A new cholesterol-lowering drug from

Schering-Plough

(SGP)

and

Merck

(MRK) - Get Report

was granted approval by the Food and Drug Administration late Friday.

The launch of Zetia, and its potential to generate billions of dollars in sales, comes at an opportune time for the struggling drug makers. Profits have plummeted at Schering-Plough because of well-publicized manufacturing problems and the looming loss of patent protection for its allergy blockbuster Claritin. Merck, while not mired in as big a slump as Schering-Plough, is also being hurt by generic competition.

Zetia is a new type of cholesterol-lowering medicine entering what is the most lucrative drug market -- an estimated $19 billion spent each year, worldwide. The drug works by preventing cholesterol from being absorbed in the intestines. So-called "statin" cholesterol drugs, like

Pfizer's

(PFE) - Get Report

Lipitor or Merck's Zocor, work by eliminating cholesterol in the liver. Statins carry higher safety risks, forcing doctors to monitor patients for liver damage.

Because Zetia works differently, Schering-Plough and Merck will be marketing the drug both alone and in combination with existing statin medicines. Zetia, when combined with either Lipitor or Zocor, cut levels of "bad" cholesterol, or LDL, an additional 25% after two months, according to a study conducted by the drug companies.

Wall Street sales estimates for Zetia range rather wildly, from a low of $1 billion to as much as $8 billion annually.

Schering-Plough shares closed Friday up 6% to $20.43 in anticipation that the FDA would act on Zetia. Merck shares closed up 5% to $52.91.