NEW YORK (CNN/Money) - A U.S. appeals court rejected Merck & Co.'s request to reconsider the patent expiration on its profitable drug Fosamax, but the company vowed it would appeal again.

Merck (up $0.21 to $34.28, Research) spokeswoman Janet Skidmore said the federal decision supersedes the 2003 action by a district court in Delaware that had ruled in Merck's favor. Fosamax, a treatment for osteoporosis, brought in $3.2 billion in sales last year and the patent is set to expire by February 2008.

"Merck intends to file an appeal with the U.S. Supreme Court," said Skidmore, who said that a challenge by Israeli drug maker Teva Pharmaceutical Industries had knocked 10 years off the drug's patent expiration date.

Merck announced a 15 percent drop in profits for the first quarter Thursday as sales again were hurt by its September withdrawal of Vioxx, an arthritis painkiller.