Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Web – sheet or filament bases; compositions of bandages; or...
Reexamination Certificate
1998-01-14
2001-06-26
Dodson, Shelley A. (Department: 1616)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Web, sheet or filament bases; compositions of bandages; or...
C424S078020, C424S078080, C424S445000, C514S772200
Reexamination Certificate
active
06251423
ABSTRACT:
The present invention relates to medical products for application to the skin or to a wound, and particularly to products which are applied in the form of a paste.
Paste or cream products for application to the skin for the treatment of medical conditions or wounds are well known; for example zinc oxide is often applied topically in the form of a cream or paste. The cream or paste may be applied by first spreading it onto a bandage or dressing and then applying the bandage or dressing to the skin. This kind of system, i.e. a paste bandage, such as those supplied by Smith and Nephew Healthcare Ltd under their VISCOPASTE trade mark, is often used for the treatment of leg ulcers which are chronic wounds which are often difficult to heal.
Such paste or cream products are usually formulated as emulsions because such formulations have desirable flow and spreading characteristics, feel “creamy” to the touch and are quite resistant to drying out. When the creams are for application to a wound, it is important to avoid the introduction of undesirable organisms, such as bacteria, into the wound and so it is desirable to sterilise the cream or paste before use. However, these emulsions are difficult or impossible to sterilise because they tend to separate when subjected to high temperatures or to sterilising radiation. As an alternative to sterilisation, such formulations may contain preservatives in order to prevent the growth of bacteria in the cream. Unfortunately many patients may be or become sensitive to the preservatives used and such sensitisation may greatly worsen the condition which the cream is intended to treat.
One approach to solving this problem is to formulate the “cream” as a gel, as described in European Patent Application No. 0040378 for example. However gels are known to dry out rapidly and this feature may limit their use in paste bandages which should be flexible when applied to the skin and which should not dry out after application so that the bandage may be removed easily when required. Also, gels, while being soft and pliable, are sometimes difficult to spread easily and evenly. The cream or paste used on a paste bandage must be spreadable both to aid its application to the bandage substrate and to allow the paste to be spread and moulded after its application to the skin or wound.
GB-A-2269745 describes a topical composition for impregnating a bandage which comprises an emulsion comprising one or more fats or oils, one or more emulsifying agents and at least one water-soluble gum and water. No preservative is added.
It is an object of the present invention to provide a sterilisable cream or paste which overcomes some, at least, of the foregoing problems.
According to the invention, a paste formulation comprises an emulsion comprising a wax or oil, at least one emulsifier and water, and a substantially water-insoluble material which forms a gel in the presence of water. The formulation results in a cream or paste which exhibits the desirable properties of an emulsion, in that it is spreadable and has the creamy consistency of an emulsion, yet which does not break down when subjected to normal sterilisation procedures, e.g. steam sterilisation, because the gel stabilises the emulsion. It also exhibits better water retention properties than a conventional gel because water is held both in the emulsion and in the gel.
The term paste used in this document should be taken to include creams and other viscous spreadable compositions such as are often applied to the skin directly or spread onto a bandage or dressing.
The formulation will normally contain as a further component a humectant to reduce the partial vapour pressure of the water in the cream thereby to greatly reduce the rate at which the cream dries out. Suitable humectants are preferably not solvents for the gel-forming material, but are misible with water to a large extent and are preferably suitable for application to the skin. Polyols are especially
suitable for the purpose and suitable polyols may include monopropylene glycol but glycerine (glycerol) to British Pharmacopoeia specification is a particularly preferred polyol for this purpose. The polyol may be present in proportions of 25-50% (by weight) of the total formulation; a preferred range is 30-40%.
This relatively high proportion of polyol also ensures that if the paste should dry out to any degree, the resulting paste remains soft and flexible because the glycerine may act as a plasticiser for the polymer. When the paste is applied on a bandage, for example, it may therefore still be removed easily from the skin when the paste has lost water without the need to cut the bandage off. The polyol also has the advantage of functioning to prevent the proliferation of bacteria in the paste when it is in contact with the skin or wound, particularly infected wounds.
The formulation will usually, but not necessarily, contain an active ingredient. Some typical active ingredients which may be used are: zinc oxide, ichthammol, calamine, silver suphadiazine, chlorhexidine acetate, coal tar, chlorhexidine gluconate, metronidazole or other anitbacterial agents, or a combination thereof. Alternative active ingredients may also be found suitable for incorporation into the cream. The concentration of active ingredient in the formulation is typically in the range 0-15% by weight but depends upon the nature of the ingredient. For example, up to about 15 wt %, of zinc oxide may be added; typically 6-10% of zinc oxide is used, possibly in combination with another ingredient such as ichthammol (0-3 wt %) and/or calamine (0-15% wt). lchthammol or calamine may also be used alone. Chlorhexidine acetate is usually used at a concentration of up to 1% by weight; 0.5 wt % is typical.
The emulsion comprises a wax or oil, at least one emulsifier and water. A preferred wax is glyceryl monostearate. It is particularly preferred to use a combination of the glyceryl mono stearate and PEG100 stearate which is available commercially as CITHROL GMS/AS/NA from Croda Universal Ltd. This combination provides both a wax and an emulsifier (PEG 100 stearate) which is especially compatible with the wax, for forming an emulsion in water. It is especially preferred to include a second emulsifier in the formulation to increase the stability of the emulsion. A preferred second emulsifier is a PEG20 stearate, such as CITHROL 1OMS which is supplied by Croda Universal Ltd. The total concentration of emulsifier in the cream should normally be in the range of from 3-15%. Where two emulsifiers are used, one may be present in a greater concentration than the other. Where the wax/emulsifier combination described above is used, the concentration of CITHROL GMS/AS/NA is usually about five times that of the CITHROL 1OMS.
The water-insoluble material forms a gel with the water of the formulation. The material is therefore hydrophilic but does not dissolve in water to any great extent. The material is most preferably a polymeric material which is a water-absorbing non water-soluble polymer. However non polymeric materials which form gels with water and which are stable at elevated temperatures could also be used, e.g. clays such as kaolin or bentonite. Preferred polymers are super-absorbent polymers such as those disclosed in WO-92/16245 and comprise hydrophilic cellulose derivatives which have been partially cross-linked to form a three dimensional structure. Suitable cross-linked cellulose derivatives include those of the hydroxy lower alkyl celluloses, wherein the alkyl group contains from 1 to 6 carbon atoms, e.g. hydroxyethyl cellulose or hydroxypropylcellulose, or the carboxy-celluloses e.g. carboxymethyl hydroxyethyl cellulose or carboxymethylcellulose. A particularly preferred polymer is a partially cross-linked sodium carboxymethylcellulose supplied as AKUCELL X181by Akzo Chemicals B.V. This polymer is a superabsorbent polymer in that it may absorb at least ten times its own weight of water. The cross-linked structure of the polymer prevents it from dissolving in water but water is easily absorbed
Dodson Shelley A.
Larson & Taylor PLC
Smith & Nephew plc
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