Abstract
The iontophoretic delivery across rat skin of a quartemary ammonium salt (isopropamide: ISP), which is positively charged over a wide pH range, was measured in vitro. The study showed that: (a) iontophoresis significantly enhanced ISP delivery compared to passive transport; (b) ISP delivery was directly proportional to the applied continuous direct current density over the range of 0–0.69 mA/ cm 2; (c) ISP delivery was also proportional to the ISP concentration in the donor compartment over the range of 0–2 × 10 −2 M; (d) sodium ion in the donor compartment inhibited the ISP transport possibly due to decreasing the electric transference number of ISP; (e) ISP delivery increased as the pH of the donor solution increased over the pH range 2–7, suggesting permselective nature of the epidermis, and inhibition of the transference number of ISP by hydronium ion; (f) some organic anions such as taurodeoxycholate, salicylate and benzoate which form lipophilic ion-pair complexes with ISP inhibited the delivery of ISP. The degree of inhibition by the organic anions was linearly proportional to the extraction coefficient ( K e) of ISP from the partition system with each counteranion between phosphate buffer (pH 7.4 ) and n-octanol. It suggests that not only sodium ion and hydronium ion but also the counteranions which form lipophilic ion-pairs with ISP are not favorable components in formulating the donor solution of ISP, a cationic drug, to achieve an effective iontophoretic delivery.
Published Version
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