CHICAGO (AP) -- A newer blood thinner is no better than the old standby at treating victims of heart attacks or chest pain, according to two major studies involving nearly 14,000 patients.

While the newer drug -- enoxaparin -- is more convenient to use than heparin, it also caused modest increases in bleeding, the studies found.

The results are likely to add to the debate among cardiologists over which drug to use.

The studies appear in Wednesday's Journal of the American Medical Association. One was funded by enoxaparin's maker, New Jersey-based Aventis Inc.

Dr. David Moliterno, author of a JAMA editorial, said the results "look pretty darn lackluster," given earlier, smaller studies clearly favoring enoxaparin over heparin.

He estimated 30 percent of heart patients receive enoxaparin but said most doctors have a favored drug and predicted the studies would do little to change their preferences.

"I think this gives some fodder for each argument -- naysayers who say we don't need to bother using enoxaparins, that they only provide a marginal benefit but still a bleeding risk. And supporters who say ... you can use this drug and it's safe," said Moliterno, chief of cardiovascular medicine at the University of Kentucky at Lexington.

A third study -- also funded by Aventis -- analyzed results from six studies including the two new ones and found that enoxaparin was more effective than the old standby, heparin. But other doctors questioned the findings since the analysis included older data from when treatment practices were different.

Heparin has been used for several decades to treat blood clots in heart patients. Enoxaparin, which is sold under the brand name Lovenox, is one of several newer, more potent heparin varieties with a lower molecular weight. Enoxaparin was approved by the Food and Drug Administration in the late 1990s for use in heart patients.

Enoxparin costs about $100 a day, several times more than heparin, Moliterno said. But enoxaparin supporters say the newer drug is ultimately the same in cost or cheaper because it is easier to administer. Unlike heparin, it can be delivered by injection rather than a continuous IV drip and does not require blood tests to monitor how it is working.

Both studies were conducted by researchers at Duke Clinical Research Institute in Durham, N.C., and other institutions.

The larger study looked at about 10,000 patients and found that 14 percent of those who got enoxaparin died or suffered repeat heart attacks in the 30 days afterward, compared with 14.5 percent of those who were given heparin.

However, patients treated with enoxaparin did experience more bleeding - usually at the site in the groin where a heart catheter was inserted - but rarely enough to cause complications.

The smaller study involved almost 4,000 patients who were also treated with other drugs commonly given to heart patients. It found no difference in effectiveness between enoxaparin and heparin.

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