as mentioned above , the present invention is based on the unexpected finding that combined administration of a 5 - ht 2c receptor agonist and a 5 - ht 6 receptor antagonist reduces food intake more than either agonist or antagonist alone . such combined administration of a 5 - ht 2c receptor agonist and a 5 - ht 6 receptor antagonist may also offer several benefits , for instance in the treatment of obesity , as compared to treatment with either agonist or antagonist alone . firstly , the combined administration requires lower doses of each compound to yield similar or improved reduction of food intake than mono - therapy . secondly , the lower doses required by the combined administration may reduce the risk of adverse events . thirdly , the lower doses required by the combined administration may reduce the risk of tolerance development and abuse liability . fourthly , therapy based on two targets may increase the individual therapeutic efficacy relative to therapy based on one target . the risk of non - responsive efficacy ( non - responders ) may be reduced as well . the beneficial effects of the combined administration of this invention is useful not only for the modulation of eating behavior , and for treating over - weight and obesity , but may also be useful for the treatment of cns disorders such as , depression , mania , schizophreniform disorders , anxiety , memory disorders ( such as alzheimer &# 39 ; s disease ) migraine headache , drug addiction , convulsive disorders , personality disorders , post - traumatic stress syndrome , and sleep disorders as well as for treatment of urinary incontinence ( or more generally overactive bladder ), sexual dysfunctions , gastrointestinal disorders and glaucoma . the term “ 5 - ht 2c receptor agonist ” as used herein refers to a compound that causes activation of the serotonin 5 - ht 2c receptor . the 5 - ht 2c receptor agonist preferably has an affinity constant , k i , of less than 50 nm , preferably less than 20 nm , and an in vitro intrinsic activity , measured as intracellular ca 2 + levels , greater than 20 %, preferably greater than 50 %, relative to 5 - ht ( 1 μm ). the term “ 5 - ht 6 receptor antagonist ” as used herein refers to a compound that causes blockade of the serotonin 5 - ht 6 receptor mediated responses . the 5 - ht 6 receptor antagonist preferably has an affinity constant , k i , of less than 50 nm , preferably less than 20 nm , and an in vitro intrinsic activity , measured as intracellular camp levels , less than 50 %, preferably less than 20 %, relative to 5 - ht ( 1 μm ). in vitro assays that may be used for determining the affinity and the intrinsic activity , respectively , of 5 - ht 2c receptor agonists and 5 - ht 6 receptor antagonists are known in the art and are also given in the experimental part below , as are assays for determining affinity to 5 - ht 2a and 5 - ht 2b receptors . generally , the 5 - ht 2c receptor agonists and 5 - ht 6 receptor antagonists should be sufficiently selective not to cause any substantial adverse side effects . the terms “ selective ” and “ substantial ” in this context are , however , to be interpreted broadly , the meanings thereof being readily apparent to the skilled person . the 5 - ht 2c receptor agonist preferably has a selectivity for the 5 - ht 2c receptor of at least 5 , preferably at least 10 and more preferably at least 20 , relative to the 5 - ht 2a , 5 - ht 2b and 5 - ht 6 receptors , respectively ( measured as the affinity ratios 5 - ht 2a / 5 - ht 2c , 5 - ht 2b / 5 - ht 2c and 5 - ht 6 / 5 - ht 2c ). the 5 - ht 6 receptor antagonist preferably has a selectivity for the 5 - ht 6 receptor of at least 5 , preferably at least 10 and more preferably at least 20 , relative to the 5 - ht 2a , 5 - ht 2b and 5 - ht 2c receptors , respectively ( measured as the affinity ratios 5 - ht 2a / 5 - ht 6 , 5 - ht 2b / 5 - ht 6 and 5 - ht 2c / 5 - ht 6 ). relevant tests to determine whether a compound is a selective 5 - ht 2c receptor agonist or a selective 5 - ht 6 receptor antagonist are known in the art , and are , as mentioned above , also outlined in the experimental part below . compounds known to be 5 - ht 2c receptor agonists are , for example , azetidine and pyrrolidine derivatives of the type described in ep - a - 0863136 ; tricyclic pyrrole derivatives of the type described in ep - a - 0657426 ; 1 - aminoethylindoles of the type described in ep - a - 0655440 ; pyrazinoindoles of the type described in ep - a - 0572863 ; piperazinylpyrazines of the type described in u . s . pat . no . 