External preparation, method of applying external preparation, iontophoresis device, and percutaneous patch

A method of applying an external preparation, comprising:

• supplying a hydrophilic polymer having an ion exchange function in a reservoir;
• spraying the hydrophilic polymer from a coating nozzle onto a biological interface;
• and
• applying a voltage between an inductor electrode in contact with the spray of the hydrophilic polymer and the coating nozzle.

An iontophoresis device, comprising a working electrode structure comprising:

• a first electrode;
• a first electrolyte solution holding part for holding an electrolyte solution in contact with the first electrode;
• a first ion-exchange membrane for selectively passing ions of a second polarity, the first ion-exchange membrane being placed on a front side of the first electrolyte solution holding part;
• a drug holding part for holding a drug solution containing drug ions of a first polarity, the drug holding part being placed on a front side of the first ion-exchange membrane;
• and
• a first liner attached to a surface on a front side of the drug holding part, the first liner being removed upon administration of the drug ion into a living body.

An iontophoresis device, comprising a working electrode structure comprising:

• a first electrode;
• and
• a drug holding part for holding a drug solution containing drug ions of a first polarity, the drug holding part receiving power from the first electrode, wherein the drug ions are administered by applying an electrical potential of the first polarity to the first electrode in a state where the drug holding part is brought into contact with a coating film formed on a biological interface, the coating film being composed of an external preparation containing:
• a hydrophilic polymer matrix agent;
• and an ion-exchange resin dispersed in the hydrophilic polymer matrix agent, the ion-exchange resin being introduced with an ion exchange group whose counter ion is of the first polarity, or an external preparation containing a hydrophilic polymer having a function of exchanging an ion of the first polarity.