Filed at 4:05 p.m. ET

CHICAGO (AP) -- A drug commonly used for short-term treatment of worsening heart failure in hospitalized patients may cause dangerously low blood pressure and abnormal heart rhythms, researchers found.

The findings suggest that the drug, milrinone, should be reserved for patients who do not respond to other medication, said Dr. Mihai Gheorghiade of Northwestern University.

The study is one of the few to compare a placebo with a drug for worsening heart failure, a condition that sends about 1 million Americans to the hospital each year. Despite the poor results, it shows that such studies can and should be done on similar drugs, Gheorghiade said.

``We should not take things for granted just because they have been approved, to assume they are useful,'' said Gheorghiade, who led the study, published in Wednesday's Journal of the American Medical Association.

An accompanying editorial says the use of other drugs commonly used in worsening heart failure, dopamine and dobutamine, should be reconsidered given the milrinone findings, since all three drugs work similarly to strengthen the heartbeat. Milrinone, sold as Primacor, was approved in 1987.

Heart failure, in which the heart gradually loses its ability to pump blood efficiently, affects nearly 5 million Americans. The condition may be chronic, but patients can develop severe attacks of breathing difficulty that require hospitalization.

Dr. Ann Bolger, an American Heart Association spokeswoman, said patients studied were generally less sick than those who typically would be given milrinone. The study shows ``there really isn't any advantage'' to giving milrinone to patients who are not acutely ill, Bolger said.

Sanofi-Synthelabo Inc., which markets milrinone in the United States, funded the study. The company's Web site warns that the drug may cause irregular heartbeats, and says milrinone should be stopped if blood pressure falls too low. It also says that the drug may not be safe or effective when given for longer than 48 hours, and that long-term oral treatment has been linked with an increased risk of hospitalization and death.

Another JAMA study shows favorable results for a newer drug called Natrecor, approved last year for worsening heart failure. Known chemically as nesiritide, the drug improved breathing and blood flow, and appeared to work more quickly than intravenous nitroglycerin.

Dr. Michael Cuffe, a Duke University cardiologist who helped lead the milrinone study, said the research looked at how patients fared over the longer term, unlike the research that led to government approval of the drug.

The study involved 949 patients given either a dummy drug or a 48-hour milrinone infusion.

Dangerously low blood pressure occurred much more frequently in milrinone patients, 10.7 percent compared with 3.2 percent of the placebo patients; as did irregular heartbeats, 4.6 percent versus 1.5 percent.

The average length of hospitalization did not differ significantly -- six days for milrinone and seven days for placebo. Sixty-day death rates -- 10.3 percent in milrinone patients and 8.9 percent in placebo patients -- also did not differ significantly.

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On the Net:

JAMA: http://jama.ama-assn.org

Sanofi-Synthelabo: http://www.sanofi-synthelabous.com