CA1297028C - Topical metronidazole formulations and therapeutic uses thereof - Google Patents

Abstract

Abstract of the Disclosure Novel topical formulations containing the drug metronidazole comprise aqueous single-phase gels. The formulations have improved specific activity and lack the comedogenic, irritant and skin-drying ingredients commonly found in prior art formulations in which the drug is dissolved in an oil phase of the formulation.
The aqueous topical formulations are particularly useful for treating rosacea and other acneform dermatological conditions, and certain forms of dermatitis.

Description

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NOVEL TOPICAL METRONIDAZOLE FORM~LA'rIONS
AND THERAPEUTIC USES THEREOE

Back~ und of the Invention Field of the Invention This invention relates to novel topical formulations containing the drug metronidazole and methods of treating skin disorders using the novel Eormulations.

Description of the Prior A_ Metronidazole, 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole, is a drug known to be effective in treating a variety of disorders. For example, the drug has direct trichomonacidal and amebacidal activity against Trichomonas vaginalis and Entamoeba histolytica and is use-ful in combatting infections caused by those microbial parasltes. Metronida~ole has also been reported to be effective (via both oral and topical application) in treating skin disorders such as rosacea ulcers infected with anaerobic bacteria, including decubitus ulcers (bed or pressure sores), venous ulcers, and diabetic Eoot ulcers, and other anaerobic infections such as post operative sepsis. There have also been reports that metronidazole is effecti~e against perioral dermatitis.
Although oral administration of the drug has been employed for the treatment of certain disorders, long-term oral administration o~ the drug in cases of chronic disorders; such as rosacea may be a5sociated with .
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~971~2~3 certain unwanted side effects, and subjects all organ syst;ems needlessly to high drug concentrations. Well-known problems associated with systemic antibiotic therapy include gastro-intestinal intolerance and vaginitis. ~hus, topical for~nulations are generally preferred for dermatological applications. ~See "Practical Advice offered on Rosacea", Dermatolo~
April, 1985).
It is known that the effectiveness of a drug against a particular illness may be profoundly af~ected by the vehicle into which the drug is incorporated. One difficulty in formulating topical compositions of metronidazole stems from the drug's low solubility in water and several other solvents. Accordingly, the topical preparations described to date for treatment of rosacea generally have been creams (oil in water emulsions) or ointments (petroleum jelly based compositions). In these formulations, the drug is dissolved in the oil phase.
Rosacea~ formerly called Acne rosacea, is a chronic skin disease primarily affecting adults, with recurring symptoms that include erythema, papules, pustules, rhinophyma, and telangiectses, primarily in the region of the nose, cheeks, and forehead. The metronidazole-containing topical formulations used to treat ros~cea generally contain oils, certain surfactants and emulsifiers, and/or other ingredients which have been found to be comedogenic, acnegenic, and/or irritating to the skin. (See Fulton et alO, Amer. Acad. of Dermatology, Vol. 10, noO 1, pp. 96-10~, (Jan. 1984)).
Patients treated with such formulations therefore often experience skin problems which include irritation, uncomfortable drying of the skin, and "stinying" or "burning" sensations. In addition, the drug is generally dissolved or dispersed in the oil phase of such ~ ~97~

preparations, which reduces the specific activity of the drug due to inhibition of drug transfer across the cell membrane. Such effects are described in Nielsen, P., British J. of Dermatolo~y, Vol. 108, pp. 327-332 (1983), for example.
Thus, a need remains for metronidazole-containing dermatological preparations suitable for topical use which avoid the problems of prior art formulations. Such dermatological preparations would be useful for treating 1~ skin disorders such as rosacea and certain types of dermatitis, including perioral dermatitis.

Summary of the Invention In accordance with the present invention, an aqueous gel composition for topical application consists essentially of a) a therapeutically effective amount of metronidazole, b) a polycarboxylated vinyl polymer in an amount effective to promote solubility of said metronidazole and to cause gelling of said composition, and c) an aqueous solvent. The single-phase aqueous gels have higher specific activity of metronidazole compared to prior art oil-based formulations, due to increased bioavailability of the drug when solubilized in an aqueous composition. The compositions comprise non-comedogenic, non irritating ingredients and thus avoid problems associated with the use of prior art formulations in the treatment of skin diseases. The aqueous gels of the present invention have properties which make them particularly suitable for the treatment of skin disorders such as rosacea and other acneform conditions and certain types of dermatitis.

