The best-selling drugs Humira and Enbrel have a lot in common. They both use biotechnology to treat rheumatoid arthritis, psoriasis and other autoimmune diseases. And they come with giant price tags approaching $50,000 a year.

Now the two companies behind the competing drugs have found common ground in keeping those prices high: They are deploying new patents to prevent patients and insurers from getting two essentially generic versions of the drugs for less money.

This week, advisers to the U.S. Food and Drug Administration recommended approval of the near generic versions. But the patents could delay introduction. And even if the drugs get to market, some patient groups say they will resist efforts by insurers to force them to use the less expensive drugs.

Six years after the Affordable Care Act cleared the way for biosimilars, as the generic versions of biotechnology drugs are called, progress has been slow. Only one biosimilar, a mimic of the white blood cell booster Neupogen, is available to patients.

“It’s a lost opportunity to reduce health care costs,” said Fiona M. Scott Morton, a professor at the Yale School of Management.

By contrast, according to a study she did, biosimilars have been available in Europe for years and have reduced costs for some drugs as much as 80 percent, although in many cases far less.

Humira and Enbrel are biologics, complex proteins made in living cells. Seven of the world’s top 10 selling drugs in 2015 were biologics. Humira was No. 1 with $14 billion in global sales, and Enbrel was No. 3 at $8.7 billion, according to the website PharmaCompass.

Until the 2010 Affordable Care Act authorized the FDA to approve biosimilars, biologics were insulated from the generic competition. Things seem to be heating up, however. A biosimilar that mimics Johnson & Johnson’s autoimmune disease drug Remicade was approved by the FDA in April. It is not yet on the market, in part because of patent issues. But Pfizer, which owns the marketing rights, hints that it is planning to introduce it this year.

And about 60 biosimilars are in clinical trials aimed at approval in the United States or Europe, according to Sanford C. Bernstein & Co., including 13 versions of Humira.