UK, United States of America. Transdermal patches. Each patch contains a hydrogel type material in which an active drug is formulated, together with a battery and a microprocessor. When an electrical current is passed through the gel it repels the drug and pushes it through the skin into the blood vessels. The technology: known as iontophoresis: has been shown to be effective in enhancing the delivery of agents with low intrinsic skin permeability, such as peptides and other highly water soluble molecules. The patch could be programmed to deliver the drug continuously or in pulses. A study has shown that the increase in systemic blood levels of the drug was proportional to the current applied. The technology is limited to small peptides (molecular weight 5,000 or less). For a drug with a molecular weight of around 300, approximately 20-50 mg per day could be delivered by iontophoresis, the limiting factor being the amount of electrical current which could be tolerated.
Key areas for which the patches are being developed include pain management, migraine, rheumatoid arthritis and chronic pain.
Implantable drug release chip. The chip consists of a number of pyramid-shaped cavities, each capable of holding 25-nL of solid or liquid and sealed with a gold membrane. The application of a small electric current causes the gold membrane to dissolve and releases the reservoir contents. Circuitry similar to that in computer chips makes it possible to select which reservoirs are opened and when, thus the chip has the potential to be developed into an implantable programmable drug release system. Such chips can contain over 1,000 reservoirs.
1) The Pharmaceutical Journal 261; p.920, 12 December 1998.
2) The Pharmaceutical Journal 262, p.180, 6 February 1999.
3) Santini JT, Cima MJ & Langer R. A controlled-release microchip. Nature 397: 335-8, 28 January 1999.