WO2013056993A1

WO2013056993A1 - Improvements in or relating to organic compounds

Info

Publication number: WO2013056993A1
Application number: PCT/EP2012/069796
Authority: WO
Inventors: Pascal Grenier; Patricia IBARRA; Guy Vergnault
Original assignee: Jagotec Ag
Priority date: 2011-10-21
Filing date: 2012-10-05
Publication date: 2013-04-25
Also published as: GB201118198D0

Abstract

A pharmaceutical composition adapted for external application to human skin comprising a semi-solid carrier material containing zileuton dissolved or dispersed therein, and its use in the treatment of dermatological conditions, particularly acne vulgaris, rosacea or atopic dermatitis.

Description

Improvements in or relating to organic compounds

The present invention is concerned with a composition for the topical administration of zileuton, and with a method of treating dermatological conditions of human skin, in particular acne vulgaris. Topical application to the skin can offer a comfortable, convenient and non-invasive way of administering drugs. The variable rates of absorption and metabolism encountered in oral treatments can be avoided, and other inherent inconveniences associated with this route, e.g. gastrointestinal irritation and the like, may be eliminated as well. However, drug delivery by the topical route is not without its complications. The human skin consists essentially of several distinct compartments or layers of tissue. The stratum corneum represents the outermost part of the skin. It consists of dead cells (in general about 15 to 20 layers) named corneocytes. The corneocytes are filled with keratins, and they are embedded in a complex matrix of organized lipid bilayers. The stratum corneum is lipophilic and contains relatively low levels of water. Immediately underneath the stratum comeum is the viable epidermis, which has a thickness of perhaps 50 to 100 microns. This layer has high water content and has a similar density to water. Beneath the viable epidermis lies the dermis. It is a structural fibrin and ranges in thickness from 2000 to 3000 microns.

The stratum corneum is the principle physical barrier to substances that come into contact with the skin. Molecules moving from the surrounding environment into and through intact skin must first penetrate the stratum corneum and any material on its surface. It is believed to be the high degree of keratinization within the corneocytes, their densely packed arrangement, as well as the lipid domains between them, which creates a substantially impermeable barrier to drug penetration. When considering how to formulate a composition that is to be applied topically to the skin, one must consider the target site for drug delivery. For example, should the drug substance that is applied to the skin, remain on the surface of the skin, as is typically the case with cosmetic ingredients, or substances such as sun-screens or insecticides? Or, is it intended that the drug substance should penetrate the skin and accumulate locally within an affected compartment of the skin, with no passage into systemic circulation? Or, is it intended to formulate a drug substance in a way that permits it to permeate through all the layers or compartments of the skin and into systemic circulation?

Whatever the intended target, the formulator must take into consideration the complex structure and properties of each compartment of the skin, and particularly the stratum corneum, in order to understand how, and to what extent, a drug substance is likely to penetrate the skin. At the same time, the formulator will recognise that owing to the unique physicochemieal properties of drug substances (e.g. molar mass, molecular size, logP, the distribution of polar and non-polar parts in the drug substance and the extent of an ionized state), the barrier effect the skin presents to one drug substance may be entirely different to that presented to another.

Still further, the extent and/or rate of penetration of a drug substance will depend not only on its particular physicochemieal properties, but also on the vehicle in which it is formulated and on the interaction between the vehicle and the drug substance, as well as the vehicle with the skin. A major challenge for formulators is to design or tune a vehicle in which the drug is formulated in order that the drug can reach its target site, whether that is on the skin surface, within a compartment of the skin, or within systemic circulation.

Formulations adapted for topical application to the skin usually contain one or more agents that modify the rate or extent to which a drug substance permeates the skin. There is a body of literature concerned with formulations containing chemical skin permeation modifiers for enhancing (or retarding) the flux of a drug substance through the skin.

Mohammadi-Samani et al in Pak. J. Pharm. Sci. p 83-88, Vol 23, No. 1 2010 examined the effect of certain excipients on the penetration of lidocaine through the skin. Polysorbate 80 and Polysorbate 20 had practically no effect, whereas DMSO had a significant penetrating effect, and alpha terpinol had the most marked effect. On the other hand, Arellano et al in Eur J Drug Metab Phamiacokinet. 1998 reported that Polysorbate 80 retarded the transdermal delivery of diclofenac sodium.

Ammar et al in the Asian Journal of Pharmaceutical Sciences, 2007, 2(3) 96-105 looked into formulations for the transdermal deliver of aspirin. It was reported that

carboxymethylcellulovse had a permeation effect, but oleic acid and urea had the greatest enhancing effect. DMSO was effective for this drug, but less so. Park et a in Drug Dev Ind Pharm 2001 Oct: 27(9): 975-80 looked at the effect of permeation enhancers to be employed in a system for the transdermal delivery of captopril in an in-vitro permeation study on rat skin. Fatty alcohols were found to provide a pronounced permeation effect, but other agents such as DMSO, N-methyl 2-pyrrolidone, oleic acid, transcutol and polysorbate 20 showed no permeation enhancing effects.

A problem with the use of permeation modifiers in topical formulations is that the candidate pool is huge, and what is effective for one drug in a particular delivery vehicle, may not be as effective, if at all, for another drug in the same or even different delivery vehicle. What makes one formulation effective for one drug substance, but not another, is not clearly understood. The quantity of drug that is able to permeate across or into the stratum corneum per unit area per unit time or "flux" is a significant parameter in determining whether or not a particular drug can be effectively delivered for a specific treatment regimen. A drug's propensity to penetrate into the stratum corneum is related to how it partitions between the delivery vehicle in which it is formulated, and the tissue of the stratum corneum. Fick's law predicts that the higher the concentration of a drug substance in a delivery vehicle, the higher will be the flux o f that drug substance flowing from the vehicle into the stratum corneum. In other words, increasing the solubility of a drug substance in a vehicle should increase its flux. On the other hand, flux should be increased if the relative solubility of the drug substance in the biological medium of the stratum corneum is higher than in the delivery vehicle. It follows from this that for a given drug substance, it would appear that one needs to find a compromise between these apparently two conflicting requirements of needing to increase a drug's solubility in a delivery vehicle and at the same time making the drug relatively less soluble in the vehicle than in the biological medium of the stratum corneum.

