Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Reexamination Certificate
2000-10-23
2002-07-16
Dodson, Shelley A. (Department: 1616)
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
C424S060000, C424S400000, C424S401000
Reexamination Certificate
active
06419908
ABSTRACT:
CROSS-REFERENCE TO PRIORITY APPLICATION
This application claims priority under 35 U.S.C. §119 of FR-99/13222, filed Oct. 22, 1999, hereby expressly incorporated by reference.
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to improving the stability of at least one UV-photoprotecting dibenzoylmethane compound with respect to UV-radiation, by formulating such dibenzoylmethane compound with an effective UV-photostabilizing amount of at least one insoluble organic UV-screening agent in the micronized form or state, the mean size of the particles of which ranging from 0.01 to 2 &mgr;m.
The present invention also relates to formulating an insoluble organic UV-screening agent in the micronized form, the mean size of the particles of which ranging from 0.01 to 2 &mgr;m, into cosmetic/dermatological compositions comprising at least one UV-photoprotecting dibenzoylmethane compound, wherein the photostability of said at least one dibenzoylmethane compound with respect to UV radiation is conspicuously enhanced.
2. Description of the Prior Art
It is known to this art that light radiation of wavelengths of from 280 nm to 400 nm permits tanning of the human epidermis, and that radiation of wavelengths more particularly of from 280 nm to 320 nm, i.e., UV-B radiation, causes erythemas and skin burns which can hinder the development of natural tanning.
For these reasons as well as for aesthetic reasons, there is a constant demand to control this natural tanning such as to thereby control the color of the skin; it is therefore advisable to screen out UV-B radiation.
It is also known to this art that UV-A radiation of wavelengths of from 320 nm to 400 nm, which promotes tanning of the skin, also is capable of causing damage thereto, in particular in the case of a sensitive skin or of a skin continually exposed to solar radiation. UV-A radiation, causes, in particular, loss of elasticity of the skin and the appearance of wrinkles which promotes premature skin aging. UV-A radiation promotes the onset of the erythema reaction or amplifies this reaction in certain individuals and may even be responsible for phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons such as the preservation of the natural elasticity of the skin for example, an increasing number of individuals seek to control the effect of UV-A radiation on their skin. It is therefore desirable to also screen out UV-A radiation.
In this respect, a particularly advantageous class of UV-A screening agents is that of the dibenzoylmethane compounds, and in particular 4-(tert-butyl)-4′-methoxydibenzoylmethane; this is because these derivatives or compounds exhibit a high intrinsic absorption power. Such dibenzoylmethane compounds, which are now well known per se as screening agents active in the UV-A range, are described, in particular, in FR-A-2,326,405 and FR-A-2,440,933 and in EP-A-0,114,607. Too, 4-(tert-butyl)-4′-methoxydibenzoylmethane is currently commercially available under the trademark “Parsol 1789” by Hoffmann Laroche.
Unfortunately, the dibenzoylmethane derivatives are compounds which are relatively sensitive to ultraviolet radiation (in particular UV-A radiation), namely, more specifically, they have an unfortunate tendency to decompose more or less rapidly under the effect or influence of UV-A radiation. Thus, this substantial lack of photochemical stability of dibenzoylmethane compounds under the influence of ultraviolet radiation, to which they are naturally intended to be subjected or exposed, does not permit a guarantee of constant protection during prolonged exposure to the sun, such that repeated applications at regular and frequent intervals of time are necessary in order to provide the user with effective protection of the skin against UV rays.
Thus, serious need continues to exist for the effective photostabilization of dibenzoylmethane compounds with respect to UV radiation.
SUMMARY OF THE INVENTION
It has now surprisingly and unexpectedly been determined that compounding/formulating the above-mentioned dibenzoylmethane compounds with an effective UV-stabilizing amount of an insoluble organic UV-screening agent in the micronized form, substantially and notably enhanced the photochemical stability (or photostability) of such dibenzoylmethane derivatives.
Briefly, the present invention features the stabilization of dibenzoylmethane compounds with respect of UV radiation (wavelengths ranging from 280 nm to 400 nm, approximately), in particular solar radiation, by formulating said dibenzoylmethane compounds with an effective UV-photostabilizing amount of at least one insoluble organic UV screening agent in the micronized form.
DETAILED DESCRIPTION OF BEST MODE AND SPECIFIC/PREFERRED EMBODIMENTS OF THE INVENTION
More particularly, according to the present invention, by the term “insoluble organic UV-screening agent” are intended organic UV-screening agents having a solubility in water at 25° C. of less than 0.1% by weight and a solubility in liquid paraffin at 25° C. of less than 1% by weight.
By the term “effective UV-photostabilizing amount of insoluble organic UV-screening agent” is intended an amount sufficient to provide a notable and significant improvement in the UV-photostability of the dibenzoylmethane compound(s) comprising UV-photoprotective cosmetic compositions. This minimum amount of UV-photostabilizing agent to be formulated, which can vary depending on the nature of the cosmetically acceptable vehicle, diluent or carrier included in the composition, can be determined without any difficulty via a conventional test for the measurement of photostability, such as that given in the examples below.
This invention thus also features formulating an insoluble organic UV-screening agent into a cosmetic/dermatological composition comprising at least one dibenzoylmethane compound for the purpose of improving the stability with respect to UV-radiation of any such dibenzoylmethane compound present.
The insoluble organic screening agents according to the invention are provided in micronized form. The mean or average size of the particles ranges from 0.01 &mgr;m to 2 &mgr;m and more preferably from 0.02 &mgr;m to 1.5 &mgr;m and even more preferably from 0.03 &mgr;m to 1.0 &mgr;m.
The insoluble organic screening agents according to the invention may be provided in the desired particulate form by any appropriate means such as, in particular, grinding in the dry state or in solvent medium, sieving, spray-drying, micronization or spraying.
The insoluble organic screening agents according to the invention in micronized form may, in particular, be provided by a method of grinding an insoluble UV-screening agent in the form of particles having a coarse size in the presence of an appropriate surfactant which makes it possible to enhance the dispersion of the particles thus obtained in the cosmetic formulations.
One embodiment of a method of micronization of insoluble organic screening agents is described in GB-A-2,303,549 and EP-A-893119 incorporated by reference herein. The grinding apparatus according to the invention may be a jet mill, a ball mill, a vibratory mill or a hammer mill and preferably a mill featuring high-speed agitation or an impact mill and more particularly a rotating ball mill, a vibratory mill, a tube mill or a rod mill.
According to this particular methodology, the alkyl polyglucosides having the structure C
n
H
2n−1
O(C
6
H
10
O
5
)
x
H in which n is an integer from 8 to 16 and x is the average degree of polymerization of the structural unit (C
6
H
10
O
5
) and ranges from 1.4 to 1.6, are included as surfactants for the grinding of the screening agents. They are advantageously selected from among C
1
-C
12
esters of a compound having the structure C
n
H
2n+1
O(C
6
H
10
O
5
)
x
H and more precisely an ester prepared by reacting a C
1
-C
12
carboxylic acid such as formic, acetic, propionic, butyric, sulfosuccinic, citric or tartaric acid with one or more free OH functions on the glucoside unit (C
6
H
10
O
5
). Such
Candau Didier
Pisson Anne-Marie
Burns Doane Swecker & Mathis L.L.P.
Dodson Shelley A.
Societe L'Oreal
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