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Genentech Corp.'s clot-busting drug, tissue plasminogen activator (TPA), was hailed as a triumph for biotechnology when it won approval by the Food & Drug Administration in 1987. A major clinical trial had shown that TPA dissolved potentially fatal blood clots in the arteries of 71% of patients within four hours, if it was injected soon after symptoms appeared. The South San Francisco biotech company estimated that the drug could save six lives a day in the U.S. -- more than 2,000 annually.
TPA became a blockbuster drug. Today, it and other so-called thrombolytic drugs, such as streptokinase, are administered routinely in emergency rooms to virtually all patients who appear to be having a heart attack. But new research suggests these lifesaving clot-busters may have a dark side. Contrary to common belief among doctors, the drugs don't benefit elderly patients. Indeed, a new study shows they may actually increase the risk of death. Researchers from Johns Hopkins University report that heart patients over the age of 75 who received thrombolytics were nearly 40% more likely to die within 30 days of treatment than their counterparts who were not given the drugs. "We found that the effectiveness of these drugs varies markedly with age," says David R. Thiemann, lead author of a paper published in the May 16 issue of Circulation, a journal of the American Heart Assn.
The researchers based their conclusion on an examination of data collected by the Health Care Financing Administration on 7,864 Medicare patients, aged 65 to 86, who arrived at hospitals with an acute heart attack and were candidates for clot-dissolving therapy. Among the patients, 5,191 were between the ages of 65 and 75 and 2,673 between the ages of 76 to 86. The study revealed that 6.8% of the younger group who received thrombolytics died within 30 days, compared with 9.8% of those who did not get the treatment. But with the older group, the numbers reversed. Of those who were treated, 18% died within 30 days, while only 15.4% of the untreated group died.
FORGOTTEN CAVEAT.
So how did this unfortunate finding go unnoticed for more than a decade? After all, the drugs were extensively tested before coming onto the market. One of the tests involved 4,000 patients in the U.S. and was conducted by the National Heart, Lung & Blood Institute, beginning in 1984. A follow-up trial, costing $55 million and funded by Genentech to compare the effectiveness of TPA and less expensive streptokinase, involved 41,021 heart attack patients from 16 countries.
Thiemann, who is an assistant professor of medicine, believes it escaped attention simply because no one looked at the data in terms of age before. "More studies on how to treat the older population are urgently needed," he adds. But there may be more to it. Doctors eager to save lives seem to have forgotten a small caveat in the FDA's 1987 announcement of the TPA approval: that it be given "with caution [to] people over 75."
Copyright 2000, Bloomberg L.P.
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