iontophoresis
/ eye-on-toh-for-EE-sis /
Phonophoresis tries to push a medication through the skin using sound; iontophoresis tries to do the same thing using a small electrical current. It rests on a simple piece of physics: like charges repel, so an electrode of the same charge as a charged drug will push that drug away from the skin surface and a little way into the tissue.
A medicated solution — for example an anti-inflammatory steroid (such as dexamethasone) or a numbing agent — is placed under an electrode, and a gentle, low electrical current is run for some minutes. The matching electrical charge drives the drug's charged molecules through the skin barrier into the shallow tissue beneath, so the medication can act on an inflamed tendon or joint without a needle. A second, opposite electrode completes the circuit on nearby skin. The person feels a mild tingling, not a shock. A related everyday use, with plain tap water rather than a drug, treats excessive sweating of the hands and feet.
Iontophoresis is needle-free and locally targeted, which patients like, and it has slightly better evidence than phonophoresis for some conditions, though still limited and inconsistent. Its reach is shallow, the amount of drug delivered is modest, and it does not address the underlying cause. The current can irritate or even burn the skin if too strong or poorly set up, so it is avoided over broken skin, in people with current-sensitive implants such as pacemakers, and where sensation is impaired.
For a patient with an inflamed heel tendon who prefers to avoid an injection, the clinician places an anti-inflammatory solution under an electrode and runs a gentle current for several minutes to drive some of the drug into the sore area.
Electricity nudges a charged drug through the skin — needle-free but shallow.
Delivery is shallow and the dose modest; too strong a current can irritate or burn the skin, so it is avoided over broken skin and where sensation is impaired.