placing it into 9mls of a neutralising solution. The numbers of organisms retrievable from the solution was then determined.

Test solution containing 62.5ppm sulphur dioxide acidified at pH=2.0 with citric acid.

Viable count logrO count/ml Test organisms Sampled after the following hours 0 hours 3 hours 24 hours Staph aureus 5.61 < 1.0 < 1.0 Pseudomonas aeruginosa 4.80 < 1.0 < 1.0 E. Coli 5.38 < 1.0 < 1.0 C. albicans 5.22 4.55 < 1.0 A. niger 5.6 < 1.0 c 1.0 S. marcescens 5.83 (1.0 < 1.0 Test solution containing 1000.0 ppm sulphur dioxide at pH=3.0 with citric acid.

Viable count log1O count/ml Test organisms Sampled after the following hours 0 hours 3 hours 24 hours Staph aureus 5.72 < 1.0 < 1.0 Ps. aeruginosa 5.68 c1.,0 (1.0 E. Coli 5.68 < 1.0 < 1.0 C. albicans 5.31 5.27 1.93 A. niger 5.74 1.3 < 1.0 S. marcescens 5.83 < 1.0 < 1.0 Demonstration of Effectiveness 2 A suspension of Candida albicans (ATCC 10231) at a concentration of 108 organisms/ml was prepared. Aliquots (20ml) of the test solutions containing benzoic acid, sulphur dioxide and a mixture of benzoic acid and sulphur dioxide were innoculated with 200 of the suspension of the test organism and mixed. The solutions were then sampled immediately and at 1 hours and 3 hours after mixing by removing 1 ml of solution and placing it into 9mls of a neutralising solution (Tryptone soya broth containing Tween (Trade mark) and (lecithin). The numbers of organisms retrievable from the solution was then determined.

Solution pH Viable count log1O count/ml Sampled after the following hours 0 1 3 0.2% Benzoic acid 2.0 6.03 5.19 2.78 0.2% Benzoic acid 3.0 5.84 5.65 5.01 25ppm Sulphur dioxide 2.0 5.76 5.84 5.75 500ppm Sulphur dioxide 3.0 5.89 5.86 5.61 0.2% Benzoic acid/ 25ppm sulphur dioxide 2.0 5.93 3.77 < 1.0 0.2% Benzoic acid/ 500ppm Sulphur dioxide 3.0 5.94 4.82 < 1.0 The results show synergy between sulphur dioxide and benzoic acid against Candida albicans in aqueous solutions which have pH of 2.0 to 3.0.

Claims

1. A method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with an aqueous solution containing sulphur dioxide and/or benzoic acid.

2. A method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with an aqueous solution containing sulphur dioxide.

3. A method as claimed in claim 1 in which the sulphur dioxoide is generated from a sulphur dioxide-liberating compound.

4. A method as claimed in claim 3 in which the sulphur dioxide-liberating compound is sodium metabisulphite.

5. A method as claimed in any of claims 2 to 4 in which the concentration of sulphur dioxide in solution is from 50ppm to 500ppm.

6. A method as claimed in claim 5 in which the pH of the solution is from 1.8 to 3.2.

7. A method for disinfecting a contact lens wherein the lens is contacted for a period of time sufficient to disinfect the lens with an aqueous solution containing an effective disinfecting amount of benzoic acid.

8. A method as claimed in claim 7 in which the solution contains from 0.01 to 0.25% benzoic acid.

9. A method as claimed in claim 8 in which the pH of the solution is from 2.5 to 4.0.

10. A method as claimed in any one of claims 1 to 9 in which the solution additionally contains an acidic component.

11. A method as claimed in claim 10 in which the acidic component is tartaric acid.

12. A method as claimed in claim 1 in which the solution contains from 0.01 to 0.25% benzoic acid and from 10 to 500ppm of sulphur dioxide.

13. A method as claimed in any one of claims 1 to 12 in which the pH value of the solution is adjusted so that when the disinfected lens is removed form the solution, the solution has a pH value of from 6 to 8.

14. A method as claimed in claim 13 in which the pH of the solution is adjusted by means of the addition to the solution of a material which has an alkaline reaction to water to the solution.

15. A method as claimed in claim 14 in which the material which has an alkaline reaction to water is present in a form which is adapted to provide slow or delayed release of the material.

16. A method according to claim 13 in which the pH of the solution is adjusted by adding an effective amount of disodium hydrogen phosphate and potassium dihydrogen phosphate.

17. A method as claimed in any of claims 1 to 16 in which the final composition of the disinfecting solution is substantially isotonic.

18. A method according to any of one of claims 1 to 17 in which there is additionally present in the solution from 0.1 to 1 % of a chelating agent.

19. A method according to any one of the claims 1 to 18 in which there is included in the system an indicator which allows visual determination that the pH of the disinfecting solution has been adjusted to the range pH 6 to 8.

20. An aqueous solution suitable for the disinfection of a contact lens contains an effective disinfecting amount of sulphur dioxide and/or an effective disinfecting amount of benzoic acid.

21. An aqueous solution as claimed in claim 20 in which the solution contains from 50 to 500ppm of sulphur dioxide.

22 An aqueous solution as claimed in claim 20 in which the solution contains from 0.01 to 0.25% benzoic acid.

23. An aqueous solution as claimed in claim 20 in which the solution contains from 0.01 to 0.25% benzoic acid and from 10 to 500ppm of sulphur dioxide and which has a pH of from 1.8 to 3.2.

24. An aqueous solution as claimed in claim 16 which solution additionally contains an acidic component.

25. An aqueous solution as claimed in claim 18 in which the acidic component is tartaric acid.

26. An aqueous solution as claimed in any one of claims 20 to 25 which the final solution is substantially isotonic.

27. An aqueous solution as claimed in any one of claims 20 to 26 in which the solution contains from 0.1 to 1% of chelating agent.

28. An aqueous solution as claimed in any one of claims 20 to 27 in which the solution contains an indicator which allows visual determination that the pH value of the disinfecting solution has been adjusted to the range pH 6 to 8.

29. A three part pack for producing a contact lens disinfecting solution, said three part pack comprising one part an aqueous solution of an effective disinfecting amount of benzoic acid and acidic component, a second part comprising a predetermined quantity of a tablet containing a sulphur dioxide liberating compound and another part comprising a predetermined quantity of a tablet adapted to slowly release or delay the release of a compound having an alkaine reaction with water.

30. A two part pack for producing a contact lens disinfecting composition, said to part pack comprising one part comprising a predetermined quantity of a tablet containing an effective disinfecting amount of acidic component and sulphur dioxide-liberating compound and a slowly dissolving or delayed release of a material which has an alkaline reaction on dissolution in water and another part comprising a predetermined quantity of an aqueous vehicle.

31. A two part pack as claimed in either of claims 24 or 25 in which the acidic component is tartaric acid.

32. A soft contact lens when disinfected by the method of claim 1.