Doctors are being warned not to give heart attack victims too much of a popular blood-thinning drug because doing so almost doubles the risk of
stroke. "We didn't know there was a dark side to heparin," said Dr. Eric Topol of the Cleveland Clinic. "We learned it has a very narrow window for
safety."Separate studies by Topol and a team of Harvard scientists uncovered the danger in April, when the trials on the drug were temporarily halted. The studies were reported in Monday's edition of the journal Circulation.
The scientists didn't warn of the danger of increasing heparin doses earlier for fear of panicking doctors. But the Food and Drug Administration insisted Monday that most patients today get lower doses that are safe, so earlier warnings were unnecessary.
"The message should be don't panic," said the FDA's Dr. Janet Woodcock. "We're unconvinced there's widespread use of higher doses of heparin."
Despite 80 years of use, nobody knew the upper limits of heparin, which is commonly given - along with clot-dissolving drugs - to thin the blood of heart attack victims.
The recommended heparin dose is 5,000 units initially, and then individualizing hourly injections until the patient's blood takes twice as long as normal to clot.
Topol and the Harvard investigators accidentally discovered heparin's upper limit while comparing its effectiveness with that of an experimental drug called hirudin. Instead of giving the normal heparin amount, they increased the standard dose by 20 percent - until it took blood three times as long to
clot. Just months into the study, researchers noticed that both drugs increased the risk of stroke two times above that normally seen in heart attack patients.