Formulation is clearly the key to successful topical drug delivery, but only by the careful formulation of a drug substance can one balance the modification of the barrier properties of the skin and at the same time optimise how a drug interacts with its delivery vehicle. The problem is that it appears there is no consensus in the literature as to how formulations influence the permeation of drug substances. Presumably this is because frequently the formulations studied do not have the same compositions, the drugs used have very different physicochemical properties, and the targets (i.e. skin surface, compartment of the skin or systemic delivery) are often different. Under such conditions, it would appear that general rules cannot be articulated and that that one would need to carry out permeation testing in appropriate in-vitro or in-vivo models to validate any given formulation approach.

Furthermore, even if a formulation is optimised from the point of view of modifying the barrier properties of the skin, if it is not optimised from a galenic perspective, such a draw back may still make the formulation undesirable for use. For example, the formulation may be difficult to apply mechanically to the skin; or it might be unacceptable from an organoleptic point of view, i.e. it may have an offensive smell, it might feel unpleasant on the skin, or it might have an unsightly appearance; or it might not have sufficient retention time on the surface of the skin to enable drug substance to penetrate the skin.

It may be possible to disregard some or all of these galenic considerations if a formulation is adapted to be used in a delivery device, such as a patch or other device in which the formulation is supported by an occlusive layer, e.g. a bandage or a plaster or the like.

However, this is not always possible as these devices can be impractical or even undesirable if there is a need to treat a large area of affected skin, or if the condition is on the head or neck of a patient, as is often the case with acne vulgaris.

Acne is considered as one of the most commonly experienced diseases. It appears in a variety of forms including white-heads, black-heads, and mild inflammatory acne. The most severe types of acne are nodular and cystic acnes. It is estimated that eighty five percent of teenagers will suffer fro outbreaks of acne between the ages of 12 to 24. Twenty five percent of these people will suffer permanent scarring as a result. Furthermore, according to the American Dertmatological Association twenty five percent of adults suffer from acne. More than fifty millions of Americans suffer active acne and ten millions of those will suffer scarring. Yet, it is estimated that only one to ten per cent of sufferers will seek medical intervention.

Current treatment include cleaners (benzoyl peroxide creams or gels), anti-acne preparations containing salicylic acid or sulphur to help unblock pores, and vitamin A- based (retinoid) creams or gels. Retin-A increases cell turnover and releases plugged materials from hair follicles. It is also noted to decrease the formation of new acne lesions, but it may enhance the skin's sensitivity towards irritation and sunlight. It has also been reported that these medications have been associated with worsening acne and skin irritation. In addition, Retin-A preparations are contra-indicated in pregnant women and those seeking to become pregnant.

Oral or topical antibiotics (doxycycline and minocycline) are sometimes used to stop infection, which can otherwise lead to acne outbreaks, but there is the issue of targetted bacteria developing immunity to these antibiotics.

The aetiology of acne vulgaris is complex. However, a number of key factors can be identified: Inflammation, particularly of the sweat glands; excessive and inflammatory sebu production by the sweat glands; and local infection of the sebaceous glands by bacteria. Tissue inflammation occurs when certain enzymes involved in the biosynthesis of the proinflammatory lipid Leukotriene (LTB4) and PGE2, are activated in the sebaceous glands of acne lesions, inhibition of LTB4 has been recognized as an attractive target for the down- regulation of the inflammatory processes in sebaceous glands.

Zileuton is an inhibitor of 5-lipoxygenase, the enzyme that catalyzes the formation of leukotrienes from arachidonic acid. Zileuton has the chemical name (±)-l-(l- Benzo[b]thien-2-ylethyl)- l -hydroxyurea and the following chemical structure:

The central role that 5-Lipoxygenase products have in the inhibition of inflammation is well known in the literature and zileuton, specifically, is known to exert an anti-inflammatory effect. Its anti-inflammatory properties are exploited in the commercially available oral modified release dosage form (Zyflo CR) that is indicated for the treatment for asthma.

Considering zileuton's anti-inflammatory properties, it has also been proposed for the treatment of acne (Zouboulis et al. Dermato Endocrinology 1 :3 188-192 May/June 2009). The treatment described in this paper comprises an oral form of zileuton for the systemic treatment of acne. However, owing to concerns of hepatotoxicity, treatment of acne by the oral route is somewhat undesirable.

The concept of combining zileuton and a cycloxygenase (COX) inhibitor to work together in the treatment of actinic keratosis and the chemo-prevention of skin cancers is also disclosed in the scientific literature. Evidence from a variety of studies demonstrate that both COX and LOX pathways are up-regulated in a variety of cancer cell types and indeed both cycloxygenase and lipoxygenase inhibition have been considered as a strategy for the treatment of cancer.

Of particular relevance to dermal cancer cell types are observations that ultra violet (UVB) exposure results in up-regulation of COX (COX2) and furthermore that COX inhibition can reduce UVB induced inflammation and tumour formation in animal models. In this regard it is important to note that UVB is regarded as a key stimulant for the development of actinic keratosis. The literature identifies prostaglandin E2 (PGE2), a product of COX metabolism, as particularly important in that it is capable of stimulating proliferation, migration and invasiveness of cancer cells.

