WO2017151651A1 - Pharmaceutical in situ gelling compositions - Google Patents

Abstract

The present disclose generally relates to pharmaceutical in situ gelling compositions comprising an aqueous mixture of an anionic polysaccharide, a source of a polyvalent cation and a polymer. The in situ gelling compositions advantageously form transparent gels upon contact with the tear fluid in the eye and are useful as drug delivery vehicles. The present disclosure also relates to in situ gelling compositions comprising a mixture of high acyl gellan, low acyl gellan and a source of a polyvalent cation. Finally, methods of administering a drug opthalmically are also provided.

Description

DESCRIPTION

PHARMACEUTICAL IN SITU GELLING COMPOSITIONS RELATED APPLICATION

[0001 ] This a pplication claims the benefit of priority to U .S. Provisional Application No. 62/301 ,273, filed on February 29, 201 6, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

[0002] The present disclose generally relates to pharmaceutical in situ gelling compositions comprising an aqueous mixture of an anionic polysaccharide, a source of a polyvalent cation and a polymer. The in situ gelling compositions advantageously form gels upon contact with the tear fluid in the eye. The present disclosure also relates to in situ gelling compositions comprising a mixture of high acyl or low acyl gellan and a source of a polyvalent cation, or high acyl gellan, low acyl gellan and a source of a polyvalent cation.

BACKGROUND

[0003] The tear film of the eye fulfils several functions, including hydration, lubrication, anti-bacterial, tra nsportation of oxygen and carbon dioxide and clearing of harmful substances. The flow of tears provides an effective defense against environmental pathogens. The eye lids can be thought of as the wiper blades of a car, with a resultant high shear rate that helps clear debris from the surface of the eye. Hea lthy human tears generally contain a n aqueous mixture of mucin, lipids, lysozyme, lactoferrin, lipoca lin, lacitin, immunoglobulins, glucose, urea, sodium, ca lcium and potassium. Tears further have a pH ra nging from 5.2 to 8.5, with mean values being about 7.4. Changes in the pH of tears can occur due to the opening time of the eyelids, when bicarbonate present in the lachrymal filmquilibrates with carbon dioxide in the air, resulting an alkalization of the film. Tear secretion and blinking lead to a decrease in pH of tears. (Chemical and physical parameters of tears relevant for the design of ocular drug delivery formulations by Vincent Baeyens and Robert Gurny, Pharmaceutica Acta Heivetiae, 72:191 -202 (1997)).

[0004] The defense mechanisms of the eye include rapid tear flow which enables the removal of foreign material from the tear fluid bathing the eye. This effective defense mechanism is an obstacle to the delivery of drugs to the anterior portion of the eye when the drug is administered as a commonly used eye drop. A proven approach to slow drug removal is to increase the viscosity of the medication. However, large increases in viscosity are often needed in order to observe any improvement in clinical effect.

[0005] The retention of ocular medications in human and animal eye have been shown to have an initial more rapid removal rate that is in turn followed by a slower rate of removal. It is thought that the initial rate of removal is due to fast reflex tear flow that is followed by a slower basal tear flow. The ability of a gel-forming solution (GFS) GFS to remain in the eye during the rapid initial removal phase has a determining affect upon the overall retention of the GFS with time. Therefore, the ability of a GFS to form a strong gel upon first interacting with the resident tear volume was selected as a measure of the GFS to be retained in the eye.

[0006] There are 217 monovalent cations on a molar basis for every one divalent cation in tears. Therefore, it is expected that a drop of GFS will encounter significantly greater number of monovalent rather than divalent cations. However, divalent cations such as Ca²⁺ and Mg2+ have been shown to more efficiently increase the gel strength of LA- gellan-formed gels than when monovalent cations (e.g., Na⁺, ⁺) are mixed with LA- gellan (Food Hydrocolloids, 2012) . Divalent cations such as Ca²⁺ result in a direct bridge between gellan polymer strands, whereas monovalent cations shield the electrostatic charges of the polymer strands to allow closer approaches to each other ( asapis, 1999).

[0007] The topical application of ophthalmic drug solutions to the eye, such as with drug-containing eye drops or eye ointments, generally results in the extensive loss of therapeutic agents. "Studies have shown that under normal circumstances the half- time of residence of a solution in the eye ranges from 10s to 4min, depending on the degree of reflex tearing elicited . . . . On average, the concentration has been shown to drop to around half of the applied topical dose in one minute, with the level decreasing to 1000^th of the initial value within 8min. Both the concentration and duration of exposure of a medication in the eye are thus determined by the character and dynamics of the pre-ocular tear film.^" (Composition and Interfacial Properties of Tears, Tear Substitutes and Tear Models by Anne M. Bright and Brian J. Tighe, Journal of the British Contact Lens Association, 1 6(2) :57-66 ( 1 993)) . Accordingly, clinicians often recommend frequent dosing of ophthalmic drugs at very high concentrations. (In-situ gels -a novel approach for ocular drug delivery by Chandra Mohan Eaga et.al., Der Pharmacia Lettre, 1 ( l ) :21 -33 (2009)) .

[0008] One of the first approaches to increasing ocular retention of pharmaceutical compositions was to increase viscosity (resistance to flow) by incorporating water soluble polymers into an aqueous medium. Initial increases in viscosity ( 1 to 100 cps) resulted in a small but significant increase in retention in the eye. However, further increases in viscosity are much less efficient at increasing residence time of the solution in the eye. Hence; a very viscous pilocarpine product (PILOPINE HS®) was developed which showed enhanced ocular effectiveness, but had to be packaged in a tube rather than an eye drop bottle in order to be dispensed by the patient. It is challenging for a patient to administer an eye medication from a tube and most patients prefer administering their medication from an eye drop.

[0009] Hydrogels are three-dimensional, cross-linked networks of water-soluble polymers. Drugs can be loaded into the gel matrix due to porosity of the gel, and subsequent drug release occurs at a rate dependent on the diffusion coefficient of the small molecule or macromolecule through the gel network. A depot formulation is created from which drugs slowly elute, maintaining a high local concentration of drug in the surrounding tissues over an extended period. Biocompatibility is promoted by the high water content of hydrogels.

[0010] In general, the rate of drug release from a linear polymer matrix is inversely proportional to its viscosity. (Hydrogels in drug delivery: Progress and challenges by Todd R. Hoare and Daniel S. ohane, Polymer 49:1 1993-2007 (2008) .) This causes a difficulty in that very large unworkable viscosities may be needed to affect a desired prolonged release. Water-soluble polymer hydrogels that are not cross-linked swell and subsequently dissolve in the aqueous in vivo environment. (Hydrogels in drug delivery: Progress and challenges by Todd R. Hoare and Daniel S. Kohane, Polymer 49: 1 1993- 2007 (2008) .) Thus, if the polymers can be cross linked, it is likely they will stay longer in an in vivo environment such as the area of the eye.

[0011 ] Cross-links between the different polymer provide networks that have visco- elastic and sometimes pure elastic behavior. Polymers can be cross linked physically in addition to chemically. Alginate, for example, can be cross linked by ionic interactions, such as through calcium ions. "In addition to anionic polymers being cross linked with metallic ions, hydrogels can also be obtained by complexation of polyanions with polycations. lonically crosslinked chitosan hydrogels are formed by complex formation between chitosan and polyanions, such as dextran sulfate or polyphosphoric acid." (Novel Crosslinking methods to design hydrogels by W.E. Hennink and C.R. van Nostrum, Advanced Drug Delivery Reviews 64:223-236 (2012) .)

