METHOD FOR THE PREPARATION OF CREAMS

Abstract: Emulsifier compositions comprise: a) at least one membrane lipid, b) at least one natural amphiphile which is not a primary emulsifier, and, optionally, c) a hydrophilic medium. These efficient emulsifying systems are characterised by the absence of synthetic emulsifiers. Stable oil-in-water emulsions or dispersions formed using these emulsifier compositions, and from which synthetic surfactants or emulsifiers are substantially absent, are described. Creams based on such emulsions or dispersions are also described and which may include lipid vesicles or liposomes, optionally with one or more biologically active compounds entrapped therein. Methods for producing the emulsions, dispersions and creams are also provided.

Description: METHOD FOR THE PREPARATION OF CREAMS This invention relates to emulsifying compositionj and emulsions formed therefrom, based on membrane lipids, chiefly phospholipids and glycolipids. Emulsions and creams are dispersions of two immiscible 5 phases either as oil droplets dispersed in water (0/W) or water globules suspended in oil (W/0). There are two important considerations to emulsion formation, i) Work energy has to be applied to obtain dispersed droplets. 10 ϋ) Surfactants are required to lower interfacial tension and prevent the globules from coalescing. These considerations lead to the use of emulsifying agents most of which are surfactants. Surfactants are normally amphiphiles, which are compounds that have a water-soluble 5 (hydrophilic) and an oil-soluble (lipophilic) moiety. It should be emphasised, however, that not all amphiphiles are efficient emulsifying agents. Empirically, emulsifying agents are classed according to their affinity for water and oil in terms of their hydrophile-lipophile-balance o (HLB). This is denoted by an arbitrary value from 1 upwards. Emulsifying agents with low HLB values (1 to about 8) form W/0 systems, whereas those with higher HLB values give rise to 0/W systems. It is also recognised that the irritancy of surfactants often increases with the HLB g number. Primary emulsifying agents are usually high HLB surfactants that form stable emulsions or dispersions of oil droplets in water. However, auxiliary or co-emulsifiers are frequently included to help further stabilise the dispersed droplets, although co-emulsifiers on their own do not form stable emulsions. Emulsifying agents are widely used in the food, cosmetic, toiletry and pharmaceutical industries to form stable dispersions of oil and water. Many types of emulsifying agents are available to obtain W/0 and 0/W dispersions. With few exceptions, the most commonly used emulsifying agents are all synthetic compounds based on soaps of fatty acids (anionic), quarternary ammonium compounds (cationic), condensation products of ethylene oxide with sugars, glycol esters and ethers, fatty acid esters and ethers (non ionic). There is growing evidence that synthetic emulsifying agents frequently give rise to toxicity and irritancy problems. Moreover, in many cases, manufacture of these compounds often involve environmentally harmful solvents and residues. Phospholipids are essential components of all cell membranes. In addition to being biocompatible, they are also thought to have useful physical and physiological functions. Therefore, phospholipids are widely used in all types of preparations intended for human use. It is well known to those skilled in the art that on their own phospholipids are poor primary emulsifying agents for 0/W systems. This is due to the inherently low HLB values of natural phospholipids which vary between 3 to 8, depending on the type of phospholipid. To overcome the problem BP 1163227 describes emulsifying agents which contain hydroxylated phospholipids modified to improve water dispersibility. Dispersions of oil-in-water relying on phospholipids as the sole emulsifier are liable to cream and phase separate on standing, even after homogenisation. Coalescence of smaller globules into larger droplets results in creaming, leading to phase separation (cracking) if the process continues. Phospholipids are, however, conventionally employed as auxiliary emulsifiers with more efficient anionic, cationic or non-ionic emulsifying agents with higher HLB numbers, to prepare 0/W emulsions and creams. Thus, GB-A- 1360021 discloses emulsifying agents based on phospholipids with glyceryl mono stearate and sodium stearate which is a soap with a very high HLB value. Where phospholipids are used as sole 0/W emulsifying agent, it is necessary to employ very high energy to obtain small oil droplets (below lu) which are more stable due to their smaller surface area. High energy processing requires generation of pressures in the order of 20000 psi and the equipment is expensive and not generally available. Therefore this method is confined to the production of intravenous fat emulsions in total parenteral nutrition (TPN). The resultant emulsion lacks the consistency of a cream, often described as 'body'. Recently, liposomes - vesicular structures prepared from membrane lipids - have found increasing favour as carriers of biologically active compounds. Frequently there is need to blend liposomes which may contain biologically active compounds into creams and emulsions, to increase the range of applications and extend their utility. However, it is now known to workers in liposome technology that relatively small amounts of synthetic surfactants that are necessary to form stable 0/W emulsions can perturb the liposome membrane and cause leakage and lysis. In the November 1992 issue of INFORM featuring LIPOSOMES, it is stated that: ''In liposomal formulations, care must be taken to avoid using surfactants and materials that can act as a co-solvent for the phospholipid or breakdown the bilayers Creams containing traditional phospholipid based liposomes are relatively difficult to formulate because the emulsion may separate or the liposome may breakdown when in contact with the oil phase it is important that companies extensively test their products to make sure the liposomes stay intact after formulation before making claims that a product contains liposomes. '' This is not yet generally recognised by manufacturers and presently there are claims to liposome-presence in commercial products that contain damaging synthetic emulsifying agents which cause destruction of liposomes. Liposome structure is usually confirmed through freeze-fracture electron microscopy and retention studies using specialised equipment and such facilities are not generally available. There is therefore an urgent need for a system of emulsification to form creams that could be blended with liposomes to obtain a liposome-containing cream in which the presence of liposomes can be verified. The present invention is in connection with emulsifyin systems which are compositions based essentially on membrane lipids, particularly phospholipids, in combination with at least one other natural amphiphile which is not an efficient primary emulsifier, ie does not form a stable emulsion by itself. It seeks to avoid the use of synthetic anionic, cationic and non-ionic surfactants with high or low HLB values to produce stable emulsions and creams, particularly of the oil-in-water type. The compositions are ideally suited for forming liposome-containing creams and emulsions. It is a further advantage of the system that relatively small proportions of phospholipids are required to obtain stable emulsions without recourse to excessive energy input. The invention results from the unexpected discovery that combinations of membrane lipid and at least one amphiphile which is not a primary emulsifier (high HLB) can form stable dispersions of oil droplets in water. In the prior art, membrane lipids are mostly combined with surfactants having high HLB values to obtain stable 0/W emulsions. In one aspect, the invention is a combination of: a) at least one membrane lipid, b) at least one natural amphiphile which is not a primary emulsifier, and c) optionally, a hydrophilic medium. These compositions are highly efficient emulsifying systems and are characterised by the absence of synthetic emulsifiers. In a second aspect, these combinations form stable 0/W creams with oils and oily substances. The dispersion of oil globules in the resultant cream is mostly below 5 u and is obtained without synthetic surfactants with high HLB values. In a third aspect, the invention also provides a stabl emulsion or a cream which may be blended with liposomes. The liposomes may be prepared by any method, eg, sonication extrusion, reverse phase evaporation, high shear mixing. However, it is preferred to incorporate liposomes which have high entrapped volumes i.e., 6 to 10 mls/gm lipid, prepared in accordance with the pro-liposome method described in EP 0158441. Examples of component a) are phospholipids such as phosphatidylcholine, phosphatidyl ethanolamine, phosphatidy inositol, phosphatidyl serine, phosphatidic acid, mixtures of phospholipids known commercially as lecithin and glycolipids eg. cerebrocides and gangliocides. The lipids may be saturated, partially saturated or unsaturated. Unsaturated lipids are prone to oxidation and it is often advantageous to use saturated lipids to give more stable compounds. The hydrocarbon region may be fully or partially saturated, depending on the degree of hydrogenation. This specification covers the use of unsaturated, partially saturated and fully saturated lipid obtained from plant or animal sources. The compositions comprise 5% to 95%, optimally between 10% to 50% of component a) which is preferably a lecithin. Preferably component b) is a fatty acid or alcohol of chain length C 12 to C 7» such as lauric, palmitic stearic and behenic acids, cetyl, stearyl and cetostearyl alcohols, or even longer chain compounds (i.e. '24 and above). Alternative amphipaths such as cholesterol, sitosterol and phytosterol may also be used in special circumstances. Combinations of fatty acid and alcohol, and chain lengths of between C^ anc ' ^22 are particularly