A large-scale international clinical trial has found that alirocumab, a cholesterol-lowering drug sold here, is effective in reducing heart attack and stroke risk.

The trial involved about 19,000 patients from 58 countries, including the United States, Britain and Singapore, who had experienced a heart attack or unstable angina (a blockage of the arteries supplying the heart with blood) that required hospitalisation. The patients had been prescribed a class of drug called statins, the typical treatment for patients with high cholesterol, but continued to have high levels of cholesterol despite taking the statins.

They were divided into two groups and given either alirocumab or a placebo. The group that took alirocumab over four years saw their risk of developing a major adverse cardiovascular event, such as another heart attack or stroke, lowered by about 15 per cent.

The drug was especially effective in patients with very high levels of bad cholesterol, defined as 100mg per decilitre (100mg/dL).

This group saw the risk of adverse events lowered by 24 per cent, and their risk of death lowered by 29 per cent. The drug was also found to cut bad cholesterol levels by about 60 per cent over a four-year period.

Alirocumab works by inhibiting a protein known as PCSK9, which is associated with high cholesterol. This makes a patient's liver more efficient at removing cholesterol.

Though it was approved for treating high cholesterol by the Health Sciences Authority in 2017, the take-up rate had been low, said Associate Professor Poh Kian Keong, 50, a senior consultant at the National University Heart Centre's cardiology department. This may be because its effects on cardiovascular morbidity and mortality had not been determined, he said.

"Alirocumab is also expensive," said Prof Poh, the principal investigator for the portion of the study conducted at the centre. "It can cost between $600 and $1,000 a month depending on whether a patient gets it from a private or a public hospital, significantly more than statins, which cost about $1 to $2 a day, or about $30 to $60 a month."

But some patients continue to have very high levels of cholesterol despite taking the maximum amount of statins they can tolerate. Others are intolerant to statins and can experience side effects like muscle aches and kidney failure.

One such patient is retired nurse Koh Chye Choon, 65, who suffered a heart attack in February.

Mr Koh said he was prescribed statins at a polyclinic, but was soon taken off them after a test found high levels of an enzyme in his blood, which could indicate muscle damage. He was referred to Prof Poh, who put him on alirocumab.

Over six weeks, Mr Koh's blood cholesterol fell from 190mg/dL to about 70mg/dL, below the Ministry of Health's recommended target of 80mg/dL for patients in the very high-risk category, Prof Poh said.

Sanofi, alirocumab's manufacturer, has applied for the drug to be prescribed for preventing heart attack, stroke and unstable angina. Prof Poh said he hopes this will make it possible for alirocumab to be subsidised by the Government, thus lowering the price for patients.