Severe kidney failure and some deaths have been reported in patients using Novartis's iron overload drug Exjade, the Food and Drug Administration said.
The problems with Exjade, which removes excess iron from certain organs in patients receiving blood transfusions, were found in post-marketing reports for the drug, which was approved in late 2005, the agency said.
Most of the patients who died already had other complications and their illness was advanced, it added.
Patients using the drug reported various blood deficiencies known as cytopenias that in some cases also led to death, the FDA said in a statement.
"The relationship of these episodes to treatment with Exjade is uncertain," the agency said, adding that most patients already had disorders often linked to bone marrow failure.
Other complications, including blood vessel inflammation, hives and hypersensitivity, were also reported.
The FDA said Novartis has already included the new concerns on the drug's label. The company has also notified doctors, who should take steps to monitor at-risk patients, the FDA said.
A company representative did not immediately return a call seeking comment.