Detailed Descri~ ion ot the Invention Substantially oil-free, aqueous formulations of metronidazole, in which the drug is solubilized in a , .~.~

7~'8 single-phase aqueous yel, are disclosed. The advantages of such aqueous formulations in treating skin disorders have been discussed above, and are presented in greater detail below.
When developing topical formulations for application to diseased skin, different aspects, such as thermodynamic activity of the drug in the vehicle (base), the release rate of the drug from the vehicle, the type and the status of the skin, and the sensitization and irritation potential of components are factors that can affect the therapeutic effectiveness of topical dermatological preparations. In the case of non-diseased skin with its intact stratum corneum, cell membrane-controlled penetration of the drug occurs.
Therefore, a high thermodynamic activity of the drug in the vehicle is desirable (low affinity to the vehicle) to promote transfer of the drug across the epidermal cell membranes. With diseased skin, the release rate of the drug from the vehicle generally is rate-determining for penetration into a patient's cells. Therefore, vehicles which dissolve the drug and have a low diffusional resistance are preferred. In general, drug concentration in the vehicle, and thus the degree of saturation, is considered to be a key formulation factor when optimizing topical delivery for maximum bioavailability.
In rosacea (and other acneform conditionsj and in certain types of dermatitis, topical formulations are usually applied to both normal and diseased areas, It is therefore desirable that a treatment have a mitigating effect on the diseased tissue and a prophylactic effect to prevent extension of involvement to the normal areas.
Therefore, the most desired vehicle and hence formulation in these conditions should contain the drug in high thermodynamic activity ta high rate of cell membrane penetration) and with a fast rate of release from the ,.. ~ ~.
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~2~t~8 vehicle. Aqueous formulations of metronidazole would appear to meet the above criteria. The low solubility o~
metronidazole in water (and in several other solvents), however, has resulted in the development of oil-based, rather than aqueous, metronidazole ~ormulations for treatment of rosacea.
In the formulations of the present invention, metronidazole is dissolved in an aqueous solution of a high molecular weight polycarboxylated vinyl polymer.
The polymer serves not only to promote solubility of the drug in water, but also imparts a desirable viscous, gelled consistency to the composition when mixed with the drug and water. The gels (>95% water formulations) of the present invention have the requisite degree of metronidazole concentration and hence thermodynamic activity for effective topical delivery and bioavailability of the drug. The gels of the present invention also have the requisite therapeutic activities as described below. The present invention therefore provides a method for the prophylactic or therapeutic treatment of humans afflicted with such skin disorders as rosacea, other acneform conditions (e.g., acne vulgaris, steriod acne, acne conglobata, or nodulocystic acne) or certain types of dermatitis (e.g., perioral dermatitis or seborrheic dermatitis~.
The viscous gelled vehicle also minimizes "pooling"
and "running" of the medication, e.g. pooling into facial creases, which sometimes occurs with dermatological cream preparations. The resulting local excesses of the creams may contribute to problematic erythema or stingingO The aqueous gels of the present invention afford more control in application, and better maintenance of a uniform distribution of the drug over the area to be treated, than would generally be expected if the drug were applied as a cream or in an aqueous solution.

3i7~3 The ideal vehicle advan~ageously functions as a "sustained delivery" system for the drug, in which the drug continuously is delivered to the cells at, or slightly above, a minimwn therapeutically effective level which is sustained over a period of time. This mode of drug release from the vehicle is preerred over vehicles which release the drug at levels much higher than the necessary therapeutic level shortly after application to the skin, followed by a sharp decrease to a level which is not therapeutically effective. The aqueous gels oe the present invention function as sustained delivery systems, whereas prior art formulations generally do not provide sustained drug delivery at a relatively constant therapeutically effective level over a period of time.
The polymer may be any suitable polymer which is hydrophilic, has free carboxylic groups and high base binding capacity, forms a gel of uniform consistency when neutralized with a base, and is effective in promotiny solubility of metronidazole in the resulting gel.
Preferred polymers for use in the formulations of the invention are high molecular weight polycarboxylated vinyl polymers, with polyacrylic acid polymers being particularly preferred. The molecular weight of the polymer is desirably between about l,250,000 and 3,000,000. Suitable polyacrylic acid polymers include, but are not limited to, those commercially availahle from B.F. Goodrich, Cincinatti, Ohio, under the trademarks Carbopol 934, 940, and 941. Carbopol 940~ is a particularly preferred polymer for use in this invention.
- The polymer is present in an amount sufficient to promote solubility of the drug in water and to cause gelling of the formulation, imparting the desired viscous consistency to the topical formulation. The metronidazole formulations advantageously comprise about ~97~

