Effect on drug utilization and expenditures of a cost-share change from copayment to coinsurance.

Background: While increases in prescription drug spending have moderated in recent years, drug spending is still a concern among managed care organizations and health plan administrators. In order to minimize cost increases from year to year, many health care plans have shifted more of the cost of medications to the member-consumer. Coinsurance, a benefit design in which the patient pays a percentage of the cost of the medication, is garnering more attention as a type of cost-sharing that differs from the traditional copayment model.