Bayer will move a heart failure drug into final-stage testing this year, boosting its ambitions in cardiovascular treatments after the experimental medicine showed a "striking" reduction in deaths in a mid-stage trial.

Having done well with recently launched drugs such as stroke prevention pill Xarelto and eye treatment Eylea, the German company is eager to show it has another potential billion-dollar-plus winner in heart drug finerenone.

Finerenone, which is still several years from reaching the market, is an improved version of a troublesome class of heart drugs called mineralocorticoid receptor antagonists (MRAs).

Existing MRAs spironolactone and eplerenone, branded as Inspra by Pfizer, are unsuitable for many patients since they can cause abnormally high levels of potassium in the

blood, leading to irregular heart beat or even cardiac arrest.

The two older medicines, whose patents have expired, are also linked to kidney problems.

Bayer's pill, however, works in a different way and appears to avoid these issues, so cardiologists are watching its development closely.

"If you can eliminate hyperkalaemia (high potassium) that would be a huge benefit to patients," said Mary Norine Walsh, vice president of the American College of Cardiology, who was not involved in the research.

Phase II trial data presented in London on Monday showed finerenone led to fewer deaths and hospital admissions among participants during 90 days of initial treatment, when compared to a control group on eplerenone.

"We were somewhat surprised by this striking reduction in CV (cardiovascular) events," Gerasimos Filippatos, the study's principal investigator, told the European Society of Cardiology's annual meeting.

LARGER TESTS NEEDED

The greatest relative risk reduction of 44 percent was seen in patients who started at 10 mg daily of finerenone, which Filippatos said appears to be the optimal dose.

"We didn't expect to see these clearly better results already in Phase II," said Frank Misselwitz, head of the therapeutic area cardiovascular and coagulation at Bayer.

Larger tests are now needed to confirm the benefit.

A blood reading to measure stress on the heart, which was the trial's primary efficacy measure, was at levels comparable to the control group, as was the level of overall side effects.

Bayer will enroll more than 3,600 patients with heart failure and diabetes and/or kidney disease in its final-stage Phase III study. It has said previously it would also start even bigger Phase III tests of the drug in diabetic kidney disease.

There has been little progress for more than a decade in treating heart failure where the heart fails to pump enough blood around the body, but competition is starting to heat up.

Novartis recently won approval for its drug Entresto that can cut the risk of cardiovascular death and hospital admissions by a fifth, and which is forecast by analysts to generate annual sales of more than $5 billion by 2020.

Finerenone may only reach the market in 2020 or 2021, according to analysts, leaving its prospects uncertain, although Berenberg and Deutsche Bank have penciled in potential sales of $1.8 billion and $2.0 billion respectively.