Xanthan Gum Therapeutic Compositions

1. Field of the Invention

This invention relates to the use of gums as adjuvants in ophthalmic compositions to potentiate the miotic response of cholinergic agents, particularly echothiophate iodide which is used in treatment of glaucoma; this allows the administration of lower, more effective dosages of said cholinergic agents, thereby alleviating side effects. In a further aspect this invention relates to a drug delivery system that is a gel and is useful for topical applications.

In this application the term "adjuvant" is defined as found in Stedman Medical Dictionary, 22nd Edition as "that which aids or assists; denoting a remedy that is added to a prescription to assist or increase the action of the main ingredient."

2. Description of the Prior Art

The prior art discloses a variety of gums and polymers used as adjuvants in ophthalmic compositions.

For example, C. Rosenblum et. al. in Arch Ophthal, 77:234-237, 1967, disclosed the use of hydroxyethyl cellulose to increase the systemic absorption by ocular tissues of dexamethasone. With drugs such as erythromycin propionate and sulfapyridazine sodium, Y. F. Maichuk, Am. J Ophthal, 74:694, 1972 taught the use of polyvinyl alcohol to potentiate their pharmacological response. Similarly, guar gum was found to increase the corneal absorption of tropicamide as reported by Lee et al, J. Pharm. Sci. 63:721, 1974.

The use of gum and polymer combinations is also disclosed, such as their application as a bactericidal cleanser, lubricant, and wetting agent, German Pat. No. 2,051,369 is illustrative, wherein is disclosed a solution containing polyethylene glycol, poly (ethyleneoxide), and an ophthalmic medicine. British Pat. No. 1,337,105 teaches a different combination of polymers for use in eye wash solution containing hydroxyethyl cellulose and polyvinyl alcohol. Still another example is presented by British Pat. No. 1,340,518 which discloses ophthalmic compositions containing an ophthalmic medicament, a polyalkylene glycol, a cellulosic derivative or mixture of such derivatives, and, optionally, polyvinylpyrrolidone. See also U.S. Pat. Nos. 3,944,427 and 3,700,451 which disclose gelable and gelled compositions containing agar, xanthan gum, and locust bean gum in a liquid medium for use as a carrier of therapeutic solutions, but particularly as a carrier for photo-processing solutions. These compositions, however, are rigid gels at room temperature.

In accordance with the present invention, xanthan gum is incorporated in ophthalmic compositions of cholinergic agents, particularly echothiophate iodide, to enhance the drug's therapuetic activity thereby allowing a reduction in dosage and a concomitant reduction in toxicity while retaining an effective level of antiglaucoma activity.

The xanthan gum, incorporated in ophthalmic solutions of echothiophate iodide, acts as an adjuvant and thus promotes the activity of the drug. The xanthan gum adjuvant is prepared by dissolving the gum in the solution i.e. the pharmaceutically acceptable liquid vehicle followed by dissolution of the echothiophate iodide.

Echothiophate iodide is described in U.S. Pat. No. 2,911,430 granted Nov. 3, 1959 to H. M. Fitch and the disclosure of that patent is incorporated herein by reference.

In this application "xanthan gum" means Xanthomonas hydrophilic colloid produced by bacteria of the genus Xanthomonas. Illustrative of such a colloid is the xanthan gum sold under the Keltrol trademark (Kelco Co., Clark, N.Y.). It may be described as a high molecular weight natural carbohydrate, or more specifically polysaccharide. The generic term xanthan gum defines exocellular biopolysaccharides which are produced in a pure culture fermentation process by the microorganism Xanthomonas campestris. Three different monosaccharides are found in the basic structure -- mannose, glucose and glucuronic acid (as a mixed potassium, sodium and calcium salt). Each repeating block within the polymer contains sixteen sugar units. The linear portion consists of five .beta., 1 .fwdarw..fwdarw..fwdarw. 4-linked D-glucose units, four .beta., 1 .fwdarw..fwdarw..fwdarw. 4-linked D-mannose units and four .beta., 1 .fwdarw..fwdarw..fwdarw. 2-linked D-glucuronic acid units. At C-3 of two glucose units there are mannose branches and at some other position, as yet undetermined, in the repeating unit is a side chain derived from pyruvic acid and glucose i.e. 4,6-O-(carboxyethylidine)-D-glucose. Each repeating unit contains an average of 3.4 acetyl groups which are believed to be connected at C.sub.6 of mannose.

