Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Cosmetic – antiperspirant – dentifrice
Reexamination Certificate
2000-09-06
2002-01-29
Dudash, Diana (Department: 1619)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Cosmetic, antiperspirant, dentifrice
C424S450000, C424S059000, C424S062000, C514S474000, C514S844000, C514S002600, C264S004100
Reexamination Certificate
active
06342238
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organogel containing an oxidation-sensitive hydrophilic compound, i.e., a composition in the form of an emulsion comprising an oily phase which is dispersed, with the aid of a specific surfactant system, in a glycerol phase containing this hydrophilic compound.
2. Description of the Background
It is known to introduce hydrophilic active agents into cosmetic and/or dermatological compositions in order to provide specific skin treatments.
For example, ascorbic acid (or vitamin C) is known to stimulate the synthesis of connective tissue and in particular of collagen, to reinforce the defenses of skin tissue against external attacking factors such as ultraviolet radiation and pollution, to compensate for vitamin E deficiency in the skin, to depigment the skin and to have a free-radical-scavenging function. These last two properties make vitamin C an excellent candidate as a cosmetic or dermatological active agent for combating or preventing ageing of the skin.
In addition, it is also known to introduce enzymes into cosmetic compositions, and in particular proteases and lipases, which are used for their proteolytic and lipolytic properties. These enzymes are desired in the cosmetics field for their smoothing and cleansing power and for their ability to remove dead cells from the skin.
Unfortunately, certain active agents, and in particular those mentioned above, are unstable on account of their sensitivity to external factors such as light, heat or the presence of oxygen either from the air or contained in water. Thus, ascorbic acid degrades over time in aqueous solutions, this also occurring under anaerobic conditions, in which it is liable to undergo a sequence of hydrolysis and oxidation reactions depending in particular on the pH of the composition and on the presence of metal ions acting as catalysts. This degradation is even faster under aerobic conditions.
This instability runs counter to the desired efficacy and can, furthermore, be a factor which users find unpleasant, for example when the instability of the active agent results in changes in the color and/or odor of the composition containing these agents.
Thus, various means have been envisaged to stabilize these active agents. For example, when the active agent comprises a reactive site, in particular in the case of ascorbic acid, one of the means for stabilizing it consists, for example, in blocking this site by esterification in particular with phosphate derivatives and in using these derivatives instead of the free active agent. Unfortunately, these derivatives are often less effective than the free active agent.
It has also been envisaged to use precursors of such active agents, such as ascorbic acid saccharide esters which, after application to the skin, are cleaved by the enzymes of the skin and then release the free active agent. However, the use of such derivatives does not always allow the active agent to be released rapidly or in sufficient amount at the surface of the skin.
It thus remains desirable to be able to use these active agents in their free, chemically unmodified active form. However, given the abovementioned problems of instability, the formulation of these active agents imposes very considerable constraints. It is thus necessary to formulate the ascorbic acid without heating, under an inert atmosphere and, above all, to store the products obtained in fully leaktight packaging.
A support, known as a hydrogel, comprises an oily phase which is dispersed, with the aid of a specific surfactant system, in a glycerol phase comprising an oxidation-sensitive hydrophilic compound, is capable of maintaining the activity of this active agent which is sensitive to oxygen in the air and/or in water, and thus of preventing its degradation.
The term “organogel” was initially used to describe a specific concept of gelation, by a gelatin solution, of a water-in-oil inverse microemulsion (see Luisi et al. Colloid & Polymer Science, 1990, vol. 268, p. 356-374). The term has recently been extended to gelled systems comprising two immiscible phases (water in oil) stabilized in lecithin enriched with phosphatidylcholine (referred to hereinbelow as PC) and usually hydrogenated (see Williman et al. Journal of Pharmaceutical Sciences, 1992, vol. 81, p. 871-874, and Schchipunov et al., Colloid Journal, 1995, vol. 57, p. 556-560). These emulsions have a lamellar phase and are in the form of gels even in the absence of gelling agents, hence the name organogels which denotes this type of emulsion irrespective of the orientation of the emulsion (W/O or O/W).
Thus, U.S. Pat. No. 5,639,740 discloses a lecithin organogel in the form of an oil-in-water emulsion, which is intended to promote the penetration of active agents such as salicylic acid, ceramides and &agr;-hydroxy acids.
Similar emulsions have since been developed, in which the water is replaced with polygls, giving rise to the formation of oil-in-glycol emulsions, stabilized with hydrogenated lecithin. For various reasons, but in particular for reasons of cost, attempts have been made to replace the PC-enriched hydrogenated lecithin with other compounds in oil-in-polyol emulsions.
Thus, U.S. Pat. No. 5,587,149 describes emulsions comprising a first phase based on polyethylene glycol, optionally also comprising glycerol and/or water and in which is dissolved ascorbic acid, and a second phase based on silicone oil, liquid paraffins and/or plant oils. The emulsion also comprises a dispersant which may be a silicone surfactant or a polysorbate 20 or 80. Under certain conditions, polysorbate 80 is capable of forming lamellar phases. However, given the low melting point of this surfactant (<0° C.), these lamellar phases lack rigidity and result in a certain level of instability of the emulsion. In addition, stability of ascorbic acid is ensured only by the encapsulation of this emulsion in a gelatin capsule.
There is thus still a need for a composition in which oxidation-sensitive hydrophilic cosmetic active agents would conserve all their properties and thus their efficacy over time, and also achieving this under aerobic conditions, so as to reduce the formulation and packaging constraints on products containing these active agents and thus their cost price.
SUMMARY OF THE INVENTION
The Inventors have now discovered, unexpectedly, that a support, an organogel, comprising an oily phase which is dispersed, with the aid of a specific surfactant system, in a glycerol phase comprising an oxidation-sensitive hydrophilic compound, is capable of maintaining the activity of this active agent which is sensitive-to oxygen in the air and/or in water, and thus of preventing its degradation.
The Inventors have now discovered, surprisingly, that organogels of the oil-in-glycerol type emulsified with surfactants having a melting point of greater than or equal to 35° C. allow effective stabilization, which is also achieved in an aerobic medium, of ascorbic acid and other readily oxidizable hydrophilic compounds. These organogels thus support the introduction of relatively large amounts of water, e.g., up to 20% without harming the stability of the active agents they contain, thus allowing them to be formulated in the form of non-greasy fluids. However, they retain a water activity which is low enough to allow them to be formulated without preservative agents, thus making them particularly suitable for sensitive skin.
The present invention thus relates to a composition in the form of an emulsion comprising an oily phase which is dispersed, with the aid of a surfactant system, in a glycerol phase containing an oxidation-sensitive hydrophilic compound, characterized in that the surfactant system contains at least one surfactant capable of forming a lamellar phase on contact with the glycerol phase and having a melting point of greater than or equal to 35° C.
Accordingly, the present invention provides an emulsion, comprising:
a glycerol phase containing an oxidation-sensitive hydrophilic compound;
an oi
Legret Sylvie
Simonnet Jean-Thierry
Dudash Diana
L'Oreal
Yu Gina C
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