unless otherwise stated , the following terms used in this application , including the specification and claims , have the definitions given below . it must be noted that , as used in the specification and the appended claims , the singular forms “ a ,” “ an ” and “ the ” include plural referents unless the context clearly dictates otherwise . “ spontaneous erectile function ” means the ability to produce an erection , including noctural penile tumescence ( npt ) or noctural penile tumescence and rigidity ( nptr ), without acute pharmacological intervention . “ intrameatally ” or “ meatally ” means applying medication to the tip of the penis into the navicular fossa by holding the penis upright , holding the meatus open and dropping the medication into the navicular fossa without introducing the medication container into the meatus . “ penile tumescence ” means the swelling of erectile tissue of the penile , including at least one of the glans , the corpora cavernosa or the corpus spongiosa . “ cavernous neurons ” means neurons that contribute processes , such as axons , to the cavernous nerve . “ fluid communication ” between a drug reservoir and a site of drug action includes transport of the drug through the vessels of the cardiovascular system and the lymphatic system as well as diffusion of the drug through the extracellular fluid . “ alkyl ” means the monovalent linear or branched saturated hydrocarbon radical , consisting solely of carbon and hydrogen atoms , having from one to twenty carbon atoms inclusive , unless otherwise indicated . examples of an alkyl radical include , but are not limited to , methyl , ethyl , propyl , isopropyl , isobutyl , sec - butyl , tert - butyl , pentyl , n - hexyl , octyl , dodecyl , tetradecyl , eicosyl , and the like . “ lower alkyl ” means the monovalent linear or branched saturated hydrocarbon radical , consisting solely of carbon and hydrogen atoms , having from one to six carbon atoms inclusive , unless otherwise indicated . examples of a lower alkyl radical include , but are not limited to , methyl , ethyl , propyl , isopropyl , tert - butyl , n - butyl , n - hexyl , and the like . “ lower alkoxy ” means the radical — o — r , wherein r is a lower alkyl radical as defined above . examples of a lower alkoxy radical include , but are not limited to , methoxy , ethoxy , isopropoxy , and the like . “ optional ” or “ optionally ” means that the subsequently described event or circumstance may but need not occur , and that the description includes instances where the event or circumstance occurs and instances in which it does not . for example , “ optional bond ” means that the bond may or may not be present , and that the description includes single , double , or triple bonds . “ pharmaceutically acceptable ” means that which is useful in preparing a pharmaceutical composition that is generally safe , non - toxic , and neither biologically nor otherwise undesirable and includes that which is acceptable for veterinary as well as human pharmaceutical use . a “ pharmaceutically acceptable salt ” of a compound means a salt that is pharmaceutically acceptable , as defined above , and that possesses the desired pharmacological activity of the parent compound . such salts include : 1 . acid addition salts formed with inorganic acids such as hydrochloric acid , hydrobromic acid , hydrofluoric acid , hydroiodic acid , trifluoroacetic acid , sulfuric acid , nitric acid , phosphoric acid , boric acid and the like ; or formed with organic acids such as acetic acid , benzenesulfonic acid , benzoic acid , camphorsulfonic acid , p - chlorobenzenesulfonic acid , cinnamic acid , citric acid , cylcopentanepropionic acid , ethanesulfonic acid , 1 , 2 - ethanedisulfonic acid , formic acid , fumaric acid , glucoheptonic acid , gluconic acid , glutamic acid , glycolic acid , hexanoic acid , heptanoic acid , o -( hydroxybenzoyl ) benzoic acid , hydroxynaphtoic acid , 2 - hydroxyethanesulfonic acid , lactic acid , lauryl sulfuric acid , maleic acid , malic acid , malonic acid , mandelic acid , methanesulfonic acid , 4 - methylbicyclo [ 2 . 2 . 2 ] oct - 2 - ene - 1 - carboxylic acid , 4 , 4 ′- methylenebis ( 3 - hydroxy - 2 - ene - 1 - carboxylic acid ), muconic acid , 2 - naphthalenesulfonic acid , oxalic acid , 3 - phenylpropionic acid , propionic acid , pyruvic acid , salicylic acid , stearic acid , succinic acid , tartaric acid , tertiary butylacetic acid , p - toluenesulfonic acid , trifluoromethanesulfonic acid , trimethylacetic acid , and the like ; or 2 . salts formed when an acidic proton present in the parent compound either is replaced by a metal ion , e . g ., an alkali metal ion , an alkaline earth ion , or an aluminum ion ; or coordinates with an organic or inorganic base . acceptable organic bases include diethanolamine , ethanolamine , n - methylglucamine , triethanolamine , tromethamine , methylamine , ethylamine , hydroxyethylamine , propylamine , dimethylamine , diethylamine , trimethylamine , triethylamine , ethylenediamine , hydroethylamine , morpholine , piperazine , and guanidine and the like . acceptable inorganic bases include aluminum hydroxide , ammonium hydroxide , calcium hydroxide , potassium hydroxide , sodium carbonate , sodium hydroxide and hydrazine . the preferred pharmaceutically acceptable salts are the salts formed from hydrochloric acid , and trifluoroacetic acid . “ subject ” means mammals and non - mammals . “ mammals ” means any member of the class mammalia including , but not limited to , humans , non - human primates such as chimpanzees and other apes and monkey species ; farm animals such as cattle , horses , sheep , goats , and swine ; domestic animals such as rabbits , dogs , and cats ; laboratory animals including rodents , such as rats , mice , and guinea pigs ; and the like . examples of non - mammals include , but are not limited to , birds , and the like . the term “ subject ” does not denote a particular age or sex . a “ therapeutically effective amount ” means an amount of a compound that , when administered to a subject for treating a disease , is sufficient to effect such treatment for the disease . the “ therapeutically effective amount ” will vary depending on the compound , the disease state being treated , the severity or the disease treated , the age and relative health of the subject , the route and form of administration , the judgement of the attending medical or veterinary practitioner , and other factors . the term “ pharmacological effect ” as used herein encompasses effects produced in the subject that achieve the intended purpose of a therapy . in one preferred embodiment , a pharmacological effect means that vasospasm symptoms of the subject being treated are prevented , alleviated , or reduced . for example , a pharmacological effect would be one that results in the prevention or reduction of vasospasm in a treated subject . 1 . preventing the disease state , i . e . causing the clinical symptoms of the disease state not to develop in a subject that may be exposed to or predisposed to the disease state , but does not yet experience or display symptoms of the disease state , 2 . inhibiting the disease state , i . e ., arresting the development of the disease state or its clinical symptoms , or 3 . relieving the disease state , ie ., causing temporary or progressive regression of the disease state or its clinical symptoms . “ pro - drug ” means a pharmacologically inactive form of a compound which must be metabolized in vivo by a subject after administration into a pharmacologically active form of the compound in order to produce the desired pharmacological effect . after administration to the subject , the pharmacologically inactive form of the compound is converted in vivo under the influence of biological fluids or enzymes into a pharmacologically active form of the compound . although metabolism occurs for many compounds primarily in the liver , almost all other tissues and organs , especially the lung , are able to carry out varying degrees of metabolism . pro - drug forms of compounds may be utilized , for example , to improve bioavailability , mask unpleasant characteristics such as bitter taste , alter solubility for intravenous use , or to provide site - specific delivery of the compound . reference to a compound herein includes pro - drug forms of a compound . in a preferred embodiment , the pharmaceutical composition comprises at least one vasoactive prostaglandin , preferably prostaglandin e 1 , an alkyl ( n - substituted amino ) ester , a polymer , a lipophilic component , and an acid buffer system . vasoactive prostaglandins are those that act as peripheral vasodilators , including naturally occurring prostaglandins such as pge 1 , pga 1 , pgb 1 , pgf 1α , 19 - hydroxy - pga 1 , 19 - hydroxy - pgb 1 , pge 2 , pga 2 , pgb 2 , 19 - hydroxy - pga 2 , 19 - hydroxy - pgb 2 , pge 3 , pgf 3α ; semisynthetic or synthetic derivatives of natural prostaglandins , including carboprost tromethamine , dinoprost tromethamine , dinoprostone , lipoprost , gemeprost , metenoprost , sulprostone and tiaprost . prostaglandin e 1 and prostaglandin e 2 are particularly preferred vasoactive prostaglandins for use in conjunction with the present method . additionally , simultaneous administration of one or more non - ecosanoid vasodilators may be desirable and may in some cases exhibit a synergistic effect . the combination of prazosin with prostaglandin e 1 has been found to be particularly advantageous in this regard ; the latter drug appears to act as a potentiator for prazosin . suitable non - ecosanoid vasodilators include , but are not limited to : nitrates such as nitroglycerin , isosorbide dinitrate , erythrityl tetranitrate , amyl nitrate , sodium nitroprusside , molsidomine , linsidomine chlorhydrate (“ sin - 1 ”) and s - nitroso - n - acetyl - d , l - penicillamine (“ snap ”); amino acids such as l - arginine ; long and short acting α - adrenergic blockers such as phenoxybenzamine , dibenamine , phentolamine , tamsulosin and indoramin , especially quinazoline derivatives such as alfuzosin , bunazosin , doxazosin , terazosin , prazosin , and trimazosin ; vasodilative natural herbal compositions and bioactive extracts thereof , such as gosyajinki - gan , satureja obovata , bai - hua qian - hu , lipotab , saiboku - to , vinpocetine , gingko biloba , bacopa , gynostemma pentaphyllum , gypenosides , evodia rutaecarpa , rutaecarpine , dehydroevodiamine , dan - shen , salviae miltiorrhizae radix , shosaikoto , zizyphi fructus , ginseng and mixtures thereof ( u . s . pat . no . 6 , 007 , 824 ); ergot alkaloids such as ergotamine and ergotamine analogs , e . g ., acetergamine , brazergoline , bromerguride , cianergoline , delorgotrile , disulergine , ergonovine maleate , ergotamine tartrate , etisulergine , lergotrile , lysergide , mesulergine , metergoline , metergotamine , nicergoline , pergolide , propisergide , proterguride and terguride ; antihypertensive agents such as diazoxide , hydralazine and minoxidil ; vasodilators such as nimodepine , pinacidil , cyclandelate , dipyridamole and isoxsuprine ; chlorpromazine ; haloperidol ; yohimbine ; trazodone and vasoactive intestinal peptides . prostaglandin e 1 is well known to those skilled in the art . reference may be had to various literature references for its pharmacological activities , side effects , and normal dosage ranges . see for example , physician &# 39 ; s desk reference , 51st ed . ( 1997 ), the merck index , 12th ed ., merck & amp ; co ., n . j . ( 1996 ), and martindale the extra pharmacopoeia , 28th ed ., london , the pharmaceutical press ( 1982 ). prostaglandin e 1 as well as other compounds referenced herein are intended to encompass pharmaceutically acceptable derivatives including physiologically compatible salts and ester derivatives thereof . the quantity of vasoactive prostaglandin , such as prostaglandin e 1 , in the pharmaceutical composition is a therapeutically effective amount and necessarily varies according to the desired dose , the dosage form ( e . g ., suppository or topical ), and the particular form of vasoactive prostaglandin used . the term “ prostaglandin ” as used generically herein refers to the prostaglandin free acid and pharmaceutically acceptable derivatives thereof , including , for example pge 1 , pharmaceutically acceptable salts and lower alkyl esters thereof ( the term “ lower alkyl ” as used herein means straight chain or branched chain alkyl containing one to four carbon atoms ). the composition generally contains when used in combination with a vasoactive prostaglandin , a piperazinyl quinazoline antihypertensive , such as prazosin , is present in the amount of about 0 . 1 mg to about 2 . 0 mg per unit dose , depending on the potency of the particular piperazinyl quinazoline antihypertensive and the type and dose of vasoactive prostaglandin used . the dose and the proportion of vasoactive prostaglandin and the piperazinyl quinazoline antihypertensive can be routinely determined by one of ordinary skill without undo experimentation . working alone , most drugs , prostaglandin formulations included , do not sufficiently permeate the skin to provide drug concentration levels comparable to those obtained from other drug delivery routes . to overcome this problem , topical drug formulations typically include a skin penetration enhancer . skin penetration enhancers also may be referred to as absorption enhancers , accelerants , adjuvants , solubilizers , sorption promoters , etc . whatever the name , such agents serve to improve drug absorption across the skin . ideal penetration enhancers not only increase drug flux across the skin , but do so without irritating , sensitizing , or damaging skin . furthermore , ideal penetration enhancers should not adversely affect the physical qualities of the available dosage forms ( e . g . cream or gel ), or the cosmetic quality of the topical composition . a wide variety of compounds have been evaluated as to their effectiveness in enhancing the rate of penetration of drugs through the skin . see , for example , percutaneous penetration enhancers , maibach h . i . and smith h . e . ( eds . ), crc press , inc ., boca raton , fla . ( 1995 ), which surveys the use and testing of various skin penetration enhancers , and büyüktimkin et al ., chemical means of transdermal drug permeation enhancement in transdermal and topical drug delivery systems , gosh t . k ., pfister w . r ., yum s . i . ( eds . ), interpharm press inc ., buffalo grove , ill . ( 1997 ). suitable penetration enhancers for use in prostaglandin topical compositions are disclosed in u . s . pat . nos . 4 , 980 , 378 , 5 , 082 , 866 and 6 , 118 , 020 and published international patent application wo 95 / 095590 , the contents of all of which are incorporated by reference . topical compositions employing such penetration enhancers for the delivery of prostaglandins are disclosed in u . s . pat . nos . 6 , 046 , 244 , 6 , 323 , 241 , 6 , 414 , 028 , and 6 , 489 , 207 . the topical composition of the present invention can contain one or more penetration enhancers . among the preferred penetration enhancers for the present invention are ethanol , propylene glycol , glycerol , ethyl laurate , isopropyl palmitate , isopropyl myristate , laurocapram ( azone ™), dioxolanes ( described in u . s . pat . no . 4 , 861 , 764 ), macrocyclic ketones , hp - 101 , oxazolidones and biodegradable penetration enhancers ( described in u . s . pat . nos . 4 , 980 , 378 and 5 , 082 , 866 to wong et al . such as alkyl - 2 -( n , n - disubstituted amino ) alkanoates ( e . g ., dodecyl n , n - dimethylamino isoproprionate ( ddaip )), n , n - disubstituted amino alkanol alkanoates ) and mixtures thereof . the penetration enhancer is present in an amount sufficient to enhance the penetration of the vasoactive prostaglandin , e . g ., prostaglandin e 1 . the specific amount varies necessarily according to the desired release rate and the specific form of prostaglandin e 1 used . generally , the penetration enhancer is present in an amount ranging from about 0 . 5 weight percent to about 20 weight percent , based on the total weight of the composition . preferably , the penetration enhancer is present in an amount ranging from about 1 weight percent to about 10 weight percent of the composition . more preferably , the penetration enhancer is present in an amount ranging from about 1 weight percent to about 5 weight percent of the composition . in general , suitable penetration enhancers can be chosen from those listed above as well as sulfoxides , alcohols , fatty acids , fatty acid esters , polyols , amides , surfactants , terpenes , alkanones , organic acids and mixtures thereof . see generally chattaraj , s . c . and walker , r . b ., penetration enhancer classification , pp . 