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[0324] 

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[0325] Since PPA-HCl is a salt of a free base, it reacts with K$_{3}$ PO$_{4}$ . The concentration of K$_{3}$ PO$_{4 }$ in the system after the reaction is completed depends on the amount of PPA-HCl added. The remaining K$_{3}$ PO$_{4 }$ concentration after the reac› tion is completed is defined as "excess K$_{3}$PO$_{4 }$ concentra› tion," which is defined by the following equation. 

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[0326] The excess K$_{3}$PO$_{4 }$ concentration for the four PPA› HCl systems was calculated, and the pH of the patch was measured as described in the Methods section. The pH of the PPA-HCl patch increased from 6.75 to 9.68 when the K$_{3}$ PO$_{4 }$ concentration in the dried patch was increased from 0% to 19.9% (or 0.2% excess K$_{3}$PO$_{4 }$ concentration). However, the pH of the PPA-HCl patch remained about the same when the excess K$_{3}$ PO$_{4 }$ concentration in the dried patch was further increased from 0.2% to 3.2%. 

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[0327] The cumulative amount of PPA-HCl across human cadaver skin was calculated using the measured PPA-HCl concentrations in the receiver solutions. 

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[0328] The cumulative amount of PPA-HCl that perme› ated across the human cadaver skin at 24 hours for PPA-10 (2055.2 µg!cm 2 ) with a calculated excess K$_{3}$PO$_{4 }$ concentra› tion of 0.2% was three times higher than that from the formulation without K$_{3}$ PO$_{4 }$ (PPA-9, 680.5 µg!cm 2 ). This result indicated that the permeation of PPA-HCl could be enhanced with an excess K$_{3}$PO4 concentration as low as 0.2%. 

[0329] The cumulative amount of PPA-HCl across human cadaver skin at 24 hours remained about the same when the excess K$_{3}$ PO$_{4 }$ concentration in the dried patch was increased from 0.2% to 3.2%. The formulations of PPA-10, PPA-11 and PPA-12, all provided up to 3-fold more phenylpropano› lamine hydrochloride flux than in the absence of K$_{3}$ PO$_{4 }$ (PPA-9). 

