The Federal Trade Commission approved Express Scripts' $28 billion purchase of Medco on April 2, one business day after drug stores, the National Association of Chain Drug Stores and the National Community Pharmacists Association filed a private antitrust lawsuit to stop the deal.

The plaintiffs said they will suffer "imminent and irreparable harm" if the deal was permitted to close. But the deal closed the same day as FTC approval. As a result, most of the harm the plaintiffs feared has already occurred and cannot be undone by a temporary restraining order, said Judge Cathy Bissoon of the U.S. District Court for Western Pennsylvania.

"The record indicates that all of the fears expressed by plaintiffs already have been realized," she wrote in her opinion. She noted that Express Scripts has terminated virtually all of Medco's senior management, including sales leadership and senior supply chain management team and that Medco's confidential and trade secrets regarding customers, pricing, clinical programs, patient data and other information already has been provided to Express Scripts.

"An order holding separate Medco from [Express Scripts] - even if such an order had been issued at the instant moment the motion had been filed - would result in a headless organization that would likely be unable to survive on its own,"

At this point, a "hold-separate" order would impose exactly the harm to Medco that the plaintiffs say they want to prevent, Bissoon said. "Given this situation, it is clear any hold-separate order issued by this court would be ineffective," she wrote.

She also found that other perceived harms that the plaintiffs said they would suffer were "speculative." The plaintiffs had argued they faced an imminent threat that Express Scripts will divert its customers to its mail order and specialty pharmacies, thus driving some independent pharmacists out of business.

Bissoon said she would rule at a later date whether to proceed with the plaintiffs' request to break up the consummated merger.

Medco's antitrust lawyers said they anticipated the private lawsuit and designed the merger agreement so that only a lawsuit from the government could relieve Express Scripts of its duty to close the deal. Express Scripts "did not have to close in the face of a lawsuit by the FTC," Dechert LLP partner Mike Cowie told a gathering of antitrust lawyers in Philadelphia Tuesday. "But a private party lawsuit did not have the same effect. We made sure of that. We did not want to be exposed to an 11th hour wacko lawsuit."