4 , 081 , 542 ; indoline derivatives of the type described in wo 00 / 12475 ; pyrroloindoles , pyridoindoles and azepinoindoles of the type described in wo 00 / 12510 ; indazole derivatives of the type described in wo 00 / 12482 ; pyrroloquinolines of the type described in wo 00 / 12502 ; 2 , 3 , 4 , 4a - tetrahydro - 1h - pyrazino [ 1 , 2 - a ] quinoxalin - 5 ( 6h ) ones of the type described in wo 00 / 35922 ; indazolylpropylamines of the type described in wo 00 / 12481 ; indazoles of the type described in wo 00 / 17170 ; piperazinylpyrazines of the type described in wo 00 / 76984 and in swedish patent applications nos . 0004244 - 0 and 0004245 - 7 , filed on nov . 20 , 2000 ; heterocycle fused γ - carbolines of the type described in wo 00 / 77001 , wo 00 / 77002 and wo 00 / 77010 ; benzofurylpiperazines of the type described in wo 01 / 09111 and wo 01 / 09123 ; benzofurans of the type described in wo 01 / 09122 ; benzothiophenes of the type described in 01 / 09126 ; pyridinylpiperazines of the type described in ep 370560 ; pyrroloquinolines of the type described in bioorg . med . chem . lett . 2000 , 10 , 919 - 921 ; aminoalkylindazoles of the type described in wo 98 / 30548 ; indoles of the type described in wo 01 / 12603 ; indolines of the type described in wo 01 / 12602 ; pyrazino ( aza ) indoles of the type described in wo 00 / 44753 ; tricyclic pyrroles or pyrazoles of the type described in wo 98 / 56768 . currently preferable 5 - ht 2c receptor agonists are of the arylpiperazine and piperazinylpyrazine compound classes , in particular compounds disclosed in wo 00 / 76984 and in swedish patent applications nos . 0004244 - 0 and 0004245 - 7 , filed on nov . 20 , 2000 . compounds known to be 5 - ht 6 receptor antagonists are , for example , piperazinylbenzenesulfonamides of the type described in wo 99 / 37623 ; sulfonylbenzene derivatives of the type described in ep - a - 0930302 ; sulfonamide derivatives of the type described in wo 99 / 02502 ; sulfonamide derivatives of the type described in wo 99 / 42465 ; sulfonamide derivatives of the type described in wo 98 / 27081 ; carboxamide derivatives of the type described in wo 98 / 27058 ; sulfonamide derivatives of the type described in ep - a - 0815861 ; pyrrolidonomethylindole derivatives of the type described in wo 99 / 47516 ; bicyclic piperidine and piperazine derivatives of the type described in wo 99 / 65906 ; pyrazolopyrimidine and pyrazolotriazine derivatives of the type described in ep - a - 0941994 ; arylsulfone - substituted hexahydroazepinoindoles of the type described in wo 01 / 05793 ; oxazinocarbazoles of the type described in wo 01 / 09142 ; aminoalkoxycarbazoles of the type described in wo 01 / 17963 ; diphenylsulfones of the type described in the international patent application pct / us00 / 30177 , filed on jun . 20 , 2000 ; and arylsulfonylindoles of the type described in the swedish patent application no . 0003810 - 9 , filed on oct . 20 , 2000 . currently preferable 5 - ht 6 receptor antagonists include the azepinoindole compound class , such as the class of arylsulfone - substituted hexahydroazepinoindoles compounds disclosed in wo 01 / 05793 . other preferred 5 - ht 6 receptor antagonists include the arylsulfonylindole compound class , such as the compound class described in the swedish patent application no . 