5 - 20 in maibach , h . i ., and smith , h . e ., ( eds . ), percutaneous penetration enhancers , crc press , inc ., boca raton , fla . ( 1995 ) and büyüktimkin , n ., et al ., chemical means of transdermal drug permeation enhancement , in gosh , t . k ., et al ., ( eds .) transdermal and topical drug delivery systems , interpharm press , inc ., buffalo grove , ill . ( 1997 ). suitable sulfoxides include dimethylsulfoxide , decylmethylsulfoxide and mixtures thereof . suitable alcohols include ethanol , propanol , butanol , pentanol , hexanol , octanol , nonanol , decanol , 2 - butanol , 2 - pentanol , benzyl alcohol , caprylic alcohol , decyl alcohol , lauryl alcohol , 2 - lauryl alcohol , myristyl alcohol , cetyl alcohol , stearyl alcohol , olcyl alcohol , linolyl alcohol , linolenyl alcohol and mixtures thereof . suitable fatty acids include valeric , heptanoic , pelargonic , caproic , capric , lauric , myristic , stearic , oleic , linoleic , linolenic , caprylic , isovaleric , neopentanoic , neoheptanoic , neononanoic , trimethyl hexanoic , neodecanoic and isostearic acids and mixtures thereof . suitable fatty acid esters include isopropyl n - butyrate , isopropyl n - hexanoate , isopropyl n - decanoate , isopropyl myristate , isopropyl palmitate , octyldodecyl myristate , ethyl acetate , butyl acetate , methyl acetate , methylvalerate , methylpropionate , diethyl sebacate , ethyl oleate , ethyl laurate and mixtures thereof . suitable polyols include propylene glycol , polyethylene glycol , ethylene glycol , diethylene glycol , triethylene glycol , dipropylene glycol , glycerol , propanediol , sorbitol , dextrans , butanediol , pentanediol , hexanetriol and mixtures thereof . suitable amides include urea , dimethylacetamide , diethyltoluamide , dimethylformamide , dimethyloctamide , dimethyldecamide , 1 - alkyl - 4 - imidazolin - 2 - one , pyrrolidone derivatives , cyclic amides , hexamethylenelauramide and its derivatives , diethanolamine , triethanolamine and mixtures thereof . suitable pyrrolidone derivatives include 1 - methyl - 2 - pyrrolidone , 2 - pyrrolidone , 1 - lauryl - 2 - pyrrolidone , 1 - methyl - 4 - carboxy - 2 - pyrrolidone , 1 - hexyl - 4 - carboxy - 2 - pyrrolidone , 1 - lauryl - 4 - carboxy - 2 - pyrrolidone , 1 - decyl - thioethyl - 2 - pyrrolidone ( hp - 101 ), 1 - methyl - 4 - methoxycarbonyl - 2 - pyrrolidone , 1 - hexyl - 4 - methoxycarbonyl - 2 - pyrrolidone , 1 - lauryl - 4 - methoxycarbonyl - 2 - pyrrolidone , n - cyclohexylpyrrolidone , n - dimethylaminopropylpyrrolidone , n - cocoalkypyrrolidone , n - tallowalkypyrrolidone , fatty acid esters of n -( 2 - hydroxymethyl )- 2 - pyrrolidone and mixtures thereof . suitable cyclic amides include 1 - dodecylazacycloheptane - 2 - one ( laurocapram , azone ®), 1 - geranylazacycloheptan - 2 - one , 1 - farnesylazacycloheptan - 2 - one , 1 - geranylgeranylazacycloheptan - 2 - one , 1 -( 3 , 7 - dimethyloctyl ) azacycloheptan - 2 - one , 1 -( 3 , 7 , 11 - trimethyloctyl ) azacycloheptan - 2 - one , 1 - geranylazacyclohexane - 2 - one , 1 - geranylazacyclopentan - 2 , 5 - dione , 1 - farnesylazacyclopentan - 2 - one and mixtures thereof . suitable surfactants include anionic surfactants , cationic surfactants , nonionic surfactants , bile salts and lecithin . suitable anionic surfactants include sodium laurate , sodium lauryl sulfate and mixtures thereof . suitable cationic surfactants include cetyltrimethylammonium bromide , tetradecyltrimethylammonium bromide , benzalkonium chloride , octadecyltrimethylammonium chloride , cetylpyridinium chloride , dodecyltrimethylammonium chloride , hexadecyltrimethylammonium chloride , and mixtures thereof . suitable nonionic surfactants include α - hydro - ω - hydroxy - poly ( oxyethylene )- poly ( oxypropyl ) poly ( oxyethylene ) block copolymers , polyoxyethylene ethers , polyoxyethylene sorbitan esters , polyethylene glycol esters of fatty alcohols and mixtures thereof . suitable α - hydro - ω - hydroxy - poly ( oxyethylene )- poly ( oxypropyl ) poly ( oxyethylene ) block copolymers include poloxamers 231 , 182 , and 184 and mixtures thereof . suitable polyoxyethylene ethers include 4 - lauryl ether ( brij 30 ), ( brij 93 ), ( brij 96 ), 20 - oleyl ether ( brij 99 ) and mixtures thereof . suitable polyoxyethylene sorbitan esters include the monolaurate ( tween 20 , span 20 ) the monopalmitate ( tween 40 ), the monostearate ( tween 60 ), and the monooleate ( tween 80 ) and mixtures thereof . suitable polyethylene glycol esters of fatty acids include the 8 - oxyethylene stearate ester ( myrj 45 ), ( myrj 51 ), the 40 - oxyethylene stearate ester ( myrj 52 ) and mixtures thereof . suitable bile salts include sodium cholate , sodium salts of laurocholic , glycolic and desoxycholic acids and mixtures thereof . suitable terpenes include d - limonene , α - pinene , β - enrene , α - terpineol , terpinen - 4 - ol , carvol , carvone , pulegone , piperitone , menthone , menthol , geraniol , cyclohexene oxide , limonene oxide , α - pinene oxide , cyclopentene oxide , 1 , 8 - cineole , ylang ylang oil , anise oil , chenopodium oil , eucalyptus oil and mixtures thereof . suitable alkanones include n - heptane , n - octane , n - nonane , n - decane , n - undecane , n - dodecane , n - tridecane , n - tetradecane , n - hexadecane and mixtures thereof . suitable organic acids include citric acid , succinic acid , salicylic acid , salicylates ( including the methyl , ethyl and propyl glycol derivatives ), tartaric acid and mixtures thereof . in a preferred embodiment , the penetration enhancer is an alkyl - 2 -( n - substituted amino )- alkanoate , an ( n - substituted amino )- alkanol alkanoate , or a mixture of these . for convenient reference , alkyl - 2 -( n - substituted amino )- alkanoates and ( n - substituted amino )- alkanol alkanoates can be grouped together under the label alkyl ( n - substituted amino ) esters . alkyl - 2 -( n - substituted amino )- alkanoates suitable for the present invention can be represented as follows : wherein n is an integer having a value in the range of about 4 to about 18 ; r is a member of the group consisting of hydrogen , c 1 to c 7 alkyl , benzyl and phenyl ; r 1 and r 2 are members of the group consisting of hydrogen and c 1 to c 7 alkyl ; and r 3 and r 4 are members of the group consisting of hydrogen , methyl and ethyl . preferred are alkyl ( n , n - disubstituted amino )- alkanoates such as c 4 to c 18 alkyl ( n , n - disubstituted amino )- acetates and c 4 to c 18 alkyl ( n , n - disubstituted amino )- propionates and pharmaceutically acceptable salts and derivatives thereof . exemplary specific alkyl - 2 -( n , n - disubstituted amino )- alkanoates include dodecyl 2 -( n , n dimethylamino )- propionate ( ddaip ); alkyl - 2 -( n - substituted amino )- alkanoates are known . for example , dodecyl 2 -( n , n - dimethylamino )- propionate ( ddaip ) is available from steroids , ltd . ( chicago , ill .). in addition , alkyl - 2 -( n , n - disubstituted amino )- alkanoates can be synthesized from more readily available compounds as described in u . s . pat . no . 4 , 980 , 378 to wong et al ., which is incorporated herein by reference . as described therein , alkyl - 2 -( n , n - disubstituted amino )- alkanoates are readily prepared via a two - step synthesis . in the first step , long chain alkyl chloroacetates are prepared by reaction of the corresponding long chain alkanols with chloromethyl chloroformate or the like in the presence of an appropriate base such as triethylamine , typically in a suitable solvent such as chloroform . the reaction can be depicted as follows : wherein r , r 3 , r 4 and n are defined as above . the reaction temperature may be selected from about 10 degrees celsius to about 200 degrees celsius or reflux , with room temperature being preferred . the use of a solvent is optional . if a solvent is used , a wide variety of organic solvents may be selected . choice of a base is likewise not critical . preferred bases include tertiary amines such as triethylamine , pyridine and the like . reaction time generally extends from about one hour to three days . in the second step , the long chain alkyl chloroacetate is condensed with an appropriate amine according to the scheme : wherein n , r , r 1 , r 2 , r 3 and r 4 are defined as before . excess amine reactant is typically used as the base and the reaction is conveniently conducted in a suitable solvent such as ether . this second step is preferably run at room temperature , although temperature may vary . reaction time usually varies from about one hour to several days . conventional purification techniques can be applied to ready the resulting ester for use in a pharmaceutical compound . wherein n is an integer having a value in the range of about 5 to about 18 ; y is an integer having a value in the range of 0 to about 5 ; and r 1 , r 2 , r 3 , r 4 , r 5 , r 6 , and r 7 are members of the group consisting of hydrogen , c 1 to c 8 alkyl , and c 1 to c 8 aryl ; and r 8 is a member of the group consisting of hydrogen , hydroxyl , c 1 to c 8 alkyl , and c 1 to c 8 aryl . the preparation of ( n - substituted amino )- alkanol alkanoates and their use as penetration enhancers is disclosed in published pct international application wo 95 / 09590 , which is incorporated by reference herein in its entirety . preferred are ( n - substituted amino )- alkanol alkanoates such as c 5 to c 18 carboxylic acid esters and pharmaceutically acceptable salts thereof . exemplary specific ( n , n - disubstituted amino )- alkanol alkanoates include the ( n , n - disubstituted amino )- alkanol alkanoates are readily prepared by reacting the corresponding aminoalkinol with lauroyl chloride in the presence of triethylamine . a solvent such as chloroform is optional but preferred . for example , 1 -( n , n - dimethylamino )- 2 - propanol can be reacted with lauroyl chloride in chloroform and in the presence of triethylamine to form 1 -( n , n - dimethyl - amino )- 2 - propanol dodecanoate ( daipd ). among the suitable penetration enhancers for the present invention ddaip is generally preferred . the penetration enhancer is present in an amount sufficient to enhance the penetration of the prostaglandin e 1 . the specific amount varies necessarily according to the desired release rate and the specific form of prostaglandin e 1 used . generally , this amount ranges from about 0 . 