A fairly new drug used to diagnose appendicitis was pulled off the market Monday, after the government linked it to two deaths and other life-threatening side effects.

The Food and Drug Administration ordered that NeutroSpec, an imaging agent, be taken off the market — and warned health workers to immediately stop using any of the drug still on their shelves.

Manufacturer Palatin Technologies agreed, saying it would suspend sales and recall past shipments.

There is no risk to anyone who already received NeutroSpec, the FDA stressed. The allergic-type reactions occur within minutes of the drug's injection.

NeutroSpec carries a radioactive tracer to white blood cells and binds to them. When standard tests can't definitively diagnose appendicitis, doctors can use the drug and a radioactivity-spotting camera to tell whether white blood cells have clustered in the appendix, a sign of infection there.

In studies, NeutroSpec was administered to 523 patients with no serious side effects, FDA said, leading the agency to approve the drug as an aid to diagnosing appendicitis.

But since sales began in September 2004, FDA has learned of 17 patients who suffered life-threatening side effects, including heart failure, as soon as the drug was injected. Two died.

Most of the side effects occurred when NeutroSpec was used to diagnose infections other than appendicitis, FDA said. While so-called off-label use is legal, doctors have less information about potential side effects than when they use drugs in an FDA-approved manner. Also, many of the side effects occurred in patients with diseases, such as diabetes, that may have made them more vulnerable, FDA said.

The agency is investigating the risk, and plans to convene a meeting of its independent scientific advisers early next year to debate if additional safety measures would allow NeutroSpec to return to the market.