[0012] Ophthalmic in situ gelling vehicles undergo a solution to gel (sol-to-gel) phase transition upon exposure to the physiological conditions present in the eye. The latter are highly advantageous over preformed gels, which do not allow for accurate and reproducible administration of a desired dosage of a drug and, after administration, often produce blurred vision, crusting of the eyelids and lacrimation. In situ gelling systems furthermore have the potential to be easily and accurately applied to the eye in liquid form while prolonging the formulation 's residence time on the surface of the eye due to gelling." (Comparison of ion-activated in situ gelling systems for ocular drug delivery. Part 1 :Physicochenmical characterization and in vitro release by llva D. Rupenthal et.al., International Journal of Pharmaceutics, 41 1 :69-77 (201 1 ). The sol-togel phase change may be triggered by increased temperature, increased pH and ionic strength of the tear film." (Eaga et al.)

[0013] Eye drop administration is preferred by patients over the use of a tube. The marketed product Timop†ic-XE® is an example of an in situ gel that is administered as a drop from an ophthalmic bottle and then forms a high viscosity gel upon instillation onto the eye. The increased Timolol bioavailability possible with Timop†ic-XE results in effective dosing occurring once a day rather than twice a day as needed with simple Timolol solution. [0014] Timoptic XE® contains low acyl (LA) Gellan. Gellan is a high molecular weight polysaccharide produced by the micro-organism Pseudomonas elodea. It is supplied in the native form as high acyl (HA) gellan. Timop†ic-XE makes use of a chemically modified gellan known as low acyl (LA) gellan. A low viscosity solution, dispensable from a bottle, of LA gellan is known to significantly increase in viscosity in the presence of cations that are present in tear fluid. Gellan has been used in various formulations to increase pre-corneal residence times with human contact times up to 20 hr being reported. In addition to gellan, other polymers have also been investigated for their abilities to gel due to ocular environmental changes in pH and temperature. Products based upon these concepts are often referred to a gel forming solutions (GFS) .

[0015] Thermo reversible hydro gels are in the liquid state at ambient temperature (20°- 25°C) and then transition into semisolid gels when held at body temperature (35°-37°C) . Pluronic F-127 is the most commonly used polymer for this purpose.

[0016] Gelation induced by pH includes using the polymer Carbopol® to form a solution with a low viscosity at acidic pH (e.g., pH of 3) that transforms into a still gel when neutralized by tears (pH of 7.4) . Such acidic compositions are disadvantageous for ophthalmic use.

[0017] Based on the above, there is a need for in situ gelling compositions that can applied to the surface of the eye that are non-irritating and provide reliable release of a desired dose of a drug. Such compositions may be easier to apply because they may dropped into the eye as a liquid and then transition into a gel in the presence of tear fluids. Thus, such gels are expected to have longer retention time and reduced loss from being washed out by the action of tears. Furthermore, such compositions are expected to improve dosing of pharmaceuticals due to the prolonged contact with the surface of the eye and improved drug retention in the gel. Compositions that provide a controlled, sta ble release of a drug would a lso improve accuracy of dosing and reduce the freq uency of dosing. Furthermore, compositions that can be applied topically to the eye that are non-irritating a nd non-blurring would improve patient complia nce. The present disclosure addresses these needs by providing an in situ gelling composition having surprising thixotropic properties and an advantageous drug release profile.

BRIEF SUMMARY

[0018] The present disclosure provides an in situ gelling pharmaceutica l composition comprising an aqueous mixture of an a nionic polysaccharide, a source of polyva lent cations and a polymer.

[0019] In an alternative embodiment, a n in situ gelling pharmaceutical composition comprises a n aqueous mixture of a high acyl gellan, a low acyl gella n, and a source of polyva lent cations.

[0020] In yet another embodiment, an in situ gelling pharmaceutica l composition comprises an aqueous mixture of a high acyl gellan a nd a low acyl gellan.

[0021 ] The present disclosure further provides a method of administering the aforementioned in situ gelling pharmaceutical composition to the surface of the eye of a patient in need thereof.

[0022] It is to be understood that both the foregoing general description and the following detailed description present embodiments of the disclosure and are intended to provide a n overview or framework for understa nding the nature and character of the disclosure as it is claimed. The description serves to explain the principles and operations of the claimed subject matter. Other a nd further features a nd advantages of the present disclosure will be readily a pparent to those skilled in the art upon a reading of the following disclosure.

[0023] All references cited herein are hereby incorporated by reference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 depicts a stepwise viscosity sweep of 1 to 1000 s- 1 for an in situ gelling composition of 0.75% low-acyl gellan with 0.0625% calcium gluconate a nd 0.375% povidone, with a pH of 7.2.

[0025] Figure 2 depicts viscosity v. shear rate of an in situ gelling composition of 0.6% low-acyl gellan and 0.4% high-acyl gellan .

[0026] Figure 3 is a Gra ph depicting k va lues of a preparation of 0.9% low-acyl gella n with 0.06% gluconate alone, in a 5: 1 ratio with ATS, or in a 5: 1 ratio of D l .

[0027] Figure 4 is a gra ph depicting the Ta u va lues of a preparation of 0.9% low-acyl gellan with 0.06% gluconate alone, in a 5: 1 ratio with ATS, or in a 5: 1 ratio of D l .

[0028] Figure 5 is a graph of timolol release rates as a function of time for various in situ gelling preparations.

[0029] Figure 6 depicts the primary and secondary viscosity of a mixed LA a nd HA gellan composition in artificial tears.

[0030] Figure 7 depicts the Tau values for a composition having 1 % sodium alginate as the polysaccharide based on percent of calcium gluconate.

[0031 ] Figure 8 depicts the va lues for a 1 .5 % sodium alginate preparation based on percent of calcium gluconate in PATS and Dl water.

DETAILED DESCRIPTION [0032] Reference now will be made in detail to the embodiments of the present disclosure, one or more examples of which are set forth herein below. Each example is provided by way of explanation of the compositions of the present disclosure and is not a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the teachings of the present disclosure without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment.

[0033] Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present disclosure are disclosed in or are obvious from the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present disclosure.

[0034] The present application is, in some embodiments, generally directed to a pharmaceutical composition comprising an anionic polysaccharide, a source of a polyvalent cation, and a polymer. In certain embodiments, the anion polysaccharide is present in an amount ranging from about 0.05 to about 2% by weight of the composition, or about 0.1 to about 2.0%, about 0.2 to about 2.0%, about 0.3 to about 1 .2%, about 0.3 to about 1 .0%, or about 0.5 to about 0.9% by weight of the composition.

[0035] The anionic polysaccharide is, in some embodiments, selected from the group consisting of gellan, alginate, pectin, xanthan gum, chondroitin sulfate, gum Arabic, gum kaya, gum tragacanth, and combinations thereof. In particular embodiments, the anionic polysaccharide is gellan, and more particularly low-acyl gellan. Low-acyl gellan is available commercially, for example from CP elco as Gelzan® or kelcogel®.