The LOX pathway also is strongly implicated in carcinogenesis. Inhibition of the LOX pathway has been demonstrated pre-clinically to be anti-proliferative and pro-apoptotic in cancer cell lines. A number of products of LOX have been identified, which can promote cancer cell growth. Leucotriene B4 (LTB4) inhibits apoptosis and has been demonstrated to be procarcinogenic and is considered a key mediator.

In this regard it is important to note inhibition of COX may result in shifting metabolism toward LOX pathways and an increase in LTB4, which in itself may be predicted to reduce the anti-cancer efficacy of a COX inhibitor. Whilst LOX inhibition leaves PGE2 activity unaltered. For these reasons it can be predicted that combined inhibition of both pathways may be required for optimal activity.

Despite acne, skin cancer and actinic keratosis being conditions affecting the skin, and the proposed usefulness o zileuton in treating these conditions, there is relatively little literature relating to topical dosage forms containing zileuton.

The treatment of various inflammatory conditions using 5 -lipoxygenase inhibitors is disclosed in US2004259920. Reference is made to zileuton as representing a 5- lipoxygenase inhibitor. Various modes of administration are contemplated. Topical administration is mentioned as one of the possible modes of administration, but no particular preference is given to it, and there is no specific technical teaching regarding the formulation of zileuton in topical formulations.

US2010/0273868 is concerned with the use of (R) zileuton in a method of treating various conditions associated with increased 5-lipoxygenase and/or leukotriene activity. Acne is mentioned as one such condition. The document discloses that zileuton may be

administered by various routes, including topical. However, as with the previous document, there is no particular preference drawn to this route of administration and no technical teaching of how one is to formulate zileuton in a topical dosage form. A topical dosage form containing celecoxib has been proposed by Fegn et al in J. Laryngol. Otol. 2009 August 123(8): 880-884. The dosage form was applied as an oil-in-water microemulsion to mice. The paper concludes that the dosage form would be effective in the treatment of skin carcinogenesis. The microemulsion formulation used in this study consisted of 22% propylene glycol dicaprylate(dicaprate) + caprylic/capric mono-/di- glycendes (2: 1), 30% polysorbate 80 and water. Whereas the formulation was optimised for dermal penetration of celecoxib as reported by Subramanian et al (Acta Pol Pharm 2004 Sept-Oct; 61(5): 335-41), Fegn does disclose that zileuton can be used in conjunction with the formulation, although there is no teaching of how zileuton is incorporated into the microemulsion and there is also no teaching regarding the extent to which zileuton penetrates mouse skin. Indeed, the study was not concerned with an assessment of systemic toxicity and so it is not even known whether zileuton passed through the skin and exerted its effect systemically, or whether it exerted an effect locally within the skin.

Reproducing this microemulsion formulation, the applicant found that it was rather user unfriendly. It had a viscosity that was substantially similar to fluid oil that did not permit of easy application, and did not allow long interactions time between the formulation and the skin.

This reference is render further remote when one considers that celecoxib is a COX-2 inhibitor, and this class of compounds promotes the production of sebaceous lipids, which is a significant causal agent in the onset of acne. Currently, applicant is unaware of there being any topical dosage forms of zileuton either in development or available commercially. The prior art teaches that zileuton should be a useful therapeutic agent in the treatment of acne. However, there is no technical teaching in the art regarding how this molecule should be formulated in order to target an affected site in the skin in an efficacious way, whilst at the same time substantially avoiding systemic circulation of the drug and possible hepatotoxicity issues.

Accordingly, there remains a need for effective methods and compositions for the topical application of zileuton to the skin. Furthermore, there is a need for said methods and formulations to be tuned such that they deliver zileuton to a localised affected area of the skin, which does not result in damage, irritation or sensitisation of the skin, and which does not create issues related to systemic hepatotoxicity. Still further, there is a need for formulations that are galenically acceptable, that is, they are organoleptically acceptable and can be applied easily to an affected area of skin and be retained at the affected area for a sufficient period of time for the drug substance to penetrate the skin.

The applicant has now found methods and formulations that address short-comings in the prior art.

The invention provides in a first aspect a pharmaceutical composition adapted for external application to human skin comprising a semi-solid carrier material and zileuton dissolved or dispersed therein.

The composition according to the present invention is intended to be applied to an affected area of human skin to treat a dermatological condition of the skin. The composition is adapted to form a depot locally within an affected site in or on the skin, rather than treating the condition systemically. The composition is to be contrasted with compositions that are applied to the skin for transdermal administration of a drug substance. Transdermal delivery relates to drugs that are applied to the skin in order to pass through the skin tissue and enter the systemic circulation to exert a pharmacological effect.

The term "semi-solid" as it applies to pharmaceutical compositions of the present invention refers to a composition that is not pourable and does not conform to a container in which it is held at ambient temperatures, and which, furthermore, does not flow in response to low shear stress and exhibits plastic flow behaviour. A semi-solid is contrasted with a liquid, such as a lotion or a solution, which flow with no or little shear threshold, display Newtonian or pseudoplastic flow behaviour and conform to containers in which they are held.

The rheological properties of a semi-solid may be demonstrated using apparatus and methods well known in the art. For example, viscosity of a sample measured as a function of applied shear can be carried out on a Brooks field viscometer apparatus such as a

Brookfield DV 1 1 1 , model RV equipped with T-Bar or Helipath spindles.

The distinction of semi-solids are liquids, rheologically, is well known in the art, and is described by Buhse et al in The International Journal of Pharmaceutics 295 (2005) 101 -1 12, which is hereby incorporated by reference in its entirety.