0003810 - 9 . the 5 - ht 2c receptor agonists and the 5 - ht 6 receptor antagonists may be the compounds as such or where appropriate the pharmaceutically acceptable salts ( acid or base addition salts ) thereof or stereochemically isomeric forms thereof ( including optical isomers , such as enantiomers and racemates ). the pharmaceutically acceptable addition salts as mentioned above are meant to comprise the therapeutically active non - toxic acid and base addition salt forms which the compounds are able to form . compounds which have basic properties can be converted to their pharmaceutically acceptable acid addition salts by treating the base form with an appropriate acid . exemplary acids include inorganic acids , such as hydrogen chloride , hydrogen bromide , hydrogen iodide , sulphuric acid , phosphoric acid ; and organic acids such as acetic acid , propanoic acid , hydroxyacetic acid , lactic acid , pyruvic acid , glycolic acid , maleic acid , malonic acid , oxalic acid , benzenesulfonic acid , toluenesulfonic acid , methanesulfonic acid , trifluoroacetic acid , fumaric acid , succinic acid , malic acid , tartaric acid , citric acid , salicylic acid , p - aminosalicylic acid , pamoic acid , benzoic acid , ascorbic acid and the like . exemplary base addition salt forms are the sodium , potassium , calcium salts , and salts with pharmaceutically acceptable amines such as , for example , ammonia , alkylamines , benzathine , and amino acids , such as , e . g . arginine and lysine . the term addition salt as used herein also comprises solvates which the compounds and salts thereof are able to form , such as , for example , hydrates , alcoholates and the like . the 5 - ht 2c receptor agonists and the 5 - ht 6 receptor antagonists may also be prodrugs or forms that may release the active ingredient in question after metabolic tranformation in vivo . conventional procedures for the selection and preparation of suitable prodrug derivatives are described , for example , in “ design of prodrugs ” ed . h . bundgaard , elsevier , 1985 . the 5 - ht 2c receptor agonists and the 5 - ht 6 receptor antagonists may be formulated into various pharmaceutical forms for administrative purposes , either in the same pharmaceutical dosage form , such as in the same tablet , or in separate pharmaceutical dosage forms . in the latter case , however , it may be advantageous to put the 5 - ht 2c receptor agonist unit dosage form and the 5 - ht 6 receptor antagonist unit dosage form in the same package , for example in the same blister . the 5 - ht 2c receptor agonists and the 5 - ht 6 receptor antagonists , in the form of free bases or salt , can be brought into suitable galenic forms , such as compositions for oral use , for injection , for nasal spray administration or the like , in accordance with accepted pharmaceutical procedures . such pharmaceutical compositions according to the invention comprise an effective amount of a 5 - ht 2c receptor agonist and a 5 - ht 6 receptor antagonist in association with compatible pharmaceutically acceptable carrier materials , or diluents , as are well known in the art . the carriers may be any inert material , organic or inorganic , suitable for oral , enteral , rectal , percutaneous , subcutaneous or parenteral administration , such as : water , gelatin , gum arabicum , lactose , microcrystalline cellulose , starch , sodium starch glycolate , calcium hydrogen phosphate , magnesium stearate , talcum , colloidal silicon dioxide , and the like . such compositions may also contain other pharmacologically active agents , and conventional additives , such as stabilizers , wetting agents , emulsifiers , flavoring agents , buffers , and the like . the compositions according to the invention can e . g . be made up in solid or liquid form for oral administration , such as tablets , pills , capsules , powders , syrups , elixirs , dispersable granules , cachets , suppositories and the like , in the form of sterile solutions , suspensions or emulsions for parenteral administration , sprays , e . g . a nasal spray , transdermal preparations , e . g . patches , and the like . the dose level of each of the specific 5 - ht 2c receptor agonist and 5 - ht 6 receptor antagonist , and the frequency of dosage of the specific combination will vary depending on a variety of factors including the potency of each specific compound employed , the metabolic stability and length of action of that compound , the patient &# 39 ; s age , body weight , general health , sex , diet , mode and time of administration , rate of excretion , drug combination , the severity of the condition to be treated ). the daily dosage may , for example , range from about 0 . 