U.2% to about 7.0~ by weight o~` the polymer, preferably about 0.5~ to about 1.5~, and most preferably abou~ 0.6 by weight oE the polymer.
Aqueous solutions of these polymers are known to form gels when neutralized with a base. Water-soluble bases which have been used to promote gelling of polymers such as carbopols include organic amines (alkylamines such as methylamine and ethylamine, dialkylamines, trialkylamines, alkanolamines, and dial~anolamines, among others) and inorganic bases such as an aqueous solution of ammonia. The drug being added to the formulation of the present invention, metronidazole, is sufficiently basic to partially neutralize the acidic polymer in aqueous solution to the desired degree and to promote gelling.
Metronidazole is employed in the compositions in an effective amount. The actual concentration of the drug may vary, depending on the nature and degree of the disorders being treated, and whether the drug is being administered for therapeutic or prophylatic purposes.
The formulations advantageously comprise from about 0.1%
to about 1.5%, pre-Eerably about 0.25~ to about 1.0%, and most preferably about 0.75% by weight of metronidazole.
Optionally, the formulation may also comprise a t'penetration enhancer", i.e., an agent that promotes penetration of the active drug into the patient's skin or tissues. Such penetration enhancers include but are not limited to, dimethyl sulfoxide (DMSO) and propylene glycol, with the latter being preferred. The composition advantayeously comprises from about 1.0% to about 50%, preferably about 2~ to about 5%, and most preferably about 3% by weight of said penetration enhancer.
Preservatives optionally may be incorporated into the compositions in an amount effective for inhibiting growth of microbes such as yeast and molds in the ~7~

composition during stoeage. Any conventional preserva-tives may be used, with parabens being preferred. A
mixture o~ methyl paraben and propyl paraben has been found particularly effective as a preservative. Most preferably, the composition comprises about 0.08~ by weight of methyl paraben and about 0.02% by weight of propyl paraben.
Ethylenediaminetetraacet:ic acid (EDTA) or one of its salts is commonly added to dermatological preparations, and may optionally be incorporated into the compositions o~ the present invention. EDTA chelates certain metals that may be present in the formulation, which is useful because some patients have adverse reactions to preparations containing metal impurities. The ~DTA will also inhibit undesirable ~browning" of the composition which may occur over time in compositions having low pH
(e.g., pH 3.5 to about 5.4). Advantageously, the formulation of the invention comprises from about 0.0l~
to about 0.1%, preferably about 0.05% by weight of EDrrA.
The ~'inal pH of the formulations of the invention may vary within a physiologically compatible range.
Advantayeously, the final pH is a physiologically compatible (i e., not harmful to biological tissue) acidic pH. The pH is preferably between about 3 and about 6.9, and most preferably between about 4 and 5.
Any suitable method of adjusting the pH of aqueous solutions may be used. Advantageously, sodium hydroxide (NaOH) is added to the formulation to bring ~he final p~
to the desired level. Gel formulations of the invention are more viscous at pH's that approach neutrality than at the more acidic pH's within the preferred range (i.e., viscosity increases as the polymer in the gel is neutralized to greater degrees, e.g. with NaOH).
The ingredients listed above may be combined in any order and ~anner that produces a formulation comprising : L2~7~

metronidazole dissolved in (and evenly dispersed throughout) a one-phase aqueous gel of the desired consistency and pH. One suitable method of preparing formulations of the invention involves preparation of an aqueous solution of the polymer, which will be called "Part A". ~dvantageously, this solution comprises the polymer in distilled water. A "Part B" is prepared comprising metronidazole. Mixing of Parts A and B
results in gelling of the composition. The optional penetration enhancer and preservative(s) are preferably included in Part B. If EDTA is to be added to the formulation, it is preferably included in Part A. The pH
may then be adjusted to the desired level, e.g., by addition of NaOH.
The resulting homogeneous gels possess the advantageous properties described above, including non-comedogenic, non-acneogenic, and non-irritating ingredients; higher specific activity of metronidazole due to increased diffusion across membranes and release from the vehicle (resulting in greater therapeutic effectiveness using smaller amounts of the drug); and a desirable consistency that prevents undesired pooling and spreading of the drug. High concentrations of skin-drying ingredients (e.g. alcohols and acetone), which are found in some dermatological preparations to promote drug solubility, are also avoided. Such ingredients at high concentration may excessively dry the patient's skin, causing undesirable flaking and discomfort.
The therapeutic effectiveness of the metronidazole formulations of the present invention is demonstrated in the following examples. These examples are meant to illustrate the invention rather than to limit its scope.
Variations in the formulations which do not adversely affect the effectiveness of the drug will be evident to . ~

