The U.S. Supreme Court on Monday rejected Eli Lilly and Co.'s appeal of a patent ruling that allowed generic drug maker Barr Laboratories Inc. to sell a version of the blockbuster antidepressant Prozac.

Without comment or dissent, the justices let stand a U.S. appeals court ruling that resulted in Lilly losing patent protection in August for Prozac, which in recent years has boosted the company into the top 10 U.S. drug makers.

Barr, based in Pomona, New York, challenged the validity of Lilly's Prozac patent in a long-running legal battle to allow generic competition for the drug, which had sales of more than $2.5 billion in 2000.

Prozac, known as fluoxetine generically, was introduced in 1988 as a new class of antidepressants that work by increasing the brain's supply of serotonin, a neurotransmitter that allows nerve cells in the brain to communicate with each other.

In August 2000, the U.S. Court of Appeals for the Federal Circuit here ruled that Lilly had ``double-patented'' Prozac and cut the patent protection to 2001 from December in 2003.

In May of last year, the appeals court upheld its earlier decision, but used different reasoning.

Lilly appealed to the Supreme Court, asking the justices to hear the case. It said the appeals court ruling prematurely ended its marketing exclusivity by 2 1/2 years.

``The Federal Circuit in this case has improperly used the judge-made law of 'double patenting' to override Congress in a case where the financial stakes could not be higher,'' Lilly's attorney, Charles Cooper, said in the appeal.

He argued the appeals court, in invalidating Lilly's basic Prozac patent, applied a judge-made test that was the exact opposite of the statutory test adopted by Congress.

``More importantly, the decision below conflicts sharply with express provisions of the patent statute and with venerable precedent, and will have irrational and disruptive repercussions throughout the patent system,'' he said.

Two trade groups, the Biotechnology Industry Organization and the Pharmaceutical Research and Manufacturers of America, supported Lilly's appeal.

Barr's lawyer, George Lombardi, replied that the appeal should be rejecting and called Lilly's arguments ``wholly insubstantial.''

He said the case's circumstances were unique, unlikely to ever occur again. He said Lily wanted the high court ``to create case-specific rules that will benefit nobody but Lilly.''

Lombardi said the appeals court correctly resolved the disputed issues over the patent.