[0036] Gellan gum is a wafer-soluble anionic polysaccharide produced by the bacterium Sphingomonas elodea (formerly Pseudomonas elodea). It was initially identified as a substitute gelling agent at significantly lower use level to replace agar in solid culture media for the growth of various microorganisms. The repeating unit of the polymer is a tetrasaccharide, which consists of two residues of D-glucose and one of each residues of L-rhamnose D-glucoronic acid. The tetrasaccharide repeat has the following structure:

[D-Glc(pl→47D-GlcA( l→4)Djhbn-Glc( 877→u8ir)L-Rha(a l→3)]_n.

As it is evident from the formula, the tetrasaccharide units are connected by (a l→3) glycosidic bonds.

[0037] Gellan gum is extremely effective at low use levels in forming gels, and is available in two types: high and low acyl content. Low-acyl gellan gums form firm, non-elastic, brittle gels, whereas high acyl gellan gum forms soft, very elastic, non-brittle gels. Varying the ratios of the two forms of gellan produces a wide variety of textures.

[0038] The uniqueness of gellan gum is the ability to suspend while contributing minimal viscosity via the formation of a uniquely functioning fluid gel solution with a weak gel structure. Fluid gels exhibit an apparent yield stress, i.e., a finite stress which must be exceeded before the system will flow. These systems are very good at suspending particulate matter since, provided the stress exerted by the action of gravity on the particles is less than the yield stress, the suspension will remain stable.

[0039] Other important properties of gellan gum fluid gels are the setting temperature, degree of structure and thermal stability. All of these properties are, as with normal unsheared gels, dependent upon the concentration of gellan gum and the type and concentration of gelling ions.

[0040] While not being bound by any particular theory, it is believed that the low-acyl (LA) form of gellan more easily transforms from a solution to a gel due to the increased ease in which cations can form bridges between the LA gellan polymer chains as compared to high-acyl (HA) gellan (Morris et.al., 1996, 1999) . High-acyl (HA) gellan solutions form gels at much higher temperatures than low acyl gellan solutions.

[0041] In some embodiments, the gellan, e.g., low-acyl gellan, is present in an amount ranging from about 0.05 to 2% by weight of the composition, or about 0.1 to about 2.0%, about 0.2 to 2.0%, about 0.3 to 1 .2%, about 0.3 to about 1 .0%, or about 0.5 to about 0.9% by weight of the composition. In other embodiments, the gellan is present in about 0.15%, 0.3%, 0.6%, 0.9%, 1 .2% or 1 .8% by weight of the composition.

[0042] Gellan may advantageously be purified prior to incorporation into the present compositions. Commercially available gellans contain small amounts of cations, such as calcium. The gellan may be purified by dialysis to remove these cations, particularly divalent cations, along with other low molecular weight impurities, thereby improving its ability to form the in situ gelling vehicle when combined with the polyvalent cation source. Accordingly, in some embodiments, the gellan is a dialyzed or purified low-acyl gellan. The term purified low-acyl gellan refers to low-acyl gellan that is free of or substantially free of low molecular weight impurities, such as calcium.

[0043] In some embodiments, the source of polyvalent cation can be a molecular cation exchange agent or cation exchange resin, and may comprise The source of the polyvalent cation can comprise any polyvalent cation, but in particular, Ca²⁺, Al³⁺, Mn²⁺, Sr²⁺, Zn²⁺, Fe²⁺, or combinations thereof. When the source of polyvalent cation is a molecular cation exchange agent, such as a water-soluble molecular cation exchange agent, e.g., such as calcium gluconate, the amount used may be in a range of about 0.01 to about 0.1 %, about 0.02 to about 0.1 %, about 0.03 to about 0.08, about 0.03 to about 0.07% by weight of the composition. Alternatively, the amount of the molecular cation exchange agent is in a range of about 0.232 to about 2.32 mMole divalent cation per kg of the composition, 0.465 to about 2.32 mMole divalent cation per kg of the composition, about 0.698 to about 1 .68 mMole divalent cation per kg of the composition, or about 0.698 to about 1 .626 mMole divalent cation per kg of the composition.

[0044] In other embodiments, the source of the polyvalent cation can be a cation exchange resin, such as a dextran cross-linked with epichlorohydrin, which is commercially available as Sephadex® (e.g. SP Sephadex C-25, available from GE Healthcare Life Sciences. A polyvalent cation especially useful with the cation exchange resin is Zn²⁺. The ion exchange agent may be present in the compositions in an amount ranging from about 0.2 to about 5 % by weight, about 0.3 to about 5 % by weight, about 0.3 to about 3% by weight, about 0.5 to about 3 % by weight, or about 0.5 to about 2% by weight, or about 0.6 to about 1 .5% by weight of the composition. Alternatively, ion exchange agents loaded with divalent cations may be present in the compositions in amounts such that 0.232 mMole divalent cation are available per kg of GFS to about 2.32 mMole divalent cation per kg of GFS, about 0.465 mMole divalent cation available per kg of gel forming solution to about 2.32 mMole divalent cation available per kg of GFS, about 0.698 mMole divalent cation available per kg of GFS to about 1 .86 mMole divalent cation available per kg of GFS, about 0.698 mMole divalent cation available per kg of GFS to about 1 .626 mMole divalent cation available per kg of GFS. 0.232 mMole divalent cation are available per kg of GFS to about 2.32 mMole divalent cation per kg of GFS, about 0.465 mMole divalent cation available per kg of GFS to about 2.32 mMole divalent cation available per kg of GFS, about 0.698 mMole divalent cation available per kg of GFS to about 1 .86 mMole divalent cation available per kg of GFS, about 0.698 mMole divalent cation available per kg of GFS to about 1 .626 mMole divalent cation available per kg of GFS. In other embodiments, the divalent cat ion exchange may be present in the compositions in amounts such that about 1 .1 62 mMole to about 1 1 .62 mMole of divalent cation are available per kg of GFS.

[0045] While not being bound by theory, it is believed that the ion exchange agent, whether molecular or cation exchange resin, makes polyvalent cations (e.g., Ca²⁺, Al³⁺, Mn²⁺, Sr²⁺, Zn²⁺, Fe²⁺) available to an ion-sensitive, viscosity increasing polysaccharide, such as gellan, after initial contact with the tear fluid in the eye at an optimized amount that is not feasible with the polysaccharide alone

[0046] More specifically, it is believed that combining the anionic polysaccharide with a polyvalent cation source advantageously exchanges the sodium and potassium present in tear fluid with the polyvalent cation. This exchange improves the in situ gelling properties of the composition once it is instilled in the eye.

[0047] Furthermore, gellan contains carboxylic and hydroxyl functional groups which may interact with other polymers through electrostatic attractions and/or hydrogen bonding. Accordingly, a polymer that interacts through electrostatic attractions with gellan is advantageously incorporated into the present compositions to improve the gelling and rheological properties of the in situ vehicles. [0048] Polymers useful in the present compositions include polyvinylpyrolidone (PVP, also referred to as povidone and available commercially, for example, as Plasdone™ -12 from Ashland, Inc.), copolymers of vinylpyrrolidone/acrylic acid/lauryl methacrylate (commercially available, for example, as Styleze® 2000), and combinations thereof. In particular embodiments, the polymer comprises a mixture of povidone and Styleze® 2000.

