WASHINGTON — Federal health officials issued stern new warnings Friday for doctors to more carefully prescribe widely used anemia drugs that can increase the risk of death and other serious problems in patients with cancer and kidney disease.

At issue are drugs sold under the brand names Procrit, Epogen and Aranesp. These drugs are genetically engineered versions of a natural protein, erythropoietin, that increases the number of red blood cells.

Anemia is common with certain forms of kidney disease, especially once a patient is on dialysis, and when cancer patients take chemotherapy.

But the Food and Drug Administration pointed to recent studies that found using too much of the drugs increased the risk of death, blood clots, strokes and heart attacks in patients with chronic kidney failure. In other studies, patients with head and neck cancer had more rapid tumor growth if they used higher-than-recommended doses.

Even when the anemia drugs were used at FDA-recommended doses, giving them to cancer patients not on chemotherapy increased the risk of death, the agency warned. Moreover, some doctors have begun giving the drugs to patients following orthopedic surgery, also increasing the risk of blood clots, FDA said.

Friday, the agency added stern warnings to each of the drug's labels urging that:

• doctors monitor patients' levels of red blood cells and use the lowest possible dose to avoid the need for blood transfusions.
• doctors and patients carefully weigh the risks of using anemia drugs vs. the risk of a transfusion if anemia gets too bad.

Amgen Inc. and Johnson & Johnson, companies that manufacture and market the drugs, did not immediately reply to calls seeking comment.