Transdermal drug delivery can involve passive diffusion and active transport. Passive diffusion of a drug through the skin is the diffusion that occurs naturally when small-molecule drugs are applied to the skin in sufficient concentration and for a sufficient period of time to enable natural diffusion through the skin. However, passive diffusion is slow and furthermore, because of the skin's natural barriers to passage of externally applied substances, passive diffusion is not suitable for most drugs. Active transdermal drug delivery techniques include sonophoresis, iontophoresis, electroporation and magnetophoresis. Sonophoresis involves the application of ultrasound, iontophoresis and electroporation involve the application of an electric field and magnetophoresis involves the application of a magnetic field.
U.S. Pat. No. 5,741,317 discloses an apparatus which includes a therapy and drug treatment tub for submersion of a treatment area of a patient in a medicated solution. The tub includes acoustic transducers and rows of electrodes and coils for delivery of respective ultrasonic, electric and magnetic radiation to the patient. The radiation facilitates active transdermal drug delivery involving phonophoretic, iontophoretic and electromagnetophoretic transport mechanisms. However, the apparatus is very large and expensive and cannot readily be used for transdermal drug delivery to a specific region of a patient.
U.S. Pat. No. 5,983,134 discloses a flexible cuff connected to a liquid drug reservoir. The cuff is designed for attachment to a patient by wrapping around part of the patient's body to form an attached sleeve. Referring to FIG. 1 of U.S. Pat. No. 5,983,134, the attached sleeve can be elongate and encircle most of a patient's leg, or squat and encircles a patient's neck. The cuff is designed to transmit electric and magnetic fields to assist transdermal delivery of drugs provided at an internal cylindrical surface of the attached sleeve. While the cuff of U.S. Pat. No. 5,983,134 is suitable for transdermal drug delivery to a specific part of a patient's body, it is cumbersome to use and is only suitable for delivery of a drug to a circumferential segment of a patient's limb, torso or neck.
U.S. Pat. No. 5,464,386 discloses a transdermal drug delivery applicator which is designed to supply a fluid medium carrying drug loaded vesicles to a patient's skin via a curved head assembly. The applicator generates a pulsed electrical field to facilitate active transdermal transport mechanisms of electroporation and iontophoresis. The applicator is capable of providing active transdermal drug delivery to a specific part of a patient's body. However, the applicator is only able to provide active transdermal drug delivery involving electric radiation.