Access is beginning to ease now, with some unusual new agreements between the manufacturers, insurers and pharmacy benefit managers who act as intermediaries. Still, these drugs offer a cautionary tale, even as pharmaceutical manufacturers bring to market costly new treatments for common diseases like migraine, nonalcoholic liver disease and severe dermatitis.

Unlike expensive drugs for cancers or rare inherited diseases, the PCSK9 inhibitors were aimed at large numbers of people — as many as 10 million Americans, a number that includes not just people with F.H. but also people with heart disease and stubbornly high cholesterol levels.

For the most part, few of those patients were able to get the medications. In one study, 80 percent of patients who tried to get the powerful cholesterol-lowering drugs were met with initial rejections by insurers; only 50 percent eventually received approval after appealing.

The drugs arrived just after what was called “the hepatitis C debacle” by Jalpa A. Doshi, a health economist at the University of Pennsylvania — the introduction of medications that cured the liver disease but cost $84,000 or more for a course of treatment.

Stunned by those costs, insurers and other payers “were scanning the horizon to see what else was coming on the market,” she said. The PCSK9 inhibitors, they learned, could cost the nation anywhere from $21 billion to $113 billion a year.

And unlike hepatitis C medications, the new cholesterol-lowering drugs would be taken for a lifetime.

“The science behind these drugs is astonishing, but the price is also astonishing,” said Dr. Steven Miller, chief medical officer at Express Scripts, the largest pharmacy benefit manager in the United States. (It is being acquired by Cigna, the health insurer.)