AU2001267697A1 - Sprayable wound care compositions - Google Patents

Description

SPRAYABLE WOUND CARE COMPOSITIONS

This invention relates to wound care compositions; more particularly, this invention relates to compositions for the treatment of wounds or other skin injury.

A variety of gels and ointments is available for application to wounds for a variety of purposes. They may, for example, be used to clean a wound; to promote healing of the wound; or to prevent infection. In certain circumstances the gel or ointment may include an active ingredient which is administered to the patient by topical application of the gel or ointment.

One example of a commercially available wound gel is LNTRASITE (trade mark). This gel contains hydrated carboxymethyl cellulose as a main ingredient and is packaged and applied to wounds in gel form as a primary treatment in order to debride the wound. The gel may also assist in preventing the wound from drying out thereby promoting healing.

Wound gels are generally in gel form at the time of application to the wound and are usually applied by being squeezed from a tube or other suitable container by hand or by other suitable means. Since gels are mobile they offer the advantage of intimate contact with the often irregular surface of a wound, something that is often not achieved with a more rigid wound dressing. The advantage of good contact is however tempered by the conflicting needs of making the gel sufficiently mobile that it can be applied to the wound but not so mobile that it runs out of the wound under the influence of gravity. Gels currently in use suffer from the disadvantage that they can run out of the wound.

GB 2305606 discloses a drug delivery composition for nasal administration of an antiviral agent and a bioadhesive material which may include a polysaccharide; for example, a gellan gum.

We have now found that it is possible to make a composition for topical application to a wound which forms an immobile gel once in contact with the wound or skin injury.

According to the first aspect of this invention, there is provided a composition for the treatment of wound or skin injury which is in sprayable form prior to application to the wound and comprises from 0.25% to 1.5% by weight of the composition of a gellan gum the viscosity of said composition increasing once applied to a wound so that an immobile gel, suitably an elastic gel, is formed. Preferably, the composition comprises from 0.5% to 1.0% of gellan gum by weight of the composition.

This gives the advantage that the composition can be applied in a mobile state to give intimate contact with the wound but forms an immobile gel once in contact with the wound as an adherent cohesive mass thereby reducing the tendency for the gel to run out of the wound. Such a composition is particularly suitable for administering active ingredients to a wound.

By the term "gellan gum" as used herein, in meant the extracellular anionic heteropolysaccharide elabriated by the bacterium Pseudomonas elodea. This heteropolysaccharide consists of the following tetrasaccharide repeat unit:

→3)-β-D-Glcp-(l→4)-β-D-GlcpA-(l→4)-β-D-Glcp-(l→4)-α-L-Rhap-(l→

which may, or may not, be partially O-acetylated on its β-D-glucopyranose (β-D-Glcp) residues. Gellan gum is described in Carbohydrate Polymers, Vol. 30,1996: SPECIAL ISSUE, GELLAN GUM: STRUCTURES, PROPERTIES AND FUNCTIONS. Ed. Nishinari K., Pub. Elsevier Science 1996 and "Physicochemical properties of Gellan gum in gel and solution." Author Tsiami Amalia A. Pub. University of East Anglia 1994.

Whilst not wishing to be bound by theory it is believed that gellan gum forms a gel once applied to a wound because molecular association of the saccharide repeat units is promoted due to exposure of the gum cations contained in the wound and wound exudate. Whilst many polysaccharides form gel structures it tends to be under specific circumstances, for example the gelation of Carrageenas is sensitive to the ion type e.g. gelling with potassium but not sodium. Glycuronans e.g. alginate gel in the presence of divalent cations but not monovalent cations. Xanthan gum will gel with divalent cations but only at high pH. Pectic materials gel on cooling if completely esterified or in the presence of divalant cations if incompletely esterified. However Gellan gum is not specific and forms a gel with almost all cations. Surprisingly, we have found that gellan gum gels at the relatively low ion concentrations found in a wound environment in contrast to other polysaccharides.

The composition may be a solution in water or a mixture of water together with another water-miscible solvent, such as propylene glycol.

Suitably, the composition may be preparable by heating the gellan gum in an aqueous medium at a temperature from 70 to 95°C, desirably from 75°C to 85°C.

The composition preferably comprises an active ingredient, suitably dissolved or dispersed in the composition; for example, dissolved or dispersed in an aqueous solution of gellan gum. The term "active ingredient" is used herein to refer to any agent which affects the metabolism or any metabolic or cellular process of the patient (including growth factor nutrients and living cells), promotes cleaning of the wound, combats infection, hypergranulation, inflammation and/or aids healing. An advantage of delivering the active ingredient in this way is that gellan gums may provide controlled release of active ingredients.

