The Food and Drug Administration, on Wednesday, ordered Amgen to change the prescribing instructions for Aranesp and similar anemia drugs to address concerns about the risks to cancer patients.

As prescribed by the FDA, labels for the drugs now must say they are not indicated for patients undergoing chemotherapy with the intention to cure the patient and instructions will also say that treatment with the drugs should not be started if patients' hemoglobin levels are greater than, or equal to, 10 grams per deciliter.

Sales of the drugs, Aranesp and Procrit, have already dropped considerably in the last year because of studies which suggest that their use to treat the anemia caused by chemotherapy could actually make cancer worse or shorten lives. Procrit is manufactured by Amgen but sold under license by Johnson & Johnson.

Sales of Aranesp fell 13 percent in the second quarter from a year earlier, to $825 million, the company announced on Monday in posting its quarterly results. In the United States alone, sales plunged 26 percent, to $427 million.

In spite of the concerns about the drug, sales of Aranesp and Amgen’s overall financial results were better than Wall Street expected in the second quarter. That as well as the positive result of a clinical trial for a new bone drug, lifted Amgen shares this week. Shares of Amgen rose 2 cents, to $62.30 Wednesday, near their 52-week high.