5 percent to about 10 percent , based on the total weight of the composition . in one embodiment , where the vasoactive prostaglandin is prostaglandin e 1 , the penetration enhancer is ddaip in the amount of about 0 . 01 to about 5 weight percent of the composition . additionally , other known transdermal penetration enhancers can also be added , if desired . illustrative are dimethyl sulfoxide ( dmso ), dimethyl acetamide ( dma ), 2 - pyrrolidone , n , n - diethyl - m - toluamide ( deet ), 1 - dodecylazacycloheptane - 2 - one ( azone ™, a registered trademark of nelson research ), n , n - dimethylformamide , n - methyl - 2 - pyrrolidone , calcium thioglycolate , oxazolidinone , dioxolane derivatives , laurocapram derivatives , and macrocyclic enhancers such as macrocyclic ketones . natural and modified polysaccharide gums are also an important ingredient of the composition . suitable representative gums are those in the natural and modified galactomannan gum category . a galactomannan gum is a carbohydrate polymer containing d - galactose and d - mannose units , or other derivatives of such a polymer . there is a relatively large number of galactomannans , which vary in composition depending on their origin . the galactomannan gum is characterized by a linear structure of β - d - mannopyranosyl units linked ( 1 → 4 ). single membered α - d - manopyranosyl units , linked ( 1 → 6 ) with the main chain , are present as side branches . galactomannan gums include guar gum , which is the pulverized endosperm of the seed of either of two leguminous plants ( cyamposis tetragonalobus and psoraloids ) and locust bean gum , which is found in the endosperm of the seeds of the carobtree ( ceratonia siliqua ). suitable modified polysaccharide gums include ethers of natural or substituted polysaccharide gums , such as carboxymethyl ethers , ethylene glycol ethers and propylene glycol ethers . an exemplary substituted polysaccharide gum is methylcellulose . other suitable representative gums include agar gum , carrageenan gum , ghatti gum , karaya gum , rhamsan gum and xanthan gum . the composition of the present invention may contain a mixture of various gums , or mixture of gums and acidic polymers . gums , and galactomannan gums in particular , are well - known materials . see for instance , industrial gums : polysaccharides & amp ; their derivatives , whistler r . l . and bemiller j . n . ( eds . ), 3rd ed . academic press ( 1992 ) and davidson r . l ., handbook of water - soluble gums & amp ; resins , mcgraw - hill , inc ., n . y . ( 1980 ). most gums are commercially available in various forms , commonly a powder , and ready for use in foods and topical compositions . for example , locust bean gum in powdered form is available from tic gums inc . ( belcam , md .). when present , the polysaccharide gums are present in the range from about 0 . 1 percent to about 5 percent , based on the total weight of the composition , with the preferred range being from 0 . 5 percent to 3 percent . in one preferred embodiment , 2 . 5 percent by weight of a polysaccharide gum is present . illustrative compositions are given in the examples , below . an optional alternative to the polysaccharide gum is a polyacrylic acid polymer . a common variety of polyacrylic acid polymer is known generically as “ carbomer .” carbomer is polyacrylic acid polymers lightly cross - linked with polyalkenyl polyether . it is commercially available from the b . f . goodrich company ( akron , ohio ) under the designation “ carbopol ™” a particularly preferred variety of carbomer is that designated as “ carbopol 940 .” other polyacrylic acid polymers suitable for use are those commercially available under the designations “ pemulen ™” ( b . f . goodrich company ) and “ polycarbophil ™” ( a . h . robbins , richmond , va .). the pemulen ™ polymers are copolymers of c 10 to c 30 alkyl acrylates and one or more monomers of acrylic acid , methacrylic acid or one of their simple esters crosslinked with an allyl ether of sucrose or an allyl ether of pentaerythritol . the polycarbophil ™ enhancer is a polyacrylic acid cross - linked with divinyl glycol . where polyacrylic acid polymers are present , they represent about 0 . 5 percent to about 5 percent of the composition , based on its total weight . in certain preferred embodiments , the semi - solid composition has a suitably chosen viscosity such that the composition is naturally retained within the fossa navicularis . the semi - solid composition can exhibit newtonian or non - newtonian rheological characteristics . in some preferred embodiments , the semi - solid composition of the present invention exhibits non - newtonian rheological characteristics , i . e . in which the apparent viscosity is dependent on the shear rate applied to the composition . preferably the composition has “ shear - thinning ” rheological properties . as used herein , “ shear - thinning ” refers to a reduction in apparent viscosity ( the ratio of shear stress to the shear rate ) with increasing shear rate , whether the reduction in apparent viscosity is time independent ( pseudoplastic ), time dependent ( thixotropic ) or associated with a yield stress , defined as a stress that must be exceeded before flow starts , ( bingham plastics and generalized bingham plastics ). see , generally , harris , j ., & amp ; wilkinson , w . l ., “ non - newtonian fluid ,” pp . 856 - 858 in parker , s . p ., ed ., mcgraw - hill encyclopedia of physics , second edition , mcgraw - hill , new york , 1993 . a suitable viscosity range of the composition is from about 5 , 000 centipoise ( cps ) to about 20 , 000 cps , preferably from about 7 , 000 cps to about 13 , 000 cps . in preferred embodiments , the vasoactive prostaglandin is released over a period of time from a drug reservoir . while it should be recognized that the release over time of a vasoactive prostaglandin from a semi - solid composition administered meatally and retained within the fossa navicularis is an embodiment of release from a drug reservoir , in other embodiments , the vasoactive prostaglandin can be released from compositions comprising other polymeric carriers that have been placed in other locations . in other preferred embodiments , a composition comprising an effective amount of a vasoactive prostaglandin and a biocompatible polymer is placed in fluid communication with the pelvic ganglion , pelvic plexus or the cavernous nerve . in preferred embodiments , the biocompatible polymer is biodegradable , and preferably flowable at room temperature . in preferred embodiments , a drug reservoir is formed that comprises a vasoactive prostaglandin and a biocompatible polymer . the biocompatible polymer remains substantially homogenous in the presence of the vasoactive prostaglandin and releases the vasoactive prostaglandin . the biocompatible polymeric material can be hydrophilic or hydrophobic , and can be selected from the group consisting of polycarboxylic acids , cellulosic polymers , including cellulose acetate and cellulose nitrate , gelatin , polyvinylpyrrolidone , cross - linked polyvinylpyrrolidone , polyanhydrides including maleic anhydride polymers , polyamides , polyvinyl alcohols , polyolefins , copolymers of vinyl monomers such as eva , polyvinyl ethers , polyvinyl aromatics , polyethylene oxides , glycosaminoglycans , polysaccharides , polyesters including polyethylene terephthalate , polyacrylamides , polyethers , polyether sulfone , polycarbonate , polyalkylenes including polypropylene , polyethylene and high molecular weight polyethylene , halogenated polyalkylenes including polytetrafluoroethylene , polyurethanes , polyorthoesters , proteins , polypeptides , silicones , siloxane polymers , polylactic acid , polyglycolic acid , polycaprolactone , polyhydroxybutyrate valerate and blends and copolymers thereof as well as other biodegradable , bioabsorbable and biostable polymers and copolymers . the biocompatible polymer may be a protein polymer , fibrin , collagen and derivatives thereof , polysaccharides such as celluloses , starches , dextrans , alginates and derivatives of these polysaccharides , an extracellular matrix component , such as hyaluronic acid , or another biologic agent or a suitable mixture of any of these . the use of an ethylene - vinyl acetate copolymer ( eva , elvax - 40 ™, dupont , wilmington , del ., usa ) and a poly - 2 - hydroxyethyl - methacrylate polymer ( hydron ™) as drug reservoirs for prostaglandins is known in the art . see , e . g ., benezra , d ., 1978 ; form , d . m ., & amp ; auerbach , r ., 1983 ; ziche , m ., et al ., 1982 and diaz - flores , l ., et al ., intense vascular sprouting from rat femoral vein induced by prostaglandins e 1 and e 2 , anat rec ., 1994 , 238 ( 1 ): 68 - 76 . such polymers , while biocompatible , have the drawback of requiring removal . silicone elastomer drug reservoirs , such as used in norplant ™ ( wyeth ) are known in the art . improvements to drug reservoirs involving modifications of the surface properties of the reservoir are disclosed in u . s . pat . no . 