Overcoming skin's barrier: the search for effective and user-friendly drug delivery.

Although hypodermic needles rapidly deliver large doses of drugs such as insulin across the skin for systemic administration, the pain, local trauma, and difficulty to achieve sustained or complex delivery profiles has motivated development of novel alternative technologies. Microneedles, jet injectors, and thermal poration make micron-scale holes in skin through which drugs can be driven in a user-friendly manner. Chemical enhancers, iontophoresis, electroporation, and ultrasound increase skin permeability by making submicron alterations in skin microstructure for continuous delivery over time.