Sept. 7 (Bloomberg) -- Wyeth fell the most in a month on the New York Stock Exchange after losing a court fight to block generic competition to a heartburn drug.

Wyeth declined by $1.82, or 3.8 percent, to $45.72 at 4 p.m. in composite trading. The last time Wyeth sank more in a day was Aug. 10, when U.S. regulators rejected the Madison, New Jersey, company's proposed new drug for schizophrenia. The drugmaker lost 6 percent then.

A U.S. District judge in Newark, New Jersey, refused yesterday to block Teva Pharmaceutical Industries Ltd. from selling a copy of Wyeth's heartburn pill Protonix before a patent-infringement trial is held. The drug generated $1.8 billion in sales last year. Teva, of Petah Tikva, Israel, is likely to begin selling the generic before a final determination, analysts said.

Generic introductions would cut Wyeth's earnings in 2008 by as much as 65 cents a share from a current estimate of $3.78, said Joseph F. Tooley, an analyst at A.G. Edwards & Sons Inc. in St. Louis, in a note today.

Catherine J. Arnold, an analyst at Credit Suisse in New York, lowered the price target for next year to $54 a share from $58, assuming a loss of revenue from Protonix.

The case is Altana Pharma AG v. Teva Pharmaceuticals USA Inc., 04cv2355, U.S. District Court, District of New Jersey (Newark).

To review the disputed patent through the U.S. Patent and Trademark Office's Web site, search for patent numbers 4,758,579 at http://www.uspto.gov/patft/index.html.

To contact the reporter on this story: Robert Greene in Washington at rgreene2@bloomberg.net.

Last Updated: September 7, 2007 16:31 EDT