6 , 274 , 159 . preferred silicon elastomers are medical grade silicon elastomers such as silastic ™ ( dow - corning , midland , mich .). such drug reservoirs , while biocompatible , also have the drawback of requiring removal . in certain preferred embodiments , the drug reservoir is formed from an absorbable or biodegradable polymer . suitable biodegradable polymers include polylactide ( pla ) and poly ( lactide - co - glycolide ) ( plga ), polyorthoesters , polyphosphazenes , polyanhydrides , and polyphosphoesters . in particularly preferred embodiments , the biodegradable polymer is a polylactide polymer or a poly ( lactide - co - glycolide ) polymer . typically the aqueous biodegradable polymer solution is about 9 - 30 % by weight biodegradable copolymer , preferably 20 - 30 % by weight . the biodegradable polymer comprising the drug reservoir can be a block copolymer . in certain preferred embodiments the polymer is an aba - or bab - type block copolymer , where the a - blocks are a relatively hydrophobic poly ( lactide - co - glycolide )( plga ) or hydrophobic poly ( lactide )( pla ) and the b - block is a relatively hydrophilic polyethylene glycol ( peg ), having a hydrophobic content of between about 51 to 83 % by weight and an overall block copolymer molecular weight of between about 2000 and 4990 , that exhibit water solubility at low temperatures and undergo reversible thermal gelation at mammalian physiological body temperatures . the making and use of such block copolymers are disclosed in u . s . pat . no . 6 , 117 , 949 and u . s . published patent application no . 20040001872 . the biodegradable triblock polymer is typically used in an aqueous solution of about 9 - 30 % by weight copolymer , preferably 20 - 30 % by weight . in further preferred embodiments , the releasable vasoactive prostaglandin drug reservoir composition is flowable at room temperature and is localized at the deposition site either due to shear - thinning properties or thermal gelation at mammalian physiological body temperatures of the biocompatible polymer . in preferred embodiments , a solution of a vasoactive prostaglandin in a c 1 to c 8 aliphatic alcohol is added to an aqueous solution of a biodegradable triblock copolymer selected from the group consisting of a plga - peg - plga copolymer , a pla - peg - pla copolymer , a peg - plga - peg copolymer and a peg - pla - peg copolymer to produce a final concentration of 0 . 001 percent to 1 percent by weight of vasoactive prostaglandin based on the total weight of the composition . another important component is a lipophilic component . as used herein “ lipophilic component ” refers to an agent that is both lipophilic and hydrophilic . one of ordinary skill in the pharmaceutical arts will understand that the lipophilic nature , or “ lipophilicity ” of a given compound is routinely quantified for comparison to other compounds by using the partition coefficient . the partition coefficient is defined by the international union of pure and applied chemistry ( iupac ) as the ratio of the distribution of a substance between two phases when the heterogeneous system ( of two phases ) is in equilibrium ; the ratio of concentrations ( or , strictly speaking , activities ) of the same molecular species in the two phases is constant at constant temperature . the c 1 to c 8 aliphatic alcohols , the c 2 to c 30 aliphatic esters , and their mixtures can serve as lipophilic component . illustrative suitable alcohols are ethanol , n - propanol and isopropanol , while suitable esters are ethyl acetate , butyl acetate , ethyl laurate , methyl propionate , isopropyl myristate and isopropyl palmitate . as used herein , the term “ aliphatic alcohol ” includes polyols such as glycerol , propylene glycol and polyethylene glycols . in one embodiment , a mixture of alcohol and ester is preferred , and in particular , a mixture of ethanol and ethyl laurate is preferred . in some embodiments , the lipophilic component includes at least one liquid polyol . in preferred embodiments , the liquid polyol is a polyethylene glycol selected from the group consisting of polyethylene glycol 200 , polyethylene glycol 400 and polyethylene glycol 600 . when polyethylene glycol is used , polyethylene glycol is present in the amount of about 1 weight percent to about 25 weight percent , based on the total weight of the composition . a preferred polyethylene glycol is polyethylene glycol 400 ( peg 400 ). when present , polyethylene glycol 400 is about 1 weight percent to about 25 weight percent , preferably about 3 weight percent to about 20 weight percent , based on the total weight of the composition . in one embodiment , the c 2 to c 30 aliphatic esters , and their mixtures comprising the lipophilic component include c 8 to c 30 aliphatic esters of glycerol selected from the group consisting monoglycerides , diglycerides , triglycerides , and mixtures thereof . suitable aliphatic esters include glyceryl esters of saturated fatty acids , unsaturated fatty acids and mixtures thereof . suitable saturated fatty acids include caproic acid , caprylic acid , capric acid , lauric acid , myristic acid , palmitic acid , stearic acid , arachidic acid , behenic acid and lignoceric acid . suitable unsaturated fatty acids include oleic acid , linoleic acid and linolenic acid . suitable glyceryl esters include glyceryl monooleate , triolein , trimyristin and tristearin , perferably trimyristin . the concentration of lipophilic component required necessarily varies according to other factors such as the desired semi - solid consistency and the desired skin penetration promoting effects . suitably the concentration of lipophilic component is in the range of 0 . 5 percent to 40 percent by weight based on the total weight of the composition . the preferred topical composition contains lipophilic component in the range of 7 percent to 40 percent by weight based on the total weight of the composition . where a mixture of aliphatic alcohol and aliphatic ester are employed , the suitable amount of alcohol is in the range of 0 . 5 percent to 10 percent . in one preferred embodiment , the amount of alcohol is in the range of 5 percent to 15 percent , while that of aliphatic ester is in the range from 2 percent to 15 percent ( again based on the total weight of the composition ). in another preferred embodiment , the amount of alcohol is in the range of 0 . 5 percent to 10 percent , while that of aliphatic ester is in the range from 0 percent to 10 percent ( again based on the total weight of the composition ). the concentration of lipophilic component required necessarily varies according to other factors such as the desired semi - solid consistency and the desired skin penetration promoting effects . the preferred topical composition contains lipophilic component in the range of 7 percent to 40 percent by weight based on the total weight of the composition . where a lipophilic component that is a mixture of aliphatic alcohol and aliphatic ester is used , the preferred amount of alcohol is in the range of 5 percent to 15 percent , while that of aliphatic ester is in the range from 2 percent to 15 percent ( again based on the total weight of the composition ). an optional , but preferred , component is an emulsifier . although not a critical factor , a suitable emulsifier generally will exhibit a hydrophilic - lipophilic balance number greater than 10 . sucrose esters , and specifically sucrose stearate , can serve as emulsifiers for the composition . sucrose stearate is a well - known emulsifier available from various commercial sources . when an emulsifier is used , sucrose stearate is present up to about 2 percent , based on the total weight of the composition , is preferred . the preferred amount of sucrose stearate emulsifier can also be expressed as a weight ratio of emulsifier to polysaccharide gum . a ratio of 1 to 6 emulsifier to gum is preferred , and a ratio of 1 to 4 is most preferred to generate the desired semi - solid