the term &# 34 ; minoxidil &# 34 ; as used herein refers to the compound 6 -( 1 - piperidinyl )- 2 , 4 - pyrimidinediamine 3 - oxide ( the uninverted name used by chemical abstracts service during the ninth and / or subsequent collective index periods and having the chemical abstracts registry number [ 38304 - 91 - 5 ]). the merck index , eleventh edition ( published by merck & amp ; co ., inc ., rathway , n . j ., u . s . a ., 1989 ) lists a number of other names , including 6 - piperidino - 2 , 4 - diaminopyrimidine 3 - oxide and 6 - amino - 1 , 2 - dihydro - 1 - hydroxy - 2 - imino - 4 - piperidinopyrimidine , one of the tautomers of minoxodil . reference is also made to u . s . pat . nos . 4 , 970 , 063 and 3 , 461 , 461 . ionic specifically cationic derivatives of minoxidil are formed according to a preferred embodiment of the present invention by means such as set forth in the following general procedure . a solution of 4 . 2 g ( 0 . 02 mole ) of minoxidil ( 6 - piperidino - 2 , 4 - diaminopyrimidine - 3 - oxide ) in 100 ml of 95 % alcohol at about 70 ° c . is placed in a 500 ml three - necked flask equipped with a reflux condenser , stirrer and a dropping funnel . the stoichiometric amount of an organic acid ( 0 . 01 mole of d - tartaric acid or 0 . 02 mole of one of the other acids listed below ) dissolved in 100 ml of 95 % ethanol at a temperature of about 70 ° c . was placed in the dropping funnel and added to the stirred minoxidil solution in a dropwise fashion over a period of about one hour . upon completion of the addition , the reaction mixture is stirred , for from 16 to 24 hours , while being maintained at a temperature of about 70 ° c . any significant amount of solid present is removed by filtration . the remaining solution is transferred to a 500 ml one - necked flask and concentrated to about 50 ml under reduced pressure using a roto vac device . the precipitates formed are collected by vacuum filtration and purified by recrystallization from absolute alcohol . seven prototype salts or cationic derivatives were prepared using the general procedure . the salt obtained from the reaction with 5 - nitro - 2 - furoic acid was bright yellow in color ; all other compounds were white solids . the salts were characterized by their melting points , elemental analyses , infrared spectra , proton nmr spectra and carbon 13 nmr spectra . the percentage yields , melting points and elemental analyses are summarized in table 1 . table 1__________________________________________________________________________ molecular meltingorganic acid formula of % point , elemental analysisreactant product yield ° c . % c % h % n__________________________________________________________________________ [ r -( r *, r *)]- 2 , 3 - c . sub . 22 h . sub . 36 n . sub . 10 o . sub . 8 87 % 212 - 214 theory 47 . 14 6 . 47 24 . 99dihydroxy - butan - found 46 . 48 6 . 19 24 . 46edioc acid ( d - tar - taric acid ) 2 , 4 , 6 ( 1h , 3h , 5h )- c . sub . 13 h . sub . 19 n . sub . 7 o . sub . 4 86 % 198 - 200 theory 46 . 29 5 . 68 29 . 06pyrimidinetrione found 45 . 05 5 . 77 28 . 16 ( barbituric acid ) 3 , 4 - dihydroxy - c . sub . 16 h . sub . 21 n . sub . 5 o . sub . 5 89 % 212 - 214 theory 52 . 89 5 . 83 19 . 27benzoic acid found 52 . 49 5 . 96 22 . 37 ( protocatechuicacid ) 2 , 3 , 4 - trihydroxy - c . sub . 16 h . sub . 21 n . sub . 5 o . sub . 6 62 % 226 - 228 theory 50 . 66 5 . 58 18 . 46benzoic acid found 50 . 22 5 . 57 20 . 133 , 4 , 5 - trihydroxy - c . sub . 16 h . sub . 21 n . sub . 5 o . sub . 6 85 % 211 - 212 theory 50 . 66 5 . 58 18 . 46benzoic acid found 50 . 63 5 . 84 21 . 82 ( gallic acid ) 5 - nitro - 2 - furoic c . sub . 14 h . sub . 18 n . sub . 6 o . sub . 6 55 % 226 - 228 theory 45 . 90 4 . 95 22 . 94acid found 45 . 81 4 . 82 22 . 845 , 5 - dimethyl - c . sub . 14 h . sub . 22 n . sub . 6 o . sub . 4 65 % 165 - 167 theory 49 . 70 6 . 55 24 . 84oxazolidine - 2 , 4 - found 50 . 21 6 . 68 26 . 16dione ( dimethadione ) __________________________________________________________________________ equations for the reactions of minoxidil with the seven organic acids listed in table 1 are listed below . the cationic derivatives of minoxidil are not limited to those produced by the seven acids which are listed but may be produced with other organic and inorganic acids . the transdermal iontophoresis of cationic derivatives of minoxidil was demonstrated in laboratory experiments utilizing fresh , full - thickness mouse skin with clipped hair , which has been reported to be an excellent model for studying the drug permeability of human skin . iontophoresis was conducted with side - by - side diffusion cells obtained from the crown glass co . a piece of mouse skin was clamped between the two half - cells , and the donor cell was filled with an aqueous solution of one of the ionic derivatives of minoxidil . the receiver cell was filled with 0 . 