The administration efficiency of a drug may be improved by establishing
compatibility between the suppression of the release of a biological
counter ion from a living body's biological interface and the maintenance
of a good state of contact between each of a working electrode structure
and a nonworking electrode structure and the biological interface.
Coating films each composed of an external preparation containing: a
hydrophilic polymer matrix agent; and an ion-exchange resin dispersed in
the hydrophilic polymer matrix agent, or coating films each composed of
an external preparation containing a hydrophilic polymer having an
ion-exchange function are formed on the biological interface, and
iontophoresis is performed through the coating films.