Patent Publication Number: US-7709012-B2

Title: Ophthalmic compositions containing a synergistic combination of two polymers

Description:
This application claims priority to U.S. Provisional Application, U.S. Ser. No. 60/478,253, filed Jun. 13, 2003. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to pharmaceutical compositions. In particular, this invention relates to topically administrable ophthalmic compositions that contain certain combinations of two polymeric components. 
     2. Description of Related Art 
     The use of polymeric ingredients in topically administrable ophthalmic compositions is well known. Polymeric ingredients are typically used in suspension compositions as physical stability aids, helping to keep the insoluble ingredients suspended or easily redispersible. In solution compositions, polymeric ingredients are typically used to increase the composition&#39;s viscosity. 
     Many polymers have been used in topically administrable ophthalmic compositions. Included among these are cellulosic polymers, such as hydroxypropyl methylcellulose, hydroxyethyl cellulose, and ethylhydroxyethyl cellulose. Also included are synthetic polymers, such as carboxyvinyl polymers and polyvinyl alcohol. Still others include polysaccharides such as xanthan gum, guar gum, and dextran. 
     Combinations of polymers have also been used in ophthalmic compositions. Certain combinations of polymers are known to provide synergistic effects on viscosity and, in some cases, even a phase transition from a liquid to a gel. For example, U.S. Pat. No. 4,136,173 discloses ophthalmic compositions containing a combination of xanthan gum and locust bean gum. 
     One approach to achieving a target viscosity in a topically administrable ophthalmic composition might involve simply adding a sufficient amount of one polymeric ingredient. Often, however, it is desirable to minimize the total amount of polymeric additives in topically administrable ophthalmic compositions. A mixed polymer system containing more than one polymer can significantly enhance the viscosity and lubrication property of a composition while minimizing total polymer concentration and cost of materials. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward aqueous ophthalmic compositions suitable for topical ophthalmic administration that comprise a viscosity enhancing amount of a polymeric ingredient wherein the polymeric ingredient consists of a certain combination of two polymeric ingredients. The ophthalmic compositions comprise a combination of polymeric ingredients selected from the group consisting of: hydroxypropyl methylcellulose and guar gum; hydroxypropyl methylcellulose and a carboxyvinyl polymer; carboxyvinyl polymer and guar gum; hydroxypropyl methylcellulose and hydroxyethylcellulose; hyaluronic acid and hydroxypropyl methylcellulose; and hyaluronic acid and guar gum. The compositions containing one of these select combinations of polymeric ingredients are useful as artificial tear products, and can also serve as vehicles for delivering ophthalmic drugs. 
     The present invention is based upon the finding that these select combinations of two polymers have a synergistic effect on viscosity. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Unless otherwise indicated, all ingredient concentrations are listed as a weight/volume percentage basis (% w/v). 
     The ophthalmic compositions of the present invention are aqueous compositions that include a select combination of two polymeric ingredients. The combination is one of the following: hydroxypropyl methylcellulose and guar gum; hydroxypropyl methylcellulose and a carboxyvinyl polymer; a carboxyvinyl polymer and guar gum; hydroxypropyl methylcellulose and hydroxyethylcellulose; hyaluronic acid and hydroxypropyl methylcellulose; and hyaluronic acid and guar gum. All five types of individual polymers are known and have been used in ophthalmic compositions. All five types of polymers are also commercially available. 
     HPMC is commercially available from the Dow Chemical Company under the brand name Methocel®. HPMC is available in a variety of grades. Most preferred for use in the compositions of the present invention is Methocel E4M, (HPMC 2910), which has a number average molecular weight of approximately 86,000 dalton. The concentration of HPMC in the compositions of the present invention will generally range from 0.05-0.5%, and will preferably be 0.3%. 
     The guar gum ingredient can be guar gum or a guar gum derivative, such as the hydroxypropyl or hydroxypropyltrimonium chloride derivatives of guar gum. Guar and its derivatives are described in U.S. Pat. No. 6,316,506, the entire contents of which are hereby incorporated by reference. For purposes of the present application, “guar gum” includes unsubstituted guar gum and its substituted derivatives. Guar gum and many of its derivatives are commercially available from Rhone-Poulenc (Cranbury, N.J.), Hercules, Inc. (Wilmington, Del.) and TIC Gum, Inc. (Belcamp, Md.). A preferred derivative for use in the compositions of the present invention is hydroxypropyl guar (“HP-Guar”). The concentration of guar in the compositions of the present invention will generally range from 0.01-0.2%, and will preferably be 0.1%. 
     Carboxyvinyl polymers suitable for use in the present invention are also known as “carbomers” or carboxypolymethylene. They are commercially available from sources such as Noveon, Inc. (Cleveland, Ohio), which distributes them under the trade name Carbopol®. Carbopol polymers are crosslinked, acrylic acid-based polymers. They are crosslinked with allyl sucrose or allylpentaerythritol. Carbopol copolymers are polymers of acrylic acid, modified by C 10-30  alkyl acrylates, and crosslinked with allylpentaerythritol. A preferred carboxyvinyl polymer for use in the compositions of the present invention is a polymer of acrylic acid crosslinked with allyl sucrose or allylpentaerythritol, which is commercially available as Carbopol® 974P. The concentration of carbomer in the compositions of the present invention will generally range from 0.01-0.2%, and will preferably be 0.1%. 