The semi-solid compositions of the present invention may be applied easily to the skin. The composition may be spread evenly over an affected area of skin, by hand, spatula or the like. Furthermore, the semi-solid composition does not flow as a liquid as a result of the shear forces generated during application. Rather, it retains its semi-solid form. This ensures even coverage of the affected site and also ensures that the drug substance is retained within the composition, and in contact with the skin for prolonged periods of time. Retention of the drug substance within its compositional vehicle and in communication with the skin surface for extended periods ensures that the drug substance may pass slowly into the skin and to form local concentrations within the affected site in or on the skin. In another aspect of the present invention there is provided a method of modifying the flux of zileuton through skin by applying to skin a pharmaceutical composition of the present invention as herein defined.

Flux can be observed by measuring the diffusion of zileuton through human or animal, e.g. mouse skin using any suitable in-vitro techniques known in the art, for example using a Franz diffusion apparatus. Basically, in the Franz cell method, diffusion cells are divided into two parts. One part is called the donor chamber and is filled with a known amount of a formulation to be tested. The second part is called the receiver or receptor chamber and is separated from the donor chamber by a piece of skin. The receptor chamber is filled with a solution in which the substance under study is soluble. A few aliquots are analysed for drug content at specific times during the experiment and the cumulative amount of drug is then plotted against time. Analysis of samples collected from a Franz cell can be made using known techniques, such as HPLC, again, as more fully described in the Examples below.

In another aspect of the invention there is provided a method of providing an antiinflammatory response in the tissue of a mammal comprising the step of applying to an affected site on the skin of a subject a pharmaceutical composition of the present invention.

In a particular embodiment of the present invention, there is provided a method of providing an anti-inflammatory response in the tissue of a mammal comprising the step of applying to an affected site on the skin of a subject, a pharmaceutical composition of the present invention. In a particular embodiment of the present invention, the anti-inflammatory response is comparable to the response zileuton administered orally.

The anti-inflammatory response to a composition according to the present invention may be measured by conducting an in-vivo study suitable for the purpose. For example, a mouse ear model study can be employed, in which oedema is induced in mouse ears by application of arachadonic acid thereto. Pharmaceutical compositions to be tested and an oral control formulation are then applied to the treated ears and the level of inhibition of arachadonic acid-induced oedema is observed by measuring relative ear-swelling as a function of time. A particular example of a mouse ear-swelling study is disclosed in Katsumi Ishii Jpn J Pharmacol 65 297-303 1994, which is hereby incorporated by reference. In such a study, the oral dose against which the topical composition is to be compared is typically chosen to be that dose that can provide an at least 50% ear swelling inhibition. A suitable oral dosage form may contain about 40 mg/kg to 80 mg/kg of zileuton.

Accordingly, in another embodiment of the present invention there is provided a method of providing an anti-inflammatory response in the tissue of a mammal comprising the step of applying to an affected site on the skin of a subject, a pharmaceutical composition of the present invention, said anti-inflammatory response being comparable to the response zileuton administered orally at about 40mg/kg to about 80 mg/kg.

In an embodiment of the present invention, an anti-inflammatory response may be considered "comparable" if the level of response is with ± 30% of the oral dosage form response. More particularly, the response is at least as great the oral dosage form response. In yet another aspect of the invention there is provided a method of treating acne vulgaris, rosacea or atopic dermatitis comprising the step of applying a pharmaceutical composition according to the present invention to an affected site on the skin of a subject in need of treatment. In a particular embodiment of the present invention, the method of treating acne vulgaris, rosacea or atopic dermatitis will involve the application of a pharmaceutical composition according to the invention to a pre-determined area of the skin that is affected by the particular condition to be treated, retaining the composition on the skin, and optionally reapplying the composition to the skin, for a period of time sufficient to provide treatment. In a method of treating acne vulgaris, rosacea or atopic dermatitis according to the present invention, the application of the pharmaceutical composition to an affected site such as an area of lesions may be performed twice daily.

The amount of pharmaceutical composition applied to an affected area will depend on the size of the area. For example, a patient should ensure that enough composition is applied to cover each affected site or lesion. Typically, one might apply about 0.5 g of composition to treat an affected site or lesion site that measures 5 cm x 5 cm.

In a method according to the present invention the duration of therapy is from 60 days to 90 days.

Pharmaceutical compositions according to the present invention may contain a solvent for zileuton.

Particular solvents are those that can dissolve zileuton to a concentration of about 190 mg/g or greater.

Generally, it is preferred if zileuton is dissolved in the pharmaceutical composition, however, it may be provided in a finely dispersed powder form, more particularly in the micro to nanoparticulate size range, still more particularly 10 nm to 5μ . in such finely divided form, zileuton will dissolve in response to the displacement of the solubility equilibrium created by the slow absorption of zileuton by the stratum corneum.

In particular, solvents may be selected from polyethylene glycols or ethylene glycol ethers, or a pyrrolidone or related compound. Said pyrrolidones or related compounds may be selected from the group consisting of N-methyl-2-pyrrolidone, 1 -butyl-3-dodecyl-2- pyrrolidone, 1 ,3-dimethyl-2-imidazolikinone, 1 ,5-dimethyl-2-pyrrolidone, 44,-dimethyl-2- undecyl-2-oxazoline, 1 -ethyl-2-pyrrol idone, 1 -hexyl-4-methyloxycarbonyl-2-pyrrolidone, 1 -hexyl-2-pyrrolidone, 1 -(2-hydroxyethyl)pyrrolidone, 3 -hydroxy-N-methyl-2-pyrro 1 idone, 1 -isopropyl-2-undecyl-2-imidazoline, 1 -!aury!-4-methyloxycarbonyl-2 -pyrrolidone, poly(N-vinylpyrrolidone), pyroglutamic acid esters and 2-pyrrolidone.

In a more particular embodiment the solvent is N-methyl-2-pyrrolidone, which is commercially available under the trade name PHARMASOLVE.

