The federal government is suing some big pharmacy benefit managers over a system of drug rebates that regulators say has made the price of insulin soar for diabetic patients. Three companies that process about 80% of prescriptions in the United States — Caremark,

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.

The Federal Trade Commission took action Friday against the three largest pharmacy benefit managers, accusing the companies of artificially inflating insulin list prices that resulted in patients paying more for the medications.