001 mg to about 150 mg per kilo of body weight , preferably from about 0 . 01 mg to about 100 mg per kilo of body weight , especially from about 0 . 1 to about 50 mg per kilo of body weight of each of the 5 - ht 2c receptor agonist and of the 5 - ht 6 receptor antagonist , administered singly or multiply in doses , e . g . dosages of from about 0 . 01 mg to about 1 g each . usually , such a combined dosage is given orally but e . g . parenteral or rectal administration may also be chosen . an exemplary tablet combination formulation may be in the form of either ( a ) two separate tablets , i . e . one tablet containing 10 mg , 20 mg or 50 mg of a 5 - ht 2c receptor agonist , and one tablet containing 10 mg , 20 mg or 50 mg of a 5 - ht 6 receptor antagonist ; or ( b ) a combined tablet containing 10 mg , 20 mg or 50 mg of a 5 - ht 2c receptor agonist and 10 mg , 20 mg or 50 mg of a 5 - ht 6 receptor antagonist . the invention will now be illustrated further by the following non - limiting experimental section . the free base of the 5 - ht 2c receptor agonist ( 2r )- methyl - 1 -{ 3 -[ 2 -( 3 - pyridinyloxy ) ethoxy ]- 2 - pyrazinyl } piperazine , fumarate (“ pnu - 183933f ”) was prepared as described in wo 00 / 76984 . the free base was converted to its fumarate salt , m . p . 126 - 129 ° c . ms m / z 315 ( m ) + . anal . ( c 16 h 2l n 5 o 2 . c 4 h 4 o 4 ) c , h , n . the 5 - ht 6 receptor antagonist 6 - methyl - 9 -( phenylsulfonyl )- 1 , 2 , 3 , 4 , 5 , 6 - hexahydroazepino [ 4 , 5 - b ] indole , hydrochloride (“ pnu - 186053a ”) was prepared as described in wo 01 / 05793 . the 5 - ht 2c receptor agonist ( 2r )- 1 -( 3 -{ 2 -[( 2 - ethoxy - 3 - pyridinyl ) oxy ] ethoxy }- 2 - pyrazinyl )- 2 - methylpiperazine , fumarate (“ bvt . 2938f ”) was prepared as described in wo 00 / 76984 . the 5 - ht 6 receptor antagonist 1 -( phenylsulfonyl )- 4 -( 1 - piperazinyl )- 1h - indole , hydrochloride (“ bvt . 5182c ”) was prepared as described in swedish patent application no . 0003810 - 9 , filed on oct . 20 , 2000 . briefly , bvt . 5182c was prepared according the general procedure depicted in scheme 1 , below , starting from commercially available 4 - piperazinoindole ( compound 1 ) that undergoes steps ( a ) to ( c ) to afford 1 -( phenylsulfonyl )- 4 -( 1 - piperazinyl )- 1h - indole , hydrochloride ( yield 80 %). hplc purity & gt ; 95 %; 1 h nmr ( dmso - d6 ) δ9 . 64 ( br s , 2 h ), 8 . 00 - 7 . 85 ( m , 3 h ), 7 . 79 ( d , j = 3 . 77 hz , 1 h ), 7 . 70 - 7 . 65 ( m , 1 h ), 7 . 63 - 7 . 60 ( m , 3 h ), 7 . 27 - 7 . 22 ( m , 1 h ), 6 . 95 ( d , j = 3 . 76 hz , 1 h ), 6 . 81 - 6 . 77 ( m , 1 h ), 3 . 30 - 3 . 20 ( m , 4 h ); 13 c nmr ( dmso - d6 ) δ144 . 79 , 137 . 02 , 135 . 22 , 134 . 62 , 129 . 82 , 126 . 85 , 125 . 63 , 125 . 54 , 123 . 49 , 111 . 15 , 107 . 87 , 107 . 76 , 47 . 81 , 42 . 86 ; ms ( poses - fia ) m / z 342 ( m + h ). 4 - piperazinoindole ( 1 eq ), dmap ( 0 . 1 eq ) and et 3 n ( 4 eq ) were dissolved in dmf . ( boc ) 2 o ( 1 . 1 eq ) was added and the reaction mixture was stirred at room temperature ( 12 h ). dmf was evaporated and the residue was purified by chromatography on silica gel using a mixture of chloroform , methanol and ammonia as eluent . hplc : 100 % purity . ms m / z 302 . 2 ( m + h ). the intermediate 2 ( 1 . 0 eq ) was dissolved in dmf and nah ( 1 . 3 eq ) was added and the suspension was stirred for 0 . 5 h under nitrogen atmosphere . benzenesulfonyl chloride ( 1 . 2 eq ) was added and the reaction was stirred overnight at room temperature . the volatiles were evaporated . the residue was dissolved in dcm , washed with a saturated solution of nahco 3 , dried ( mgso 4 ), filtered and concentrated to give an oily residue that was purified by chromatography on silica gel using a mixture of hexane and ethylacetate ( 7 : 3 ) as eluent to give tert butyl 4 -[ 1 -( benzenesulfonyl )- 1h - indol - 4 - yl )]- 1 - piperazinecarboxylate ( 3 ). hplc 100 %. nmr ( 1 h and 13 c ) and ms analyses support the stated structure . the boc group on intermediate 3 was removed by dissolving the compound in methanol followed by addition of ether saturated with hcl gas . the hcl salt ( 4 ) was filtered and dried . tablet ingredients mg / tablet 1 . 