NEW YORK_The battle over the patent on Merck and Co.'s allergy and asthma drug Singulair, the best-selling drug of one of the world's largest drug makers, continued Friday as a group of drug distributors and health insurers sued Merck.

The filers say Merck should never have been awarded one of the key patents supporting the drug, and that is has wrongfully intimidated rivals by suing them for patent infringement, which has kept competing versions of Singulair off the U.S. market and allowed Merck to charge a higher price for Singulair.

The companies say Merck kept a monopoly on the drug, and as a result, they have overpaid for Singulair over the last six years. The claimants in the cases are Louisiana Wholesale Drug Co., Burlington Drug Co., Miami-Luken Inc., District Council 37 Health & Security Plan and The Guardian Life Insurance Co.

Singulair is Merck's top-selling product, with $4.3 billion in sales in 2008, and $4.4 billion to $4.7 billion expected this year. The drug was approved in the U.S. in February 1998, and the patents supporting the drug are scheduled to expire in 2012.


The companies say Merck did not tell the U.S. Patent and Trademark Office about research that made Singulair's chemical makeup "obvious," meaning it could have been discovered by any other researchers. Patents are not given to drugs that are deemed obvious, and obviousness is one reason a patent can be thrown out.

Merck said it was aware of the complaints, but had not been served with the antitrust lawsuits.

Generic drugmakers Roxane Pharmaceuticals, Teva Pharmaceutical Industries Ltd. and Mylan Inc. have all received Food and Drug Administration approval for versions of Singulair. Merck sued those companies for patent infringement, and none of the generics have reached the market.

The companies say a generic would have gone on sale in August 2003 if not for Merck's actions. A new generic drug costs 70 to 80 percent of the price of the branded original, the drug wholesalers said, and the prices decline as additional versions reach the market. They added that in its first year, a generic will take about half the market share of the original drug.

Merck shares were unchanged at $30.98 on Friday, and held steady in aftermarket trading. Teva shares rose 16 cents to $51.55, and Mylan stock was unchanged at $13.99.