Abbott Laboratories (ABT) has filed a lawsuit against Johnson & Johnson (JNJ) alleging J&J's new Simponi arthritis drug infringes a patent for a competing drug from Abbott.

Abbott's suit was filed Friday in U.S. District Court for the District of Massachusetts, and J&J disclosed it in a regulatory filing Tuesday.

Abbott, of Abbott Park, Ill., markets Humira, a treatment for rheumatoid arthritis and other conditions, which competes with J&J's Remicade. J&J's follow-up to Remicade, Simponi, was approved by the U.S. Food and Drug Administration on April 24. Schering-Plough Corp. (SGP) markets both Remicade and Simponi outside the U.S. in a partnership with J&J, New Brunswick, N.J.

Humira had $4.5 billion in sales last year and has been a big reason for Abbott's solid financial performance in recent years.

The drugs belong to a category known as anti-tumor necrosis factor, or anti-TNFs, which are either injected or infused intravenously. Simponi is a once-monthly injection, which J&J hopes patients and doctors will view as more convenient than Humira's regimen of injections every other week.

According to the lawsuit, a U.S. patent was issued to Abbott in 2007 covering certain methods for treating rheumatoid arthritis, by using an antibody that neutralizes TNF together with a drug called methotrexate, an immunosuppressant drug. Humira can be used with methotrexate, and so can Simponi.

Abbott is seeking a court declaration that Simponi infringes Abbott's patent, as well as damages.

"We are currently reviewing the complaint and will vigorously contest it," said Brian Kenney, spokesman for J&J's Centocor Ortho Biotech unit, which markets both Remicade and Simponi. "We believe we have rights to all of the intellectual property we need to market Simponi."

Abbott spokesman Scott Stoffel said: "Abbott believes that Simponi, as prescribed and used for the treatment of RA in combination with methotrexate, infringes its patent and will vigorously defend its intellectual property."

Credit Suisse analyst Catherine Arnold noted that J&J and Abbott and have been in patent disputes related to their respective anti-TNF drugs for several years. "The latest patent challenge by [Abbott] could be part of an overall competitive dispute between" the two companies, she wrote in a note to clients.

J&J shares recently fell 66 cents to $53.70, while Abbott was off 75 cents at $42.98. Shares of Schering-Plough, which has agreed to be taken over by Merck & Co. (MRK), fell 15 cents to $22.92.

-By Peter Loftus, Dow Jones Newswires; 215-656-8289; peter.loftus@dowjones.com