5 - ht 2c receptor agonist 10 . 0 2 . 5 - ht 6 receptor antagonist 10 . 0 3 . cellulose , microcrystalline 57 . 0 4 . calcium hydrogen phosphate 15 . 0 5 . sodium starch glycolate 5 . 0 6 . silicon dioxide , colloidal 0 . 25 7 . magnesium stearate 0 . 75 the active ingredients 1 and 2 are mixed with ingredients 3 , 4 , 5 and 6 for about 10 minutes . the magnesium stearate ( 7 ) is then added , and the resultant mixture is mixed for about 5 minutes and compressed into tablet form with or without film - coating . 5 - ht 2c receptor affinity is determined in competition experiments , where the ability of a compound in serial dilution to displace 3 h - labeled 5 - ht , bound to membranes prepared from a transfected hek293 cell line stably expressing the human 5 - ht 2c receptor protein , is monitored by scintillation proximity assay ( spa ) technology . non - specific binding is defined using 5 μm mianserin . 5 - ht 2a receptor affinity is determined in competition experiments , where the ability of a compound in serial dilution to displace 3 h - labeled ketanserin or lysergic acid diethylamide ( lsd ), bound to membranes prepared from a transfected cho cell line stably expressing the human 5 - ht 2a receptor protein , is monitored by measuring the radioactivity of filtered membrane homogenates on glass fiber filters in a scintillation counter . non - specific binding is defined using 5 μm mianserin . 5 - ht 2b receptor affinity is determined in competition experiments , where the ability of a compound in serial dilution to displace 3 h - labeled 5 - ht , bound to membranes prepared from a transfected cho cell line stably expressing the human 5 - ht 2b receptor protein , is monitored by scintillation proximity assay ( spa ) technology . non - specific binding is defined using 5 μm mianserin . the agonist efficacy at the 5 - ht 2c receptor is determined by the ability of a compound to mobilise intracellular calcium in transfected hek293 cells , stably expressing the human 5 - ht 2c receptor protein , using the calcium - chelating fluorescent dye fluo - 3 ( sigma , st . louis , mo ., u . s . a .). relative efficacy (%) is measured relative to that of serotonin at 1 μm . the radioligand binding assay uses [ 3 h ]- lysergic acid diethylamide ( lsd ). the assay is carried out in 96 - well sample plates by the addition of 11 μl of the test compound at the appropriate dilution ( the assay employs 11 serial concentrations of samples run in duplicate ), 11 μl of radioligand , and 178 μl of a washed mixture of wga - coated spa beads and membranes in binding buffer prepared from hek293 - cells containing cloned human 5 - ht 6 receptor . the plates are shaken for about 5 minutes and then incubated at room temperature for 1 hour . the plates are then loaded into counting cassettes and counted in a scintillation counter . the specifically bound cpm obtained are fit to a one - site binding model using graphpad prism ver . 2 . 0 . estimated ic 50 values are converted to k i ( affinity constant ) values using the cheng - prusoff equation ( cheng , y . c . et al ., biochem . pharmacol . 1973 , 22 , 3099 - 3108 ). the antagonist potency at the 5 - ht 6 receptor is determined by the ability of a compound to antagonize the increase in camp induced by 5 - ht in hek293 cells , stably expressing the human 5 - ht 6 receptor protein , using a camp spa direct screening assay system ( rpa559 , amersham pharmacia biotech , uppsala , sweden ). 5 - ht 2c receptor agonists ( 2r )- methyl - 1 -{ 3 -[ 2 -( 3 - pyridinyloxy ) ethoxy ]- 2 - pyrazinyl } piperazine , fumarate (“ pnu - 183933f ”) and ( 2r )- 1 -( 3 -{ 2 -[( 2 - ethoxy - 3 - pyridinyl ) oxy ] ethoxy }- 2 - pyrazinyl )- 2 - methylpiperazine , fumarate (“ bvt . 2938f ”) were dissolved in saline ( 0 . 9 % nacl ) and diluted in the same vehicle to the appropriate concentration . 