the subject invention is directed toward a treatment for impotence . impotence is the consistent inability to achieve or sustain an erection of sufficient rigidity to have sexual intercourse . specifically , the subject invention is a method for inducing or enhancing an erection by administering in an effective amount , preferably in low doses to the penis , a compound of formula i : ## str2 ## or a pharmaceutically acceptable salt thereof , wherein r 1 is independently hydrogen , or a c 1 - 8 alkyl , c 2 - 8 alkenes , c 3 - 8 cycloalkyls and isomeric forms thereof ( which includes straight and branched chains ). preferably , formula i is n - cyano - n &# 39 ;( 1 , 1 - dimethyl propyl )- n &# 34 ;- 3 - pyridinyl guanidine ( r l is hydrogen and r 2 is 1 , 1 - dimethyl propyl ). preferably , the compound is administered by injection to the penis and preferably into the corpus cavernosum of the penis . more preferably the drug can be delivered in a pharmaceutical preparation , diluent or gel , by injection or topical application , respectively . for injection , the active compound can be diluted in a saline solution , purified water or combination thereof . topical preparations can include the active compound with n - methyl pyrrolidone , oleyl alcohol , propylene carbonate , dimethyl sulfoxide ( dmso ) or combinations thereof . the preferred compound of the subject invention is n - cyano - n &# 39 ;( 1 , 1 - dimethyl propyl )- n &# 34 ;- 3 - pyridinyl guanidine although its related compounds as disclosed in u . s . pat . no . 4 , 057 , 636 and its reissue u . s . pat . no . re 31 , 244 ( herein incorporated by reference ) can be effective also . the compound of formula i is administered in an effective amount which is sufficient to cause or enhance the erection . typically , the dose is from about 0 . 5 micrograms to about 1000 micrograms preferably from about 5 micrograms to about 10 micrograms in man . the response appears to be dose related and therefore increasing amounts are directly related to the duration or size of the erection . of course , different male mammal species would have dosages relative to their anatomical size and weight . calculation of dosages would be a routine calculation to anyone of ordinary skill of the art such as a veterinarian , urologist , or physician . the pharmaceutical properties of the subject compounds to behave as a vasodilator was confirmed utilizing an in vitro rabbit mesenteric artery assay . rabbit mesenteric artery tissue was equilibrated at one gram resting tension for one hour in physiological saline solution ( pss ) prior to producing a first norepinephrine contraction . at the plateau of the first norepinephrine contraction , acetylcholine ( ach 1 μm ) was added to study endothelium - dependent vasodilation . thus , ach - induced relaxation was routinely used as a test for the presence of functional endothelium . the tissues were washed with pss , and were again left at the resting tension for one hour , before challenging them with the second norepinephrine contraction . at the plateau of the second norepinephrine contraction , the subject compounds were tested at concentrations of 0 . 01 μm to 0 . 5 μm . each concentration was tested for about ten minutes or until relaxation plateaued . all compounds were not tested at all levels where vasodilation effect was or was not apparent . the percent relaxation was measured for each compound as shown in table 1 . the data was generated from 28 mesenteric rings from four rabbits . table i______________________________________compound ( i ) % relaxationr . sub . 1 r . sub . 2 0 . 01 μm 0 . 05 μm 0 . 1 μm 0 . 5 μm______________________________________1 h 1 , 1 - dimethyl 81 . 8 81 . 0 -- -- propyl2 h 1 , 1 - dimethyl 9 . 6 73 . 0 -- -- propene3 h 1 , 1 - diethyl 11 . 3 76 . 0 -- -- propene4 * h 1 , 1 - dimethyl 2 . 6 5 . 3 7 . 4 10 . 6 ethylbenzene5 * h 1 , 1 - dimethyl 0 6 . 1 0 0 methylbenzene6 * h 1 , 1 - dimethyl -- 11 . 2 6 . 6 34 . 6 butyne7 h 1 , 1 - dimethyl 42 . 0 76 . 3 -- -- butane8 h 1 - methyl cyclo - 10 . 5 81 . 0 -- -- pentane______________________________________ * inactive vasodilators , not compounds of the subject invention . pharmaceutical evidence of a treatment to induce or effect an erection was studied using tranquilized , male cynomolgus macaque monkeys . intracavernous injections of test compound were given in 0 . 15 ml normal saline containing 0 . 2 % dmso . prior to each injection , a band was placed at the base of the penis , the injection was made using a 27 gauge needle and the band removed 2 minutes later . an increase to maximal penis length , elevation off the scrotum ( rigidity ), the evidence of cardiac pulse in the organ ( pulse ) are good indicators of a full erection . length was measured from the tip of the penis to a reference point marked on the abdomen near the base . changes in length were monitored at various intervals during the trials after injection . latency to full erection and duration of erection were recorded . the subject compound n - cyano - n &# 39 ;( 1 , 1 - dimethyl propyl )- n &# 34 ;- 3 - pyridinyl guanidine , was administered to monkeys and the data collected as shown in table ii . the pulse and rigidity values represent the number of monkey that achieved a pulse in the penis and rigidity ( penis elevated off scrotum ) which are the best indicators of an erection . table ii______________________________________ time durationconcentration pulse rigidity to erection of erection______________________________________15 μg injection 6 / 10 6 / 10 4 . 5 min . ± 0 . 7 18 . 8 ± 5 . 51 . 5 μg injection 7 / 10 7 / 10 3 . 6 min . ± 0 . 5 14 . 0 ± 3 . 3zero , ( dmso 0 / 5 0 / 5 -- -- only ) 15 mg topical 0 / 5 0 / 5 -- -- ______________________________________ compound n - cyano - n &# 39 ;( 1 , 1 - dimethyl propyl )- n &# 34 ;- 3 - pyridinyl guanidine , (&# 34 ; test compound &# 34 ;) was compared against pinacidil to demonstrate its superior effects on inducing an erection . both compounds were administered to monkeys and the data collected as shown in table iii . the data indicates the number of monkeys that achieved an erection per monkeys dosed at the specified concentration . table iii______________________________________compound concentration pulse and rigidity______________________________________test * . 3 μg 1 / 4 . 6 μg 2 / 4 1 . 5 μg 4 / 4pinacidil 1 . 6 μg 0 / 3 8 μg 0 / 3 16 μg 0 / 3 32 μg 3 / 4______________________________________ * n - cyano - n &# 39 ; ( 1 , 1dimethyl propyl ) n3 - pyridinyl guanidine the test compound when compared to pinacidil was superior and showed the unexpected result of providing an erection in monkeys at significantly reduced dosage **. in fact , pinacidil at the lower dosages had no noticeable effect .
a method to induce or enhance an erection or treat erectile dysfunction through the administration of a pyridylguanidine compound , preferably , n - cyano - n &# 39 ;- n &# 34 ;- 3 - pyridinyl guanidine , in low doses to the penis . administration can be by injection into the corpus cavernosum of the penis or transdermal application .