preferred. The proportion of component b) is between 95% to 5%, preferably between 10% to 90%, ideally between 40% to 80% Conventionally, fatty acids and alcohols are used in combination with high HLB surfactants eg, cetomacrogol emulsifying wax. The reason they form efficient 0/W emulsifiers in combination with phospholipids which are poor emulsifiers may be due to formation of bilayered vesicular structures in the aqueous phase, some of which contain and segregate the oil droplets. When liposomes are added to the creams in one embodiment of the invention, some reorganising of the bilayers take place. The final proportion of phospholipid to fatty acid/alcohols in liposome-containing creams should be between 6:1 and 1:6, preferably not less than 1:3. The vesicular structures present in the creams prepared by this emulsifying system contain aqueous spaces and the entrapped volumes given by inulin inaccessible space determination range from about 20% to over 60% of the total water present in the creams. Optionally, the composition may also contain minor proportions, up to 25% of c), a hydrophilic medium comprising an aliphatic alcohol eg. ethanol, isopropyl alcohol, propylene glycol and glycerol, singly or in combination. The hydrophilic medium is not essential for emulsification. It mainly helps to dissolve the components. The emulsifying compositions disclosed herein give stable dispersions of oil globules. The oil may be a vegetable triglyceride, medium chain triglyceride, mono or polyhydric alcohol ester, branched chain alcohol, paraffin, squalane or any water immiscible substance that is conventionally referred to as an oil or waxy material. In some cases, an oil soluble biologically active compound can be dissolved in the oil. The ratio of emulsifying agent to oil is between 1:0.5 to 1:20, preferably between 1:1 to 1:10, ideally between 1:2 to 1:8. In forming oil-in-water dispersions, the oily phase comprising oil and emulsifiers should constitute between 5% and 60% of the total, whilst the continuous aqueous phase comprises from 40% to 95%. Above approximate 50% of oil, phase inversion could lead to a water-in-oil system. In practice, a number of factors have to be optimised to obtain the most stable dispersion. Variables such as membrane lipid and its concentration, fatty acid/alcohol mixture, ratio of emulsifier to oil, type of oil, level of oil, have all to be taken into account. By optimising the parameters, stable 0/W and in some cases W/0 dispersions can be obtained without requiring synthetic surfactants. Furthermore, the resultant creams are carriers of liposomes with or without biologically active compounds. These may be present in the oil globules the continuous aqueous phase, or entrapped in the liposomes Stability and quality of the creams can be assessed by observing the rate of creaming or phase separation after storage and or centrifugation at medium speeds (2000 to 5000 rpm). Stable preparations should show minimum creaming and no phase separation. Assessment of compatibility between the cream and liposomes was carried out as follows. Liposome integrity and structure were determined by means of inulin inaccessible space measurements and freeze fracture electron microscopy. Entrapped volume was determined by adding a precise amount of labelled inulin to a known suspension of liposome containing cream, followed by centrifugation at 100000 g to separate the liposomes from the cream. If the liposomes were intact, the entrapped aqueous space should be impermeable to inulin. Therefore, the concentration of labelled inulin recovered in the supernatant after allowance for the known volume of the emulsified oil present in the cream gave a measure of the internal volume. Liposome structure was further confirmed by means of freeze fracture electron microscopy through identification of bilayers across the fracture plane. The following examples describe the invention in greater detail. 1 to 4 are typical examples of emulsifying systems disclosed in this specification. Formulations 5 to 8 are stable creams and emulsions which contain varying proportions of an oil stabilised with the system disclosed and not relying on synthetic emulsifiers. Example 9 is a typical formulation of a liposome-containing cream with added liposomes, according to the invention. EMULSIFYING COMPOSITIONS Example 1 Hydrogenated soya bean lecithin 50% Cetyl alcohol 50% The 2 components were co-dissolved at 80 to 85 C to obtain a uniform mixture. This mixture set to a hard wax at room temperature. The composition may be used as such or powdered . Example 2 Hydrogenated soya bean lecithin 20% Palmitic acid 20% Cetyl alcohol 60% The 3 components were melted at 80 to 85 C to obtain a homogeneous emulsifying composition, which is a hard wax at room temperature. As in example 1, the composition may be pulverised or spray congealed into small droplets or free flowing powders. The hydrogenated lecithin can be replaced with unsaturated or partially saturated lecithin. Example 3 Hydrogenated soya bean lecithin 15% Laurie acid 15% Glycerol 15% Cetostearyl alcohol 55% The 4 components were heated to about 80 C until a uniform composition was obtained, solidifying to a waxy solid at room temperature. Example 4 Hydrogenated soya bean lecithin 15% Palmitic acid 15% Ethanol 10% Glycerol 15% Cetyl alcohol 45% The solids were dissolved in the mixture of ethanol and glycerol at 65 to 70 C, in a covered container to prevent loss of alcohol. A soft waxy mass formed on cooling. In the above examples, the saturated phospholipids can be replaced by unsaturated or partially saturated lipids. 