     HEC is commercially available from Hercules Inc. (Aqualon Division) in a variety of grades, including Natrasol 250 LR, Natrasol 250 MR and Natrasol 250 HR. A preferred HEC for use in the compositions of the present invention is the NF grade material, which is commercially available as Natrasol 250HR. The concentration of HEC in the compositions of the present invention will generally range from 0.05-0.5%, and will preferably range from 0.1-0.2%. 
     Hyaluronic acid is commercially available from a variety of sources, including Genzyme and Hyaluron Inc. Hyaluronic acid is available in many grades, with molecular weights ranging from 100,000 to greater than 3 million dalton. 
     The aqueous compositions of the present invention contain one of the specified combinations of polymers in a total polymer concentration range of 0.05-3.0%, preferably 0.2-2.0%. 
     In addition to the required combination of two polymeric ingredients, the aqueous compositions of the present invention may contain other ingredients as excipients. For example, the compositions may include one or more pharmaceutically acceptable buffering agents, preservatives (including preservative adjuncts), non-ionic tonicity-adjusting agents, surfactants, solubilizing agents, stabilizing agents, comfort-enhancing agents, emollients, pH-adjusting agents and/or lubricants. Preferably, the aqueous composition does not contain any polymeric ingredients, other than the synergistic combination of the two polymeric ingredients specified above, with the exception of polymeric preservatives for compositions that contain a preservative. If the compositions contain a carbomer as one of the two polymers, then the compositions of the present invention do not contain any ionic tonicity-adjusting agent, such as sodium chloride, or other ionic excipients, such as boric acid, as these ingredients have a significant, detrimental effect on the composition&#39;s viscosity. 
     The compositions of the invention have a pH in the range of 5-9, preferably 6.5 7.5, and most preferably 6.9 7.4. If the compositions contain a carbomer as one of the two polymers, it is critical that the compositions are formulated so that the target pH is not exceeded. Once a target pH has been exceeded in compositions containing a carbomer, adding an acid such as hydrochloric acid to adjust the pH downward can compromise the synergistic viscosity. Even relatively small amounts of acid or salts, on the order of 0.005%, can have a significant effect on the viscosity of compositions containing a carbomer. 
     The compositions of the present invention generally have an osmolality in the range of 220-320 mOsm/kg, and preferably have an osmolality in the range of 235-260mOsm/kg. 
     The aqueous compositions of the present invention are suitable for use as artificial tear products to relieve symptoms of dry eye. Alternatively, the compositions of the present invention may act as a vehicle for an ophthalmic drug. The compositions of the present invention may also be used as irrigating solutions for ophthalmic or other surgical procedures. Ophthalmic drugs suitable for use in the compositions of the present invention include, but are not limited to: anti-glaucoma agents, such as beta-blockers including timolol, betaxolol, levobetaxolol, carteolol, miotics including pilocarpine, carbonic anhydrase inhibitors, prostaglandins, seretonergics, muscarinics, dopaminergic agonists, adrenergic agonists including apraclonidine and brimonidine; anti-angiogenesis agents; anti-infective agents including quinolones such as ciprofloxacin, and aminoglycosides such as tobramycin and gentamicin; non-steroidal and steroidal anti-inflammatory agents, such as suprofen, diclofenac, ketorolac, rimexolone and tetrahydrocortisol; growth factors, such as EGF; immunosuppressant agents; and anti-allergic agents including olopatadine. The ophthalmic drug may be present in the form of a pharmaceutically acceptable salt, such as timolol maleate, brimonidine tartrate or sodium diclofenac. Compositions of the present invention may also include combinations of ophthalmic drugs, such as combinations of (i) a beta-blocker selected from the group consisting of betaxolol and timolol, and (ii) a prostaglandin selected from the group consisting of latanoprost; 15-keto latanoprost; travoprost; and unoprostone isopropyl. 
     Although the amount of drug included in the compositions of the present invention will be whatever amount is therapeutically effective and will depend upon a number of factors, including the identity and potency of the chosen drug, the total concentration of drug will generally be about 5% or less. 
     The compositions of the present invention are preferably not formulated as solutions that gel upon administration to the eye. The compositions illustrated in the Examples below do not gel upon administration to the eye. 
     The following examples are presented to illustrate further various aspects of the present invention, but are not intended to limit the scope of the invention in any respect. 
     EXAMPLES 
     Example 1 
     Artificial Tear Composition 
     A representative formulation for an artificial tear product according to the present invention is shown in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Ingredients 
                 Concentration (% w/v) 
               