In the compositions of this invention, the concentration of xanthan gum is from about 0.01% to about 2.5% weight by volume. It will be appreciated that as the concentration of the gum is increased, it is accompanied by an increase in viscosity. Thus, at concentrations of gum above about 1.0% and up to about 2.5%, a gel like consistency is attained. This gel like consistency permits various topical applications of drug such that the drug is maintained at the site of administration over a longer period than is possible by a liquid composition. By a gel it is meant a colloid in which the disperse phase has combined with the continuous phase to produce a semi-solid such as a jelly.

The preferred concentration of xanthan gum for dropwise ophthalmic applications is from about 0.02% to about 1.0% weight/volume. When echothiophate iodide, a drug used in the treatment of glaucoma, is the ophthalmic drug incorporated in said gum composition, its concentration can vary from about 0.005% to about 0.25% weight/volume. An advantage of this invention is that the systemic side effects observed at higher concentrations of echothiophate iodide may be reduced due to the potentiation of the drug's pharmacological response by xanthan gum thereby permitting the administration of reduced concentrations of drug. Illustratively, it was observed that a composition containing 0.03% echothiophate iodide and 0.2% xanthan gum potentiated a greater pharmacological response than one containing 0.25% echothiophate iodide and no gum.

Potentiation of pharmacologic response was observed to increase with increasing concentrations of xanthan gum. Also, required or preferred concentrations of gum needed to achieve optimum results will vary from drug to drug. Thus, while with echothiophate iodide a concentration of xanthan gum from about 0.02% to about 1.0% is preferred; with the aldose reductase inhibitor, 1,3-dioxo-1 H-benz[de]isoquinoline-2(3H)-acetic acid a concentration of xanthan gum from about 0.5% to about 1.5% is preferred. The xanthan gum composition has also been found suitable as a vehicle for widely varied concentrations of drug. For example, these compositions have been found suitable for delivering as little as 0.005% weight/volume of echothiophate iodide or as much as 12.0% of Alrestatin. The choice is usually limited only by the need to incorporate a therapeutically effective dosage of drug within the compositions of this invention.

An advantage of the herein disclosed invention is its superiority as an adjuvant over such previously art known adjuvants as polyvinyl alcohol, hydroxyethyl cellulose, and ethylene oxide polymer as demonstrated in tests conducted with echothiophate iodide. Also, while the compositons of this invention may be prepared in an aqueous solvent, these compositons are also feasible in liquid vehicles containing water and water miscible solvents; thus, it will be appreciated that these compositions are equally well adapted to the delivery of drugs with varying degrees of solubility. By way of illustration, these compositions are stable in the presence of such non-aqueous solvents as ethanol, propylene glycol, 1,3-butanediol, glycerin, sorbitol and the like when such solvents compose up to about 1/2 by volume of the carrier system, i.e. the liquid vehicle comprises 50-100% water.

The compositions of this invention can be designed by first selecting the drug to be used and the pharmacological response desired. A composition can then be designed to produce that pharmacological response comprising the xanthan gum adjuvant and the selected drug in a pharmaceutically acceptable liquid vehicle.

Any of the drugs used to treat the eye and surrounding tissues can be incorporated in the ophthalmic compositions of this invention.

