NEW YORK (AP) _ Drugmaker Pfizer Inc. says a new patent on one of its top drugs, anti-inflammatory painkiller Celebrex, extends its U.S. patent protection by 18 months, potentially bringing the company a few billion dollars in additional revenue.

Shares of New York-based Pfizer jumped nearly 2 percent on news of the patent ruling. Pfizer also said it's suing several generic drugmakers to try to prevent them from selling generic versions of Celebrex before the new patent runs out.

Pfizer says the U.S. Patent & Trademark Office has granted what's called a "reissue patent." It covers methods of treating arthritis and other conditions with the drug's active ingredient, celecoxib. The new patent won't expire until Dec. 2, 2015, about 18 months after the basic patent for Celebrex expires on May 30, 2014.