An experimental cholesterol-lowering drug, alirocumab, from Sanofi and Regeneron Pharmaceuticals roughly cut in half the number of heart attacks and strokes in a clinical trial, the two companies reported at the European Society of Cardiology's annual meeting in Barcelona on Aug. 31. Results are not conclusive, as the analysis was done retrospectively, but the study is said to provide the first evidence that targeting a protein known as PCSK9 could reduce cardiovascular risks for millions of patients. Confirmation is expected from a much larger trial.

The drug is from a new class of medicines, which are also being developed by Amgen and Pfizer, targeting the so-called bad cholesterol LDL. The treatments are expected to reap multibillion-dollar sales.

The finding is likely to spur enthusiasm about the drugs, which could reach the market next year. In July of this year, Sanofi and Regeneron said nine studies had shown consistent LDL reductions with alirocumab, which is injectable.

In the trials, two groups of patients received conventional anti-cholesterol statin pills in addition to alirocumab or a placebo. Among the alirocumab group, 1.4% of patients suffered a major cardiovascular event compared with 3% of those in the placebo group, Sanofi said.

The 2,341-patient study, called Odyssey Long Term, is expected to conclude in early 2015, but researchers said the early sign of effectiveness was clearly positive.

No other drug maker has previously released data suggesting reduced cardiovascular risk from PCSK9 inhibitors.

Dr. Patrick T. O'Gara of the Brigham and Women's Hospital in Boston and president of the American College of Cardiology said that the finding was "biologically plausible," but that the retrospective nature of the analysis necessitated caution.