US firms Cadwalader Wickersham & Taft and Sullivan & Cromwell have taken the lead roles on the world’s largest corporate deal of the year, the $60bn merger of pharmaceuticals companies Pfizer and Pharmacia.

The transaction – also the third-largest ever in the pharmaceuticals sector – will send both firms to the top of the rankings for M&A deals by value for 2002, which has seen the lowest levels of deal activity for more than five years.