One of the skin's primary roles is to provide protection against infection and physical damage. This barrier is so effective that it prevents many pharmaceutical compounds from crossing into the bloodstream. To overcome this defense, both passive and active drug transport across the skin (transdermal) barrier are being developed.
Passive transdermal delivery allows a drug to diffuse through the skin and act locally or penetrate the capillaries and have a systemic effect. Passive delivery usually occurs with a patch, cream, or spray. Passive Transdermal delivery only works with small molecule drugs, such as nicotine and aspirin. Insulin is far too large to get through the skin passively.
Active transdermal delivery, on the other hand, involves a chemical or mechanical disruption of the skin barrier. By using an applied force, such as ultrasound or an electrical current, active transdermal systems are capable of delivering proteins and other large molecule formulations through the skin and into the bloodstream.
Though the skin is a formidable barrier, companies are developing various active transdermal delivery technologies to overcome this challenge. The hope is to open up the transdermal market to the delivery of products that were previously considered undeliverable via this route.
Dermisonics U-Strips (No Longer Active)
Dermisonics has integrated microelectronics and ultrasonic science into a skin pad called the U-Strip™. It uses alternating ultrasonic waveforms to enlarge pore diameter sufficiently for large molecules like insulin to proceed through the skin and ultimately reach the bloodstream. The system consists of 4 parts: the Medi-Cap, Ultrasonic Applicator, the dose controller and the dose report for the physician.
The Medi-Cap, the transdermal patch that holds the insulin, is applied to the skin. The Ultrasonic Applicator and Dose Controller generates ultrasonic transmissions to dilate the pores and allow large molecule drugs to enter the blood stream. It adjusts rate and frequency to vary dose delivery, records the dose delivered, and keep this in memory for 60 days. This data can be downloaded via modem in a dose report to your physician to enable individualized dose tracking and management.
Concerns about this approach center on whether skin breakdown may occur and on whether sufficient insulin can be delivered in a brief period of time to handle larger carb meals.
Vyteris transdermal drug delivery uses an iontophoretic delivery technology that delivers drugs comfortably through the skin using low-level electrical energy. This technology is claimed to allow precise dosing, with control of the rate, dosage, and pattern of drug delivery. This may offer therapeutic, economical, and lifestyle advantages over existing methods of drug administration.
There are numerous potential applications for each of these technologies so insulin delivery is only the beginning. Each of these companies hopes to be able to apply these methods to assist in the treatment of a variety of diseases.
Links to Transdermal Companies
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