Fried Frank Harris Shriver & Jacobson and Wachtell Lipton Rosen & Katz have secured lead roles on Merck's $41bn (£28.4bn) acquisition of US pharma rival Schering-Plough.

The two firms have long been major M&A counsel to the two companies with Fried Frank advising Merck and Schering instructing Wachtell.

The deal comes roughly two months after Pfizer's $68bn (£47.2bn) acquisition of Wyeth and is the latest signal that pharmaceutical companies facing patent expirations on key drugs are willing to spend big to acquire rivals with deeper pipelines.

In Merck's case, revenues from two major cholesterol treatment drugs (Zetia and Vytorin) fell by more than a third last year (Merck already had split those revenues with Schering), and generic drugs will begin competing with Merck mainstays over the next five years.

Merck is financing the deal with $9.8bn (£6.8bn) in reserves and an $8.5bn (£5.9bn) loan from JPMorgan Chase.

David Shine and Philip Richter led the Fried Frank team representing Merck along with partners William Reindel and Damian Ridealgh, who handled the financing.

Wachtell's team was led by name partner Martin Lipton and corporate partner Andrew Brownstein. The New York law firm also advised Schering on its $14bn (£9.7bn) acquisition of Netherlands-based Organon BioSciences in 2007.

Other Wachtell partners on the deal included corporate partner Gavin Solotar, antitrust partners Michael Byowitz and David Schwartz, executive compensation specialist Jeremy Goldstein and tax partner Jodi Schwartz.

This article first appeared on The Am Law Daily blog on americanlawyer.com.