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one skilled in the art, and are within -the scope of this invention. For example, addi-tional ingredients such as coloring agents, sunscreens, and the like may be included in the formulations as long as -the resulting formulation retains the desirable properties (non-comedogenicity, high specific activity, etc.) described above.
The drug 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole and various derivatives thereof are described in U.S. Patent No. 2,944,061. The term "metronidazole" as used in this application is meant to include not only 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole, but also those analogs and derivatives of the drug which are solubilized in the gel formula-tions previously described and which have therapeutic activity when topically applied.

Example_I

A 30 kilogram (kg) batch of a formulation of the present invention was prepared as follows. 0.18 kg of Carbopol 940 (0.6% by weight of the final weight of the formulation) was dissolved in 16.5 liters of distilled water containing 15 g of EDTA disodium dihydrate. Suf-ficient 10% NaOH was added to bring the pH to about 5.
This aqueous polymer solution was called "Part A".
"Part B" was prepared by mixing 0.9 kg of propylene gly-col (3% by weight of the final weight) with 24 grams of methyl paraben (0.08% by weight as above), 6.0 grams of propyl paraben (0.02% by weight as above) and adding to 0.225 kg of metronidazole in 11.4 liters of distilled water maintained at 50 C. Parts A and B were then mixed thoroughly and gelling of the formulation resulted. A
cold aqueous solution of NaOH was then used to adjust the final pH to 5.25, and distilled water was added to give , , : - ,' ' .' : ' ~ ~':

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the desired 30 kilogram final weight. The NaOH and water were thoroughly mixed into the viscous gel.

Examp~e II

A randomized, double blind, placebo controlled clinical trial was conducted to demonstrate t:he positive clinical eEficacy of the aqueous metronidazole-containing gel formulation prepared in Example I in treating rosacea. The study included patients who had received no prior treatment for rosacea, as well as patients who had been treated by conventional methods. Patients discontinued treatment, i~ any, at least 21 days prior to the start of this study. Each patient received metronidazole in the gel formulation on one side of the face and the formulation gel ~placebo control) without metronidazole on the other side of the face. Therefore, in this study, each patient served as their own control.
The effectiveness o the treatment was rated, at the time points indicated in the Tables below, in six different categories, namely, reduction in inflammatory lesions (papules and pustules), erythema, stinging, burniny, itching, and dryness. The data are shown in the Tables below~
Table I-A shows the percent reduction in inflammatory lesions (papules and pustules) from baseline values for active (i.e., metronidazole-treated3 and placebo-treated sides. Inflammatory lesions were progressively reduced from 46.7% to 59.9% or active-treated sides while placebo-treated sides reflected an exacerbation. There was an 8206% difference in inflammatory lesions at the end of drug treatment on the metronidazoIe versus placebo-treated sides.
Table I-B shows mean erythema values for active- and placebo-treated sides. Statistically significant . ~
-!2 differences were found at visits 2, 3, 4 and 5 for the active sides and at visits 3 and 4 for the placebo sides, when compared to baseline values. Active- and placeb~side values were significantly different from each other at visits 3, 4 and 5. A concommitant improvement in reduction of erythema was seen at the same time point on the treated side and on the placebo side, both statistically significant from baseline with the metronidazole treated side significantly more improved than the placebo side.
Table II-A shows mean stinging scores for active-and placebo-treated sides. Statistically signlEicant differences were found at visits 3, 4 and 5 for both the active and placebo sides, when compared to baseline values. Active- and placebo-side values were not significantly different from one another.
Table II-B shows mean burning scores or active- and placebo-treated sides. Statistically signi~icant differences were found at all visits (2, 3, 4, 5) for both the active and placebo sides, when compared to baseline values. Active- and placebo-side values were not significantly different from one another.
Table II-C shows mean itching scores for active- and placebo-treated sides. Statistically significant differences were found at all visits ~2, 3, 4, 5) for both the active and placebo sides, when compared to baseline values. Active- and placebo-side values were not significantly different from one another.
Table II-D shows mean deyness scores for active- and placebo treated sides. Statistically significant differences were found at visits 3, 4 and 5 for active sides and at visits 4 and 5 Eor placebo sides, when compared to baseline values. Active- and placebo-side values were not significantly different from one another.