consistency and separation resistance . other emulsifiers are also suitable including polyoxyethylene sorbitan esters , long chain alcohols , preferably cetostearyl alcohol , and fatty acid glycerides . suitable polyoxyethylene sorbitan esters include the monolaurate ( tween 20 , span 20 ) the monopalmitate ( tween 40 ), the monostearate ( tween 60 ), and the monooleate ( tween 80 ) and mixtures thereof . preferred fatty acid glycerides include glyceryl monooleate , triolein , trimyristin and tristearin . the composition includes an acid buffer system . acid buffer systems serve to maintain or buffer the ph of compositions within a desired range . the term “ buffer system ” or “ buffer ” as used herein has reference to a solute agent or agents which , when in a water solution , stabilize such solution against a major change in ph ( or hydrogen ion concentration or activity ) when acids or bases are added thereto . solute agent or agents which are thus responsible for a resistance to change in ph from a starting buffered ph value in the range indicated above are well known . while there are countless suitable buffers , potassium phosphate monohydrate has proven effective for compositions of the present invention . the final ph value of the pharmaceutical composition may vary within the physiologically compatible range . necessarily , the final ph value is not irritating to human skin or the site of drug reservoir placement . without violating this constraint , the ph may be selected to improve prostaglandin e 1 stability and to adjust consistency when required . in one embodiment , the preferred ph value is about 3 . 0 to about 7 . 4 , more preferably about 3 . 0 to about 6 . 5 , most preferably from about 3 . 5 to about 6 . 0 . the remaining component of the composition is water , which is necessarily purified . the composition contains water in the range of about 50 to about 90 percent , based on the total weight of the composition . the specific amount of water present is not critical , however , being adjustable to obtain the desired consistency and / or concentration of the other components . prostaglandin e 1 stabilizers , coloring agents , rheological agents , and preservatives can be added to the extent that they do not overly limit prostaglandin e 1 skin penetration or prevent the desired semi - solid consistency . in preferred embodiments , the dosage forms of the semi - solid pharmaceutical composition are creams , gels , ointments , colloidal suspensions and the like , also including but not limited to compositions suitable for use with transdermal patches and like devices . the ingredients listed above may be combined in any order and manner that produces a stable composition comprising a prostaglandin e 1 evenly dispersed throughout a semi - solid formulation . one available approach to preparing such compositions involves evenly dispersing the polysaccharide gum ( or polyacrylic acid polymer ) in a premixed water / buffer solution and then thoroughly homogenizing ( i . e . mixing ) the resulting mixture , which can be labeled “ part a .” when present , the emulsifier is added to the water / buffer solution before dispersing the polysaccharide gum . any suitable method of adjusting the ph value of part a to the desired level may be used , for example , by adding concentrated phosphoric acid or sodium hydroxide . separately , the prostaglandin e 1 is dissolved with agitation in the lipophilic component , which itself may be a mixture of alcohols , esters , or alcohol with ester . next , the penetration enhancer is added . alternatively , when the lipophilic component includes both an alcohol and an ester , the prostaglandin e 1 can be dissolved in the alcohol before adding the penetration enhancer followed by the ester . in either case , the resulting mixture can be labeled “ part b .” the final step involves slow addition ( e . g . dropwise ) of part b into part a under constant mixing . the resulting topical composition , when compared to exhibits the advantageous properties described above , including improved prostaglandin e 1 permeation and bioavailability without drug overloading , reduced skin damage and related inflammation , and increased flexibility in design of dosage forms . these compositions can be used for prolonged treatment of peripheral vascular disease , male impotency and other disorders treated by prostaglandin e 1 , while avoiding the low bioavailability and rapid chemical decomposition associated with other delivery methods . application of prostaglandin e 1 in a topical composition to the skin of a patient allows a predetermined amount of prostaglandin e 1 to be administered continuously to the patient and avoids undesirable effects present with a single or multiple administrations of larger dosages by injection . by maintaining a sustained dosage rate , the prostaglandin e 1 level in the patient &# 39 ; s target tissue can be better maintained within the optimal therapeutic range . in one embodiment , a composition comprises about 0 . 01 percent to about 5 percent modified polysaccharide gum ; about 0 . 001 percent to about 1 percent of a vasoactive prostaglandin selected from the group consisting of pge 1 , pharmaceutically acceptable salts thereof , lower alkyl esters thereof and mixtures thereof ; about 0 . 05 percent to about 10 percent ddaip or salts thereof ; about 0 . 5 percent to about 10 percent of a lower alcohol selected from the group consisting of ethanol , propanol , isopropanol and mixtures thereof ; about 0 . 5 percent to about 10 percent on an ester selected from the group consisting of ethyl laurate , isopropyl myristate , isopropyl laurate and mixtures thereof ; based on the weight of the composition , and an acid buffer . preferably the composition also comprises up to about 2 percent sucrose stearate . in preferred drug reservoir embodiments , the vasoactive prostaglandin is 0 . 05 percent to 1 percent , preferably from 0 . 1 percent to 0 . 5 percent prostaglandin e 1 , based on the total weight of the composition . preferably , the biocompatible polymer is selected from the group consisting of a medical grade silicone elastomer , a biodegradable polymer and a shear - thinning polymeric thickener . in preferred embodiments , a solution of prostaglandin e 1 in a c 1 to c 8 aliphatic alcohol is added to an aqueous solution of a biodegradable copolymer . typically the aqueous biodegradable polymer solution is about 9 - 30 % by weight , preferably 20 - 30 % by weight . if necessary , the ph is adjusted to the preferred ph range of about 3 . 0 to about 7 . 4 , more preferably about 3 . 0 to about 6 . 5 , most preferably from about 3 . 5 to about 6 . 0 . if the biodegradable polymer itself does not provide sufficient buffering capacity to maintain the composition in the desired ph range , a suitable buffer , such as a phosphate buffer , may be added as needed . typically , the composition also includes a lipophilic component selected from the group consisting of a c 1 to c 8 aliphatic alcohol , a c 8 to c 30 aliphatic ester , and a mixture thereof . in preferred embodiments , the composition includes a penetration enhancer selected from the group consisting of an alkyl - 2 -( n - substituted amino )- alkanoate ester , an ( n - substituted amino )- alkanol - alkanoate , or a mixture thereof . optionally the composition also comprises up to about 5 percent emulsifier . preferably , the composition also comprises up to about 2 percent emulsifier . suitable emulsifiers include polysorbates such as tweens , glyceryl monooleate , triolein , trimyristin and tristearin . a preferred emulsifier is trimyristin . the practice of the present invention is demonstrated in the following examples . these examples are meant to illustrate the invention rather than to limit its scope . variations in the treating compositions which do not adversely affect the effectiveness of prostaglandin e 1 will be evident to one skilled in the art , and are within the scope of this invention . for example , additional ingredients such as coloring agents , anti - microbial preservatives , emulsifiers , perfumes , prostaglandin e 1 stabilizers , and the like may be included in the compositions as long as the resulting composition retains desirable properties , as described above . when present , preservatives are usually added in amounts of about 0 . 05 to about 0 . 