Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Reexamination Certificate
2000-02-28
2002-07-23
Dodson, Shelley A. (Department: 1616)
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
C424S060000, C424S400000, C424S401000, C514S241000
Reexamination Certificate
active
06423302
ABSTRACT:
The present invention relates to light protection formulations, in particular to cosmetic and dermatological light protection compositions.
The harmful effect of the ultraviolet part of sun radiation on the skin is generally known. While rays with a wavelength of less than 290 nm (the UV-C region) are absorbed by the ozone layer in the earth's atmosphere, rays in the region between 290 nm and 320 nm, the UV-B region, cause erythema, simple sunburn or even burns of greater or lesser severity.
A maximum erythema activity of sunlight is given as the narrower region around 308 nm.
Numerous compounds for protecting against UV-B radiation are known; these are derivatives of 3-benzylidenecamphor, 4-aminobenzoic acid, cinnamic acid, salicylic acid, benzophenone and also 2-phenylbenzimidazole.
It is also important to have available filter substances for the region between about 320 nm and about 400 nm, the UV-A region, since the rays of this region can also cause damage. For a long time it was incorrectly assumed that the long-wave UV-A radiation with a wavelength between 320 nm and 400 nm has only a negligible biological action and that, accordingly, the UV-B rays are responsible for most light-induced damage to human skin. However, in the meantime numerous studies have shown that UV-A radiation is much more harmful than UV-B radiation with regard to the triggering of photodynamic, specifically phototoxic, reactions and chronic changes in the skin. The harmful effect of UV-B radiation can also be intensified by UV-A radiation.
Thus, it has inter alia been found that even UV-A radiation, under quite normal everyday conditions, is sufficient to damage, within a short time, the collagen and elastin fibres, which are of essential importance for the structure and strength of the skin. This results in chronic light-induced changes in the skin—the skin “ages” prematurely. The clinical manifestation of light-aged skin includes, for example, wrinkles and lines, and also an irregular, furrowed relief. In addition, the areas affected by light-induced skin ageing can have irregular pigmentation. The formation of brown spots, keratoses and even carcinomas or malignant melanomas is also possible. Skin which has been prematurely aged as a result of everyday UV stress is further characterized by a lower activity of the Langerhans' cells and slight, chronic inflammation.
Approximately 90% of the ultraviolet radiation which reaches the earth consists of UV-A rays. Whilst the UV-B radiation varies widely depending on numerous factors (e.g. time of year and day or degree of latitude), the UV-A radiation remains relatively constant day after day irrespective of the time of year and day or geographical factors. Additionally, the majority of the UV-A radiation penetrates the living epidermis, whilst about 70% of the UV-B rays are held back by the horny layer.
Preventive protection against UV-A rays, for example by applying light protection filter substances in the form of a cosmetic or dermatological formulation to the skin, is therefore of fundamental importance.
Generally speaking, the light absorption behaviour of light protection filter substances is very well known and documented, not least because most industrialized countries have positive lists for the use of such substances, which impose very strict standards on the documentation. For the concentration of the substances in the finished formulations, the absorbance values can at best be a guide, since interaction with substances within the skin or with the surface of the skin itself may result in imponderables. In addition, it is usually difficult to estimate beforehand how uniformly and thickly the filter substance is distributed in and on the horny layer of the skin.
To test the UV-A protection performance, use is usually made of the IPD method (IPD≡immediate pigment darkening). Similarly to the determination of the light protection factor, this method gives a value which indicates how much longer the skin protected with the light protection composition can be irradiated with UV-A radiation until the pigmentation which occurs is the same as for the unprotected skin.
Another test method which has become established throughout Europe is the Australian Standard AS/NZS 2604:1997. Here, the absorption of the preparation in the UV-A region is measured. In order to satisfy the standard, the preparation must absorb at least 90% of the UV-A radiation in the region 320-360 nm.
The use concentration of known light protection filter substances which, in particular, also exhibit high filter action in the UV-A region is often limited by the very fact that they are combined with other substances which are in the form of solids. There are therefore certain formulation difficulties in achieving relatively high light protection factors or UV-A protection performance.
Since light protection filter substances are usually expensive and since some light protection filter substances are additionally difficult to incorporate in relatively high concentrations into cosmetic or dermatological preparations, an object of the invention was to obtain, in a simple and cost-effective manner, preparations which, despite having an unusually low concentration of conventional UV-A light protection filter substances, nevertheless achieve acceptable or even high UV-A protection performance.
UV radiation can, however, also lead to photochemical reactions, in which case the photochemical reaction products intervene in the skin's metabolism. Such photochemical reaction products are predominantly free-radical compounds, for example hydroxyl free radicals. Undefined free-radical photoproducts which form in the skin itself can also display uncontrolled secondary reactions because of their high reactivity. However, singlet oxygen, a non-free-radical excited state of the oxygen molecule, can also be formed during UV irradiation, as can short-lived epoxides and many others. Singlet oxygen, for example, differs from normal triplet oxygen (free-radical ground state) by virtue of its increased reactivity. However, excited, reactive (free-radical) triplet states of the oxygen molecule also exist.
In order to prevent these reactions, it is possible additionally to incorporate antioxidants and/or free-radical scavengers into the cosmetic or dermatological formulations.
Known and advantageous light protection filter substances are dibenzoylmethane derivatives, for example 5-isopropyidibenzoylmethane (CAS No. 63250-25-9), and also 4-(tert-butyl)4′-methoxydibenzoylmethane (CAS No. 70356-09-1). However, precisely because they are in combination with other substances which are in the form of solids, their use concentration is limited. There are therefore certain formulation difficulties in achieving relatively high light protection factors.
Another advantageous light protection filter substance is 4-methylbenzylidenecamphor. This is an extremely advantageous light protection filter substance, which is solid under normal conditions and is notable per se for good UV filter properties. However, precisely because of its combination with other substances which are in the form of solids, its use concentration too is limited. There are therefore certain formulation difficulties in achieving relatively high light protection factors here as well.
Another advantageous UV filter is 2,4-bis-{[4-(2-ethylhexyloxy)-2-hydroxy]phenyl}-6-(4-methoxyphenyl)-1,3,5-triazine, which is characterized by the following structure:
This UV filter substance is marketed by Ciba Specialty Chemicals Holding Inc. under the trade name Tinosorb® S and is characterized by good UV absorption properties.
The main disadvantage of 2,4-bis-{[4-(2-ethylhexyloxy)-2-hydroxy]phenyl}-6-(4-methoxyphenyl)-1,3,5-triazine is its poor solubility in lipids. Known solvents for this UV filter can dissolve a maximum of about 10% by weight of this filter, corresponding to about 1% by weight of dissolved, and thus active, UV filter substance in light protection preparations.
There are therefore
Gers-Barlag Heinrich
Müller Anja
Beiersdorf AG
Dodson Shelley A.
Norris & McLaughlin & Marcus
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