Two pharmacy benefits managers are combining forces in an effort to negotiate better deals with pharmaceutical makers, a move that could in theory lead to lower drug prices for consumers.

A unit of the UnitedHealth Group said it had agreed to acquire the Catamaran Corporation in an all-cash deal worth nearly $13 billion, the companies announced on Monday.

UnitedHealth will pay $61.50 a share for Catamaran, a 27 percent premium over Friday’s closing price of $48.32 a share. It is the latest big acquisition in the health care industry, which is in the midst of a surge of deal activity. And it represents a further consolidation of the pharmacy benefits management business.

Last month, Rite Aid, a big pharmacy chain, acquired Envision Pharmaceutical Services, for $2 billion in cash and stock.