iontophoresis

Iontophoresis uses a small, painless electric current to push a charged drug through the skin, the way a like-charged electrode repels a like-charged molecule away from itself and into the tissue. It is electricity giving the medicine a gentle shove across a barrier it could not easily cross on its own.

Two electrodes are placed on the skin, with the drug loaded under the electrode that carries the same charge as the drug ion. When a low-voltage current flows, the drug ion is electrostatically repelled from that electrode and migrates toward the oppositely charged one through the skin (a process called electromigration). A second effect, electroosmosis, carries even uncharged or large molecules along with the bulk solvent flow, typically from the positive electrode. The delivered amount rises roughly in proportion to the current applied and the time, giving an electronically tunable dose.

Because it actively transports drug, iontophoresis extends transdermal delivery to more polar or somewhat larger molecules than passive patches allow, and the rate can be switched on and off or programmed. Practical limits include skin tolerance to current (irritation or tingling if too strong), the need for a powered device, and an upper size ceiling that still excludes most large biologics. It is best suited to potent, water-soluble, ionizable drugs needing controllable or on-demand delivery.