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Some heart patients are given too large a dose of blood thinner at the hospital, which can lead to excessive bleeding, researchers said on Tuesday.

The dosing errors found in 42 percent of more than 30,000 cases stemmed from factors including physicians using a "one size fits all" dosing criteria, underestimation of the importance of using the right dosage or a lack of information about a patient's weight or other indicators.

The dosing errors with three classes of blood thinners -- unfractionated heparin, low-molecular-weight heparin and glycoprotein IIb/IIIa inhibitors -- most often affected patients more vulnerable to bleeding such as the elderly, women, low-weight patients, diabetics, or patients with diminished renal function, the study said.

The purpose of quickly administering blood thinners, or antithrombotic therapy, is to prevent another heart attack or stroke, the report published in the Journal of the American Medical Association said.

Lead author Karen Alexander of Duke University in Durham, North Carolina, wrote that experts recognize that most drugs must be administered within a "therapeutic window" -- too much or too little can do harm.

Of the patients at 387 U.S. hospitals studied over nine months, up to 15 percent of those who received excessive doses of blood thinners had major bleeding events likely attributable to the too-large dose.

"Patients receiving excess antithrombotic (anti-clotting) therapy also had higher mortality and longer length of (hospital) stays," Alexander wrote.

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