30 %. suitable preservatives include methylparabens ( methyl paba ), propylparabens ( propyl paba ) and butylhydroxy toluene ( bht ). suitable perfumes and fragrances are known in the art ; a suitable fragrance is up to about 5 percent myrtenol , preferably about 2 percent myrtenol , based on the total weight of the composition . the topical composition can further include at least one local anesthetic . suitable local anesthetics include those approved for topical application (“ topical anesthetics ”), including , but not limited to ambucaine , amolanone , amylocalne hydrochloride , benoxinate , benzocaine , betoxycaine , biphenamine , bupivacaine , butacaine , butamben , butanilicaine , butethamine , butoxycaine , carticaine , chloroprocaine hydrochloride , cocaethylene , cocaine , cyclomethycaine , dibucaine hydrochloride , dimethocaine , diperodon hydrochloride , dyclonine , ecgonidine , ecgonine , ethyl chloride , etidocaine , beta - eucaine , euprocin , fenalcomine , fomocaine , hexylcaine hydrochloride , hydroxytetracaine , isobutyl p - aminobenzoate , leucinocaine mesylate , levoxadrol , lidocaine , mepivacaine , meprylcaine , metabutoxycaine , methyl chloride , myrtecaine , naepaine , octacaine , orthocaine , oxethazaine , parethoxycaine , phenacaine hydrochloride , phenol , piperocaine , piridocaine , polidocanol , pramoxine , prilocalne , procaine , propanocaine , proparacaine , propipocaine , propoxycaine hydrochloride , pseudococaine , pyrrocaine , ropivacaine , salicyl alcohol , tetracaine hydrochloride , tolycaine , trimecaine , zolamine and mixtures thereof . when a topical anesthetic is included , the topical anesthetic comprises about 0 . 01 to about 10 % by weight . typical topical anesthetics include lidocaine , dyclonine , dibucaine , pharmaceutically acceptable salts and mixtures thereof . in one preferred embodiment , the topical anesthetic is about 0 . 5 to about 1 percent dyclonine , based on the weight of the composition . the pharmaceutical preparation is preferably in unit dosage form . in such form the preparation is subdivided into unit doses containing appropriate quantities of the active component . the unit dosage form is a packaged preparation , where the package containing the discrete quantities of the pharmaceutical preparation is , e . g . a rigid plastic dispenser or flexible packet . another aspect of the invention is an article of manufacture that comprises a composition for treating erectile dysfunction as described above in a suitable container , preferably in a container such as the dispenser disclosed in u . s . pat . no . 6 , 224 , 573 , in combination with labeling instructions . alternatively , the container can be a tube with a suitable orifice size , such as an extended tip tube , pouch , packet , or squeeze bottle and made of any suitable material , for example rigid plastic or flexible plastic . the labeling instructions can come in the form of a pamphlet , a label applied to or associated with the packaging of the article of manufacture . the labeling instructions provide for administering a composition of the invention to the meatus of the penis of a patient suffering from erectile dysfunction , directing the patient to hold the penis upright , hold the meatus open and place the composition in the navicular fossa without introducing the container into the meatus about 5 - 30 minutes , before sexual intercourse . printed labeling instructions are functionally related to the composition of the invention inasmuch as such labeling instructions describe a method to treat erectile dysfunction according to the present invention . the labeling instructions are an important aspect of the invention in that before a composition can be approved for any particular use , it must be approved for marketing by the responsible national regulatory agency , such as the united states food and drug administration . part of that process includes providing a label that will accompany the pharmaceutical composition which is ultimately sold . while the label will include a definition of the composition and such other items such as the clinical pharmacology , mechanism of action , drug resistance , pharmacokinetics , absorption , bioavailability , contraindications and the like , it will also provide the necessary dosage , administration and usage . thus , the combination of the composition with the dispenser with appropriate treatment instructions is important for the proper usage of the drug once it is marketed to the patient . such treatment instructions will describe the usage in accordance with the method of treatment set forth herein before . the fossa navicularis is a natural expanded chamber suitably adapted to receive and retain semisolid medicaments . a semi - solid medicament , such as the composition of the present invention , when placed into the meatus has higher impedance to flow at narrowed exits of this space , the meatus and the urethra . the impedance to flow is proportional to the product of the cross sectional area of the path and the path length . thus , a semi - solid medication of suitably chosen viscosity is naturally retained within the fossa , facilitating the absorption of active agents such as vasodilators and the like . the viscosity of the composition suitably ranges from about 5 , 000 cps to about 20 , 000 cps , preferably from about 7 , 000 cps to about 13 , 000 cps . in preferred embodiments , the viscosity of the composition is selected so that about 90 % to about 99 % of the applied composition is retained in the fossa navicularis for up to about thirty minutes . more preferably about 93 % to about 98 % of the applied composition , optimally more than 98 % is retained in the fossa navicularis for up to about thirty minutes . the quantity of active component in a unit dose preparation may be varied or adjusted from 0 . 01 mg to 1 g according to the particular application and the potency of the vasoactive prostaglandin . for example , where the vasoactive prostaglandin is prostaglandin e 1 , about 0 . 05 mg to about 0 . 8 mg prostaglandin e 1 is present , preferably about 0 . 1 mg to about 0 . 5 mg and in another embodiment , about 0 . 2 mg to about 0 . 3 mg . the composition can , if desired , also contain other compatible therapeutic agents , such as a piperazinyl quinazoline antihypertensive . unless otherwise indicated , each composition is prepared by conventionally admixing the respective indicated components together . exemplary composition a was prepared as follows . part a was formed by dissolving 0 . 4 parts prostaglandin e 1 ( alprostadil usp ) in 5 parts ethyl alcohol . next , 5 parts dodecyl 2 -( n , n - dimethylamino )- propionate were mixed into the alcohol - prostaglandin e 1 solution , followed by 5 parts ethyl laurate . part b was prepared starting from a ph 5 . 5 water / buffer solution . the water / buffer solution was prepared by adding sufficient potassium phosphate monohydride to purified water to create a 0 . 1 m solution . the ph of the water / buffer solution was adjusted to 5 . 5 with a strong base solution ( 1 n sodium hydroxide ) and a strong acid ( 1 n phosphoric acid ). the buffer solution represented about 80 parts of the total composition . all parts specified herein are parts by weight . to the buffer solution , was added 0 . 5 parts ethyl laurate . next , the locust bean gum ( in powder form ) was dispersed in the buffer solution and homogenized using a homogenizer . table 1 , below , contains a list of ingredients . the resulting composition was a spreadable , semi - solid suitable for application to the skin without the need for supporting devices such as patches and adhesive strips . the composition was both homogenous in appearance and resistant to separation . additional exemplary compositions b — i are prepared in the same manner using the components listed in table 1 . as noted above , in other embodiments , such as composition h , the composition may include a modified polysaccharide gum , suitably a modified galactomannan gum , such as a guar gum . alternatively , a polyacrylic acid polymer may be used instead of the polysaccharide gum . pge 1 was found to enhance neurite outgrowth in primary cultures of nadph positive cells derived from dorsocaudal regions of rat major pelvic ganglia . the dorsocaudal regions of 24 major pelvic ganglia ( dcr - mpg ) were dissected from sprague - dawley rats . each sample was placed on a reduced - growth factor matrigel coated glasscover slide in a culture dish filled with serum - free medium . pge 1 ( sigma ) was added to the medium at a final concentration of 1 , 10 , 20 , 30 , 60 , or 100 micromoles ( μm ). the ganglia cultures were incubated at 37 ° c . in a humidified atmosphere with 5 % co 2 . digital photographs were taken of neurite growth after 96 hours . the control group ( 6 samples ) was incubated in matrigel in serum free medium without pge 1 . growth factor reduced matrigel ( passaniti , a ., et al ., lab . invest . 