The pharmaceutical composition according to the present invention has a consistency or body such that when applied to an affected area of human skin, both zileuton and the vehicle in which it formulated are maintained essentially in a reservoir that is in transmitting relationship with the affected surface of the skin.

The pharmaceutical composition may be in the form of a gel, ointment, cream or paste. The carrier material may comprise any of those materials known in the art useful in the formation of these types of dosage form. In addition, they should be non-toxic and should not interact with any other components contained in the composition in a deleterious manner.

Ointments, as is well known in the art of pharmaceutical formulation, are semi-solid preparations that are typically based on petrolatum or other petroleum derivatives. The specific ointment foundation to be used, as will be appreciated by those skilled in the art, is one that will provide for optimum drug delivery, and, preferably, will provide for other desired characteristics as well, e.g. emolliency or the like. As with other carriers or vehicles, the ointment foundation should be inert, stable, non-irritating and non-sensitizing. As explained in Remington: The Science and Practice of Pharmacy, 21^st edition (Lippincott Williams & Wilkins, 2005), ointment foundations may be grouped in four classes:

oleaginous, emulsifiable, emulsion, and water-soluble. Oleaginous ointment foundations include, for example, vegetable oils, fats obtained from animals, and semisolid

hydrocarbons obtained from petroleum. Emulsifiable ointment foundations, also known as absorbent ointment foundations, contain little or no water and include, for example, hydroxystearin sulfate, anhydrous lanolin and hydrophilic petrolatum. Emulsion ointment foundations are either water-in-oil (W/O) emulsions or oil-in-water (O/W) emulsions, and include, for example, cetyl alcohol, glyceryl monostearate, lanolin and stearic acid. Preferred water-soluble ointment foundations are prepared from polyethylene glycols of varying molecular weight.

Creams, as also well known in the art, and are typically in the form of semisolid emulsions, of either oil-in-water or water-in-oil types. Cream foundations are water-washable, and contain an oil phase, an emulsifier and an aqueous phase. The oil phase, also called the "internal" phase, is generally comprised of petrolatum and a fatty alcohol such as cetyl or stearyl alcohol. The aqueous phase usually, although not necessarily, exceeds the oil phase in volume, and generally contains a humectant. The emulsifier in a cream formulation is generally a non-ionic, anionic, cationic or amphoteric surfactant. As will be appreciated by those working in the field of pharmaceutical formulation, gels are semi-solid, suspension-type systems. Single-phase gels contain organic macromolecules distributed substantially uniformly throughout the carrier liquid, which is typically aqueous, but also, preferably, contain an alcohol and, optionally, an oil. Preferred organic macromolecules, i.e. gelling agents, are crosslinked acrylic acid polymers such as the "carbomer" family of polymers, e.g., carboxypolyalkyl enes that may be obtained commercially under the Carbopol(R) trade mark. Also preferred are hydrophilic polymers such as polyethylene oxides, polyoxyethylene-polyoxypropylene copolymers and polyvinylalcohol; cellulosic polymers such as hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl methylcellulose phthalate, and methyl cellulose; gums such as tragacanth and xanthan gum; sodium alginate; and gelatine. In order to prepare a uniform gel, dispersing agents such as alcohol or glycerine can be added, or the gelling agent can be dispersed by trituration, mechanical mixing or stirring, or combinations thereof.

Pastes are semi-solid dosage forms in which a drug substance is suspended in a suitable foundation. Depending on the nature of the foundation, pastes are divided between fatty pastes or those made from single-phase, aqueous gels. The foundation in a fatty paste is generally petrolatum or hydrophilic petrolatum or the like. The pastes made from single- phase aqueous gels generally incorporate carboxymethylcellulose or the like as the foundation. Compositions of the present invention may also be prepared with liposomes, micelles, and microspheres. Liposomes are microscopic vesicles having a lipid wall comprising a lipid bi layer, and can be used as drug delivery systems herein as well. Liposomal preparations for use in the instant invention include cationic (positively charged), anionic (negatively charged) and neutral preparations. Cationic liposomes are readily available. Anionic and neutral liposomes are readily available as well, or can be easily prepared using readily available materials. Such materials include phosphatidyl choline, cholesterol, phosphatidyl ethanolamine, dioleoylphosphatidyl choline, dioleoylphosphatidyl glycerol,

dioleoylphoshatidyl ethanolamine, among others. These materials can also be mixed with N-[ 1 -2,3-dioleyloxy)propyl]-N,N,N-triethylammonium (DOTMA) in appropriate ratios. Methods for making liposomes using these materials are well known in the art.

Micelles are known in the art and are comprised of surfactant molecules arranged so that their polar head groups form an outer spherical shell, while the hydrophobic, hydrocarbon chains are oriented towards the centre of the sphere, forming a core. Micelles form in an aqueous solution containing surfactant at a high enough concentration so that micelles naturally result. Surfactants useful for forming micelles include, but are not limited to, potassium laurate, sodium octane sulfonate, sodium decane sulfonate, sodium dodecane sulfonate, sodium lauryl sulfate, docusate sodium, decyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide,

tetradecyltrimethyl-ammonium chloride, dodecylammonium chloride, polyoxyl 8 dodecyl ether, polyoxyl 12 dodecyl ether, nonoxynol 10 and nonoxynol 30.

In a particular embodiment of the present invention the carrier material may comprise hyaluronic acid. Hyaluronic acid is well known in the art. its viscoelastic properties and excellent biocompatibility means that it can be used to provide a strong gel-like matrix support material for both cosmetic or drug delivery applications intended for use on the skin.

