Despite its decision last month to water-down safety warnings, the Food & Drug Administration (FDA) says it is still concerned about potentially fatal side effects associated with the heart imaging agents, Definity and Optison. Just last month, the FDA dropped a ban on giving the agents to acutely ill patients, such as those with congestive heart failure. The FDA also changed monitoring requirements for the drugs. The black box warning had originally called for monitoring all patients for 30 minutes after they receive the agents, but the revised warning said only patients with pulmonary hypertension or unstable cardiopulmonary conditions need to be monitored.

Definity, marketed by Lantheus Medical Imaging, and Optison, distributed by General Electric, consist of microscopic gas-filled spheres that sharpen ultrasound pictures. Definity and Optison are used during echocardiograms, ultrasound imaging procedures that take a detailed, moving picture of the heart. If the image is unclear, contrast agents such as Definity and Optison can be given intravenously to help make the heart easier to see.

According to the FDA, there have been more than 200 reports of serious cardiac reactions involving the use of Definity and Optison. In October 2007, the FDA said that it knew of at least 7 deaths associated with the administration of either Definity or Optison. Four of those fatalities occurred either during infusion or within 30 minutes following the administration of the contrast agent. The FDA said that most of the serious but non-fatal reactions also occurred in the same time frame.

As a result of these reports, the FDA requested that the labeling on Definity and Optison be modified to include a black box warning about the cardiac problems associated with these agents. A black box warning is the FDA’s strictest type of warning. But many cardiologists questioned the restrictions the FDA placed on Definity and Optison. Those complaints prompted the FDA to scale back the black box warning.

But apparently, Definity is still causing serious side effects in some patients. According to documents released by the FDA, four more deaths have been reported to the agency since October 2007. So far, Definity has accounted for most of the reactions and deaths, probably because Optison was off the market between November 2005 and October 2007. GE Healthcare voluntarily withdrew Optison after an FDA inspection found problems with a contract manufacturer. So far, no adverse events have been reported in relation to Optison since it returned to the market.