By Susan Heavey

WASHINGTON (Reuters) - Sales of blockbuster

New warnings of deaths and life-threatening heart problems in some patients have sparked concern at the Centers for Medicare and Medicaid Services (CMS) -- the nation's largest health-care payer.

The agency, which covers the poor, elderly and disabled, is examining its coverage of the drugs, called erythropoiesis-stimulating agents. Private insurance carriers could follow suit.

"I think at the very least you're going to see a plateauing of the use of erythropoietins and probably over time... you'll see some reductions in use," Bernstein Research analyst Geoffrey Porges told Reuters.

Any Medicare changes could dent sales of Aranesp, Amgen's best-selling drug that brought in $4.1 billion in 2006. Johnson & Johnson's Procrit, which some analysts say has become a less critical product for the company, saw $3.18 billion in sales.

That could also affect Roche Holding AG, which is seeking approval for a rival product, Mircera.

Merrill Lynch analyst Eric Ende, in a research note, said the long-term use of Aranesp in cancer patients undergoing chemotherapy could fall 32 percent.

The Food and Drug Administration announced new warnings this month aimed at encouraging use of the lowest dose possible to avoid blood transfusions. The FDA also expressed concern about using the drugs in non-chemotherapy cancer patients.

The injectable drugs, man-made versions of a natural protein that boosts oxygen-carrying hemoglobin in red blood cells, are approved for anemia in people with chronic kidney failure and in cancer patients receiving chemotherapy. They also treat some HIV and surgery patients.

Some experts have suggested that doctors, especially those paid by CMS, use too much of the drugs.

CMS, which was already examining its coverage for kidney failure patients, said on Wednesday it would review all relevant policies.

Regional Medicare providers have already begun halting erythropoietin payments for cancer. CMS will make a nationwide decision later this year.

The FDA will hold a May meeting of outside experts. More changes to the drugs' labels could follow, officials have said.

"The question still remains -- is the black box warning enough to get physicians to materially change their use of Epo (erythropoietins)," Stanford Group Company analyst Gary Lieberman told Reuters. "If CMS made some kind of change, that would definitely have some kind of effect."

Dr. Barry Straube, CMS's chief medical officer, said the agency is trying to balance its rules so as not to overpay providers while not leaving patients who need the drugs without. "This is not as black and white as some people might think it is," he told Reuters.