               
                   
                   
               
             
            
               
                   
                 Carbopol 974P 
                 0.1 
               
               
                   
                 HP-Guar 
                 0.1 
               
               
                   
                 Mannitol 
                 4.0 
               
               
                   
                 NaOH/HCl 
                 Qs to pH 7.0 
               
               
                   
                 Purified water 
                 Qs to 100 
               
               
                   
                   
               
            
           
         
       
     
     The composition shown in Table 1 can be prepared by at least two methods. One method involves adding the following ingredients slowly and in the following order to heated purified water (70-80° C.) (approximately 80% of the desired batch volume) with mixing: mannitol, Carbopol 974P, and HP-Guar (waiting until each ingredient is mixed well before adding the next). pH is then adjusted with 1N NaOH, and the remaining amount of purified water is added. The composition is then autoclaved at 121° C. for thirty minutes and subsequently cooled to room temperature with constant stirring. 
     An alternative method of preparing the composition shown in Table 1 is as follows. In a first container, add heated purified water (70-80° C.) (approximately 60% of the desired batch volume), then mix in mannitol, and then Carbopol 974P, waiting until each ingredient is mixed well before adding the next. Autoclave the resulting composition at 121° C. for thirty minutes, then allow the composition to cool to room temperature with constant stirring (“the Carbopol composition”). In a separate container, add purified water (approximately 30% of the desired batch volume), then mix in HP-Guar. Adjust the pH of the HP-Guar composition with 1N NaOH to pH 9. Autoclave the HP-Guar composition at 121° C. for thirty minutes, then allow it to cool to room temperature with constant stirring (“the HP-Guar composition”), then aseptically combine the HP-Guar composition with the Carbopol composition, and aseptically adjust the final pH to 7.0, if necessary, with 1N NaOH. 
     Example 2 
     Synergistic Effect on Viscosity (HPMC+Guar; HPMC+Carbomer; Carbomer+Guar) 
     The compositions shown in Table 2 were prepared and their viscosity was determined using a Brookfield cone/plate viscometer with number 42 cone/plate set (30 rpm, at 25° C.) for less viscous samples (viscosity less than 20 cps) and number 52 cone/plate set (3 rpm, at 25° C.) for more viscous samples (viscosity more than 20 cps). Two people independently prepared the indicated samples and measured their viscosity values (n=1) for each person. The averages of each set of results are shown in Table 2. 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Composition (% w/v) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Ingredient 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Mannitol 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
               
               
                 HPMC 2910 
                 — 
                 0.3 
                 — 
                 — 
                 0.3 
                 0.3 
                 — 
               
               
                 Carbopol 974P 
                 — 
                 — 
                 0.1 
                 — 
                 0.1 
                 — 
                 0.1 
               
               
                 HP-Guar 
                 — 
                 — 
                 — 
                 0.1 
                 — 
                 0.1 
                 0.1 
               
