Pfizer has clinched a blockbuster merger with a fellow drug maker, one worth more than $150 billion, that can best be described in superlatives.
When it is announced — most likely on Monday, people briefed on the matter said — the deal to buy Allergan, the maker of Botox, would be one of the biggest ever takeovers in the health care industry. And it would be the largest acquisition yet in a banner year for mergers.