[0049] The polymer is present in an amount ranging from about 0.05 to about 1 % by weight of the composition. In other embodiments, the polymer is present in an amount ranging from about 0.05 to about 0.5%, about 0.1 % to about 0.5% by weight of the composition.

[0050] In alternative embodiments, the present disclosure provides compositions comprising low and high acyl gellan. Both high- and low-acyl gellans form hydrogels in the presence of cations in a temperature-dependent manner.

[0051 ] It is believed that a mixture of high acyl and low acyl gellan in combination with a polyvalent cation source surprisingly provides an in situ gelling vehicle that increases in viscosity upon exposure to tear fluid. The high-acyl gellan and low-acyl gellan in some embodiments have a weight ratio ranging from about 0.5:1 to about 1 :0.5. In other embodiments the weight ratio of high and low acyl gellan is about 1 :1 .

[0052] Furthermore, the low-acyl gellan is, in some embodiments, present in the composition in an amount ranging from about 0.1 to about 1 .0% by weight. In other embodiments the low acyl gellan is present in an amount of about 0.1 , 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9% by weight. The high-acyl gellan is, in some embodiments, present in the composition in an amount ranging from about 0.1 to about 1 .0% by weight. In other embodiments the high acyl gellan is present in an amount of about 0.1 , 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9% by weight. [0053] As discussed above, commercially available gellans contain small amounts of cations, such as calcium. Accordingly, the gellan used in a mixed high- and low-acyl in situ gelling composition described herein may be purified, for example by dialysis, to remove these cations. Accordingly, in some embodiments, the low- and high-acyl gellans are dialyzed and purified low- and high-acyl gellans. The term purified low-acyl gellan and purified high acyl gellan refers to gellan that is free of or substantially free of calcium.

[0054] In some embodiments, the source of polyvalent cation can be a molecular cation exchange agent or cation exchange resin, and may comprise The source of the polyvalent cation can comprise any polyvalent cation, but in particular, Ca²⁺, Al³⁺, Mn²⁺, Sr²⁺, Zn²⁺, Fe²⁺, or combinations thereof. When the source of polyvalent cation is a molecular cation exchange agent, such as a water-soluble molecular cation exchange agent, e.g., such as calcium gluconate, the amount used may be in a range of about 0.01 to about 0.1 %, about 0.02 to about 0.1 %, about 0.03 to about 0.08, about 0.03 to about 0.07% by weight of the composition. Alternatively, the amount of the molecular cation exchange agent is in a range of about 0.232 to about 2.32 mMole divalent cation per kg of the composition, 0.465 to about 2.32 mMole divalent cation per kg of the composition, about 0.698 to about 1 .68 mMole divalent cation per kg of the composition, or about 0.698 to about 1 .626 mMole divalent cation per kg of the composition.

[0055] In other embodiments, the source of the polyvalent cation can be a cation exchange resin, such as a dextran cross-linked with epichlorohydrin, which is commercially available as Sephadex® (e.g. SP Sephadex C-25, available from GE Healthcare Life Sciences. A polyvalent cation especially useful with the cation exchange resin is Zn²⁺. The ion exchange agent may be present in the compositions in an amount ranging from about 0.2 to about 5 % by weight, about 0.3 to about 5 % by weight, about 0.3 to about 3% by weight, about 0.5 to about 3 % by weight, or about 0.5 to about 2% by weight, or about 0.6 to about 1 .5% by weight of the composition. Alternatively, ion exchange agents loaded with divalent cations may be present in the compositions in amounts such that 0.232 mMole divalent cation are available per kg of GFS to about 2.32 mMole divalent cation per kg of GFS, about 0.465 mMole divalent cation available per kg of GFS to about 2.32 mMole divalent cation available per kg of GFS, about 0.698 mMole divalent cation available per kg of GFS to about 1 .86 mMole divalent cation available per kg of GFS, about 0.698 mMole divalent cation available per kg of GFS to about 1 .626 mMole divalent cation available per kg of GFS. 0.232 mMole divalent cation are available per kg of GFS to about 2.32 mMole divalent cation per kg of GFS, about 0.465 mMole divalent cation available per kg of GFS to about 2.32 mMole divalent cation available per kg of GFS, about 0.698 mMole divalent cation available per kg of GFS to about 1 .86 mMole divalent cation available per kg of GFS, about 0.698 mMole divalent cation available per kg of GFS to about 1 .626 mMole divalent cation available per kg of GFS.

[0056] While not being bound by theory, it is believed that the ion exchange agent, whether molecular or resin, makes polyvalent cations (e.g., Ca²⁺, Al³⁺, Mn²⁺, Sr²⁺, Zn²⁺, Fe²⁺) available to the mixed high- and low-acyl gellan after initial contact with the tear fluid in the eye.

[0057] More specifically, it is believed that combining the anionic polysaccharide with a polyvalent cation source, such as an ion exchange agent, advantageously exchanges the monovalent cations, such as, sodium and potassium present in the gellan with the polyvalent cation. This exchange improves the in situ gelling properties of the compositions once it is instilled in the eye.

[0058] The in situ gelling compositions disclosed herein may advantageously be used as ophthalmic drug delivery vehicles to administer drugs directly to the surface of the eye. It is believed that the compositions provide an increased exposure time to the drug by slowing the ability for natural tears to wash away the compositions. The in situ gelling vehicles described above also help prolong the release of the drug and reduce systemic exposure to the drug. Alternatively, the present compositions may be used independent of additional pharmaceutical ingredients in order to provide relief to dry eye or injury to the surface of the eye. The size of drops from ophthalmic containers may vary from about 30 to 50 μί. and the resident tear volume differs from 7 to 10 μί.. The eye is thought to be able to hold about 30 μί. without spillage. Therefore, the ratio of eye medication to resident tear volume after administration of a drop could reasonably range from as much as 50:7 (7.1 to 1 .0) to as little as 30:10 (3.0 to 1 .0).

[0059] The compositions, in some embodiments, have a pH ranging from about 5 to about 8, about 5.5 to about 7.5, about 6 to about 7.5, or about 6 to about 7.2. The pH of the compositions can be adjusted by conventional means known in the art, for example by adding appropriate acid or base solutions until the desired pH is achieved. For example, the pH may be adjusted by the addition of NaOH or HCI as needed. The present compositions may further comprise a buffer, such as sodium lauryl sulfate, docusate sodium, polyethylene glycol 400, and TR 1 .

[0060] The present compositions may in some embodiments further comprise a preservative. Any preservative or combination of preservatives routinely used in the art may be employed. Examples of suitable preservatives include, without limitation, sorbic acid, chlorobutanol, phenylethanol, edetate and its salts, benzalkonium chloride, methyl and ethyl parabens, hexetidine, phenyl mercuric salts and the like and mixtures thereof. The amounts of preservative components included in the present compositions are such to be effective in preserving the compositions and can vary based on the specific preservative component employed, the specific composition involved, the specific application involved, and the like factors. Preservative concentrations often are in the range of about 0.00001 % to about 0.05% or about 0.1 % (w/v) of the composition, although other concentrations of certain preservatives may be employed.

