Aggrenox and stress testing.

To the Editor: A new medication, Aggrenox, a formulation of aspirin and extended-release dipyridamole, is being actively marketed to physicians for the treatment of patients with transient ischemic attacks and ischemic stroke. Physicians involved in pharmacological stress testing should be aware that patients taking this medicine may also be referred for pharmacological stress perfusion testing with adenosine. Dipyridamole indirectly increases local adenosine levels; therefore, Aggrenox would be expected to exaggerate the response to administered adenosine, including the induction of hypotension and atrioventricular block. Consequently, patients referred for pharmacological stress testing with adenosine should be specifically queried about their use of Aggrenox (or other dipyridamole-containing products) and should not receive adenosine; instead, they should receive intravenous dipyridamole for perfusion imaging.