A new study revealed that treating cancer patients with anemia drug increases their risk of blood clots and death, especially if given in the wrong doses.

The anemia drugs, also known as ESAs, or erythropoiesis-stimulating agents, include popular Aranesp from Amgen Inc., as well as Epogen, and Johnson & Johnson’s Proscrit. According to the U.S. National Institutes of Health, ESAs work by stimulating the bone marrow to produce new red blood cells. The drugs have been successful at helping patients avoid blood transfusions, which are necessary to boost red-blood-cell levels that fall too low.

Dr. Charles Bennett, an oncologist and medical professor at Northwestern University’s Feinberg School of Medicine in Chicago and lead author of the study and colleagues looked at 51 Phase III clinical trials completed between 1985 and 2005 with 13,611 patients to examine survival. According to their findings, these anemia drugs increase the risk of death by 10 percent and the risk of blood clots known as venous thromboembolisms (VTE) by 57 percent.

“Our findings, in conjunction with basic studies, raise the concern that the drug may be stimulating cancer and shortening cancer patients’ survival,” Dr. Bennett said in a statement, according to Reuters. “Patients should be informed of the risks and benefits of these drugs,” he added.

This is not the first time health experts draw attention on ESAs. Due to their concerns, the U.S. Food and Drug Administration last year had the drugs’ manufacturers add a “black box” warning to the medications. This warning says the drugs should be used at the lowest possible doses to avoid risks like blood clots, heart attacks, stroke, congestive heart failure, increased tumor growth, and an increased risk of death.

The FDA decision has already affected sales of these blockbuster drugs, which dropped 14 percent for the entire class of drugs from 2006 to 2007.

An advisory committee will be held on March 13, when the FDA will discuss whether to impose further restrictions on the use of the anemia drugs.

J & J released a statement in response to the study saying its conclusions “do not provide an accurate reflection of the safety profile” of ESAs when used to treat chemotherapy-induced anemia. “When used according to product labeling, ESAs remain safe and effective and are the only proven treatment alternative to blood transfusions for patients with chemooterapy-induced anemia,” the company said, according to Reuters.

Also, Asheligh Koss, Amgen’s representative said the risks revealed by the new study are already included in current labeling.

The study was published in the February 27 issue of the Journal of the American Medical Association.