05 molar sodium chloride solution . an electric current was applied across the two half - cells using silver / silver chloride electrodes inserted into both cells through teflon plugs . the donor cell electrode was always the anode ( positive pole +) except where otherwise noted . an electric stimulator was used to apply a 0 . 8 milliamp , current to a diffusion area of 0 . 64 cm 2 for periods of up to 90 minutes , and the iontophoretic mobility of the ionic derivatives of minoxidil was determined by sampling the receiver cell compartment at various times throughout the study . the concentration of cationic derivatives of minoxidil in the receiver cell was measured by ultraviolet spectrophotometry . data was also obtained under passive conditions without any electric current . the results of 4 to 8 separate experiments with each minoxidil ionic derivative were used to calculate the average flux for passive and active iontophoretic conditions and these data are shown in table 2 below . iontophoresis significantly enhanced the skin permeation of the minoxidil ionic derivatives . the minoxidil tartrate derivative of those tested showed significant improvement in iontophoretic mobility across the skin . these results demonstrate that iontophoresis can be used to enhance the delivery of minoxidil to the skin . table 2__________________________________________________________________________active ( iontophoretic ) and passive flux ( ug / cm . sup . 2 / h ) of minoxidilionic derivates . sup . 1minoxidil ionicderivates . sup . 2 5 - 30 minutes 30 - 90 minutes 5 - 90 minutes__________________________________________________________________________dimethadione 0 . 1 % active 68 . 6 ± 10 . 3 136 . 0 ± 19 . 8 95 . 8 ± 13 . 3passive 25 . 7 ± 5 . 5 25 . 8 ± 2 . 4 17 . 2 ± 1 . 6dimethadione 0 . 2 % active 74 . 0 ± 15 . 3 146 . 6 ± 9 . 9 97 . 7 ± 6 . 6passive 34 . 9 ± 5 . 8 29 . 2 ± 1 . 7 19 . 5 ± 1 . 2tartrate 0 . 1 % active 65 . 4 ± 19 . 4 189 . 7 ± 36 . 2 144 . 6 ± 23 . 0passive 59 . 2 ± 17 . 6 25 . 6 ± 6 . 2 29 . 6 ± 6 . 6tartrate 0 . 2 % active 74 . 3 ± 21 . 8 180 . 4 ± 26 . 7 140 . 9 ± 22 . 7passive 23 . 3 ± 4 . 7 20 . 6 ± 6 . 8 20 . 2 ± 5 . 8trihydroxybenzoate 0 . 1 % active 37 . 2 ± 5 . 8 62 . 4 ± 9 . 9 59 . 7 ± 7 . 8passive 24 . 7 ± 4 . 3 24 . 5 ± 3 . 4 21 . 9 ± 3 . 6trihydroxybenzoate 0 . 2 % active 53 . 2 ± 5 . 6 173 . 9 ± 29 . 0 115 . 9 ± 19 . 4passive 4 . 3 ± 1 . 9 6 . 0 ± 1 . 8 4 . 0 ± 1 . 2__________________________________________________________________________ . sup . 1 values are the mean and standard error of 4 to 8 separate studies . . sup . 2 the terminology for the derivatives is expressed as the common nam for the acid used and the concentration is expressed as percentage of minoxidil base . in practice , one method of practicing the invention is to mix the cationic derivative salt of minoxidil as a distilled water solution in proportion of 0 . 1 mg / ml to a saturated solution . an iontophoretic device such as manufactured and sold by general medical co . under the registered mark lectro patch would be used . both treatment pads are saturated with the minoxidil salt solution . the saturated treatment pads are placed on the skin where enhanced growth is desired . this particular device will only accept up to 1 milliamp ( ma ) of current . other iontophoretic devices , such as new life litronic stimulator manufactured by mid - western electronics inc . model no . 0880 can deliver up to 0 . 5 ma per cm 2 can also be used . the tolerance of an individual patient determines time and milliamp limits above 0 . 5 ma per cm 2 . while the invention has been described with a certain degree of particularity , it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure . it is understood that the invention is not limited to the embodiment set forth herein for purposes of exemplification , but is to be limited only by the scope of the attached claimed or claims , including the full range of equivalency to which each element thereof is entitled .
this invention relates to a method of applying a cationic derivative of minoxidil which is transported by means of iontophoresis to hair follicles where the cationic derivatives promote hair growth . each of the cationic derivatives of minoxidil are synthesized by reacting the minoxidil parent compound with an organic or an inorganic acid to form the cationic derivative .