In the wake of a key Senate subcommittee hearing this month, and on the heels of the collapse of the blockbuster AT&T and T-Mobile merger, four more U.S. lawmakers have joined the growing ranks of consumer groups, members of Congress and employers questioning the proposed mega-merger of pharmacy benefit managers Express Scripts and Medco Health Solutions.

Pharmaceutical services provider Omnicare celebrated its 30th anniversary as a public company by ringing the closing bell at the New York Stock Exchange at 4 p.m. on Thursday, the company said.