Active ingredients may include other polysaccharides such a hyaluronic acid, salts of hyaluronic acid, esters of hyaluronic acid andhydrocolloids such as sodium carboxymethyl cellulose, pectin and alginate, antiseptic agents such as povidone iodine, antifungal agents such as nystatin and Econazole nitrate and antibacterial agents such as polymyxin, metronidazole and silver sulphadiazine. Preferably, the active ingredient is selected from the group consisting of hyaluronic acid, esterified hyaluronic acid, an antiseptic, an antifungal or an antibacterial agent and mixtures thereof. Suitably, the active ingredient is present in an amount of 0.1 to 10% by weight of the composition.

Preferably, the composition of this invention is contained in a spray device which on actuation discharges a metered dose of the composition.

In accordance with a further aspect of this invention, there is provided the use of a composition according to the invention in the preparation of a medicament for the treatment of wounds. The composition used may be any composition of the invention disclosed herein.

For administration to a patient the composition of the invention may be placed in an apparatus. In a further aspect the invention provides an apparatus for forming an immobile gel dressing on a wound or skin injury, the apparatus comprising: a) a composition comprising from 0.25% to 1.5% by weight of the composition of a gellan gum b) a vessel containing the composition c) a dispensing means in fluid concentration with the composition so that the composition can be applied to the wound or skin injury.

The apparatus may be adapted to spray the composition and may be a container fitted with a mechanical pump or container pressurised with a propellant, for example a conventional aerosol propellant such as nitrogen or a hydrocarbon. The spray device preferably discharges a metered dose of the composition on actuation. In general the metered dose may be up to 0.2g per actuation.

This invention further provides a method of forming in situ an immobile gel on a wound or skin injury comprising the step of: dispensing an effective amount of a composition at a locus including the wound or skin injury, the composition comprising from 0.25% to 1.5% by weight of the composition of a gellan gum so that the viscosity of said composition increases and forms an immobile gel. Preferably, the dispensing step comprises spraying the composition on the wound or skin injury.

The composition used in the apparatus or method maybe any composition of the invention disclosed herein.

The composition prior to application to a wound preferably has a viscosity from 0.1 Pas to 12 Pas as measured by a Cammed CSL 100 Rheometer at 35.5°C and 1Hz.

Compositions with these viscosities have been found particularly suitable for application by spraying. Once delivered to the wound the composition develops into a gel that has a viscosity typically from 13 Pas to 800 Pas, usually after a period of from 0.5 to 40 minutes.

The invention is illustrated by the following Examples in which parts are by weight.

Examples

Sprayable gel compositions for the treatment of wounds were prepared by mixing gellan gum (Kelcogel F low acyl content ex Kelco Nutrasweet) with propylene glycol, buffered to pH 7 using a phosphate buffer solution as described in the US Pharmacopoeia 1990 (9% by weight of total weight of gel), water and sodium hyaluronate to yield the following compositions.

The time to gel onset and viscosity of the compositions was measured using a rheometer. A sample of the composition is injected on to a pad soaked in 0.9%w/w saline placed on the bottom plate of a parallel pair (see Figure 1.).

A sufficient volume of sample is injected into the space between the plates so as to be in contact with the top plate and the saline soaked pad. During the experiment the force required to rotate the top plate of the pair by a small angle is measured. The movement of the top plate is in the form of a small amplitude oscillation.

Figure 1 Schematic of a parallel plate

When the distance moved by the plate and the force required to oscillate the plate are plotted, the two curves are displaced from each other. This displacement may be measured in degrees and is termed the phase angle. For an ideal liquid this angle is 90° and for a solid it is 0° and for most real materials it is somewhere between the two extreme values. During the gelation process for the gellan materials this phase angle is observed to rapidly fall and then the rate of change reduces. This is associated with an increase in viscosity and is taken as the time at which the gelation starts for these examples. As the solution becomes less able to flow the phase angle falls and the material starts to behave as a conventional solid. This process continues for a considerable time after the onset of gelation, as the system approaches its new equilibrium conformation. The time taken for the gel onset to occur, the viscosity of the solution and the stiffness of the final gel are dependent on the concentrations of the ions present and their type (sodium, potassium, calcium etc.), temperature, and the composition of the gel solution. The following parameters were set.

Plate diameter and type 4cm diameter acrylic

Plate spacing 2.500mm

Test frequency 1Hz

Temperature 35.5°C

Controlled variable Displacement

Applied amplitude 1.250x10^"3 rad.

Pad Paper 68 to 72 gsm

Pad size 5 cm by 5 cm.

Pad fluid handling 8 g per g to 9 g per g

The sample used to be tested was heated in a water bath to 35.5°C. A 5cm by 5cm minimum square of the pad material was soaked in 0.9% saline and placed on the lower heated platen of the rheometer and readings started. After the first two data points have been established the sample to be tested is injected into the gap between the top plate of the rheometer and the pad. This is the initial time point of the experiment. The experiment is allowed to continue to 45 minutes.

Gel onset is the first point of inflection after the sample was introduced in the phase angle/time plot. The results were as follows:

Viscosity of the compositions as they cure.

Table 2. Viscosity data for example 2.

