CVS's $69 billion deal to acquire Aetna is the latest in big healthcare consolidations — the entire industry is headed in the same direction. Unfortunately for Express Scripts, the biggest pharmacy benefit manager in the country, it's running out of companies to partner with. No one wants to be the odd man out. The news of CVS's $69 billion deal to buy Aetna broke on Sunday night, and by Monday it was already clear who would lose out — the largest pharmacy benefit manager (PBM) in the country, Express Scripts. PBMs are basically gatekeepers that manage the list of drugs an insurer will pay for.