Hyaluronic acid can form cross-linked gels alone, or in combination with other hydrophilic polymers. Examples of said hydrophilic polymers include other polysaccharides, synthetic and natural, such as hydroxyethyl cellulose, carboxymethyl cellulose, xanthan gum, chondroitin sulfate, heparin, proteins of various types, such as collagen, elastin, albumin, a globulin, sulphated proteins such as keratin sulfate and sulphated

aminoglycosaminoglycans, synthetic water-soluble polymers, such as polyvinyl alcohol and its co-polymers, co-polymers of poly-(hydroxethyl) methacrylate and the like

Hyaluronic acid may be employed typically at about 2 to 3% by weight based on the weight of the pharmaceutical composition. Hyaluronic acid matrices employed in drug delivery vehicles are described in US patents 5,639, 738,5, 985,950, 5,929, 048,5, 792,753, 5,852, 002,5, 914,322 and 6,147, 059, all of which documents are hereby incorporate by reference.

In another particular embodiment of the present invention the composition comprises a carrier material comprising a crystalline network of monoglycerides. In this particular embodiment a solution of zileuton is incorporated into a network comprising a dispersion of solid crystals of polar lipids.

The lipids may have a crystallisation temperature of between 20 °C and 100 "C.

Preferable lipid crystals are (3 -crystals from a monoglyceride of a fatty acid having a chain length of 12-18 carbon atoms or monoglycerol ethers having ether chains of the

corresponding length or fatty acid esters of ascorbic acid with a fatty acid chain length o 12-18 carbon atoms or mixtures thereof. The fatty acids as well as the ethers may be saturated or unsaturated, preferably saturated ones.

The fatty acids may therefore include lauric acid (CI 2), myristic acid (C14), palmitic acid (CI 6) or stearic acid (CI 8), although CI 3, Clsor CI 7 acids could also be used. Preferable monoglycerides may be a 1-or 2-monoglyceri de, preferably a 1- monolaurin, 1- monomyristin, 1 -monopalmitin and 1 -monostearin or a mixture of two or more of these such as a mixture of 1 -monolaurin and 1 -monomyristin.

Examples of unsaturated monoglycerides are monopalmitolein, monoolein, monolinolein and monoliniolenin. The composition consists essentially of a dispersion of the above lipid crystals in water or any other polar liquid or mixtures thereof having the ability to allow crystal formation. Examples of polar lipids for use in accordance with the invention are water, glycerol, propylene glycol and ethylene glycol or mixtures thereof, however other suitable polar lipids may also be used. Such compositions and methods for their preparation are set out in more detail in

WO2004/O54549, which is hereby incorporated by reference.

Further cream bases suitable for use in topical applications consisting of a crystalline network of monoglycerides are described in W087/02582, W082/03173 and W093/20812, all of which documents are hereby incorporated by reference. Examples of such crystalline networks of monoglycerides are known as CrystalipTM.

In yet another particular embodiment of the present invention the composition is in the form of a microemulsion.

The term "microemulsion" can be defined as a system of water, oil, and surfactants, which typically are clear or otherwise transparent, and which are thermodynamically stable liquid. Typically, a microemulsion is transparent and bluish (Tyndall scattering) due to light scattering by colloidal droplets that will reflect more or less the light depending on the wavelength. Microemulsions exhibit high solubilisation power due to the combination of surfactant and co-surfactant in presence of oil and water. These systems are very stable and characterized by nano droplets having a size under 200 nm.

A problem with microemulsions, as typified by the Fegn formulation discussed

hereinabove, is that typically they have a very low viscosity, which is usually in the order of the viscosity of water phase. Whereas, it might be possible to formulate such low viscosity systems supported in a device such as a patch, plaster, bandage or the like, there are difficulties in applying such formulations directly to an affected area of skin and of ensuring that a reservoir of drug substance is retained on the affected site for any useful length of time.

Accordingly, when a composition of the present invention is in the form of a

microemulsion, it should preferably contain a gelling agent or a thickener. Gelling agents may include agents that gel when triggered by triggering agent that is reactive with the gelling agent, or gelling agents may be thermal gelling agents, both of which types of gelling agents are well known in the art.

Suitable gelling agents include, but are not limited to, natural gums, acrylic acid and acrylate polymers and copolymers, and cellulose derivatives (e.g. hydroxymethyl cellulose and hydroxypropyl cellulose), hydrogenated butylene/ethylene/styrene copolymer and hydrogenated ethylene/propylene/styrene copolymer.

Particular gelling agents include crosslinked acrylic acid polymers such as the "carbomer" family of polymers, e.g., carboxypolyalkylenes that may be obtained commercially under the Carbopol(R) trademark. Also preferred are hydrophilic polymers such as polyethylene oxides, polyoxyethylene-polyoxypropylene copolymers and polyvinylalcohol; cellulosic polymers such as hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl methylcellulose phthalate, and methyl cellulose; gums such as tragacanth and xanthan gum; sodium alginate, and gelatine.

It is typical to employ gelling agents in pharmaceutical compositions according to the invention at about 0.1 % and 5%,

Thickeners include, but are not limited to cellulose and derivatives such as cellulose, carboxymethyl hydroxyethylcellulose, cellulose acetate propionate carboxylate, hydroxyethylcel lulose, hydroxyethyl ethylcellulose, hydroxypropylcellulose,

hydroxypropyl methylcellulose, methyl hydroxyethylcellulose, microcrystalline cellulose, sodium cellulose sulfate, and mixtures thereof. Also useful herein are the alkyl substituted celluloses. Examples of alkyl groups useful herein include those selected from the group consisting of stearyl, isostearyl, lauryl, myristyl, cetyl, isocetyl, cocoyl (i.e. alkyl groups derived from the alcohols of coconut oil), palmityl, oleyl, linoleyl, linolenyl, ricinoleyl, behenyl, and mixtures thereof. The material sold under the tradename Natrosol(T ). CS Plus from Aqualon Corporation may be used.