[0061] Examples of preservative components in the present compositions also include, but are not limited to, chlorite components. Other useful preservatives include antimicrobial peptides. Among the antimicrobial peptides which may be employed include, without limitation, defensins, peptides related to defensins, cecropins, peptides related to cecropins, magainins and peptides related to magainins and other amino acid polymers with antibacterial, antifungal and/or antiviral activities. Mixtures of antimicrobial peptides or mixtures of antimicrobial peptides with other preservatives are also included within the scope of the present invention.

[0062] In certain embodiments, the above-described compositions exhibit thixotropic behavior. Thixotropy is a time-dependent shear thinning property of certain fluids. Specifically, certain gels or fluids that are viscous under static conditions will flow, becoming less viscous or even liquid over time when shaken, agitated, or applied with a shear force. Such fluids or gels will then return to a more viscous state after being static for a period of time. Thus, the compositions, upon forming a gel in the eye, will thin under the shear stress of an eyelid. Accordingly, the present compositions are believed †o advantageously prevent discomfort and blurring that is often associated with the application of gels and ointments to the eye.

[0063] Examples are provided to illustrate some embodiments of the in situ gelling compositions of the present disclosure but should not be interpreted as any limitation thereon. Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from the consideration of the specification. It is intended that the specification, together with the examples, be considered to be exemplary only, with the scope and spirit of the disclosure being indicated by the claims which follow the example.

EXAMPLES

[0064] One purpose of this study was to determine if the addition of calcium gluconate to LA gellan solution results in a stronger gel structure upon initial exposure to tear fluid due to the displacement of calcium from the gluconate ion by tear monovalent cations (Na⁺, ⁺). Another purpose of this study was to explore whether low molecular weight water soluble polymers could enable bridging between gellan strands in an additive manner to cation induced gelation.

[0065] It is believed that the LA form of gellan more easily transforms from a solution to a gel due to the increased ease in which cations can form bridges between the LA gellan polymer chains as compared to HA gellan (Morris et.al., 1 996, 1999) . High acyl gellan solutions form gels at much higher temperatures than low acyl gellan solutions. An additional purpose of this investigation was to determine if mixtures of LA and HA gellan form stronger gels than LA-Gellan alone.

[0066] The release rates of a model drug, Timolol, was also evaluated.

Material and Methods [0067] Povidone 12 and Styleze™ 2000 (vinyl pyrrolidone and acrylate backbone with a hydrophobic pendant C-12 chain) were both provided by Ashland Inc. Both LA gellan gum sourced from Spectrum Chemical and from CP elco were used in this study. HA gellan was provided from CP Kelco.

[0068] 1 .0 mmoles each of Aluminum Nitrate, Zinc Nitrate, and Ferric Nitrate were added to ten grams of the cation exchange resin SP Sephadex C-25. The total ionic capacity of Sephadex C-25 is given by the vendor as 2-2.6 mmol/g. The salt and resin suspensions were stirred at ambient temperature for > 24 hrs. The suspension was centrifuged, the supernatant removed, and the resin washed with deionized water. The resin :deionized water suspension was stirred for >8 hr. At the end of the stirring time; the resin was centrifuged, the supernatant removed, and washed again with deionized water (qs 10 g). The resin was washed with this procedure three times and then suspended in deionized water after the final washing. It was assumed that 1 .394 g of loaded resin is equivalent to 0.06% calcium gluconate solution.

[0069] Most test preparations made use of gellan as provided by the vendors. However, both LA and HA gellan polymers were further purified by the use of dialysis for specified experimentation. For purification, gellan solutions at concentrations of 0.3% to 2.0%, were placed into about 3 meters of Spectrum Biotech CE dialysis tubing (MWCO = 300-500D) using a plastic syringe and large diameter catheter. The gellan filled tubing was clamped close and then placed into one to four liters of deionized water. This experimental set up allows low MW components such as calcium etc. to pass out of the gellan solutions and into the deionized water. LA gellan polymer solutions were dialyzed at 23° C, whereas HA gellan or LA/HA gellan mixtures were dialyzed at 90° C. The conductivity of the deionized wash water was measured regularly using a Venier conductivity probe. Once the conductivity readings had stabilized, the deionized water was discarded and replaced with fresh deionized water. The wash cycles were continued until the measured conductivity approached that measured with deionized water. Dialyzed gellan solutions were harvested by carefully squeezing the gellan solutions out of the tubing.

[0070] Concentrated solutions or slurries of polymers were prepared and allowed to hydrate for at least 12 hours. Ingredients were measured according to target weights and thoroughly mixed together. Deionized water was added to give a final batch weight of 80 to 90% of final target. If a target pH was desired for the candidate formulation, then Sodium hydroxide or hydrochloric acid was used to adjust the pH to target values of 6.0, 6.5, or 7.2. Sufficient deionized water was added to the preparations to give a final batch weight of 100 or 200 g.

[0071] Two types of simulated tear fluid were used in the study. Artificial tear solution (ATS) contains divalent calcium at the combined molar concentration of both calcium and magnesium. A citric acid buffer is used in ATS rather than the carbonic acid buffer that is present in tears. The pH of water buffered at physiological pH, such as tear fluid, changes with time because of an exchange of carbonic acid with air that results in an increased pH. The calculated p a of carbonic acid is given as 6.05. The calculated p a values for citric acid are given as 3.05, 4.67, and 5.39. At the pH of 7.4, 95.6% of carbonic acid would be in the ionized form and 99% of the citric acid would be in the fully ionized form. Both acids have carboxylate functional groups and it is assumed that citric acid (4.1 mmol -L^"1) at 1 /3 the molar concentration is an appropriate substitution for carbonic acid (12.4 mmol -L^-1). Initial screening studies were conducted using ATS. The second type of simulated tear fluid is referred to as physiological artificial tear solution (PATS). It contains the following additional components at their physiological concentrations; magnesium, lysozyme, and carbonate. The potassium carbonate added to PATS provides both the potassium and carbonate ions that are normally present in the tears. Immediately after manufacture, PATS is stored at 4°C in 100 mL air tight containers with minimal head space. The pH of stored PATS was measured before use and readjusted if needed. Typically, about 0.04 to 0.1 mL of 1 N HCI was sufficient to readjust 100 mL of PATS to the pH range of 7.0-7.8. Confirmatory studies were conducted using PATS. Compositions of the two types (ATS and PATS) of simulated tear fluid (STF) are shown in tables 1 and 2.

Table 1: Artificial Tear Solution (ATS)

Table 2: Physiological Artificial Tear Solution (PATS)

Component Concentration Notes

Sodium chloride 128.7 mmol/L

Calcium chloride 0.32 mmol/L

Magnesium chloride 0.35 mmol/L Chicken egg lysozyme from Sigma

Potassium carbonate 2.07 mg/mL This will provide both the potassium and

carbonate ions normally present in the tears

Lysozyme chloride q.s. to pH 7.4

I N NaOH and/or 1 NHCI q.s. to pH 7.4

[0072] The components of the STF were added with mixing to water at about 80% of the final batch weight. The resulting solution was titrated to a target pH of 7.4±0.4 using sodium hydroxide or hydrochloric acid. Deionized water was added in quantities sufficient to achieve the final target batch weight.

