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UPDATE: 5/7/14, 9:43 a.m. EDT. Allen & Overy, Jones Day and leading German firm Gleiss Lutz also had roles advising Bayer on its over-the-counter drug buy from Merck, which is being advised on European antitrust matters by Cleary Gottlieb Steen & Hamilton, according to German legal publication Juve.

In the latest large M&A deal in the pharmaceutical sector, a trio of Am Law 100 firms are advising on the $14.2 billion sale of Merck & Co.’s consumer care business to German drug giant Bayer AG.

The transaction, announced Tuesday, will make Bayer the world’s second-largest consumer health care company should the deal close as expected in the second half of this year. Bayer won an auction for the business—home to allergy medications like Afrin and Claritin, Coppertone sun care products and the Dr. Scholl’s foot care brand—that will make it one of the top providers of over-the-counter health products and drugs.

David Shine, cohead of the M&A practice at Fried, Frank, Harris, Shriver & Jacobson in New York, is leading a team from the firm advising Merck that includes corporate partner Abigail Bomba, antitrust partner Peter Guryan, executive compensation partners Amy Blackman and Donald Carleen, IP and technology partner Daniel Glazer and tax partners Michael Alter and Robert Cassanos.

“I did some research on this, and this is one of the largest carve-out transactions in history,” says Shine, a longtime legal adviser to Merck, who counseled the company on its $41 billion acquisition of Schering-Plough in 2010, a mammoth deal that nabbed him Am Law Daily Dealmaker of the Week honors. “Carve-outs are kind of a deal lawyer’s dream. They’re among the hardest to do because it’s not like simply selling a subsidiary—you have to identify and collect all of the individual assets and liabilities being sold.”

Other transactions that Shine and Fried Frank have handled for Merck in recent years include the company’s $430 million acquisition of Inspire Pharmaceuticals in 2011; the $4 billion sale of a stake in an animal health joint venture to Sanofi-Aventis in 2009; the $350 million purchase of NovaCardia in 2007 and the $1 billion buy of Sima Therapeutics in 2006.

Morgan, Lewis & Bockius is also advising Whitehouse Station, N.J.–based Merck through business and finance partners Alan Leeds, David Glazer and Randall Sunberg, the latter of whom coheads the firm’s life sciences transactions practice. The firm took the lead on a sidecar deal that will see Merck pay $1 billion to Bayer to codevelop and market treatments for cardiovascular diseases.

Other Morgan Lewis lawyers advising Merck include antitrust head Scott Stempel, antitrust partner Harry Robins, business and finance partner Nils Rahlf and associates Martin d’Halluin, Michael Engel Amanda Goceljak, Dov Hass, Oren Livne and Benjamin Pensak. In 2012 Merck hired former Morgan Lewis litigation partner Michael Holston to become the company’s chief ethics and compliance officer.

Holston works closely with Merck general counsel Bruce Kuhlik, who in turn reports to its chairman and CEO, former Drinker Biddle & Reath partner Kenneth Frazier, who was promoted to the company’s top role in January 2011 after having previously spent nearly eight years as Merck’s general counsel. Covington & Burling life sciences cochair John Hurvitz, special counsel Sarah Hoaglund and associate James Myers are also advising Merck in connection with the sale of certain assets to Bayer.

Sullivan & Cromwell, a longtime legal adviser to Bayer, is advising the Leverkusen-based company on its current deal with Merck through M&A partner Matthew Hurd in New York. Hurd, cohead of S&C’s health care and life sciences group, was named an Am Law Daily Dealmaker of the Week in late 2011 for his role advising Princeton-based Pharmasset on its $11 billion sale to Gilead Sciences.

The Am Law Daily reported in December on Hurd and S&C’s role advising Bayer on its $2.9 billion acquisition of Norwegian cancer drug maker Algeta. Hurd and S&C also advised Bayer last year on its $1.1 billion buy of U.S. birth control company Conceptus and ultimately unsuccessful $1.2 billion bid in late 2012 for Schiff Nutrition International, which was eventually sold to the U.K.’s Reckitt Benckiser.

As Bayer awaits antitrust approval of its proposed Merck consumer business purchase, Europe’s largest pharmaceutical and chemicals conglomerate is reportedly exploring a future carve-out of its own. Bloomberg reported last week that Bayer is considering the sale of a $10 billion plastics unit to focus on its expanding health business.

Such a sale would merely be the latest in a frothy M&A market for large outside law firms servicing pharmaceutical clients. The Am Law Daily reported last month on S&C’s role advising Canada’s Valeant Pharmaceuticals on its $47 billion bid to acquire Botox cosmetics treatments maker Allergan in tandem with activist investor William Ackman’s Pershing Square Capital Management.

Skadden, Arps, Slate, Meagher & Flom, which is also advising Valeant on that offer, is counseling New York–based pharmaceutical giant Pfizer on its whopping $106 billion takeover bid for London-based AstraZeneca, which has yielded roles for Clifford Chance, Davis Polk & Wardwell and Freshfields Bruckhause Deringer, according to our previous reports. (AstraZeneca rejected Pfizer’s offer last week.) Clifford Chance is also advising Silom Medical, Thailand’s largest generic drug company, on its $100 million sale to Actavis, a specialty drug maker being advised by Hogan Lovells, which The Am Law Daily reported last month is also advising Switzerland’s Novartis on its $16 billion acquisition of GlaxoSmithKline’s cancer drugs business and the formation of a consumer joint venture.

Actavis, which shifted its headquarters to Dublin last year for tax purposes after its $5 billion buy of Irish rival Warner Chilcott, is currently also being advised by Latham & Watkins on its $25 billion bid earlier this year for New York–based Forest Laboratories. Last week Forest Labs bid $1.5 billion to acquire Furiex Pharmaceuticals, which has turned to Kirkland & Ellis for counsel on the proposed deal. Kirkland is also representing Bristol-Myers Squibb on its $725 million acquisition of San Francisco–based biotech firm iPierian and private equity firm Swander Pace Capital on its $750 million sale of Insight Pharmaceuticals to Tarrytown, N.Y.–based Prestige Brand Holdings.

Fried Frank’s Shine, speaking generally when asked what was driving all of the deal activity in the pharmaceutical industry, says that while pent-up demand and capital have been cited as contributing factors for the merger mania, sometimes it’s the simple fact that business development managers at rival companies like to do deals that match those of their competitors. “Hopefully they’ll continue,” Shine says.

Besides filling the coffers of corporate practices at Am Law 100 firms left dry by a dearth of transactional work in recent years, the increase in deal volume by big drug companies is also proving to be a boon to lobbyists, according to a recent report by Roll Call.

Like many large pharmaceutical firms, Bayer and Merck maintain robust lobbying rosters. U.S. Senate records show that Merck made no payments to Am Law 100 firms over the past 16 months for lobbying work, but Bayer’s U.S. unit—whose general counsel is Lars Benecke—and two affiliates have kept a trio of firms busy. (Merck separated from former German parent Merck KGaA during World War I and the two companies remain independent entities.)

Dickstein Shapiro received $90,000 from Pittsburgh-based Bayer Corp. during the first quarter of this year to advise on chemical facilities and toxic substances regulations, and Bayer Material Science has paid another $540,000 to DLA Piper since 2012 to advise on federal procurement matters, according to records on file with the Senate. Last month Bayer Healthcare terminated a contract that had paid nearly $3 million to Sidley Austin since 2005 to lobby on Medicare-related matters. The firm continues to advise Bayer on other issues.