The case takes aim at the major pharmacy benefit managers, agency officials said, claiming that they favored more expensive insulin products and forced patients to pay more.

Months earlier, the agency released a report alleging the companies drove up the costs of some medications, including insulin.

The Federal Trade Commission on Friday filed a lawsuit over insulin prices against the three largest pharmaceutical middlemen that negotiate prescription drug prices, arguing that the companies artificially inflate the costs of the lifesaving diabetes drug for patients.