[0073] Viscosities were measured from 1 to 1 ,000 sec-1 at 23° C for GFS preparations using a Haake Viscotester 550. Experimental preparations were mixed thoroughly with simulated tear fluid (STF) at a 5:1 ratio. That is, 10 g of ATS (screening studies) or PATS (confirmatory studies) was added to 50 g of the gellan sample GFS preparation. For initial screening studies; the gellan and STF mixtures were set aside for at least 15 minutes, gently transferred to the water jacketed cup, and then viscosities were measured from 1 to 1 ,000 sec-1 at 34°±1 C.

[0074] Thixotropic behavior has been reported for gellan gums. To account for thixotropic behavior in the confirmatory studies, the gellan and gellan:STF mixtures were placed into polypropylene bottles stored upside down and with diameters slightly less than the receiving cup of the viscometer. The filled bottles were set aside for at least 12 hr prior†o the very gentle transfer to the viscometer receiving vessel. Both the gellan experimental preparations (23° C) and the gellan:PATS mixtures (34°±1 C) were assessed using a high shear rate viscosity sweep ( 1 -1000 sec-1 ) that was quickly (< 5 min.) followed with a low shear rate viscosity sweep (1 -20 sec-1 ). Each viscosity curve was modeled using the Ostwald-de-Waele viscosity model (larger k = larger viscosity) and Bingham yield value model curve fits. Thixotropic behavior was assessed by performing a 1 to 1 ,000 sec^-1 viscosity sweep, hold for 30 sec, and followed by a 1 ,000 to 1 sec¹ viscosity sweep. The area of hysteresis was determined by the instrument's software.

[0075] The Ostwald-De Waele model allows for the viscosity related constant (k) and flow behavior index (n) to be determined according to the equa†ion:T=ky ^'An, where τ is the shear stress and γ ^' is the shear rate. The higher the k value, the more viscous the gel preparation is. Fluids are considered to be Newtonian if n is equal to 1 . Fluids are considered to be pseudoplastic (shear thinning) if n is less than 1 and considered more shear thinning as the value for n decreases. The Bingham model allowed for the calculation of the yield value for each gel preparation.

[0076] All preparations used in measuring Timolol release were manufactured with a final Timolol maleate concentration of 0.68% (w/w). Timolol solution was prepared by dissolving the appropriate amount of Timolol maleate in Dulbecco's Phosphate Buffered Saline (DPBS). A 1 .36% solution of Timolol in deionized water was combined with concentrated solutions of polymers at target concentrations given in Table 3. Deionized water was added to give a weight of 80 to 90% of final target. Sodium hydroxide was used to adjust the pH to target values. Sufficient deionized water was added to the preparations to give a final batch weight of 10 g. The preparations were tested for Timolol transmembrane diffusion characteristics within 3 days after manufacture.

[0077] A UV-Visible Spectrophotometer was used to measure the amount of UV absorbance at 295 nm of Timolol maleate standard solutions at nine different concentrations. A calibration curve was generated between Timolol maleate absorbance at 295 nm and concentration. The equation was not forced to a Y- intercept of zero and had a r2 value of 0.995. Concentrations of Timolol in experimental samples were determined using the standard curve.

[0078] Ten centimeter segments of cellulose ester dialysis membrane (molecular weight cut off of 3,500-5,000 Da) were soaked in deionized water for greater than 24 hr in order to remove preservative and any other water soluble contaminants. The molecular weight cut off was selected so as to easily allow the diffusion of Timolol Maleate (MW = 432.492 Da) through the semipermeable membrane while restricting the movement of polymers through the membrane. Prior to the experimental runs, washed dialysis membrane segments were equilibrated with citrate buffered saline (CBS) for 24 hours or longer at ambient temperature (23° C). The dialysis tubing was removed from the soaking CBS, closed at one end, filled with approximately 1 g of preparation, and the top end was clamped. Each filled dialysis membrane bag was placed in a beaker filled with 100 mL of fresh CBS to elicit sink conditions. A stir bar was placed in the beaker that was then covered with parafilm. Each sample set up was placed on a multi-station stir plate at ambient temperature and stirred at 1000 rpm. Total weight was documented for each experimental set up and deionized water was added, if needed {>] % deviation), to compensate for water loss due to evaporation. [0079] The absorbance (295 nm) of Timolol in the CBS receiving fluid was measured af regular timed intervals using a UV-Vis Spectrophotometer and dedicated disposable UV cuvettes. Timolol/CBS samples were returned to the set up after measurement using dedicated disposable transfer pipettes. Therefore, the CBS receiving fluid in each set up was not diluted by adding CBS in order to compensate for measured samples being set aside.

[0080] Timed samples of the CBS receiving fluid were collected and assayed. Each experimental run was conducted for at least 29.7 hrs for the Timolol solution and for at least 32.0 hrs for the gel forming solutions. Experimental studies were conducted until near equilibrium conditions were achieved. That is, transmembrane diffusion data was collected until it was clear that small differences in Timolol sample absorbance were occurring with large differences in sampling time. Eleven or more sampling times were performed for each experimental run with five or six experimental runs being conducted for each preparation.

[0081] The amount of Timolol that diffused through the dialysis membrane into CBS was measured and plotted as concentration (mg/mL) versus the time at which the sample was pulled from the receiving fluid. The general form of a logistic function ( aleidaGraph) was used for sigmoidal curve fitting. The four variable equation used in the sigmoidal curve fitting of the data as defined in KaleidaGraph is: Y=M1 + (M2 - Μ1 )/(1 + (Χ/Μ3)^ΛΜ4 ). Y is the amount of Timolol released (mg/mL) at X (time in minutes). M2 corresponds to the concentration before the dialysis run begins and Ml corresponds to the concentration at time infinity. The data was initially fit using the sigmoidal equation with M2 held constant and the other three variables being allowed to vary. The fitted value for Ml was considered the total possible Timolol that can be released. The theoretical value for Ml is 0.067 mg/mL and the average of the variable values for Ml was 0.069 ± 0.007. The values for release were redefined as the % total release which is equal to the measured amount of Timolol (mg/mL) divided by the fitted value for Ml (mg/mL) and times 100. The amount of Timolol that diffused through the dialysis membrane into CBS was expressed as % total release and plotted versus the time at which the sample was pulled from the receiving fluid. The curve fit parameters Ml (100 %) and M2 (0%) were held constant at their theoretical values in order to improve the degrees of freedom for the fitting procedure. The parameters M3 and M4 were left to vary in value during the curve fitting process. The M3 parameter is the time at which the midpoint (50% theory) or point of inflection is reached between the lowest (0.0%) and highest amounts (100%) of Timolol release. The parameter M4 is considered a shape parameter and has no direct physical significance. It gives much less information as to how rapidly Timolol is being diffused as compared to M3.

[0082] The generated M3 values for each individual experimental run were treated as independent data points. Prior to statistical analysis, any outliers for the different preparation's M3 values for each experimental run were detected using Dixon-type tests. Outlier experimental runs were discarded in further statistical analysis. One way analysis of variance (ANOVA) and the Tukey's post-hoc test were used to determine statistical significance (< 0.05) for M3 values of the different preparations. The average M3 and M4 values of the individual experimental runs for each preparation are treated as being representative of the preparation.

