A pair of cholesterol-lowering drugs called PCSK9 inhibitors were controversial as soon as they hit the market in 2015. They cost an average $14,300 a year, and prescriptions require prior authorization by health insurance companies — which a new study shows isn’t a guarantee.

Only 47 percent of patients were able to get insurance approval, according to a study published Monday in Circulation.

PCSK9 inhibitors Repatha (evolocumab) and Praluent (alirocumab) work by increasing the removal of low-density lipoprotein (LDL), or “bad” cholesterol, from the blood. They have been shown to reduce LDL by 60 percent and decrease major cardiac events.

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“With the controversy surrounding whether or not these drugs were cost-effective, we were anticipating that there might be some reluctance by insurance companies to cover these medications,” said the study’s senior author Robert Yeh, M.D., director of the Smith Center for Outcomes Research in Cardiology at Beth Israel Deaconess Medical Center in Boston.

“However, we were surprised by the very high rate of rejection, even when prescribed to patients with known atherosclerotic cardiovascular disease, very high LDL levels and those who were intolerant of statins, for example,” he said.

Sixty percent of patients in the study had a history of plaque-buildup of the arteries. The study analyzed pharmacy claims with electronic medical records lab test results of 9,357 patients prescribed a PCSK9 inhibitor between July 2015 and August 2016.

The type of insurance was the biggest predictor of approval, with Medicare patients receiving the most approvals and people with private insurance most likely to get turned down.

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The study could not determine whether patients suffered any harm from having the prescriptions rejected.

“Whether or not we can agree on the cost-effectiveness of these drugs, I believe most would agree that one’s access to medications should be driven primarily by the strength of the indications for the prescription as opposed to what drug plan you happen to carry,” said Yeh, who is also an associate professor of medicine at Harvard Medical School.

Insurers need to provide more uniform guidelines about what will and will not be covered, he said.

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