A judge has denied a bid by Amneal Pharmaceuticals Inc. and Lupin Ltd. to launch a generic version of Actavis plc’s oral contraceptive Lo Loestrin. The ruling is a big-dollar win for Covington & Burling; Fitzpatrick Cella Harper & Scinto; and McCarter & English.

In a 43-page ruling issued on Friday, U.S. District Judge Joel Pisano in Trenton, N.J. upheld Actavis’s patent on the low-estrogen chemical formulation in Lo Leostrin. That patent was developed by Warner Chilcott Co., which Actavis acquired in October 2013 as part an $8.5 billion stock-for-stock transaction. Pisano rejected arguments by Amneal and Lupin that the patent is invalid on obviousness grounds.

Warner Chilcott brought suit in May 2012, seeking to block the generic companies from launching their own versions of Lo Lestrin. Pisano held a seven-day bench trial in October. Warner Chilcott was represented George Pappas and Jeffrey Elikan of Covington; Fitzpatrick partners Dominick Conde and Brian Slater; and William O’Shaughnessy of McCarter & English. Amneal was represented by Paul Kochanski and Charles Kennedy of Lerner David Littenberg Krumholz & Mentlik. Lupin was represented by Karen Confoy and Christopher Kinkade of Fox Rothschild.

Friday’s ruling could be worth big money to Actavis. Lo Loestrin has the lowest level of estrogen of any U.S.-approved oral contraceptive—a feature that’s proven popular with women concerned about the hormone’s side effect. Annual sales jumped from $80 million in 2011 to about $250 million in 2013. The patent upheld in Friday’s ruling expires in 2029, so Actavis has a long period of market exclusivity ahead of it.

Lupin and Amneal’s lawyers made an obviousness challenge, pointing out that oral contraceptives with slightly more estrogen predated Lo Loestrin by decades. Warner Chilcott’s lawyers countered that argument by putting on the stand an expert witness who testified that many researchers were initially skeptical of Lo Loestrin’s effectiveness and commercial viability.

Warner Chilcott’s arguments swayed Pisano. Medical researchers “seeking to reduce estrogen dose in a new contraceptive regimen would have balanced the potential benefit from a safety standpoint with the expected loss of efficacy and cycle control, and likely would have concluded that these factors weight against lowering estrogen,” the judge wrote.