               
                 NaOH/HCl 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
               
               
                   
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
               
               
                   
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
               
               
                 Purified Water 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 100 
               
               
                   
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Viscosity (cps) 
                 1.1 
                 8.2 
                 488.1 
                 5.3 
                 1339.5 
                 32.3 
                 1273.0 
               
               
                 Subst. Synergy @   
                 — 
                 — 
                 — 
                 — 
                 Yes 
                 Yes 
                 Yes 
               
               
                   
               
               
                   @ Subst. Synergy = substantial synergy: greater than 150% of the simple sum of the two respective single polymer solutions 
               
            
           
         
       
     
     Example 3 
     Synergistic Effect on Viscosity (HPMC+HEC) 
     The compositions shown in Table 3 were prepared and their viscosity determined using a Brookfield cone/plate viscometer with number 42 cone/plate set (30 rpm, at 25° C.) for less viscous samples (viscosity less than 20 cps) and number 52 cone/plate set (3 rpm, at 25° C.) for more viscous samples (viscosity more than 20 cps). The HEC used in this experiment was Natrasol 250HR as shown in the following Table. Two people independently prepared the indicated samples and measured their viscosity values (n=1) for each person. The averages of each set of results are shown in Table 3. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Composition (% w/v) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Ingredient 
                 8 
                 9 
                 10 
                 11 
                 12 
                 13 
                 14 
                 15 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Mannitol 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
               
               
                 HPMC 2910 
                 — 
                 0.3 
                 — 
                 — 
                 — 
                 0.3 
                 — 
                 — 
               
               
                 HP-Guar 
                 — 
                 — 
                 0.1 
                 — 
                 — 
                 — 
                 0.1 
                 — 
               
               
                 Carbopol 
                 — 
                 — 
                 — 
                 0.1 
                 — 
                 — 
                 — 
                 0.1 
               
               
                 974P 
               
               
                 Natrasol 
                 — 
                 — 
                 — 
                 — 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 250HR 
               
               
                 NaOH/HCl 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. pH 
               
               
                   
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
                 7.0 
               
               
                   
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
               
               
                 Purified 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
               
               
                 Water 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Viscosity 
                 1.0 
                 8.0 
                 5.2 
                 465.9 
                 3.0 
                 27.7 
                 10.9 
                 642.0 
               
               
                 (cps) 
               
               
                 Subst. 
                 — 
                 — 
                 — 
                 — 
                 — 
                 Yes 
                 No 
                 No 
               
               
                 Synergy @   
               
               
                   
               
               
                   @ Subst. Synergy = substantial synergy: greater than 150% of the simple sum of the two respective single polymer solutions 
               
            
           
         
       
     
     Example 4 
     Lack of Synergistic Effect on Viscosity (Polyvinyl Alcohol+Chondroitin Sulfate; Polyvinyl Alcohol+Polyvinylpyrrolidone; Chondroitin Sulfate+Polyvinylpyrrolidone) 
     The compositions shown in Table 4 were prepared and their viscosity determined using a Brookfield cone/plate viscometer with number 42 cone/plate set (30 rpm, at 25° C.) for less viscous samples (viscosity less than 20 cps) and number 52 cone/plate set (3 rpm, at 25° C.) for more viscous samples (viscosity more than 20 cps). Two people independently prepared the indicated samples and measured their viscosity values (n=1) for each person. The averages of each set of results are shown in Table 4. Airvol 523S is a commercially available polyvinyl alcohol polymer. Chondroitin sulfate is a commercially available polymer. PVP K90 is a commercially available polyvinyl pyrrolidone polymer. 
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Composition (% w/v) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Ingredient 
                 16 
                 17 
                 18 
                 19 
                 20 
                 21 
                 22 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Mannitol 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
               
               
                 PVA (Airvol 523S) 
                 — 
                 0.2 
                 — 
                 — 
                 0.2 
                 0.2 
                 — 
               
               
                 Chondroitin Sulfate 
                 — 
                 — 
                 0.2 
                 — 
                 0.2 
                 — 
                 0.2 
               
               
                 PVP (K90) 
                 — 
                 — 
                 — 
                 0.2 
                 — 
                 0.2 
                 0.2 
               
               
                 NaOH/HCl 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. pH 
               
               
                   