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Tables II-A, II-B, II-C, and II-D show an unexpec~ed but dramatic improvement in local tolerance data. This data represents the patients' subjective assessments of stinging, burning, itching and dryness on each side of their faces before and during drug or placebo treatment.
The data shows that there was ~ dramatic (highly statistically significant) improvement in the patients' perceptions of these attendant complications of the disease. Since both sides improved to the same degree (no statistically significant difference can be found), the improvement apparently comes from the gel formulation per se.
This data confirms the effectiveness of metronida-zole in the gel formulation for treatment of acne rosacea and also demonstrates the unique therapeutic effects of the gel formula~ion.
Table I-A
Inflammatorv Lesions (Efficac ~ Subjects) On Drug __ Off Drug Visit 2 Visit 3 Visit 4Visit 5 Weeks 3-5Weeks 6-8 Weeks 9-11Weeks 12~17 . _ Active _ (Percent Reduction from Baseline)46~7 55.1 59O9 41.6 Placebo .
(Percent Reduction from aaseline)-22.5 - 4.2 -22.7 -46.8 Difference (Active-Placebo Percent Difference) 69.2 59.3 82.6 88.4 7~2~

Table I-B
Erythema (Efficacy Data From 20 Sub]ects) Visit 1 Visit 2 Vnis t ~3 V' it 4 ffi~Y
W~eksWeeks Weeks Weeks BaseIine 3-5 6-8 9-11 12 17 Active 10(Mean Values) 2.10 1.55*** 1.05*** 1.05*** 1.15***
Placebo . . . _ (Mean Values) 2.10 1~901.55***1.55*** 1.70 3=Severe 2=Moderate l=Mild 0=Absent *** p<.Ol ccmpared to ~aseline values.
Active Versus Placebo ~ cant DifferencesNo No (p values) Difference Difference p<.O~ p<.O2 p<.O2 .

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Stinging (Local Tolerance D=ta from 20 Subjects) _ On Dr Off Dru Vi~it 1 Visit 2 ~ isit 4 Visit 5 Weeks Weeks Weeks Weeks Baseline 3-5 6~8 9-11 12-17 Active (Mean Values) 0.70 0.25 0.15** 0.00*** 0.00***
lacebo (Mean Values~ 0.65 0.30 0.15* 0.20* 0.05***

3=Severe 2~oderate l=Mild 0=Absent * p~.05 compared to baseline values ** p<.02 oompared to baseline values *** p<.Ol compared to baseline values Active Versus Placebo Significant Differences No No No No ~o (p values) Difference Difference Difference Diffrence Difference .

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Table II-B
~urnin~
(Local Tolerance Data from 20 Sublects) __ _ On Drug ____ Off Dr~g Visit 1 Visit 2 Visit 3 Visit 4 Visit S
Weeks Weeks Weeks Weeks _seline 3-5 6-8 _9-11 12-17 Actlv2 (Mean Values) 1.25 0.30** 0.10*** 0.05*** 0.05***
Placebo (Mean Values) 1.05 0.30***0.05*** 0.10*** 0.05***
3=Severe 2--Moderate l~Mild 0-Absent ** p<.02 ccmpared to baseline values *** p<.Ol compared to baseline values Active Versus Placebo Signiflcant Differences No No No No No (p values) Difference Difference Difference Diffrence Difference :: :

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Table II-C
Itch ng (Local Toleran_e Data from 20 Sub~Pcts) __ _ On Drug Off Drug Visit 1 Visit 2 Visit 3 ~isit 4 Visit 5 ~eeks Weeks Weeks Weeks Baseline 3-5 6-8 9-11 12-17 Active (Mean '~alues)1.45 0~55***0.15***0.20*** O.lO***
Placebo (Mean Values) 1.40 0.70***0.25***0.20*** 0.15***
3=Severe 2=Moderate l=Mild 0=Absent *** e~-l oonpared to baseline values Active Versus Placebo Significant Di~ferences Nb Nb No No No (y ~ Differenc~ Difference Difference Diffrence Difference , '~-., , , ~,97l~ ~

