Too high blood-thinner doses harmful to patients

Dec 29 2005

According to a new analysis by cardiologists at the Duke Clinical Research Institute, in the prescribing of common but powerful anti-clotting drugs, 42 percent of patients rushed to emergency rooms with symptoms of a heart attack received doses intended to stop clotting in coronary arteries above the recommended range.

The researchers say that though the drugs can save lives, correct dosing is crucial, and too much of the drug can lead to bleeding episodes, while too little may be ineffective at stopping the clotting process.

They believe some heart patients are given too large a dose of blood thinner at the hospital, which can lead to excessive bleeding.

Apparently the dosing errors stemmed from factors including physicians underestimating the importance of using the right dosage or a lack of information about a patient's weight or other indicators.

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

Bleeding episodes usually involved oozing at the site of a catheterization insertion in the leg, but also included the more dangerous bleeding within the gastrointestinal tract or within the brain.

Also, other research has shown that the transfusion of donated blood to replace blood loss may not be as benign as once thought.

As a rule the blood thinners are given immediately to prevent another heart attack or stroke occurring.

Lead author Karen Alexander of Duke University in Durham, North Carolina, and the study's lead author says that though experts recognize that most drugs must be administered within a "therapeutic window", too much or too little can be harmful.

The study found that 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 which were attributable to an over large dose.

Alexander also says that patients receiving excess antithrombotic (anti-clotting) therapy also had higher mortality and longer hospital stays.

The report is published in the Journal of the American Medical Association.