The Use of Ion-exchange Fibers in Controlled Transdermal Iontophoretic Drug Delivery

Transdermal iontophoresis is a method where the movement of ionic drugs (and sometimes also neutral drug molecules) across skin is enhanced using an externally applied potential difference. Iontophoretic devices contain three distinct components; 1) the drug reservoir which contains one electrode, the polarity chosen depends on the charge of the drug, 2) the return electrode and 3) the electronic controller. In this study ion-exchange fibers were investigated as a drug reservoir material for iontophoretic device. The parameters affecting the drug release from the ion-exchange fibers without applied current were studied experimentally and theoretically modeled using five model drugs and four different ion-exchange fibers. It was found that lipophilic drugs were retained more strongly and for longer in the fibers than hydrophilic drugs. The hydrophilic drugs were also released more readily from fibers containing strong ion-exchange g roups, whereas the lipophilic drugs attached more strongly to strong ion-exchange groups and released more easily from the weak ion-exchange groups. The salt concentration and the choice of the salt also had an effect; when using equimolar amounts of sodium chloride at lower salt concentrations, more drug was released. Incorporation of calcium chloride in the bathing solution increased considerably both the drug release rate and the total amount of drug released when compared to sodium chloride alone. The d rug release from the fibers were studied in vitro and in vivo using iontophoresis. Due to significantly different release properties, tacrine and metoprolol were chosen for screening of their suitability for this kind of iontophoretic system, using an in-house designed in vitro cell. It was found that the rate of tacrine release from the device could be controlled by adjusting the salt concentration and the current density used but the rate of metoprolol release could not be controlled this way. A semi-quantitative and pragmatic interpretation of the results also showed that it should be possible to manufacture a transdermal iontophoretic patch to delivery tacrine. It was also determined in vivo that clinically relevant plasma concentrations of tacrine could be achieved in a human volunteer using an in-house designed and manufactured iontophoretic transdermal drug delivery patch. My warmest thanks to my ex-and present officemates Eeva, Annika and Kirsi who had to cope with me (and the mess I made in my part of the office) during these years. I also thank all the personnel of the Laboratory of Physical Chemistry. I also wish to thank Kenneth …