Table II-D
~y~ness (Local Toleran e Data Erom 20 Sub~ects) . _ _ _ _ _ _ On Drug Off Drug Visit 1 ViS'lt 2 Visit 3 Visit 4 Yisit S
WeeksWeeks Weeks Weeks Baseline 3-5 6 8 9-11 12-17 Active .
(Mean Values) 1.45 0~85 0.50***0.25*** 0.25***
- Placebo __ , (Mean Values) 1.40 0.85 0.75 0.20*k* 0.45***
3=Severe 2=~erate l=Mild 0=Absent *** p<.Ol compared to baseline values Active Versus Placebo Significant Differences No Nb No No No (p values) Diference Difference Difference Diffrence Diference ~ . , ,, .
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Claims (62)

1. A dermatological preparation for topical application in the form of an aqueous gel composition consisting essentially of a) a therapeutically effective amount of metronidazole, b) a polycarboxylated vinyl polymer in an amount effective to promote solubility of said metronidazole and to cause gelling of said composition, and c) an aqueous solvent, and d) from about

2% to about 5% by weight of a penetration enhancer, wherein said preparation is substantially free of comedogenic, acneogenic, irritating, and skin-drying ingredients.
2. The composition of claim 1 wherein the concentration of metronidazole is from about 0.1% to about 1.5% by weight.

3. The composition of claim 2 wherein the concentration of metronidazole is from about 0.25% to about 1.0% by weight.

4. The composition of claim 3 wherein the concentration of metronidazole is about 0.75% by weight.

5. The composition of claim 1 wherein said polymer is present in an amount of from about 0.2% to about 7.0%
by weight.

6. The composition of claim 5 wherein said polymer is present in an amount of from about 0.5% to about 1.5 by weight.

7. The composition of claim 6 wherein said polymer is present in an amount of about 0.6% by weight.

8. The composition of claim 1 wherein said polymer is a hydrophilic, high-molecular weight polycarboxylated vinyl polymer.

9. The composition of claim 8 wherein said polymer is a polyacrylic acid polymer.

10. The composition of claim 9 wherein the molecular weight of said polymer is from about 1,250,000 to about 3,000,000 daltons.

11. The composition of claim 1 which additionally consists of an effective amount of ethylenediamine-tetraacetic acid (EDTA).

12. The composition of claim 1 wherin the concentration of said penetration enhancer is about 3% by weight.

13. The composition of claim 1 wherein said penetration enhancer is DMSO or propylene glycol.

14. The composition of claim 1 which additionally consists of an effective amount of a preservative.

15. The composition of claim 14 wherein said preservative consists of one or more parabens.

16. The composition of claim 15 wherein said preservative consists of about 0.088% by weight of methyl paraben and about 0.02% by weight of propyl paraben.

17. The composition of claim 1 wherein the pH of said composition is a physiologically compatible acidic pH.

18. The composition of claim 17 wherein said pH is between about 3 and about 6.9.

19. The composition of claim 18 wherein said pH is between about 4 and 5.

20. The composition of claim 1 wherein said aqueous solvent is distilled water.

21. A composition for use in the prophylactic or therapeutic treatment of a human afflicted with a skin disorder, which is a topical dermatological preparation comprising an aqueous gel composition consisting essentially of a) a therapeutically effective amount of metronidazole, b) a polycarboxylated vinyl polymer in an amount effective to promote solubility of said metronidazole and to cause gelling of said composition, and c) an aqueous solvent.

22. The composition of claim 21 wherein the concentration of metronidazole is from about 0.1% to about 1.5 by weight.

23. The composition of claim 22 wherein the concentration of metronidazole is from about 0.25% to about 1.0% by weight.

24. The composition of claim 23 wherein the concentration of metronidazole is about 0.75% by weight.

25. The composition of claim 21 wherein said polymer is present in an amount of from about 0.2% to about 7.0% by weight.

26. The composition of claim 25 wherein said polymer is present in an amount of from about 0.5% to about 1.5% by weight.

27. The composition of claim 26 wherein said polymer is present in an amount of about 0.6% by weight.

28. The composition of claim 21 wherein said polymer is a hydrophilic, high-molecular weight polycarboxylated vinyl polymer.

29. The composition of claim 28 wherein said polymer is a polyacrylic acid polymer.

30. The composition of claim 29 wherein the molecular weight of said polymer is from about 1,250,000 to about 3,000,000 daltons.

