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THE CUTTING EDGE / TECHNOLOGY IN MEDICINE | SCIENCE
WATCH / LEE DYE

Tiny Drug Pump Could Supply IV Users With Control and Precision

June 02, 1997|LEE DYE

Michael Huff, an electrical engineer at Case Western Reserve University in Cleveland, has battled diabetes nearly all his life. And his personal fight has led him to a technical breakthrough that could revolutionize the way many drugs are delivered.

Huff has developed a tiny pump--no bigger than a contact lens--that can precisely administer drugs intravenously. It gives doctors and patients a new level of control, and when combined with sensors, which are still in development, it could open the way to a whole new breed of automated drug treatments.

Most of Huff's funding comes from the Defense Department, which is seeking miniature pumps for everything from detection devices for chemical or biological weapons to advanced fuel injection systems for high-performance aircraft. But as head of a biomedical engineering team at Case Western and a diabetic, Huff has had plenty of opportunity to observe the methods currently used to introduce drugs into human veins.

Typically, intravenous drugs are administered from a bag suspended above the patient. The drug flows down a plastic tube, which is pinched together to restrict the flow to the desired level.

"But these things are unbelievably inaccurate," Huff says. The system may be adequate for such things as antibiotics, but for highly toxic or expensive drugs, they are not nearly as reliable as they should be, he says. They depend, for example, on a nurse's ability to maintain the right dosage by restricting the rate of flow.

The solution, Huff decided, was to create a tiny pump, controlled by a microchip, that could deliver the exact amount of medication. His team built a prototype using two thin layers of a titanium-nickel alloy sandwiched around a layer of silicon. Small electric pulses cause the alloy to flex, drawing fluid into one valve and then forcing it out another, sort of the way air is pumped through a fireplace bellows.

The prototype is small, but not small enough. Huff wants it to be so small that it can be implanted on the patient or carried at all times.

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Dr. Saul Genuth, an endocrinologist who specializes in diabetes at Mount Sinai Medical Center in Cleveland, has worked with Huff, and he sees a miniature pump as one important component in the development of improved drug delivery systems. But, Genuth says, that is only part of the solution.

"Instead of a [diabetes] patient pricking his finger and measuring blood glucose and deciding how much quick-acting insulin to take before a meal, which is basically what we do now," Genuth says, the system should be able to measure the glucose continuously and then automatically deliver the right amount of insulin.

What is missing today, Genuth says, is a sensor that can do that.

"People have been working on that all over the world for 25 years," he says.

He's a bit mystified as to why it has proved so difficult but thinks the problem lies in the fact that the "human body's defense systems are just too good."

Most of the sensors tried so far consist of a needle implanted into the patient that can periodically draw trace amounts of blood for analysis. But the blood's ability to shut off leaks and prevent bleeding will soon "plug up any of the systems that have been developed so far," Genuth says.

One U.S. company is developing a system in which the needle can be changed on a weekly basis. Genuth sees that as a step forward--but Huff thinks the answer may ultimately lie in electronics.

Pulse oximeters, now used widely in hospitals, are able to measure such things as the level of oxygen in the blood without a sample even having to be drawn. The device sends an infrared pulse through the skin, and the rate at which that pulse is absorbed tells how much oxygen there is in the blood. Huff believes that someday such a sensor should also be able to measure glucose levels for diabetes patients.

"You need a drug delivery system that is small, compact, lightweight and ambulatory in the true sense of the word," Huff says. "It should be carried on the patient without any restrictions on lifestyle or movement. And it should be self-correcting."

Huff sees many other applications for his small pump in the meantime.

"A lot of drugs that are coming out are very, very costly," he says. And since current delivery systems may be inaccurate, an excess amount is normally administered to be sure the minimal level is achieved.

"That's a lot of waste," he says.

In addition, some drugs are very toxic.

"The new chemotherapies and the new AIDS drugs are much more potent than drugs in the past," he says. "It used to be that a 10% to 20% slop in the drugs was OK. But for the newer drugs, 5% is the norm. And that's really hard to do."

And he will keep waiting for that sensor to come along that will tell him automatically when he needs a shot of insulin.

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Lee Dye can be reached via e-mail at leedye@compuserve.com

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