the active ingredients ( ie . imidazole antifungal compounds ) are known in the art , as taught in u . s . pat . no . 5 , 041 , 278 . such compounds can be employed in the powder compositions in amounts ranging from about 5 to about 0 . 5 percent by weight of the powder composition , preferably from about two to about one percent by weight , more preferably about one percent . mixtures of various imidazole antifungal compounds can be employed , generally in ratios ranging from four to one parts of a first imidazole antifungal compound ( ie . clotrimazole ) to one part of a second imidazole antifungal compound ( ie . miconazole ), generally in about equal parts . the term hydrophobic refers to the property of a substance that , upon its coating of uncoated talc , causes the surface of the coated talc to become substantially repellant to water . talc , also known as talcum , soapstone , steatite or french chalk , is a grayish - white , very fine , odorless , crystalline powder available from numerous manufacturers and fine chemical supply houses . chemically , talc is a finely divided native hydrous magnesium silicate . one of ordinary skill in the art will recognize that talc from different sources or even the same source can vary greatly with regard to morphology and surface properties , such as surface charge and surface area . the present invention has the advantage of providing imidazole powder compositions with consistent stability over a variety of talc sources . hydrophobic coatings which can modify the surface - active properties of talc and retard degradation of the imidazole compounds include waxes , tetrafluorethylene fluorocarbon polymers or silicone . the hydrophobic coatings are believed to minimize surface interactions of the imidazole antifungal compound and the talc by causing the surface of the talc to become more inert , ie . by surface modification . suitable waxes include natural waxes such as animal ( beeswax , lanolin , shellac wax , chinese insect wax ), vegetable ( carnauba , candelilla , bayberry , sugar cane ) or mineral ( fossil or earth waxes such as ozokertie , ceresin or montan or petroleum waxes such as paraffin , microcrystalline , slack or scale wax ). other suitable waxes include synthetic waxes , such as ethylenic polymers and polyol ether - esters (&# 34 ; carbowax ,&# 34 ; sorbitol ), such as chlorinated naphthalenes (&# 34 ; halowax &# 34 ;) and such as the hydrocarbon type waxes via fischer - tropsch synthesis . preferably the wax is an ethanolamide of stearic acid . tetrafluoroethylene ( tfe ) fluorocarbon polymers , also known as teflon ® polymers can also be employed as a suitable hydrophobic coating . silicones represent any of a large group of siloxane polymers based on a structure consisting of alternate silicon and oxygen atoms with various organic radicals attached to the silicon , as described in g . hawley , the condensed chemical dictionary , 10th edition , van nostrand reinhold company , new york , n . y ., 1135 pages . the amount of hydrophobic coating present on the talc should be sufficient to minimize decomposition of the imidazole antifungal compound . based upon an accelerated stability test of one month at 50 ° c . or three months at 37 ° c ., this amount should be about 2 % or less . generally , the amount of hydrophobic coating in the powder composition can range from about 0 . 5 to about 5 percent (%) by weight , more preferably from about 0 . 5 to about 2 %, most preferably about 1 %. other diluents , such as starch , can be added to the powder composition to absorb moisture . such diluents can be employed in amounts ranging from about one to about 50 % by weight of the powder composition , preferably from about 5 to about 20 % by weight , more preferably from about 10 to about 20 % by weight of the composition . the uncoated talc can be coated with a hydrophobic coating by dry blending at elevated temperatures . alternatively , the uncoated talc can be coated with the hydrophobic coating by dissolving the hydrophobic coating in a suitable solvent such as an alcohol , ether , chlorinated hydrocarbon , alkane , mixtures thereof and the like , spraying the solvent containing the hydrophobic coating onto the uncoated talc and removing the organic solvent by conventional procedures such as evaporation , heating , distillation and the like to give talc coated with a hydrophobic coating . the talc coated with the hydrophobic coating can then be dry blended or sprayed with the imidazole antifungal compound to give the desired powder composition . a diluent such as starch can be added to the powder composition by dry blending the diluent with the powder composition . alternatively , the starch and the imidazole antifungal compound can be mixed together and the subsequent mixture can be dry blended with the talc coated with a hydrophobic coating to give the desired powder composition . the powder compositions of the present invention can be prepared in any inert mixing vessel made of suitably inert materials such as glass or stainless steel . alternatively , commercially available talc coated with a hydrophobic coating but which does not contain any of the imidazole active ingredients can be used . one preferred coated hydrophobic talc is supra - a smm of cyprus industrial minerals company , englewood , colo . supra - a smm is 200 mesh platy italian talc coated with 1 % monamid s ™. monamid s ™ contains stearamide monoethanolamine ( mea ), a hydrophobic coating . the talc in this product has a typical particle size which is about 70 microns diameter to about 0 . 4 microns , with a median particle size of about 15 microns diameter . the following example serves to illustrate some of the powder compositions and the manner by which they can be practised , but as such , should not be construed as limitations upon the overall scope of the same . effect of talc coated with a hydrophobic coating on the stability of clotrimazole mix clotrimazole with the same volume of talc and pass the mixture through a 60 mesh sieve . mix this mix with the remaining talc and pass it through a 30 mesh sieve . mix again . test for stability by exposing the talc mixture to a temperature of 50 ° c . for one month and analyze for clotrimazole using a validated method using high pressure chromatography ( hplc ). results are presented in table 1 . effect of talc coated with a hydrophobic coating with an added starch diluent on the stability of clotrimazole mix clotrimazole and starch and pass the mixture through a 60 mesh sieve . mix this mixture with talc and pass it through a 30 mesh sieve . mix again . test as in example 1 . results are presented in table 1 . table i______________________________________treatment loss of clotrimazole______________________________________uncoated talc 7 . 2 % wax coated talc 1 . 4 % wax coated talc + 0 . 8 % 10 % starch______________________________________ the data from table 1 indicate the surprising and unexpected results that clotrimazole is significantly more stable in powder compositions formulated with wax coated talc , or with wax coated talc plus starch , compared to talc having no coating ( ie . uncoated ).
a stable powder composition comprising an anti - fungal effective amount of an imidazole antifungal compound and talc coated with a hydrophobic coating is described . a method for stabilizing an imidazole antifungal compound in a talc composition is also described which comprises either using talc coated with a hydrophobic coating or coating talc with a hydrophobic coating , prior to adding the imidazole antifungal compound to the talc .