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
                 7.0 
               
               
                   
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
               
               
                 Purified Water 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
               
               
                   
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Viscosity (cps) 
                 1.0 
                 1.5 
                 1.3 
                 1.4 
                 1.7 
                 1.9 
                 1.8 
               
               
                 Subst. Synergy @   
                 — 
                 — 
                 — 
                 — 
                 No 
                 No 
                 No 
               
               
                   
               
               
                 *slight, transparent precipitate observed 
               
               
                   @ Subst. Synergy = substantial synergy: greater than 150% of the simple sum of the two respective single polymer solutions 
               
            
           
         
       
     
     Example 5 
     Lack of Synergistic Effect on Viscosity (Polyvinyl Alcohol+Carbomer; Chondroitin Sulfate+Carbomer; Polyvinyl pyrrolidone+Carbomer) 
     The compositions shown in Table 5 were prepared and their viscosity determined using a Brookfield cone/plate viscometer with number 42 cone/plate set (30 rpm, at 25° C.) for less viscous samples (viscosity less than 20 cps) and number 52 cone/plate set (3 rpm, at 25° C.) for more viscous samples (viscosity more than 20 cps). Two people independently prepared the indicated samples and measured their viscosity values (n=1) for each person. The averages of each set of results are shown in Table 5. Airvol 523S is a commercially available polyvinyl alcohol polymer. Chondroitin sulfate is a commercially available polymer. K90 is a commercially available polyvinylpyrrolidone polymer. 
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 Composition (% w/v) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Ingredient 
                 17 
                 18 
                 19 
                 23 
                 24 
                 25 
                 26 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Mannitol 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
               
               
                 PVA 
                 0.2 
                 — 
                 — 
                 — 
                 0.2 
                 — 
                 — 
               
               
                 (Airvol 523S) 
               
               
                 Chondroitin 
                 — 
                 0.2 
                 — 
                 — 
                 — 
                 0.2 
                 — 
               
               
                 Sulfate 
               
               
                 PVP 
                 — 
                 — 
                 0.2 
                 — 
                 — 
                 — 
                 0.2 
               
               
                 (K90) 
               
               
                 Carbopol 
                 — 
                 — 
                 — 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 974P 
               
               
                 NaOH/HCl 
                 q.s. pH 
                 q.s. pH 
                 q.s. pH 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
               
               
                   
                 7.0 
                 7.0 
                 7.0 
                 pH 
                 pH 
                 pH 
                 pH 
               
               
                   
                   
                   
                   
                 7.0 
                 7.0 
                 7.0 
                 7.0 
               
               
                 Purified Water 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
               
               
                   
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Viscosity (cps) 
                 1.5 
                 1.3 
                 1.4 
                 441.6 
                 323.8 
                 12.7 
                 N/A* 
               
               
                 Subst. 
                 — 
                 — 
                 — 
                 — 
                 No 
                 No 
                 No 
               
               
                 Synergy @   
               
               
                   
               
               
                 *PVP was incompatible with Carbopol 974P - it formed a precipitate. 
               
               
                   @ Subst. Synergy = substantial synergy: greater than 150% of the simple sum of the two respective single polymer solutions 
               
            
           
         
       
     
     Example 6 
     Lack of Synergistic Effect on Viscosity (HPMC+Dextran; Guar+Dextran; Carbomer+Dextran) 
     The compositions shown in Table 6 were prepared and their viscosity determined using a Brookfield cone/plate viscometer with number 42 cone/plate set (30 rpm, at 25° C.) for less viscous samples (viscosity less than 20 cps) and number 52 cone/plate set (3 rpm, at 25° C.) for more viscous samples (viscosity more than 20 cps). Two people independently prepared the indicated samples and measured their viscosity values (n=1) for each person. The averages of each set of results are shown in Table 6. 
     