0/W CREAMS Examples 5,6,7 & 8 10% 20% 30% 40% Emulsifying composition 5 5 Oil 10 20 Distilled water 85 75 The examples are typical formulations. The emulsifying base was prepared according to Example 2. In each case , it was melted in the oil at about 65 to 75 C, depending on the oil. Distilled water at a similar temperature was gradually added with stirring. It is to be understood that this specification also covers creams that are prepared by simply incorporating the components typically disclosed in examples 1 to 4 separately. It is only necessary to have in the finished cream preparation the appropriate phospholipids and fatty acids/alcohols in the correct proportions. The resultant creams can be homogenised using eg. a high speed stirrer, colloid mill, or any suitable homogeniser. Smooth, structured 0/W creams were obtained on cooling. Examples 5 to 8 may also be prepared with any of the other emulsifiers given in Examples 1 to 4. The proportion of lipid to oil and the level of oil can be varied up or down to obtain lotions or full-bodied creams. However, levels of oil above 40% tend to give rise to W/0 systems. The type of oil used could affect the viscosity and rheology of the final product, and therefore the proportion of emulsifier may have to be adjusted to give a cream of the required consistency. Blends of oils can be used. Lipophilic compounds eg. cholesterol & phytosterol may also be included in the formulations to modify the physical properties without affecting stability. Biologically active lipophilic compounds may additionally be dissolved in the oil. The creams according to this invention are characterised by the absence of synthetic emulsifiers. It should be noted that although it is neither necessary nor preferred, in some cases minor proportions of these substances can be included to modify the rheology of the creams. Viscosity improving gums and thickeners conventionally included in creams may also be added in small amounts, usually not more than 1%. LIPOSOME CREAMS Example 9 Cream (Examples 5 to 9) 60% Liposome suspension (with 50% entrapped volume) 40% The cream was prepared in accordance with Example 5 to 9. The liposome suspension, with or without a biologically active compound was prepared using Lucas Meyer's PR0-LIP0, pro-liposome composition. The liposome suspension was blended in with the cream with simple stirring to obtain a liposome cream. Alternatively, a pro-liposome composition may be added, so that conversion to liposomes occurs in situ in the continuous phase of the cream. In any event, it is importan that the lipid to fatty acid/alcohol ratio in the liposome containing cream is between 6:1 and 1:6, preferably not less than 1 part of lipid to 3 parts of fatty acid/alcohol. The oil content should preferably be between 10% to 20% of the total. Electron micrographs of the liposome pellet separated from a liposome cream is shown in Fig 1. It should be noted that liposome containing creams may also be formed in situ by; i. Dispersing 5 to 10 parts of a composition shown in examples 1 to 4 in 60 to 90 parts of water to obtain an intermediate oil-free preparation using a suitable production apparatus with mixing and heating facilities, ii. Adding the pro-liposome or liposome component (Example 9), preservatives and perfumes to make up 100 parts. iii. Packing into smaller containers for use by the end users. iv. Applying the composition contained in (iii) to the skin, mopping up (emulsifying) oily secretions and grease by rubbing, and at the same time forming a cream in situ, v. Optionally, rinsing off with water when further emulsification and rearrangement of the bilayers occur leaving liposomes on the skin surface. This specification describes emulsifying systems containing membrane lipids and natural amphiphiles and the resultant creams prepared without the aid of synthetic emulsifying agents. In one embodiment, it discloses emulsifying compositions comprising at least one membrane lipid together with at least one other natural amphiphile which is not a primary emulsifier. In a second embodiment, it relates to preparations of dispersed oil droplets in water, containing natural amphiphiles and not requiring synthetic emulsifiers to form stable emulsions and creams. In a further embodiment, it is a liposome-containing cream prepared with an emulsifying system comprising membrane lipids and fatty acids/alcohols, to which liposome or liposome forming pro-liposome compositions are added.

