The U.S. Food and Drug Administration (FDA) is warning health care professionals of the rare but serious risk of heart attack and death with use of the cardiac nuclear stress test agents Lexiscan (regadenoson) and Adenoscan (adenosine). We have approved changes to the drug labels to reflect these serious events and updated our recommendations for use of these agents. Health care professionals should avoid using these drugs in patients with signs or symptoms of unstable angina or cardiovascular instability, as these patients may be at greater risk for serious cardiovascular adverse reactions.
This was already reflected in the labeling but the warning has been strengthened. The risk is believed to be low, though the denominator is unknown. The last sentence in the quoted text is of concern, given a general perception that these agents should be safer in potentially unstable patients as opposed to dobutamine or treadmill exercise.