Washington, D.C. ? 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.