Claims: CLAIMS 1. An emulsifier composition which comprises:- a) at least one membrane lipid, b) at least one natural amphiphile which is not a primary emulsifier, and, optionally, c) a hydrophilic medium. 2. A composition as claimed in claim 1, wherein the membrane lipid is a phospholipid. 3. A composition as claimed in claim 1 or claim 2, wherein the natural amphiphile component comprises a C12 to C22 fatty acid or alcohol. 4. A composition as claimed in claim 1 or claim 2, wherein the natural amphiphile component comprises a mixture of C 12 to C22 fatty acids and alcohols. 5. A composition as claimed in any of the preceding claims, wherein the hydrophilic medium comprises one or more aliphatic alcohols. 6 - A composition as claimed in any of the preceding claims, which comprises a) from 10 to 50% by weight of at least one membrane lipid and b) from 90 to 50% by weight of at least one natural amphiphile. 7. A composition as claimed in any of the preceding claims, wherein the hydrophilic medium of component c) is present in an amount of up to 25% by weight. 8. An oil-in-water emulsion or dispersion which includes:- a) at least one membrane lipid, and b) at least one natural amphiphile which is not a primary emulsifier, and from which synthetic surfactants or emulsifiers are substantially absent, the mean diameter of the oil droplets or globules in the emulsion or dispersion being within the range of from 1μ to 5μ. 9. An oil-in-water emulsion or dispersion as claimed in claim 8, comprising bilayered structures segregating oil droplets and having entrapped volumes of at least about 20% of the total aqueous phase. 10. A method of forming an oil-in-water emulsion or dispersion that involves adding oil to an emulsifier composition which comprises :- a) at least one membrane lipid, b) at least one natural amphiphile which is not primary emulsifier, and, optionally, c) a hydrophilic medium, and dispersing the resulting mixture in an aqueous medium so as to form said emulsion or dispersion. 11. A method of forming an oil-in-water cream that involves adding oil to, or adding to oil, a composition which comprises:- a) at least one membrane lipid, b) at least one natural amphiphile which is not a primary emulsifier, c) an aqueous phase, and, optionally, d) a hydrophilic medium, so as to form the said oil-in-water cream. 12. A preparation in the form of a cream that is based on an oil-in-water emulsion or dispersion and which includes :- a) at least one membrane lipid, and b) at least one natural amphiphile which is not a primary emulsifier, and, optionally, lipid vesicles or liposomes. 13. A preparation as claimed in claim 12, wherein there are present one or more biologically active compounds. 14. A preparation as claimed in claim 13, wherein the one or more biologically active compounds are present in the oil globules and/or the continuous aqueous phase and/or are entrapped within the lipid vesicles or liposomes. 15. A method of producing a preparation in the form of a cream containing lipid vesicles or liposomes, which involves blending an oil-in-water emulsion or dispersion as claimed in claim 8 or claim 9 together with lipid vesicles or liposomes, or precursor components thereof, and, optionally, one or more biologically active compounds. 16. A method as claimed in claim 15, wherein the one or more biologically active compounds are entrapped within the lipid vesicles or liposomes.

Inventors: LEIGH STEVEN, LEIGH, STEVEN
Applicants: LEIGH STEVEN, PHARES PHARMA HOLLAND, LEIGH, STEVEN, PHARES PHARMACEUTICAL HOLLAND B.V.
Application year: 1993
Main classification: A61K9
IPC codes: A61K8, A61K9, A61K47, A61Q19