Duke Clinical Research Institute cardiologists say 42 percent of ER patients with symptoms of a heart attack received doses outside of the recommended range, but numerous clinical trials have proven that the drugs need correct dosing.

The therapeutic window is narrow and too much of the drug can lead to bleeding episodes, while too little may be ineffective at stopping the clotting process, said lead investigator Dr. Karen Alexander.

"Our analysis, which includes patients treated in all types of hospitals across the country, shows that dosing errors occur more often in vulnerable patients, such as women, the elderly, or those with kidney insufficiency or low body weight," she said.

The findings are published in the Journal of the American Medical Association.