5 - ht 6 receptor antagonists 6 - methyl - 9 -( phenylsulfonyl )- 1 , 2 , 3 , 4 , 5 , 6 - hexahydroazepino [ 4 , 5 - b ] indole , hydrochloride (“ pnu - 186053a ”) and 1 -( phenylsulfonyl )- 4 -( 1 - piperazinyl )- 1h - indole , hydrochloride ( 5 - ht 6 receptor antagonist (“ bvt . 5182c ”) were dissolved and diluted in 25 % cyclodextrin . male mice 8 - 9 weeks old ( c57bl / 6jbom - lep ob ( ob / ob ), bomholtsgaard , denmark ) with an average body weight of 45 g were used . the animals were housed singly in cages at 23 ± 1 ° c ., 40 - 60 % humidity and had free access to water and standard laboratory chow . the 12 / 12 h light / dark cycle was set to lights off at 5 p . m . the animals were conditioned for at least one week before start of study . during experimental sessions , the animals obtained special chow ( bioserv , frenchtown , n . j ., usa dust - free precision pellets weighing 20 mg each ). at the start of the study the animals were transferred to special cages “ operant test cages ” ( habitest modular animal behavior test system ; colbourn instr , allentown , pa ., usa ). these cages consist of a feeder trough with sensors for measurement of food intake , an optic lickometer for registration of water intake and an infrared - based monitor for recording overall general motor activity . the monitors are coupled to a computer , which controls and monitor events continuously . food pellets were weighed to the amount needed for one whole study and water bottles were filled with fresh tap water and weighed . the animals were conditioned to their new environment for three days to establish baseline values . the animals were weighed at 3 p . m . at the start and at the end of the study . the compounds were administered between 4 . 20 and 5 . 00 p . m . before dark onset . three groups of animals received ( i ) 5 - ht 6 antagonist in 25 % cyclodextrin ; ( ii ) 5 - ht 2c agonist in saline ; and ( iii ) the combination 5 - ht 2c agonist / 5 - ht 6 antagonist , respectively . when combined , 5 - ht 6 antagonist or saline was administered 30 min before administration of the 5 - ht 2c agonist or 25 % cyclodextrin . a fourth group received respectively vehicle administered in the same way . the study ended on the fifth day . weighing was performed with a computer - assisted mettler - toledo pr5002 / pr802 balance . each dose group consisted of 12 - 16 animals . data were corrected for food spillage based on the weighed spillage during 22 hours and assumed to be proportional over time . calculations were performed for the data before and after treatment . the values were expressed as % of basal food intake ( mean ± sem ) for the difference between food intake before treatment and 3 h ( 5 pm - 8 pm ), 6 h ( 5 pm - 11 pm ), 12 h ( 5 pm - 5 am ), 21 h ( 5 pm - 2 pm ). the results shown in fig1 indicate that combined treatment with the 5 - ht 6 receptor antagonist “ pnu - 186053a ” ( 50 mg / kg subcutaneously ) and the 5 - ht 2c receptor agonist “ pnu - 183933f ” ( 50 mg / kg per orally ) decreased food consumption significantly more than the compounds given alone . correspondingly , the results shown in fig2 indicate that combined treatment with the 5 - ht 2c receptor agonist “ bvt . 2938f ” ( 5 mg / kg subcutaneously ) and the 5 - ht 6 receptor antagonist “ bvt . 5182c ” ( 3 mg / kg subcutaneously ) decreased food consumption , at 12 and 21 hours following administration , significantly more than the compounds given alone . thus , it is apparent that combined therapy with a 5 - ht 2c receptor agonist and a 5 - ht 6 receptor antagonist reduces food intake more efficiently as compared to treatment with either agonist or antagonist alone .
the invention relates to method of preventing or treating a disease related to the 5 - ht 2c receptor and the 5 - ht 6 receptor , comprising administering to a human or animal subject in need thereof a 5 - ht 2c receptor agonist and a 5 - ht 6 receptor antagonist in sufficient amounts to provide a therapeutic effect . the invention also relates to a pharmaceutical composition comprising an effective amount of a combination of a 5 - ht 2c receptor agonist and a 5 - ht 6 receptor antagonist , and optionally a pharmaceutically acceptable carrier .