Studies of a new class of experimental cholesterol-lowering drugs signal that they can reduce by half the risk of heart attack and other major cardiovascular problems compared to standard treatment alone.

Doctors at the annual meeting of the American College of Cardiology, where the studies were presented, called the results “encouraging”, but said larger, controlled trials are needed to fully understand the drugs, known as PCSK9 inhibitors.

An analysis of about 4,500 patients who stayed on treatment for nearly a year after completing earlier trials of Amgen Inc’s Repa­tha, also known as evolo­cumab, found that 0.95 per cent of those given the drug and standard therapy suffered a cardiovascular ‘event’, compared with 2.18 per cent of the group on standard treatment, that ranged from diet changes to drugs such as statins. Amgen defined ‘event’ as death, heart attack, stroke or ‘mini-stroke’, unstable chest pain or heart failure requiring hospitalisation, or the need for a procedure to restore bloodflow to the heart.

Side effects more frequent, but still rare, in patients treated with Repatha included neurocognitive problems, such as confusion, something the US Food and Drug Administration (FDA) has said should be monitored closely. Neurocognitive side effects were also more common in the treatment arm of an 18-month, 2,300-patient trial of a rival PCSK9 drug being developed by Sanofi SA and Regeneron Pharmaceuticals Inc.

The drug, Praluent, was shown to reduce the risk of cardiovascular problems from 3.3 per cent for placebo patients to 1.7 per cent for the treatment group. ‘Events’ in this trial were defined only as death, heart attack, stroke and chest pain requiring hospitalisation.

Numerous trials have shown that PCSK9 inhibitors significantly lower blood levels of ‘bad’ LDL cholesterol, but investors expect widespread use will hinge on whether the drugs are proven to prevent death, heart attacks and other serious heart problems.

The experimental drugs are antibodies, given by injection, designed to target the PCSK9 protein that maintains LDL cholesterol in the blood. They work differently from statins – low-cost generic pills, that block the liver’s production of LDL cholesterol in the first place.

Both Amgen and Sanofi/ Regeneron have filed for FDA approval of their drugs, based on trials showing that they lower LDL in patients whose cholesterol is not controlled by other drugs, those who cannot tolerate other drugs and people who are genetically predisposed to high cholesterol.