New U.S. guidelines on heart health that favor potent statins may threaten future use, or even approval, of a hot new class of experimental cholesterol drugs called PCSK9 inhibitors that have been billed as potential blockbuster treatments, analysts said on Wednesday.

But use of Merck & Co’s widely prescribed Zetia, which is not a statin, and Vytorin, a related drug, will likely not be badly hurt anytime soon, analysts said, because doctors will need time to understand and accept the new guidelines.

The Merck drugs have combined annual sales of more than $4 billion, or 10 percent of overall company revenue.

“I read the new guidelines as a negative for any drugs that aren’t statins, including PCSK9 inhibitors,” said Jon LeCroy, an analyst with MKM Partners.

The guidelines, issued by two leading U.S. medical organizations on Tuesday, recommend strong measures for patients at particularly high risk of heart attack or stroke, including use of more potent statins, although not the addition of other types of medicines that have not proven their worth.

In fact, statins are the only class of cholesterol-lowering medicines that the guidelines recommend for patients who can tolerate them.

The guidelines dropped an emphasis on specific targets for lowering LDL levels. Instead, they suggest that individual patient risk of developing heart disease rather than an LDL number should be used to determine the need for more intensive treatment.

Even though Zetia has been on the market since 2002, Merck has not yet proven it reduces heart attack risk and stroke. A costly “outcomes trial” that has been under way for years is expected to answer that question by the second half of 2014.

“I don’t think sales of Zetia and Vytorin will fall away rapidly,” said Atlantic Equities analyst Richard Purkiss. He said most doctors will wait for the Zetia trial results before abandoning the drug and Vytorin, which pairs Zetia with the generic form of Merck’s statin Zocor (simvastatin).

LeCroy expects insurers to eventually put up bigger barriers to use of Zetia and Vytorin because of the guidelines, in favor of cheaper generic statins. “But it will probably take another year before the Merck drugs feel it.”

A number of other non-statin cholesterol drugs could eventually also be hurt by the guidelines, analysts said. They include AbbVie Inc’s Niaspan, which raises “good” HDL cholesterol, AbbVie’s Trilipix, used to cut blood fats called triglycerides, and Amarin Corp’s recently approved Vascepa prescription fish oil product.

“You need to take a hard look at how much benefit we get from those drugs. If we can’t show that adding drugs to the statin makes a difference, than we have to think twice before doing it,” Dr. Neil Stone, chairman of the panel that wrote the new guidelines, said in a telephone interview.

Statins, such as AstraZeneca Plc’s Crestor and generic forms of Pfizer Inc’s similarly potent Lipitor (atorvastatin), are the most widely used cholesterol treatments and work by blocking the liver’s production of “bad” LDL cholesterol. Zetia instead works by curbing absorption of cholesterol by the intestines.

If the outcomes trial definitively shows that Zetia cuts the risk of heart attack and stroke, Stone said, “then that will have to be taken into account. Guidelines exist to be updated.”