Results

[0083] It has been reported that Gellan GFS are thixotropic with recovery from induced shear taking 6 hr. The data presented here also indicate that the various forms of Gellan GFS are thixotropic in nature. The primary viscosity curve gives a measure of the Gellan structured system's gel strength. The secondary viscosity curve was measured after the gel structure has been broken by high shear ( 1 ,000 sec^-1 ) . It reflects the flow characteristics of ophthalmic preparations that have been subjected to the high shear of being sha ken in the ophthalmic bottle by the patient and the very high shear rate (40,000 sec^-1 ) of the eye lid blink after administration. The and τ values for the same GFS were measured at 0, 5, 10, 1 5, and 65 min after the primary viscosity curve was performed. The (viscosity measure) and ^"[ values (yield strength measure) were plotted versus the corresponding rest times and linear regressions performed (r2 = 0.96 (K) a nd 0.97 (τ) ) . The linear fits indicate that rest times of 4.5 and 10.5 hr are needed for gels to return to their initial gel strength following high sear. If the secondary viscosity curve is taken 5 min after the primary viscosity curve is complete, then a n error of about 0.1 units for both the and τ values will occur. The secondary viscosity curve values were subtracted from the primary viscosity values for four different GFS and linearly regressed versus their thixotropic difference values as ca lculated by instrument software. A strong correlation (r2 = 0.92) was obtained and indicates that the differences between the primary and secondary viscosity curve K and ^"[ va lues are good measures of thixotropic properties of the GFS. Gellan experimental preparations demonstrated thixotropic behavior both before and after addition of STF. Figure 1 depicts a stepwise viscosity sweep of 1 to 1000 s^_1 for an in situ gelling composition of 0.75% low-acyl gellan with 0.0625% calcium gluconate and 0.375% povidone, with a pH of 7.2. Figure 2 depicts viscosity v. shear rate of a n in situ gelling composition of 0.6% low-acyl gellan and 0.4% high-acyl gellan . [0084] Screening results indicated that the viscosities of gellan GFS increased as the added calcium gluconate was increased in concentration, with particularly good results achieved at a concentration of 0.6% by weight. It appears that calcium ions were in equilibrium between being in association with gluconate or gellan molecules. As calcium gluconate concentrations were increased, equilibrium favored a greater association with gellan and hence a larger viscosity for the GFS before it was mixed with STF. Screening results indicated that Gellan (0.9%) in solution with 0.06% calcium gluconate resulted in an efficient GFS. Tables 3-4 indicate that the simple addition of 0.06% calcium gluconate to 0.9% LA-gellan results in a large increase in both the viscosity (K) and yield value (τ) when this GFS is mixed with ATS. It also results in a stronger gel when subjected to an initial tear contact environment than 0.6% LA-gellan.

Table 4: Viscosity of LA-gellan and calcium gluconate in ATS

Table 5: Viscosity of LA-gellan, calcium gluconate and povidone in ATS

[0086] A drop in viscosity and yield value occurs when GFS is mixed with Dl at the same ratio as with GFS due to a dilution effect and the lack of cations. Secondary viscosity curve data for LA gellan with 0.06% calcium gluconate is depicted in Figures 3 and 4. A decrease in both the and τ values was observed when the GFS is diluted with PATS and Dl. The strength of the formed gel appears to be independent of pH for low-acyl gellan sourced from elco. A trend of decreasing gel strength with increasing pH is possibly occurring with the gellan sourced from Spectrum (See Table 7).

Table 6: Primary and secondary viscosity data (K values) for gellan and 0.06% calcium gluconate from two different sources.

Table 7: Tau values for gellan and 0.06% calcium gluconate from two different sources.

[0087] The results of formulating an insoluble ion exchange resin rather than gluconate and loaded with alternate cations to calcium are shown in tables 8 and 9. The divalent cation zinc appears to act in a similar manner to divalent calcium. Aluminum and iron cations do not appear to be as efficient in improving gellan gel strength as calcium. Formulations composed of LA Gellan with Zn2+ bound to a classic ion exchange resin (rather than Ca Gluconate) resulted in LA Gellan-Zn Resin-STF solutions (gels) with increased gel strength than gellan alone. The use of an insoluble cation exchange resin with zinc results in a GFS that produces stronger gels than calcium gluconate containing GFS.

Table 8: values of low-acyl gellan with an insoluble ion exchange resin and alternate

Table 9: Tau values of low-acyl gellan with an insoluble ion exchange resin and alternate polyvalent cations

[0088] In order†o show that the artificial tear solution is still effective without magnesium, lysozymes, and carbonic acid, LG solutions were tested with both ATS and PATS and the results compared.

[0089] Similarly, Alginate-Calcium Gluconate-STF (k= 25.3 PaS) gels were found to be of higher strength than Alginate-STF gels (k=0.2 PaS) alone.

[0090] Optimal amounts of Polyvinylpyrrolidone (PVP) appear to be effective in improving the initial STF-gel strength (k= 10.2-13.4 PaS) of LA Gellan-Ca Gluconate solutions (k=8.7-12.0 PaS). Timolol release was found to be statistically significantly slowed when formulated in a LA Gellan-Ca Gluconate-PVP formulation (T50=165 min) as compared to LA Gellan alone (T50=100 min). The M3 and M4 values for various preparations of timolol are shown in Table 10:

Table 10: Average M3 and M4 values for various Timolol Maleate preparations. Preparation Ave. 3 Ave. M4

Solution. Calcium Citrate BS M3 116.040 1.460

0.6% Ge!ian, 0.68% Timoioi aieate 99.819 1.456

0.6% LA +0.4% HA Gellan, 0.68% Tlmo!oi Maieate 85.073 1.607

0.9% LA - Gluc-PVP, 0.68% Tlmoloi Maieate 165.475 1.169

1% CaP - 0.9% LA - 0.075% Glue - 0.375% PVP, 0.68% Tsr 112.309 1.671

2% CaP - 0.9% LA - Giuc-PVP, 0.68% Timolol Maieate 102.973 1.446

Figure 5 further depicts the release rates of timolol from various in situ gelling preparations as a function of time.

[0091] A mixture of purified high acyl (HA) and LA Gellan in solution results in a stronger initial gel (k= 10.1 ) than when LA Gellan alone (k=4.6) was used, especially if Ca Gluconate is present (k=16.3). Importantly, the formed HA and LA combination gels resist being dissolved by STF. Tables 1 1 -1 6 show values and Tau values of compositions of low-acyl gellan, calcium gluconate and povidone or Styleze®.

Table 1 1 : values of preparations of 0.75% low-acyl gellan, calcium gluconate and povidone.

Sfeorala 0.3?S% Fa &crs K12 7.1 1.81 1

[0092] Table 12: Tau values of preparations of 0.75 % low-acyl gellan, calcium gluconate and povidone.

Table 13: K values of preparations of 0.9% low-acyl gellan, calcium gluconate and povidone.

Table 14: Tau values of preparations of 0.9% low-acyl gellan, calcium gluconate and povidone.

Sfuoorats 4-0.375% Povidoi^ K12 7.2 13.25 3.584

Table 15: values of preparations of 0.9% low-acyl gellan, calcium gluconate a Styleze®.