Other useful thickeners include acacia, agar, algin, alginic acid, ammonium alginate, amylopectin, calcium alginate, calcium carrageenan, carnitine, carrageenan, dextrin, gelatin, gellan gum, guar gum, guar hydroxypropyltrimonium chloride, hectorite, hyaluronic acid, hydrated colloidal silica, hydroxypropyl chitosan, hydroxypropyl guar, karaya gum, kelp, locust bean gum, natto gum, potassium alginate, potassium carrageenan, propylene glycol alginate, sclerotium gum, sodium carboxymethyl dextran, sodium carrageenan, tragacanth gum, xanthan gum, and mixtures thereof. Also useful are acrylic acid/ethyl acrylate copolymers and the carboxyvinyl polymers sold by the B.F. Goodrich Company under the trade mark o Carbopol resins.

The compositions of the present invention may comprise a thickener from about 0.1% to about 20%, by weight preferably 0.1 to 5%.

Various additives, known to those skilled in the art, may be included in the pharmaceutical composition of the present invention. For example opacifiers, antioxidants, fragrance, colourants, stabilizers, surfactants and the like. Other agents may also be added, such as antimicrobial agents, to prevent spoilage upon storage, i.e. to inhibit growth of microbes such as yeasts and molds. Suitable antimicrobial agents are typically selected from the group consisting of the methyl and propyl esters of p-hydroxybenzoic acid (i.e., methyl and propyl paraben), sodium benzoate, sorbic acid, imidurea, and combinations thereof.

The compositions of the present invention may also contain irritation-mitigating additives to minimize or eliminate the possibility of skin irritation or skin damage resulting from the drug, or other components of the composition. Suitable irritation-mitigating additives include, for example: [alpha] -tocopherol; monoamine oxidase inhibitors, particularly phenyl alcohols such as 2-phenyl- 1 -ethanol; glycerine; salicylic acids and salicylates; ascorbic acids and ascorbates; ionophores such as monensin; amphiphilic amines;

ammonium chloride; N-acetylcysteine; cis-urocanic acid; capsaicin; and chloroquine. The concentration of zileuton in the pharmaceutical composition of the present invention will typically depend upon a variety of factors, including the severity of the disease or condition to be treated, the desired effect, possible adverse reactions, the ability and speed of zileuton to reach its intended target, and other factors within the particular knowledge of the patient and physician. Preferred compositions will typically contain on the order of about 0.5-30 wt %, preferably about 5- 10 wt %, active agent and will be applied twice daily

There follows a series of examples that serve to illustrate the invention. Example 1

Solubility of zileuton in various solvents

Solvent Solubility (mg/g) Transcutol™ 195

PEG 400 197

Solutrol HS15™ 7 mPEG 350 194

Pharmasolve™ 192 Labrafil CS 1944™ Not detectable

Glycerol 9 Lauroglycol™ Not detectable Labrafac WL 1349™ Not detectable

Labrafac PG™ Not detectable

Cremophor RH 40™ 6

Cremophor EL™ 118 Tween 80 1

SLS (2%) 2

Span 85™ Not detectable

Vit E TPGS (20% ) TM 9

DMSO 129 Arsasolve™ 130

Example 2

In vitro permeation of zileuton from solutions across human skin

The test was carried out in a Franz Cell apparatus consisting of a cylindrical glass diffusion chamber comprising an upper and lower part. Human skin is clamped between the two parts and represents a permeation barrier. The two halves of the cell are held together by means of a ball and socket clamp. The lower (acceptor) chamber has a volume of approximately 12 mL, while the volume of the upper (donor) chamber may be variable. The acceptor medium is a Krebs Ringer Buffer solution (pH 7.4) with sodium azide added at 0.05% (w/v) as an anti -microbial agent. The temperature of the cell was 32°C and the cell was stirred at 400 rpm. The diffusion area of the skin in the cell was approximately 1.77 cm². Permeation of zileuton through the skin was monitored at 24 and 48 hours by withdrawing 200 microlitre samples for analysis. Withdrawn sample volume was replaced with acceptor medium at 32°C.

Skin was prepared by excision during surgery and cooled to 4"C after removal and dried. The skin was removed from subcutaneous fatty tissue. The skin thickness was approximately 500 microns, but as the stratum corneum is the principle barrier to permeation, the thickness was not an issue. Test samples included zileuton in transcutol P (135 mg/g); zileuton in PEG 400 (135mg/g); zileuton in mPEG (135mg/g); Pharmasolve (135mg/g). All test samples resulted in flux through the skin. However, the best performance was achieved when Pharmasolve was used as the solvent with approximately 260 micrograms of zileuton permeating through the skin during the course of the test.

Example 3

Formulation based on hyaluronic acid carrier:

Process:

Mix the mPEG 350, the benzyl alcohol and the Transuctol HP into a 250ml beaker (for 200g formulation) with a magnetic stirrer at 350rpm. Dissolve the zileuton in the mix under stirring at 350rpm (addition in approx. 1 min than stirring for 40min)

Remove the magnet stirrer, and add the water in 15min under stirring at 300rpm with an IKA apparatus with the two wings big blade. Add the sodium hyluronate quickly in 2 min under stirring at 400rpm than 550rpm when the viscosity is building.

Keep for 2 hours the stirring at 550rpm than stop stirring and let the formulation rest at least 24 hours to allow the removal of the air bubbles. Example 4

Microemulsion formulation

Material Quantity (%)

Zileuton 5.0

Labrasol 47.5

Plurol oleic 25.0

Isopropyl myristate 17.4

Purified Water 5.1

Process:

Dissolve the Zileuton into the Labrasol under stirring with a magnet stirrer

Add under stirring the Plurol Oleic and the Isopropyl Myristate.