31. The composition of claim 21 wherein the concentration of said composition additionally consists of an effective amount of ethylenediamine-tetraacetic acid (EDTA).

32. The composition of claim 21 wherein said composition additionally consists of a penetration enhancer.

33. The composition of claim 32 wherein the enhancer is from about 2% to about 5% by weight.

34. The composition of claim 33 wherein the concentration of said penetration enhancer is about 3% by weight.

35. The composition of claim 32 wherein said penetration enhancer is DMSO or propylene glycol.

36. The composition of claim 21 wherein said composition additionally consists of an effective amount of a preservative.

37. The composition of claim 36 wherein said preservative consists of one or more parabens.

38. The composition of claim 37 wherein said preservative consists of about 0.08% by weight of methyl paraben and about 0.02% by weight of propyl paraben.

39. The composition of claim 21 wherein the pH of said composition is a physiologically compatible acidic pH.

40. The composition of claim 39 wherein said pH is between about 3 and about 6.9.

41. The composition of claim 40 wherein said pH is between about 4 and 5.

42. The composition of claim 21 wherein said aqueous solvent is distilled water.

43. The composition of claim 21, 22 or 25 wherein said skin disorder is rosacea.

44. The composition of claim 21, 22 or 25 wherein said skin disorder is acne vulgaris.

45. The composition of claim 21, 22 or 25 wherein said skin disorder is chosen from steroid acne, acne conglobata, nodulocystic acne, perioral dermatitis, and seborrheic dermatitis.

46. A dermatological preparation for topical application in the form of an aqueous gel composition comprising :
a therapeutically effective amount of metronidazole as the sole active ingredient;
a gelled, hydrophilic and water-dispersible polymer having free carboxylic groups which is a polyacrylic acid polymer having a molecular weight in the range of about 1,250,000 to about 3,000,000 daltons; and an aqueous solvent for said metronidazole.

47. The preparation in accordance with claim 46 wherein the concentration of said metronidazole is at least about 0.1 percent by weight based on the total weight of said composition.

48. The preparation in accordance with claim 47 wherein the concentration of said metronidazole present is in the range of about 0.25 percent to about 1.0 percent by weight based on the total weight of said composition.

49. The preparation in accordance with claim 48 wherein the concentration of said metronidazole present is about 0.75 percent by weight based on the total weight of said composition.

50. The preparation in accordance with claim 46 wherein said polymer is present in a range of about 0.2 percent to about 7.0 percent by weight based on the total weight of said composition.

51. The preparation in accordance with claim 50 wherein said polymer is present in a range of about 0.5 percent to about 1.5 percent by weight based on the total weight of said composition.

52. The preparation in accordance with claim 51 wherein said polymer is present in an amount of about 0.6 percent by weight based on the total weight of said composition.

53. The preparation in accordance with claim 46 further including a penetration enhancer.

54. The preparation in accordance with claim 53 wherein said penetration enhancer is propylene glycol present in a range of about 2 percent to about 5 percent by weight based on the total weight of said composition.

55. The preparation in accordance with claim 53 wherein said penetration enhancer is present in an amount of about 3 percent by weight based on the total weight of the composition.

56. The preparation in accordance with claim 46 further including a preservative.

57. The preparation in accordance with claim 56 wherein said preservative comprises at least one paraben.

58. The preparation in accordance with claim 57 wherein said preservative is methyl paraben present in an amount of about 0.08 weight percent and propyl paraben present in an amount of about 0.02 weight percent, based on the total weight of said composition.

59. The preparation in accordance with claim 46 further including ethylenediaminetetraacetic acid in a range of about 0.01 percent to about 0.1 percent by weight based on the total weight of said composition.

60. A composition for use in the treatment of a human afflicted with a skin disorder which is a member of the group consisting of acne, rosacea, perioral dermatitis and seborrhoeic dermatitis, said composition comprising a topical dermatological preparation in the form of an aqueous gel composition comprising:
a therapeutically effective amount of metronidazole as the sole active ingredient;
a gelled hydrophilic and water-dispersible polymer having free carboxylic groups which is a polyacrylic acid polymer having a molecular weight in the range of about 1,250,000 to about 3,000,000 daltons; and an aqueous solvent for said metronidazole.

61. The composition of claim 60 wherein said skin disorder is rosacea.

62. The composition of claim 60 wherein said skin disorder is acne vulgaris.