Although the use of the xanthan gum adjuvant has principally been described with respect to drug delivery systems for the administration of ophthalmic drugs, it will be appreciated that the gum may be employed as well in a wide variety of bioerodable compositions for administering drugs to the other areas of the body. Thus, the pharmacuetical delivery systems of this invention may be employed to advantage in external and internal erodable drug delivery compositions such as, for example, topical, oral, nasal and buccal preparations. In each instance, the composition employs xanthan gum in combination with the selected drug and is of a shape or form appropriate for implantation or insertion in the described body tissues or cavities respectively or for application to a particular body area.

Suitable drugs for use in therapy with the compositions of the invention include antibacterials, such as, bacitracin, chloramphenicol, gentamycin, gramicidin, polymyxin, sulfacetamide, sulfisoxazole, and tetracycline; antiglaucomatous agents, such as, acetazolamide, epinephrine, and echothiophate iodide; sympathomimetic agents, such as, epinephrine, phenylephrine, cocaine, and ephedrine; parasympatholytics, such as, atropine, homatropine, scopolamine, tropicamide and cyclopentolate; parasympathomimetics, such as, carbachol, echothiophate, pilocarpine, and isoflurophate; sympatholytics, such as, dibenamine and tolazoline; anti-inflammatory agents, such as, cortisone, hydracortisone, prednisolone, prednisone, and dexamethasone; and others, such as antipyrine, antazoline, LH-RH, LH-FSH, and 1,3-dioxo-1H-benz[de]isoquinoline-2(3H)-acetic acid.

The term "drug" as used herein is intended to be interpreted in its broadest sense as including any composition or substance that will produce a pharmacologic response, either at the site of application or at a site remote therefrom.

Additionally, the compositions of the invention may include a variety of additives including preservatives, buffers, electrolytes, antioxidants, stabilizers, and pharmaceutically acceptable liquid vehicles as described earlier.

The invention may be illustrated in part through the following examples.

These formulations were prepared by dissolving sodium phosphate, boric acid, mannitol, chlorobutanol or phenylethyl alcohol in distilled water; dispersing the gum in the solution; autoclaving the solution at 121.degree. C. for 60 minutes; adjusting the solution's pH to 3 where noted and filtering. Then, dissolve echothiophate iodide to prepare the test solution.

Rabbit's eyes were treated with 2 drops of the test solutions of example 1 and pupillary diameters were measured with a cathetometer. The miotic response intensity was computed by taking the difference in pupillary diameters at zero time and time "T" (i.e. hours after instillation) and dividing it by the pupillary diameter at zero time. The table below illustrates the average miotic response for all eyes as a function of hours after instillation.

By comparing Formulations B-E with formulation A and G, it is clear that the former group potentiated significantly higher miotic response intensities than those formulations not having xanthan gum. Thus, it was observed that the dosage level of gum containing formulations can be reduced. It was also observed that the gum containing formulations could be used to deliver a sustained and controlled dosage regimen of echothiophate iodide over a 24 hour period.

Formulations containing pilocarpine hydrochloride were prepared as in example 1.

Rabbit's eyes were treated and tested as in example 1, the results are listed in the following table.

These results indicated that xanthan gum potentiates the miotic response of pilocarpine hydrochloride. It therefore appears that the dose of pilocarpine can be reduced when use in combination with xanthan gum.

Formulations containing the aldose reductase inhibitor, 1,3-dioxo-1H-benz[de]isoquinoline-2(3H)-acetic acid, Alrestatin.RTM. were prepared as in example 1:

Potentiation of the aldose reductase inhibitor was demonstrated by measuring its ocular penetration following instillation in the eyes of unanesthesized rabbits, see below:

These results illustrate increased ocular penetration in formulations containing xanthan gum in combination with aldose reductase inhibitor.

Manufactured as described in example 1, formulations containing carbachol, 2-[(Aminocarbonyl)oxy]-N,N,N-trimethylethanaminium chloride were prepared.

The stability of carbachol containing formulations was evaluated and found to be satisfactory.