A combination of drugs that drastically lowers "bad" cholesterol levels appears safe for heart patients, but whether it prevents heart attacks or strokes isn't yet known, researchers report.
"It may be that people need very low cholesterol levels to get a benefit in terms of heart attacks and stroke reduction, but that remains to be determined," said lead researcher Dr Jennifer Robinson. She directs the University of Iowa's Preventive Intervention Centre.
It had been feared that very low levels of bad (LDL) cholesterol might trigger memory problems or nervous system disorders, but all the researchers found was a slightly increased risk of cataracts.
That increased risk may have shown up because some of the people in the study were older and already prone to cataracts, although it could be something about the treatment itself, Robinson said.
Combination of cholesterol drugs
In the study, patients were given statins and injections of Praluent (alirocumab), which belongs to a class of drugs called PCSK9 inhibitors. These drugs help the liver flush LDL cholesterol out of the bloodstream by blocking a protein called PCSK9, the researchers said. Other drugs in the class include Repatha and Inclisiran.
To determine whether PCSK9 inhibitors can reduce heart attacks, strokes and deaths, Robinson said she is waiting for the results of two trials involving over 18,000 people that will end in the next year or two.
"That will give us a better feel for the safety of these drugs," she said. "We are also expecting good results in terms of the reduction in heart attacks, stroke and deaths."
Statins remain best
For most people, however, she recommends a statin as the best way to lower cholesterol. Common statin drugs include Lipitor and Crestor.
"Statins work well and are safe and inexpensive," Robinson said. "It's kind of cheap insurance and a lot safer than aspirin."
Adding drugs like Praluent to a statin is not for everybody, Robinson noted.
"They are really expensive and are only going to be used with people with genetically high cholesterol or people with very high cardiovascular risk, like people with heart disease and diabetes or kidney disease – very high-risk patients," she said. "They are not appropriate for the majority of people, largely because of cost."
Cholesterol is measured in milligrams per deciliter (mg/dL). LDL levels of above 160 mg/dL are considered high, according to the Mayo Clinic. For people with heart disease or diabetes, levels below 70 mg/dL are considered ideal. Levels at or below 25 mg/dL are considered very low.
Dr Brendan Everett, director of general cardiology inpatient service at Brigham and Women's Hospital in Boston, is also waiting for the results of those large trials.
"These trials will give us the results in terms of reductions in heart attack, stroke and deaths, which is what we as doctors and patients care about," he said.
"It's not clear that treating someone with an expensive medication when their LDL is at 51 mg/dL is really a wise policy," said Everett, who wrote an editorial that accompanied the study. He is also an associate physician at Brigham and Women's and an instructor in medicine at Harvard Medical School.
"Initial signs indicate that having very low LDL cholesterol levels is safe, but we really need to know from other trials whether pushing LDL cholesterol this low really reduces heart attack and stroke, and what the risks of achieving low LDL levels are in patients followed for a long period," Everett said.
How the study worked
For the study, Robinson and colleagues collected data on more than 5,200 patients from 14 randomised trials who had been receiving alirocumab for up to two years.
Specifically, the team looked for side effects among participants whose cholesterol was lowered to less than 25 mg/dL (25 percent of patients) or less than 15 mg/dL (9 percent of patients) on two consecutive occasions.
An LDL level of 25 mg/dL was used because it appears to be the level needed for normal cell function, the researchers explained.
Overall, patients receiving alirocumab or a placebo had similar side effects, including muscle pain, memory problems, and kidney and liver problems.
In addition, no increase in diabetes occurred, which had been seen in other studies among patients taking statins with LDL cholesterol below 30 mg/dL.
A slight increase in cataract risk was seen among patients whose LDL cholesterol was below 25 mg/dL.
However, the patients whose LDL was 25 mg/dL tended to be older people and people with diabetes and heart disease, who are already at risk for cataracts, Robinson said. "So we don't know if they got cataracts because of their condition or if it's something in the treatment itself," she noted.
The report was published in the Journal of the American College of Cardiology. The study was funded by Sanofi and Regeneron Pharmaceuticals Inc., the maker of Praluent.