The initial gelation process is the start of a chain of events which changes the gel solution from a liquid to a solid. This change of state results in a change of the phase angle measured for the gel. The phase angle reduces as the solution solidifies. This solidification is associated with an increase in the measured viscosity. The results in Table 1 & 2 show for examples 1 & 2 (Tables 1 & 2) that although the initial solution viscosities are different, there are similar percentage changes in the two solutions as the initial gelation occurs (35% +/- 7% for example 1 and 37% +/- 4% for example 2). The data in the tables that relate viscosity to time show that the gelation process continues for many minutes after the initial gel onset, resulting in a 166 fold increase in the viscosity of example 1 and a 28 fold increase in example 2 after 40 minutes.

Shear modulus of the compositions as they cure.

Table 3. Shear modulus data for example 1.

Table 4. Shear modulus data for example 2.

s described previously when the gel solution converts from a liquid to a solid, there is a change in the measured phase angle for the gel. These results (Tables 3 & 4) demonstrate that the initial gelation increases the modulus of the solution and that although the initial moduli of examples 1 & 2 are different, they both increase by similar percentages in the initial gelation (35% +/- 7% for example 1 and 37% +/- 4% for example 2). The data in Tables 3 & 4 that relate sample shear modulus to time, demonstrates that the gelation process continues for many minutes after the initial gel onset. The gelation process resulting in a 62 fold increase in the viscosity of example 1 and a 17 fold increase in example 2 after 40 minutes.

Example 2 of GB 2305606 (WO 96/03142) discloses a composition comprising:

gellan gum 10 mg

1 lmg/ml antiviral agent 1.8 ml 4mg/ml benzalkonium chloride 0.05 ml Water 0.15 ml

The composition was prepared by stirring the contents at room temperature for 24 hours to disperse the gellan gum.

A like solution was prepared but omitting the antiviral agent and working at a 200 ml scale:

gellan gum l g benzalkonium chloride 0.02 g water 200 ml

The suspension was divided into two equal portions. The first (sample 1) was reserved for Comparative Example 3 while the second (sample 2) was reserved for Example 4.

COMPARATIVE EXAMPLE 3

Sample 1 was stirred at room temperature for 24 hours. The sample then has its viscosity measured in the same manner a detailed in relation to Examples 1 and 2. The results are shown in Table 5.

EXAMPLE 4

Sample 2 was heated to 75°C until the solution clarified (approximately 1 minute). It was then allowed to cool to room temperature and stirred at room temperature for 24 hours. The sample then had its viscosity measured in the same manner as detailed in relation to Examples 1 and 2. The results are shown in Table 5.

Table 5

The nature of the differences between the samples is clarified by the phase angle data. The phase angle achieved by Sample 1 at the end of gelation is still that typical of a viscous solution or suspension whilst that achieved by Sample 2 is of the very low value expected of a Newtonian solid.

Whilst the chemical composition of GB 2 305 606 Example 2 is similar to the composition to that employed in our system, the difference in the preparation method, results in a very different product. The product prepared by the method of the invention yields a Newtonian solid. Whilst the preparation described in GB 2 305 606 remains as a suspension.

Claims (11)

1. A composition for the treatment of wound or skin injury which is in spray able form prior to application to the wound and comprises from 0.25% to 1.5% by weight of the composition of a gellan gum the viscosity of said composition increasing once applied to a wound so that an immobile gel is formed.

2. A composition as claimed in claim 1 , which is preparable by heating the gellan gum in an aqueous medium at a temperature from 70 to 95°C.

3. A composition as claimed in claim 1 or 2 comprising an active ingredient dissolved or dispersed in the composition.

4. A composition as claimed in claim 3 wherein the active ingredient is selected from the group consisting of hyaluronic acid, esterified hyaluronic acid, an antiseptic, an antifungal or an antibacterial agent and mixtures thereof.

5. A composition as claimed in claim 3 or claim 4 wherein the active ingredient is present in an amount of 0.1 to 10% by weight of the composition.

6. A composition as claimed in any preceding claim which has a viscosity from 0.1 to 12 Pas prior to application to the wound.

7. A composition as claimed in any preceding claim in a spray device which on actuation discharges a metered dose of the composition.

8. Use of a composition according to any of the preceding claims in the preparation of a medicament for the treatment of wounds.

9. An apparatus for forming an immobile gel dressing on wound or skin injury, the apparatus comprising: a) a composition comprising from 0.25% to 1.5% by weight of the composition of a gellan gum b) a vessel containing the composition c) a dispensing means in fluid connection with the composition so that the composition can be applied to the wound or skin injury.

10. A method of forming in situ an immobile gel on a wound or skin injury comprising the step of: dispensing an effective amount of a composition at a locus including the wound or skin injury, the composition comprising from 0.25% to 1.5% by weight of the composition of a gellan gum so that the viscosity of said composition increases and forms an immobile gel.

11. The method of claim 10 wherein the dispensing step comprises spraying the composition on the wound or skin injury.