Incorporate the water under stirring.

Example 5

Monoglyceride based formulation

Material Quantity (%)

Zileuton 2.0

Rylo MG 12 (glyceryl monolaurate) 6.0

Rylo MG 14 (glyceryl monomyristate) 18.0 Propylene Glycol 10.0

Purified Water 64.0

Process:

Put 7.5g of Rylo MG12 and 22.5g of Rylo MG14 into a 150ml beaker at 70°C (overage to compensate losses during transfer). Stir at 700rpm (magnet stirring) and when all is melted, add the required amount of zileuton multiplied by 1.25 (ex: 1% formulation add 1.25g). Mix for at least 10m in to complete dissolution.

In a 250ml beaker (200g formulation) mix the water and propylene glycol (IKA two wings big blade) and heat the mix at 70°C in a water bath.

As soon as the temperature of the mix water/PG reach 70°C, add the exact required amount of mix MG12/14 and zileuton under stirring at 325rpm.

Turn off the heating and allow the formulation to cool slowly (beaker still in the water bath) under stirring at 325rpm.

When the temperature of the formulation reaches 44°C, increase the stirring speed to 500rpm. At 39°C decrease the speed to 75rpm, move the blade up at the limit of the formulation surface and manually move up and down the beaker in order to keep a homogenous cream.

Around 33°C an exothermic crystallisation reaction is observed (temperature moves back to 35°C) and the appearance of a shiny cream.

When the reaction is completed (the temperature falls under the starting temperature of the reaction), remove the beaker from the water bath and put it into another but cold tap water bath.

Maintain the manual shaking to have a homogenous cream until the temperature falls between 25-29°C, than stop the stirring, remove the beaker from the bath.

Example 6 Mouse ear-swelling test The effects of Zileuton-containing formulations set out in Examples 3 to 5 as well as an oral zileuton control formulation (40 mg/Kg i.g. in 200 microlitres) on the arachidonic acid- induced ear swelling. Male Swiss mice were allowed to acclimatise for a minimum of 72 hours and then assigned to groups for testing.

Treatments were given at To hour. Treatments were given by applying a 20 μΐ volume of each of the formulations of Examples 3 to 5 to the dorsal surface of both the right and left ears of each animal. A spatula was used to aid even distribution of the material across the dorsal surface of the pinna. For oral Zileuton treatment, unanaesthetised animals received treatment intragastrically via a suitable catheter tube attached to a syringe.

At 2 hours post-treatment, animals were challenged with a topical application of 1 mg of arachidonic acid in acetone onto the ventral surface of the left ear. The ventral surface of the right ear received a topical application of acetone only as a negative control. Arachidonic acid was applied in a volume of 20 μΐ pipetted over gently onto the surface and the head of the anaesthetised animal was held until the material was fully absorbed. One hour after challenge with arachidonic acid the thickness of the ears was measured using callipers and increases expressed as the difference in thickness between the challenged and unchallenged ears. After all measurements animals were sacrificed.

Levels of oedema were reduced following treatment with all formulations. Levels of inhibition with topical Zileuton formulations were in line with those seen following oral treatment.

Claims

Claims:

I . A pharmaceutical composition adapted for external application to human skin comprising a semi-solid carrier material containing zileuton dissolved or dispersed therein.

2. A pharmaceutical composition according to claim 1 wherein the carrier material contains hyaluronic acid.

3. A pharmaceutical composition according to claim 1 wherein the carrier material comprises a crystalline network of monoglycerides.

4. A pharmaceutical composition according to claim 1 in the form of a micro- emulsion.

5. A pharmaceutical composition according to claim 4 comprising a gelling agent or a thickening agent.

6. A pharmaceutical composition according to any of the preceding claims containing a solvent for zileuton.

7. A pharmaceutical composition according to any of the preceding claims wherein the solvent can dissolve zileuton at 190 mg/g or greater.

8. A pharmaceutical composition according to claim 7 wherein the solvent is a pyrrolidone.

9. A pharmaceutical composition according to claim 8 wherein the pyrrolidone is selected from the group consisting of N-methyl-2 -pyrrolidone, 1 -butyl-3 -dodecyl-2- pyrrolidone, 1 ,3-dimethyl-2-imidazolikinone, 1 ,5-dimethyl-2-pyrrolidone, 44,-dimethyl-2- undecyl-2-oxazoline, 1 -ethyl-2-pyrrolidone, 1 -hexyl-4-methyLOXycarbonyl-2-pyrrolidone, 1 -hexyl-2-pyrrolidone, 1 -(2-hydroxyethyl)pyrrolidone, 3 -hydro xy-N-methyl-2-pyrro 1 idone, l-isopropyl-2-undecyl-2-imidazoline, 1 -lauryl-4-methyLOXycarbonyl-2-pyrrolidone, poly(N-vinylpyrrolidone), pyroglutamic acid esters and 2-pyrrolidone.

10. A pharmaceutical composition according to claim 9 wherein the pyrrolidone is N- methy!-2-pyrrolidone (PHARMASOLVE).

I I . A pharmaceutical composition according to any of the preceding claims in the form of gel, ointment, cream or paste.

12. A method of providing en anti-inflammatory response in the human skin tissue comprising the step of applying to an affected site on the skin of a human subject a composition as defined in any of the preceding claims,

13. A method of providing an anti-inflammatory response in the human skin tissue comprising the step of applying to an affected site on the skin of a human subject a composition according to any of the claims 1 to 11, said anti-inflammatory response being comparable to the response of 40 to 80 mg/kg zileuton administered orally,

14. A method of treating acne vulgaris, rosacea or atopic dermatitis comprising the step of applying to an affected area of the human skin, a composition according to any of ^'the claims 1 to 1 1.