Salix Pharmaceuticals announced late Thursday that it has agreed to pay $2.6 billion to acquire specialty pharmaceutical company Santarus and its portfolio of drugs aimed at battling gastrointestinal disorders such as acid reflux.

The deal, which Salix is financing with $800 million in cash and $1.95 billion in debt backed by Jefferies LLC, has yielded roles for two leading Am Law 100 firms.

Covington & Burling, a firm known for its life sciences and biotech M&A expertise, is advising Salix on both acquisition and finance aspects of the transaction through a team of lawyers led by corporate partners Edward Britton and Catherine Dargan in Washington, D.C.

Britton and Dargan, who cochairs Covington’s M&A group, advised Raleigh-based Salix two years ago this month on its $300 million acquisition of privately held urology treatment provider Oceana Therapeutics.

Rounding out the Covington team counseling Salix on acquisition of Santarus are finance partner D. Michael Lefever, capital markets partner Kerry Burke, securities partners David Martin and Keir Gumbs, life sciences partner Amy Toro, employee benefits partner Michael Francese, food and drug practice cochair Peter Safir and regulatory partner Scott Cunningham, tax partner Robert Heller, antitrust vice chair James Dean Jr., life sciences of counsel Edward Dixon, real estate of counsel Heather Haberl, health care compliance of counsel Anna Kraus and special counsel Stefanie Doebler. The Covington associates working on the matter are Stephanie Bignon, Jeff Bozman, James Burke IV, Sarah Burnham, Noellyn Davies, Dena Feldman, Matthew Franker, Mingham Ji, Patrick Manchester, Sara Needles, Kyle Rabe, Christen Sewell, Nicholas Simon, James Toy and James Wawrzyniak.

Thomas D’Alzono, the independent chairman of Salix’s board of directors, is himself an attorney, while the company’s general counsel William Bertrand moved into that job this summer. U.S. Senate records show that Salix has paid $53,000 through the first three quarters of the year to Jeffrey J. Kimbell & Associates for lobbying work.

Santarus, meanwhile, has turned to Latham & Watkins for counsel on its sale to Salix. Scott Wolfe, a Latham corporate partner in the firm’s North San Diego office—which will consolidate with the downtown office in a new locale next year—is leading a team working on the matter.

Other Latham lawyers lining up for Santarus include executive compensation partner Jim Barrall, IP partner John Wehrli, tax partner Laurence Stein, antitrust partner Tad Lipsky, life sciences regulatory partner Ben Haas, finance partner Christopher Plaut, antitrust counsel Sydney Smith. The associates from the firm working on deal are Matthew Bush, Nicole Fanjul, Matthew Grant, Max Kamer, Michelle Khoury, Jason Morelli, Tomas Nilsson, Betty Pang and Tali Weiss.

Carey Fox serves as general counsel of San Diego–based Santarus, whose drugs are also used to fight cholesterol, diabetes, and heartburn. Alessandro Della Cha, a senior partner at leading Italian commercial law boutique Edoardo Ricci e Associati in Milan, is a member of the company’s board.

The boards of both Santarus and Salix have approved their merger, which is expected to close on in the first quarter of 2014.