SWALLOWING a pill or being given a shot may not be the best way to take
medicine. American researchers have designed a more efficient and less painful
alternative: a smart patch that uses an electric charge to drive drugs through
tiny slits in the skin.
The use of skin patches, such as the nicotine patch that helps people quit
smoking, has been limited because they rely on passive diffusion to shuttle
drugs across skin, which is thick and mostly impermeable.
A few years ago, however, scientists realised that applying an electric
charge to the skin could help drugs cross the barrier. Many drug molecules are
electrically charged in solution and will be repelled by a electrode that
matches their charge, travelling through the skin and into the tissues.
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Based on this idea, researchers at ALZA Corporation in Mountain View,
California, have created a patch with an integrated electronic circuit. Now in
phase III clinical trials, the device can quickly give painkillers to patients
suffering from post-operative pain.
Even with an electric boost, however, large molecules such as insulin can鈥檛
easily get through the skin. So ALZA has now fitted its electric patch with an
array of tiny blades, researcher Peter Daddona told the conference. The idea of
making microscopic holes in the skin to deliver drugs is not new, in fact ALZA
patented it over 20 years ago. 鈥淲hat鈥檚 new is the ability to do it,鈥� says Mark
Prausnitz of the Georgia Institute of Technology in Atlanta.
The blades are tiny flaps鈥攁bout one tenth of a millimetre
long鈥攑unched out from chemically etched titanium foil. Although being
sliced by an array of blades may seem worse than an injection with a hypodermic
needle, the blades are so small that you feel nothing when they鈥檙e pressed
against the skin. 鈥淭here really isn鈥檛 any sensation,鈥� says Daddona. And unlike
pills, the device keeps drugs away from the potentially destructive actions of
the gut and liver.
In an early trial, the patch gave healthy volunteers insulin doses similar to
those required between meals by people with diabetes. 鈥淚t鈥檚 quite impressive,鈥�
says Mark Saltzman of Cornell University in Ithaca, New York, a designer of
drug-delivery implants. Some researchers, however, worry that unwanted materials
such as bacteria could seep into the body via the patches. But so far, the 60
volunteers who have used the array have shown no signs of infection or
irritation.
