A host of US and Irish firms have won top mandates in what is believed to be the biggest pharmaceuticals deal in history, between Pfizer and Allergan.

Skadden Arps Slate Meagher & Flom is representing Pfizer in its $160bn merger with Allergan, after advising the former on its failed takeover of UK pharmaceuticals company AstraZeneca last year.

Pfizer is also working with Wachtell Lipton Rosen & Katz in the US and A&L Goodbody in Ireland. Cleary Gottlieb Steen & Hamilton and Latham & Watkins are acting for Allergan, with Arthur Cox serving as Irish counsel.

Debevoise & Plimpton is advising financial advisers Guggenheim Securities and Goldman Sachs & Co.

The transaction is due to close in the second half of 2016. The pharmaceuticals industry continues to be active this year, with Allergan recently selling its generics business to Teva Pharmaceutical Industries.

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