Polypyrrole as a model membrane for drug delivery

The possibility of using the conductive polymer polypyrrole as an ion gate membrane for the controlled release of anionic drugs has been studied using three model substances with therapeutic activity: salicylate, naproxen and nicoside. In addition, the release of tosylate, used for the electrosynthesis of the membrane, was investigated. The electrochemical quartz crystal microbalance was used to determine the mass changes occurring in 150 nm thick membranes loaded with the anion as a result of cathodic polarisation, Thicker membranes, 1-6 mu m, were grown on a large gold electrode. The release of drugs from these membranes as a result of negative potential steps was followed using HPLC. It was found that the stability of the membrane doped with the appropriate drug towards chloride exchange in a 0.1 M NaCl solution was very good. Less than 5% of the theoretical amount of anion in the membrane was spontaneously released. Negative potential step experiments showed that salicylate, naproxen and tosylate, but not nicoside, could be released from the membrane in a controllable way. These results show that controlled release of a drug from polypyrrole membranes can be achieved using simple electrochemical step or staircase signals. Thus tailor made parts for iontophoretic devices can be manufactured. The amount of drug which can be released is, however, small and the application may therefore be restricted to drugs with high therapeutic activity. (C) 1998 Elsevier Science S.A. All rights reserved.