A shortage of a key leukemia drug that started last year has worsened, causing many major cancer centers such as the Johns Hopkins Hospital to start rationing the drug and others to turn away patients from community hospitals that have run out of the medication.

The three companies that make the drug, called cytarabine, have all suffered production difficulties in the past year. Only one of them, Hospira Inc., is currently shipping the drug, but only in limited quantities that are not nearly enough to meet demand. A shortage in 2010 of the active ingredient used to make cytarabine slowed production at Hospira.

"I really think what's happening is a national tragedy," said Dr. Hagop Kantarjian, chairman of the leukemia department at the University of Texas M. D. Anderson Cancer Center in Houston, one of the world's leading cancer-treatment facilities.

Last week, Dr. Kantarjian sent an email to cancer doctors around the country asking them to share their stories to raise awareness of the shortage, which is affecting patients with a form of leukemia known as acute myeloid leukemia, or AML. He said he received responses from doctors in 30 states.

Dr. Kantarjian and other doctors say there is no alternative treatment for AML and that people will die without it. Cytarabine is also widely used for another form of leukemia known as acute lymphoblastic leukemia, or ALL, but the impact of removing it from the treatment regimen for that disease isn't yet known.

About 43,000 new cases of leukemia are diagnosed each year in the U.S., with about half the cases being AML or ALL, according to the American Cancer Society.

Food and Drug Administration spokeswoman Shelly Burgess said the agency was working "non-stop" with all three manufacturers on the supply issues and was also seeking to allow the importation of cytarabine from overseas as a backup. 

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