Which statement best describes the difference between phonophoresis and iontophoresis?

• A. Phonophoresis uses electrical current to drive charged drugs through the skin.
• B. Phonophoresis uses ultrasound to enhance drug delivery; iontophoresis uses electrical current to drive charged drugs through the skin.
• C. Phonophoresis uses ultrasound to enhance drug delivery; iontophoresis uses thermal heating only.
• D. Phonophoresis uses ultrasound to enhance drug delivery; iontophoresis uses laser energy.

Answer: (C)

Phonophoresis uses ultrasound energy to increase skin permeability and boost drug diffusion through the skin. Iontophoresis relies on an electrical current to move charged drug molecules into and through the skin by electrostatic forces and ion migration. The core distinction is the energy form driving delivery: ultrasound versus electrical current. While heating can occur as a secondary effect, iontophoresis is not defined as thermal heating only, since its primary mechanism is electrical transport of ions.