U.S.-based Pfizer Inc. and Ireland-based Allergan PLC today announced plans to merge, a move that would create the world’s largest drug manufacturer by sales volume. Under the so-called “inversion” deal, reportedly worth more than $150 billion, the new company, Pfizer PLC, would be based in Ireland, thereby significantly lowering its corporate tax rate. The companies said they expect the deal to close next year, after antitrust regulators, including the Federal Trade Commission, have completed their review.