TRENTON, N.J. (AP) — Drugmaker Pfizer Inc. said Tuesday that 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 the news before giving up part of that gain. Pfizer also filed a lawsuit against five generic drugmakers to try to prevent them from selling generic versions of Celebrex before the new patent runs out in December 2015.