The US Food and Drug Administration (FDA) has issued a new warning that Lexiscan (regadenoson) and Adenoscan (adenosine), two intravenously-administered drugs used during cardiac nuclear stress tests, are associated with "rare but serious" side effects that can result in heart attack and death.

Cardiac nuclear stress tests are used to assess the body's capacity to circulate blood by capturing images of the heart during states of rest and physical activity. They are generally used in cases when a basic (i.e. exercise) stress test is not feasible or did not generate conclusive results.

Both Lexiscan and Adenoscan are used to dilate the arteries of the heart during the procedure, thereby allowing the scan to determine where blockages or obstructions exist in nearby arteries.

As explained by FDA in its 20 November 2013 announcement, the drugs already contained labeling indicating the risk of heart attack and death.

"However, recent reports of serious adverse events in the FDA Adverse Event Reporting System (FAERS) database and the medical literature prompted us to approve changes to the drug labels to include updated recommendations for use," FDA explained. "Some events occurred in patients with signs or symptoms of acute myocardial ischemia, such as unstable angina or cardiovascular instability," it added.

Regulators said they believed this occurs as a result of blood flowing disproportionately toward healthier or unobstructed arteries during the test, reducing the flow to other areas and causing a heart attack.

As a result, FDA said precautionary measures should be taken during all cardiac nuclear stress tests. For example, cardiac resuscitation equipment should be on hand along with staff trained in its use. These warnings will be reflected in newly updated labels for the drugs, FDA stated.

Both Adenoscan and Lexiscan are manufactured by Astellas.

FDA Announcement