the instant invention involves , in a preferred embodiment , the administration of an oral suspension , containing pyrimethamine and a sulfonamide , such as sulfadiazine , designed to overcome the shortcomings of currently available treatments of epm and to provide a more effective drug combination for horses and other equines infected with an organism of the genus sarcocystis . as previously mentioned , pyrimethamine may be given in a preferred dose of about 1 mg / kg equine with a sulfonamide in a dose of about 15 to 30 mg / kg . equine , preferably 20 mg / kg . it has been found that a 30 ml dose of an oral suspension ( such as that described , below ) daily on an empty stomach will provide adequate dosing for the treatment of epm that neither pyrimethamine nor sulfadiazine can treat alone . since epm is a protozoal infection of the central nervous system , the appropriate drug combination must penetrate to the cns and treat the protozoal infection . in general , the composition to be administered may comprise about 10 - 20 gm pyrimethamine and about 150 - 600 gm sulfonamide , preferably 200 - 400 gm sulfonamide , per liter of composition . the liquid or solid composition may be prepared in unit dosage form depending upon the minimum size of the equine . such unit dosage forms comprise a relative weight ratio of pyrimethamine to sulfonamide in a range of about 1 : 15 to about 1 : 30 , preferably about 1 : 20 . typically , the unit dosage forms contain about 0 . 3 - 0 . 7 gm of pyrimethamine and about 6 - 14 gm of sulfonamide , most preferably 0 . 5 gm pyrimethamine and about 10 gm sulfonamide . the present invention has been found to successfully inhibit the growth of the organism sarcocystis neurona in equines , such as mules , ponies and horses . it has been observed that the preferred sulfonamide , sulfadiazine , has resulted in better than about a 70 % rate of efficacy . in fact , the effectiveness of the present compositions and methods appears to be at least about 80 % or 90 % of the cases , and probably even higher . in line with the foregoing , it is within the contemplation of the present invention to employ compositions utilizing one or more sulfonamides and / or pyrimidine derivative in treating epm . examples of other suitable pyrimidine derivatives include , but are not limited to , 2 , 4 - diamino - 5 - benzylpyrimidines substituted in the phenyl ring , such as 2 , 4 , diamino - 5 -( 3 , 5 - dimethoxy - 4 - methoxyethoxybenzy )- pyrimidine ( tetroxoprim ) and 2 , 4 - diamino - 5 -( 3 , 5 , dimethoxy - 4 - methylthiobenzyl )- pyrimidine ( metioprim ). still other useful pyrimidines may be 2 , 4 - diamino - 5 -( 4 - bromo - 3 , 5 - dimethoxybenzyl )- pyrimidine , 2 , 4 - diamino - 5 -[ 3 , 5 - diathoxy - 4 -( pyrrol - 1 - yl )- benzyl ]- pyrimidine , 2 , 4 - diamino - 5 -( 3 , 5 - dimethoxy - 4 - dimethylaminobenzyl )- pyrimidine , 2 , 4 - diamino - 5 -( 3 , 4 - dimethoxybenzyl )- pyrimidine ( diaveridine ) and 2 , 4 - diamino - 5 -( 2 - methyl - 4 , 5 - dimethoxybenzyl )- pyrimidine . in a similar manner , numerous sulfonamides may be suitably utilized in the present invention , including those previously disclosed in u . s . pat . no . 5 , 273 , 970 , whose disclosure is incorporated in its entirety by reference herein . in particular , those sulfonamides having a dinitrogen aromatic ring are especially useful , such as acetyl sulfamethoxypyrazine , n - 2 - formylsulfisomidine , salazosulfadimidine , sulfachlorpyridazine , sulfadimethoxine , sulfadoxine , sulfalene , sulfamerazine , sulfameter , sulfamethazine , sulfamethomidine , sulfamethoxypyridazine , sulfaperine , sulfaphenazole , sulfapyrazine and sulfisomidine . still other sulfonamides known to be useful in veterinary applications can be adventitiously used , including phthalylsulfacetamide , phthalylsulfathiazole , succinylsulfathiazole , sulfabenzamide , sulfacetamide , sulfaethidole , sulfaguanidine , sulfamethizole , sulfamethoxypyridazine , sulfanilamide , sulfanilamidomethanesulfonic acid triethanolamine salt , sulfanitran , sulfapyridine , sulfathiazole and sulfisoxazole . the above - mentioned sulfonamides may be used in place of the preferred sulfadiazine or in addition thereto . the present compositions may be administered by routes well known to those skilled in the veterinary and formulation sciences . therefore , although the pyrimethamine and sulfadiazine , for example , are conveniently administered orally , depending on the circumstances , the pharmaceutical composition may be administered parentally , topically , intramucosally ( e . g ., intravaginally ), or by other routes known to those skilled in this art . compositions suitable for oral administration , in addition to suspensions , include tablets , capsules , gels , pastes , boluses , or preparations in the form of powders , granules , or pellets . preferred orally administered compositions - include suspensions and tablets . alternatively , the composition may be administered parenterally by sub - cutaneous , intramuscular , intraperitoneal , or intravenous injection , or by implantation . the composition can be given as an intramammary injection whereby a suspension or solution is introduced into the udder . pharmaceutically acceptable carriers present in the compositions of the present invention are materials recommended for the purpose of administering the medicament . these may be liquid , solid , or gaseous materials , which are otherwise inert or medically acceptable and are compatible with the active ingredients . the same applies for any added excipients . for oral administration , fine powders or granules