Table 16: Tau values of preparations of 0.9% low-acyl gellan, calcium gluconate and Styleze®.

The viscosity parameters of various high-acyl and low-acyl preparations are depicted in Tables 1 7-20.

Table 17: K values of high and low acyl gellan compositions.

Table 18: Tau values of high and low acyl gellan compositions.

Table 19: values of high and low acyl gellan compositions with calcium gluconate.

Table 20: Tau values of high and low acyl gellan compositions with calcium gluconate.

[0093] Figure 6 depicts the primary and secondary viscosity of a mixed LA and HA gellan composition in artificial tears.

[0094] An alternative polysaccharide, sodium alginate, was also investigated. Figure 7 depicts the Tau values for a composition having 1 % sodium alginate as the polysaccharide based on percent of calcium gluconate in PATS, and Figure 8 depicts the values for a 1 .% sodium alginate preparation based on percent of calcium gluconate in PATS and Dl water.

Conclusions

[0095] It appears possible to enhance the initial in situ gel forming properties of LA Gellan by adding a divalent cation bound to an ion exchange molecule or resin. Select polymers can be added to LA Gellan solutions to produce GFS preparations that, when compared to LA Gellan alone, can: ( 1 ) form stronger initial gels upon addition to the tear fluid, (2) slow the diffusion of drug from the formed gel, and (3) resist dissolution of the formed gel by tears.

Claims

CLAIMS What is claimed is:

1 . A pharmaceutical in situ gelling composition comprising an aqueous mixture of: an anionic polysaccharide

a source of a polyvalent cation, and

a polymer.

2. The composition of claim 1 , wherein the anionic polysaccharide is selected from the group consisting of gellan, alginate, pectin, xanthan gum, chondroitin sulfate, gum Arabic, gum kaya, gum tragacanth, and combinations thereof.

3. The composition of claim 2, wherein the anionic polysaccharide is gellan.

4. The composition of claim 3, wherein the gellan is a low acyl gellan.

5. The composition of any one of claims 1 to 4, wherein the source of polyvalent cations comprises Ca²⁺, Al³⁺, Mn²⁺, Sr²⁺, Zn²⁺, Fe²⁺, or a combination thereof.

6. The composition of claim 5, wherein the source of polyvalent cations is a molecular ion exchange agent or an ion exchange resin.

7. The composition of claim 6, wherein the ion exchange resin is a dextran cross-linked with epichlorohydrin.

8. The composition of claim 7, wherein the ion-exchange resin comprises divalent cations, such as Zn²⁺ cations.

9. The composition of claim 6, wherein the molecular ion exchange agent comprises calcium gluconate.

10. The composition of any one of claims 1 to 9, wherein the polymer is selected from the group consisting of polyvinylpyrrolidone (PVP), copolymers of vinylpyrrolidone/acrylic acid/lauryl methacrylate and combinations thereof.

1 1. The composition of any one of claims 1 to 10, wherein the polymer is polyvinylpyrrolidone.

12. The composition of any of claims 1 to 1 1 , comprising:

an anionic polysaccharide in an amount ranging from about 0.05-3.0% by weight a source of a polyvalent cation in an amount ranging from about 0.01 -0.10% by weight, and

a polymer in an amount ranging from about 0.05-0.5 by weight.

13. The composition of any one of claims 9 to 12, wherein the aqueous mixture comprises about 0.05 to about 2.0% by weight of low-acyl gellan, about 0.01 to about 0.10 % by weight of calcium gluconate and about 0.05 to about 0.5% by weight of povidone.

14. The composition of any one of claims 7, 8 or 10 to 12, wherein the aqueous solution comprises about 0.05 to about 2.0% by weight gellan, about 0.2 to about 5 % by weight of a cationic exchange resin and about 0.05 to about 0.5% by weight of povidone.

15. The composition of any one of claims 1 to 14, wherein the pH is in a range from about 5-8.

16. The composition of any one of claims 1 to 15, further comprising at least one pharmaceutical agent.

17. The composition of any one of claims 1 to 16, which forms a clear gel upon contact with the eye.

18. A method of administering a pharmaceutical compound to a surface an eye, comprising applying to the eye a composition of claim 14.

19. The method of claim 18, where about 30-50 μΐ of the composition is administered to the surface of the eye.

20. A pharmaceutical composition comprising an aqueous mixture of high acyl gellan and low acyl gellan and a source of polyvalent cations.

21. The composition of claim 20, wherein the high acyl gellan and low acyl gellan have a weight ratio ranging from about 0.5:1 to 1 :0.5.

22. The composition of claim 20 or 21 , wherein the source of polyvalent cations comprises Ca²⁺, Al³⁺, Mn²⁺, Sr²⁺, Zn²⁺, Fe²⁺, or a combination thereof.

23. The composition of any one of claims 20 to 22, wherein the source of polyvalent cations is a molecular ion exchange agent or an ion exchange resin.

24. The composition of claim 23, wherein the ion exchange resin is a dextran cross- linked with epichlorohydrin.

25. The composition of claim 24, wherein the ion-exchange resin comprises Zn²⁺ cations.

26. The composition of claim 23, wherein the molecular ion exchange agent comprises calcium gluconate.

27. The composition of claim 23, wherein the compositions comprises 0.01 to 0.1 % by weight of the calcium gluconate.

28. The composition of any one of claims 20 to 27, wherein the high acyl gellan is present in an amount ranging from about 0.1% to about 1 % by weight.

29. The composition of any one of claims 20 to 28, wherein the low acyl gellan is present in an amount ranging from about 0.1 to about 1 % by weight.

30. The composition of any one of claims 20 to 29, wherein the composition has a pH ranging from about 5 to 8.

31 . The composition of any one of claims 20 to 30, wherein the high acyl gellan and low acyl gellan are substantially free of calcium.

32. The composition of any one of claims 20 to 31 , further comprising a pharmaceutical agent.

33. A method of administering a pharmaceutical agent to an eye of a patient in need thereof comprising administering to the eye of the patient the composition of claim 21 .

34. A pharmaceutical in situ gelling composition comprising an aqueous mixture of: an anionic polysaccharide, and

a source of a polyvalent cation.

35. The composition of claim 34, wherein the anionic polysaccharide is selected from the group consisting of gellan, alginate, pectin, xanthan gum, chondroitin sulfate, gum Arabic, gum kaya, gum tragacanth, and combinations thereof.

36. The composition of claim 35, wherein the anionic polysaccharide is gellan.

37. The composition of claim 36, wherein the gellan is a low acyl gellan.

38. The composition of any one of claims 34 to 37, wherein the source of polyvalent cations comprises Ca²⁺, Al³⁺, Mn²⁺, Sr²⁺, Zn²⁺, Fe²⁺, or a combination thereof.

39. The composition of claim 38, wherein the source of polyvalent cations is a soluble molecular ion exchange agent or an ion exchange resin.

40. The composition of claim 39, wherein the ion exchange resin is a dextran cross- linked with epichlorohydrin.

41 . The composition of claim 40, wherein the ion-exchange resin is loaded with divalent cations.

42. The composition of claim 39, wherein the molecular ion exchange agent comprises calcium gluconate.