UPDATE 1-Merck heart failure drug shows promise in study

(Adds quotes from lead researcher, study details, background)

CHICAGO, April 1 (Reuters) - An experimental heart failure drug being developed by Merck & Co (MRK.N: Quote, Profile, Research, Stock Buzz) showed promise in a pilot study as it improved breathing and kidney function, researchers said on Tuesday.

The drug, rolofylline, may also lead to fewer readmissions to hospital due to worsening heart failure, according to researchers who presented the data at the American College of Cardiology annual scientific meeting.

Rolofylline, which Merck picked up through an acquisition, is an adenosine A1 receptor antagonist intended to improve renal, or kidney, function. Heart failure occurs when the heart can no longer efficiently pump blood throughout the system and often leads to worsening kidney function.

The study, which involved 301 patients hospitalized for acute heart failure and renal impairment, tested the drug at three doses against a placebo. Acute heart failure is a serious form of the disease in which a patient develops symptoms such as chest pain or respiratory distress.

The highest 30 milligram dose was more effective than the two lower doses -- 10 mg and 20 mg -- and placebo, researchers said. That is the dose expected to be tested in the large phase 3 study that will be used to seek approval of the medicine.

"Clearly the signal that we saw for protection against worsening of renal function was most apparent with the 30 mg dose and that is the reason we are moving forward with that dose," Dr. Barrie Massie, the study's lead researcher, said in an interview.

"Preserving kidney function is an important goal for improving the prognosis of patients with acute heart failure," he said.

While the medicine was administered along with intravenous diuretics for just three days, Massie said 30 mg of rolofylline appeared to continue to provide protection after 14 days.