Researchers report that arsenic trioxide, a newly approved leukemia treatment, is responsible for the sudden of three leukemia patients. The patients were participating in a study of the new treatment. Acute promyelocytic leukemia (APL) is very rare. Only 800 to 1,000 people are diagnosed with APL annually in the United States. Patients turn to arsenic trioxide, also known as Trisenox, when their illness does not respond to traditional treatments.

Trisenox was approved by the Food and Drug Administration (FDA) in September 2000.

In a recent study, however, three of ten APL patients being treated with arsenic trioxide suddenly died. The cause of their deaths is unclear but researchers believe that arsenic in the medication may have triggered abnormal heart rhythms.