1992 67 : 518 - 528 ) was purchased from becton dickinson ( mountain view , calif .). cell culture grade pge 1 was purchased from sigma chemical . ( st . louis , mo .). rpim - 1640 and other cell culture reagents were purchased from gibco invitrogen corp . ( grand island , n . y .). male sprague - dawley rats , two - months old , were used in this study . all animal care , treatments , and procedures were approved by the institutional committee on animal research . the rats were sacrificed by intraperitoneal injection of sodium pentobarbital ( 50 mg / kg ) followed by bilateral thoracotomy and the removal of the dorsocaudal region of the major pelvic ganglia ( dcr - mpg ). each rat supplied a pair of dcr - mpg ; one was used as control and the contralateral ganglion was treated with pge 1 . the dcr - mpg isolated from sprague - dawley rats were cultured attached to matrigel - coated glass coverslips . the coverslips were used as the supporting platform to facilitate samples processing for histological staining and examination . coverslips were coated as follows . growth factor reduced matrigel ( becton dickinson , mountain view , calif .) was diluted 3 - fold in serum - free rpmi - 1640 in a 35 - mm culture dish on ice . the diluted matrigel was then spread onto cold sterilized glass coverslips using a sterilized glass slide as spreader . the coated coverslips were placed in 35 - mm culture dishes and incubated at 37 ° c . for 1 hr to allow the matrigel to solidify . each freshly dissected dcr - mpg was rinsed in phosphate - buffered saline ( pbs ), cut into equal thirds , placed on top of matrigel coated coverslips and covered by 50 μl cold growth factor reduced matrigel which had been kept in liquid form . after a 5 - min incubation at 37 ° c . to allow the matrigel to polymerize , 3 ml of serum - free rpmi 1640 medium supplemented with 1 × penicillin - streptomycin - fungizone ( cell culture facility , university of california , san francisco ) was added . pge 1 ( sigma , inc ., usa ) was added to the medium at a final concentration of 1 , 10 , 20 , 30 , 60 and 100 μm . the ganglia cultures were maintained at 37 ° c . in a humidified atmosphere with 5 % co 2 . after 2 to 3 days of incubation , the ganglia and outgrowing neurites were stained for nicotinamide adenine dinucleotide phosphate ( nadph ) diaphorase as an indication of nitric oxide synthase ( nos ) expression . the culture medium was removed from each culture and replaced with a fixative solution of 2 % formaldehyde , 0 . 002 % picric acid in 0 . 1 m phosphate buffer , ph 8 . 0 . after 20 min of fixation , the tissue was rinsed three times , 10 min each , with phosphate buffer , ph 8 . 0 . the tissue was then incubated with 0 . 1 mm nadph , 0 . 2 mm nitroblue tetrazolium , 0 . 2 % triton x - 100 in buffer for approximately 30 min at room temperature with constant microscopic monitoring for color development . when a deep blue color was detected for nadph - diaphorase positive nerves , the reaction was terminated by washing the tissues with buffer three times , 10 min each . the coverslips containing the ganglia were then mounted onto glass slides using buffered glycerin as mounting medium . neurites were photographed using a professional dcs - 420 digital camera ( eastman kodak , rochester , n . y .) connected to an olympus microscope and an apple macintosh powermac computer . all samples were photographed and the images were stored for later analysis . the digital images were analyzed using chemilmager 4000 software ( alpha innotech corporation , san leandro , calif .) to determine the maximum length of the outgrowing neurites fibers . statistical analysis was performed using computer software from primer of biostatistics , 3 rd ed . ( glantz sa , mcgraw - hill , inc . new york , 1992 ). the data involving different time points were first analyzed by one - way analysis of variance ( anova ). if anova indicated a significant difference , the student - neuman - keuls test was used to perform pair - wise comparisons . the results are shown in fig1 . four pairs of dcr - mpg were isolated and cultured as described in example 2 . the left side dcr - mpg were treated with pge 1 at a final concentration of 10 μm and the right served as controls . after 96 hr of culturing , significant outgrowth of neurites could be seen in pge 1 treatment dcr - mpgs when compared with the controls . the maximum neurite length of pge 1 treatment was 229 . 33 ± 10 . 7 μm and the control was 93 . 33 ± 28 . 4 μm ( p & lt ; 0 . 001 ). eight pairs of dcr - mpg were used in a study to explore the relationship between pge 1 dose and neurite outgrowth . pge 1 was added to the medium at a final concentration of 1 , 10 , 20 , 30 , 60 or 100 μm . see table 2 , below . the maximum pge 1 effect was observed at 30 μm pge 1 , which induced 250 ± 38 . 1 μm of fiber length . the difference is significant ( p & lt ; 0 . 05 ). a semi - solid prostaglandin topical composition , such as composition h , is used to promote the recovery of spontaneous erectile function after nerve - sparing radical retropubic prostatectomy in a group of patients needing such treatment . treatment is started during the first post - operative year , typically beginning , if appropriate , as early as the one - month follow - up visit after surgery . treatment is performed according to a regime of periodic intrameatal administration of the prostaglandin topical composition at least once weekly , preferably at least three times weekly , for a period of at least three months , preferably at least six months . each patient is instructed to place the medication in the navicular fossa by holding the penis upright , holding the meatus open and dropping the medication into the navicular fossa without introducing the medication container into the meatus . recovery of spontaneous erectile function is observed after 3 - 6 months treatment . combination therapy involving an implantable prostaglandin reservoir in conjunction with meatal administration of a semi - solid prostaglandin topical composition , such as composition h , is used to promote the recovery of spontaneous erectile function after nerve - sparing radical retropubic prostatectomy in a group of patients needing such treatment . a drug reservoir comprising a vasoactive prostaglandin and a biocompatible polymer is placed in fluid communication with the pelvic plexus and / or the cavernous nerve during the prostatectomy . in preferred embodiments , the biocompatible polymer is biodegradable . in preferred embodiments , the biocompatible polymer is flowable at room temperature . meatal treatment is started during the first post - operative year , typically beginning , if appropriate , as early as the one - month follow - up visit after surgery . treatment is performed according to a regime of periodic meatal administration of the prostaglandin topical composition at least once weekly , preferably at least three times weekly , for a period of at least three months , preferably at least six months . each patient is instructed to place the medication in the navicular fossa by holding the penis upright , holding the meatus open and dropping the medication into the navicularfossa without introducing the medication container into the meatus . recovery of spontaneous erectile function is observed after 3 - 6 months treatment . intrameatal application of a topical composition comprising a vasoactive prostaglandin and a penetration enhancer provides a method of promoting the recovery of spontaneous erectile function in patients with erectile dysfunction associated with diabetic neuropathy . a topical prostaglandin composition , suitably composition h of example 1 , is provided to the patient in need of treatment . each patient is instructed to apply the medication intrameatally , i . e . applying medication to the tip of the penis into the navicular fossa by holding the penis upright , holding the meatus open and dropping the medication into the navicular fossa without introducing the medication container into the meatus . the topical composition provides a tumescence - inducing , preferably an erection - inducing , dose of pge 1 . treatment is performed according to a regime of periodic intrameatal administration of the topical prostaglandin composition at least once weekly , preferably at least thrice weekly , for a period of at least three months , preferably at least six months . intrameatal application of the topical prostaglandin composition produces penile tumescence , and in the majority of applications , an erection sufficient for vaginal penetration . recovery of spontaneous erectile function is observed after 3 - 6 months treatment . while the foregoing is intended to be illustrative of the present invention , the scope is defined by the appended claims . numerous variations and modifications may be effected without departing from the true spirit and scope of the invention .
the present invention provides compositions and methods of use for treatment of erectile dysfunction associated with neuropathy related to diabetes , prostatectomy , cysto - prostatectomy , radical cystectomy , abdominoperineal resection of the rectum , cryoablation or radiation therapy .