       
         
           
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 Composition (% w/v) 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Ingredient 
                 27 
                 28 
                 29 
                 30 
                 31 
                 32 
                 33 
                 34 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Mannitol 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
               
               
                 HPMC 2910 
                 — 
                 0.3 
                 — 
                 — 
                 — 
                 0.3 
                 — 
                 — 
               
               
                 HP-Guar 
                 — 
                 — 
                 0.1 
                 — 
                 — 
                 — 
                 0.1 
                 — 
               
               
                 Carbopol 
                 — 
                 — 
                 — 
                 0.1 
                 — 
                 — 
                 — 
                 0.1 
               
               
                 974P 
               
               
                 Dextran 70 
                 — 
                 — 
                 — 
                 — 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 NaOH/HCl 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
               
               
                   
                 pH 7.0 
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
                 pH 
               
               
                   
                   
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
                 7.0 
               
               
                 Purified 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
                 q.s. 
               
               
                 Water 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Viscosity 
                 1.1 
                 7.9 
                 5.2 
                 461.6 
                 1.4 
                 8.4 
                 5.2 
                 379.3 
               
               
                 (cps) 
               
               
                 Subst. 
                 — 
                 — 
                 — 
                 — 
                 — 
                 No 
                 No 
                 No 
               
               
                 Synergy @   
               
               
                   
               
               
                   @ Subst. Synergy = substantial synergy: greater than 150% of the simple sum of the two respective single polymer solutions 
               
            
           
         
       
     
     Example 7 
     Effect of Salt on Viscosity for a Polymer Combination that Contains Carbomer 
     The compositions shown below in Table 7 were prepared to determine the effect of the addition of salt (NaCl) on viscosity. The viscosity of each sample was determined using a Brookfield cone/plate viscometer (52 cone, 3 rpm). The results are shown in Table 7. 
     
       
         
           
               
               
             
               
                   
                 TABLE 7 
               
             
            
               
                   
                   
               
               
                   
                 Composition (% w/v) 
               
            
           
           
               
               
               
               
               
               
            
               
                 INGREDIENT 
                 35 
                 36 
                 37 
                 38 
                 39 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Mannitol 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
               
               
                 HPMC 2910 
                 0.3 
                 0.3 
                 0.3 
                 0.3 
                 0.3 
               
               
                 Carbopol 974P 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 NaCl 
                 0 
                 0.001 
                 0.005 
                 0.01 
                 0.05 
               
               
                 NaOH/HCl 
                 q.s. pH 7.0 
                 q.s. pH 7.0 
                 q.s. pH 7.0 
                 q.s. pH 7.0 
                 q.s. pH 7.0 
               
               
                 Purified Water 
                 q.s. 100 
                 q.s. 100 
                 q.s. 100 
                 q.s. 100 
                 q.s. 100 
               
               
                 Viscosity (cps) 
                 737 
                 430 
                 359 
                 212 
                 49 
               
               
                   
               
            
           
         
       
     
     Example 8 
     Effect of Boric Acid on Viscosity for a Polymer Combination that Contains Carbomer 
     The compositions shown below in Table 8 were prepared to determine the effect of the addition of boric acid on viscosity. The viscosity of each sample was determined using a Brookfield cone/plate viscometer (52 cone, 3 rpm). The results are shown in Table 8. 
     
       
         
           
               
               
             
               
                   
                 TABLE 8 
               
             
            
               
                   
                   
               
               
                   
                 Composition (% w/v) 
               
            
           
           
               
               
               
               
               
               
            
               
                 INGREDIENT 
                 40 
                 41 
                 42 
                 43 
                 44 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Mannitol 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
               
               
                 HPMC 2910 
                 0.3 
                 0.3 
                 0.3 
                 0.3 
                 0.3 
               
               
                 Carbopol 974P 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
                 0.1 
               
               
                 Boric acid 
                 0 
                 0.001 
                 0.005 
                 0.01 
                 0.05 
               
               
                 NaOH/HCl 
                 q.s. pH 7.0 
                 q.s. pH 7.0 
                 q.s. pH 7.0 
                 q.s. pH 7.0 
                 q.s. pH 7.0 
               
               
                 Purified Water 
                 q.s. 100 
                 q.s. 100 
                 q.s. 100 
                 q.s. 100 
                 q.s. 100 
               
               
                 Viscosity (cps) 
                 657 
                 534 
                 362 
                 233 
                 65 
               
               
                   
               
            
           
         
       
     
     The invention has been described by reference to certain preferred embodiments; however, it should be understood that it may be embodied in other specific forms or variations thereof without departing from its spirit or essential characteristics. The embodiments described above are therefore considered to be illustrative in all respects and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description.