will contain diluting agents , for example , calcium carbonate , calcium phosphate , mineral carriers , etc ., disbursing and / or surface active agents , for example , polysorbates , and may be presented in a drench , in water or in a syrup , in a bolus , paste , or in capsules or sachets in the dry state or in a non - aqueous suspension , or in a suspension in water or syrup . where desirable or necessary , preserving , suspending , thickening or emulsifying agents can be included . if intended for oral use , a bolus will be provided with retention means to inhibit regurgitation . for example , it may be weighed with a heavy density materials such as iron or tungsten or the like or may be retained by its shape , for example , by wings which spring after administration . boluses may contain disintegrating agents such as maize starch or calcium or sodium methylcelluloses , hydroxypropylmethylcellulose , guar based vegetable gums , sodium alginates or sodium starch glycolates ; granulating or binding agents , such as starch in the form of mucilage , starch derivatives , such as methylcellulose , calcium stearate , talc , gelatin or polyvinylpyrrolidone ; and / or lubricating agents , such as magnesium stearate or stearic acid . other compounds which may be included are for example , medically inert ingredients , e . g . solid and liquid diluents , such as starch or calcium phosphate for tablets , boluses or capsules ; olive oil or ethyl oleate for soft capsules ; and water or vegetable oil for suspensions or emulsions ; lubricating agents such as talc or magnesium stearate ; gelling agents such as colloidal clays ; thickening agents such as gum tragacanth or sodium alginate ; dedusting agents such as liquid paraffin , fixed oils and surfactants and other therapeutically acceptable accessory ingredients , such as humectants , preservatives , buffers , and anti - oxidants , which are useful as carriers in such formulations . when desired , other medicaments and / or nutrients , such as vitamins or the like , unless contraindicated , may also be included . it is also to be understood that while the preferred formulation is administered once a day , it may be given two or more times a day , depending on the circumstances . it should be understood that while it is convenient to administer the pyrimidine and sulfonamide concurrently , they can be given separately with equal efficacy . however , the other optimum conditions , such as the administration of the drug combination on an empty , preferably at least about one hour before the horse is fed should be observed . a further appreciation of the invention may be gleaned from the following specific examples . these specific examples are provided for illustration only and are not to be regarded as restricting the invention in any way . veterinary compositions effective for the general treatment of epm are provided , below , in the form of an oral suspension . the amounts of each component are based on a liquid suspension having a total volume of about 1 liter . as mentioned above , a useful dosage , e . g ., for a 1 , 000 pound horse infected with sarcocystis neurona ( as evidenced by the presence of the protozoan in a sample from the subject &# 39 ; s cerebrospinal fluid ) is about 30 ml of the suspension , once a day , given on an empty stomach in the morning . preferably , the composition does not contain substantial amounts of natural sugars . most preferably , the composition is substantially free of natural sugars as some of the sulfonamides may be sensitive to the presence of naturally occurring sugars . optionally , folic acid may also be administered to the subject , either concurrently or at a separate time . typically , the subject may receive about 40 mg of folic acid per 500 - to 1000 - pound equine . a stepwise procedure for the preparation of the oral suspension is provided below : 1 . weigh out the powders and triturate from the smallest quantity of powder to the largest quantity of powder , so that all powders are evenly mixed together . 2 . in a separate container mix all the liquids and add half the volume of water needed for one liter . 3 . mix together the materials prepared in steps 1 and 2 in a large container and q . s . to one 1 , 000 liter with the remaining water . 4 . beat the suspension on a micronizer for five minutes , being certain said suspension is evenly mixed . 5 . package the final product and refrigerate when not in use . the suspension should be shaken well prior to use . as further illustrations of the composition of the invention , the following descriptions of suitable alternative formulations are provided . the preceding two formulations provide powders , which can be conveniently divided into individual packets , each containing 30 g of the inventive composition . only the preferred embodiments of the invention and but a few examples of its versatility are shown and described in the present disclosure . it is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes and modifications within the scope of the inventive concept as expressed herein . for example , the active ingredients of the contemplated veterinary composition can simply be mixed in an aqueous medium to provide a mixture that can be administered to the affected equine , usually by mouth .
the present invention relates to compositions and methods for treating equines , such as horses , afflicted with equine protozoal myeloencephalitis or epm . the therapeutic compositions comprise a combination of pyrimethamine and a sulfonamide , preferably , sulfadiazine , in the absence of known therapeutic amounts of trimethoprim .