the present invention relates to iontophoretically enhanced transdermal delivery of nicotine salts . more particularly , this invention relates to the iontophoretic transdermal delivery of certain nicotine salts which have been discovered to have an improved nicotine flux when compared to other nicotine salts and reduced lagtime in delivering nicotine . in particular , nicotine maleate , nicotine citrate and combinations thereof are useful for iontophoretic transdermal delivery of nicotine in a nicotine replacement therapy regimen . the following methodology was employed in the examples described herein : dermatomed human skin stored at − 80 ° c . was thawed just prior to use . each permeation experiment consisted of four replicates . the skin for each replicate was obtained from a different donor so that the variation was randomized . skin was mounted on valia - chien ( horizontal ) diffusion cells for these in vitro permeation studies , with stratum corneum side facing the donor side . the receptor compartment was filled with ph 7 . 4 phosphate buffer ( 50 mm ). to the donor compartment , 1 % nicotine or its salt was added according to the examples that follow . prior to use , both donor and receptor solutions were degassed by helium sparging . the temperature of the water bath was set to 32 ° c . both donor and receptor compartments were continuously stirred . for iontophoresis , silver wire was used as the anode in the donor compartment and silver / silver chloride as cathode in the receptor compartment . a current of 0 . 5 ma / sq . cm was applied for 4 hours . samples taken periodically from the receptor compartment were analyzed by hplc assay . an xterra rp18 column was used and the detection wavelength was 261 nm . the mobile phase was 85 : 15 buffer : acetonitrile , pumped at 1 ml / min and retention time was about 3 minutes . permeation of nicotine base was studied under two different sets of conditions . i ) nicotine in 50 mm hepes ([ 4 -( 2 - hydroxyethyl )- 1 - piperazine ethanesulfonic acid ) buffer ph 5 . 5 with 50 mm nacl . ii ) nicotine in 500 mm citrate buffer ph 8 with 50 mm nacl . nicotine is a diacidic base with pka values of 3 . 4 and 8 . 2 . it exists as a free base above ph 9 . in between ph 4 . 8 - 7 . 5 it is present in the form of freebase and monocations . passive transport of nicotine was higher at ph 8 , when the drug predominantly exists in the non - ionized form , as compared to the monocationic form of nicotine at ph 5 . 5 . iontophoresis enhanced nicotine permeation compared to passive nicotine delivery in both of the conditions evaluated ( fig1 and 2 ). transdermal delivery of nicotine salts by passive diffusion and iontophoresis in 500 mm citrate donor buffer passive and iontophoretic permeation of nicotine salts ( equivalent to 1 % nicotine ), specifically nicotine bitartrate and nicotine hemisulfate , were studied in 500 mm citrate buffer with 50 mm nacl . iontophoretic current was terminated after 4 hours . the iontophoretic flux of nicotine was similar in both the salt forms , which was less than the flux from the passive delivery of nicotine base at ph 8 ( fig3 ). when ph of the donor solution was measure after the experiment , it was found that the ph of donor solutions did not change . comparison of the iontophoretic delivery of nicotine bitartrate salt in 50 mm hepes donor buffer vs 500 mm citrate donor buffer iontophoresis of nicotine bitartrate salt was studied in 50 mm hepes buffer ph 5 . 5 . nicotine bitartrate salt decreased the ph of hepes buffer to about 3 . 5 , which was then adjusted to about ph 5 . 5 with naoh . from the comparison plot ( fig3 ), it is seen that the flux of nicotine from 50 mm hepes buffer is higher than the nicotine flux from a 500 mm citrate buffer . it appears that a higher buffer strength of citrate buffer contributed to more buffer ions which competed with the drug ions to be delivered across the skin , thereby reducing the nicotine permeation . there was some indication of this in the conductivity measurements . the 500 mm citrate buffer solution had a conductivity of 66400 μmhos / cm , compared to 16300 μmhos / cm measured for the 50 mm hepes buffer solution . the ph measure at the end of the experiment with 50 mm hepes solution indicated that it did not change significantly . comparison of the iontophoretic delivery of nicotinium dihydrochloride salt versus nicotine bitartrate salt iontophoretic delivery of nicotinium dihydrochloride salt was also studied in 50 mm hepes buffer , adjusted to ph 5 . 5 with naoh . the delivery profile was similar to that obtained from nicotine bitartrate salt in 50 mm hepes buffer ( fig5 ). the conductivity of each donor solution was similar , 15400 μmhos / cm and 16300 μmhos / cm for nicotinium dihydrochloride in 50 mm hepes and nicotine bitartrate in 50 mm hepes , respectively . when the current was terminated at 4 hrs , the flux of nicotine from the both the salts decreased sharply ( fig6 ). comparison of the iontophoretic delivery of various nicotine salts in 50 mm hepes buffer iontophoretic permeation of various nicotine salts , i . e . maleate , dihydrobromide , dihydrosulfate , tetrahydrosulfate , citrate and dihydrohexanoate ( equivalent to 1 % nicotine , except citrate salt which was approximately 0 . 92 %) were studied in 50 mm hepes buffer , ph 5 . 5 . each respective nicotine salt was added to 50 mm hepes , then ph was adjusted to 5 . 5 with naoh . all the salts were directly dissolved in hepes buffer , except nicotine dihydrohexanoate salt which was dissolved in hepes buffer with the aid of 20 % ethanol . the permeation profiles of the salts were compared to that of nicotine bitartrate and nicotine dihydrochloride salt ( fig6 ). the conductivity , flux and lagtime of permeation of nicotine ( passive , donor ph 8 ) and nicotine salts ( iontophoresis , donor ph 5 . 5 ) are listed in table 1 . the flux is calculated at steady state when current is present for the iontophoresis experiments . iontophoresis of nicotine salts , in particular , nicotine maleate and nicotine citrate reduced the lagtime , 4 min and 9 min , respectively , compared to passive permeation of nicotine base ( 87 min ). iontophoresis of the nicotine salts also increased the flux of nicotine , flux ranging from 0 . 2073 mg / cm 2 - hr for nicotine bitartrate to 0 . 332 mg / cm 2 - hr for nicotine citrate , compared to passive permeation of nicotine base ( 0 . 1053 mg / cm 2 - hr ). fig8 compares passive permeation of nicotine base ( ph 8 ) with iontophoresis of nicotine maleate and nicotine citrate at ph 5 . 5 . flux of nicotine is increased with iontophoresis of the nicotine salts , compared with passive permeation of nicotine base . lagtime during iontophoresis of the nicotine salts is also reduced .
the present invention relates to iontophoretic transdermal delivery of nicotine salts useful for nicotine replacement therapy for an individual in need thereof . the present invention further relates to the iontophoretic transdermal delivery of nicotine maleate and nicotine citrate . methods of reducing skin irritation generally caused by transdermal nicotine delivery by iontophoretic transdermal delivery of nicotine salts are also disclosed .