From Du Pont, A Faster Way To Pinpoint Chest Pain

Posted: October 20, 1987

Thousands of times a year, patients rush to hospital emergency rooms complaining of chest pains. In each case, medical specialists must determine whether the pain is a harbinger of a heart attack or a symptom of a less- serious problem.

All too often, emergency-room physicians can't tell the difference until they see the results of extensive, time-consuming tests. Frequently, they can't determine the cause of the problems for several days.

Now, researchers for the Du Pont Co. say they have developed a product for diagnostic imaging of the heart that could close this life-threatening information gap.

The company on Friday filed a new-drug application with the federal Food and Drug Administration for a nuclear imaging agent. If Du Pont's Cardiolite lives up to expectations, the product may allow cardiologists to get clearer, sharper images of the heart and to get them much faster than previously possible.

Jeffery Lipton, Du Pont vice president for medical products, said sales of the substance could reach "a couple of hundred million dollars" a year, enough to make a significant contribution to company profits.

More important, the drug could transform the treatment of heart-attack patients by giving cardiologists far better information than they can get with current imaging techniques.

Existing technology for imaging the heart makes use of a radioactive form of the metal thallium. To observe the heart, an imaging agent containing thallium is injected into a patient's vein. In minutes, the substance migrates through the bloodstream to the heart, where it is absorbed by healthy heart tissue.

As the radioactive thallium decays, it emits nuclear particles that can be detected electronically. Computerized detection and imaging equipment translates emissions into pictures of the heart. Such images show clear differences between healthy heart tissue and areas that are not getting an adequate supply of blood or have been damaged by heart attack.

Of the one million people who survive heart attacks in the United States each year, about 25 percent later receive thallium tests, according to Brian M. Gallagher, new-product-development manager for Du Pont's diagnostic-imaging division in Boston.

Though thallium imaging gives cardiologists important data, its usefulness has been limited by the nature of the material.

Thallium remains radioactive for at least a couple of weeks. Therefore, specialists in nuclear medicine must administer very small doses to minimize the patient's exposure to radiation. This low dosage means that radioactive emissions are weak. The resulting images are generated slowly and often are unclear.

Radioactive thallium that lingers in the body presents another problem. The imaging process cannot be repeated until the material is purged, or else the residue from one test interferes with the next. So cardiologists sometimes must postpone imaging.

Radioactive thallium also is difficult to obtain and handle. The material is produced at a handful of nuclear laboratories. Hospitals get fresh supplies to meet scheduled needs but cannot keep a supply on hand for emergencies.

"There has been a real need for a better isotope," said Dr. David M. McCarthy, director of the nuclear cardiology laboratory at the Hospital of the University of Pennsylvania.

Du Pont's researchers think they have it: an imaging agent that uses an isotope of technetium instead of thallium.

A radioactive metal, technetium already is the mainstay of nuclear medicine, but the material has not been used commercially for imaging of the heart. For such an application, technetium material offers several advantages over thallium.

Technetium decays much faster, so cardiologists can administer a dose that is 10 times more radioactive than a dose of thallium. The more radioactive dose produces much sharper images than a thallium dose and generates them more quickly. Because technetium decays promptly, the cumulative amount of radiation absorbed by the patient is about the same as that produced by the smaller dose of thallium.

The rapid decay of technetium also means that tests can be repeated within a day, giving physicians the ability to watch the heart more closely during critical periods.

Technetium also is much easier for hospitals to handle. Because the substance already is used widely for imaging of other organs, most hospitals have a source of technetium on hand.

The material does not occur in nature, but Du Pont and other suppliers of radiopharmaceuticals sell "technetium generators" for hospital use. These generators contain radioactive molybdenum, which produces a continual supply of technetium as it decays.

Du Pont intends to sell Cardiolite as a two-part product. To prepare a dose of imaging agent, hospital pharmacists will have to mix a nonradioactive chemical with technetium from the institution's technetium generator.

This feature means that Cardiolite should be available on very short no tice, enabling cardiologists to order imaging whenever they want it.

It probably will take the FDA about two years to evaluate Du Pont's application. If the regulatory agency approves sales of the substance, Gallagher expects a tremendous increase in the nuclear imaging of the heart.

"Every survivor of a heart attack becomes a candidate for technetium studies," he said. So, too, do all those people stricken with chest pains.

Now, thallium testing is done in conjunction with routine stress tests of heart function. Thallium tests also are done after coronary-bypass operations to determine whether the bypasses are delivering enough blood to the heart muscle.

Because technetium imaging is more convenient, Gallagher expects tests to be given in emergency rooms and in situations where thallium testing would have been impossible.

"There's tremendous untapped potential," he said.

To make the new imaging agent, Du Pont chemists had to develop a compound that would attach to the tissue of the heart, but not to other organs. The answer was a class of chemicals known as isonitriles.

Next, researchers had to find a way of linking molecules of technetium to the isonitrile carrier.

The research and development was done at Du Pont's diagnostic imaging division in Boston and the medical products laboratory in Glasgow, Del.

The benefit to Du Pont from Cardiolite could be substantial. Industry analysts said that worldwide sales of radiopharmaceuticals totaled about $250 million last year, with Du Pont claiming about 20 percent.

If Cardiolite turns out to be as important as company officials expect, it could propel Du Pont to a dominant position in the field.

The medical implications are "exciting," said McCarthy at Penn. Though he has not had a chance to use Cardiolite with patients, he's followed the technical reports on the development of the drug.

"We're all waiting for it," he said.

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