Principal Financial Group Inc. is owed nearly $1 million by a subsidiary of CVS Caremark Corp. after being misled on changes to a prescription drug benefits plan, according to a lawsuit filed in federal court in Des Moines.


CaremarkPCS Health LLC provided prescription drug management services for Principal's employees from 2005 to Dec. 31, 2013. Caremark guaranteed it would provide Principal a minimum discount from the average wholesale price for generic prescription drugs.


In 2011, Principal entered a pricing agreement that would save the company 7 percent on generic drugs, in addition to savings negotiated under the master agreement. The original plan also provided that Caremark would be responsible for any expenses for additional discounts it provided to plan participants, according to the lawsuit.


According to the lawsuit, Caremark has agreed that it owes Principal slightly more than $20,000 on unrealized savings under the plan.


However, Principal argues that Caremark calculated pharmacy-generated discounts in determining that number. Principal argues that those discounts should not have been included.


However, Caremark did include the discount and as a result, owes Principal $944,782. The lawsuit accuses Caremark of breach of contract and two forms of fraud.


At the beginning of the year, OptimRX became Principal's pharmacy provider. The company is part of UnitedHealthcare, which also carries Principal's health insurance plan.