Determining Effects of Cost Sharing on Concurrent Adherence

Measure definitions to estimate the effects of cost sharing on adherence to medications prescribed together (ie, concurrent adherence) are lacking. A study published in Journal of Managed Care & Specialty Pharmacy found that different measure definitions in this area have led to different findings on the effects of cost sharing on concurrent adherence.

The researchers compared estimates of cost-related nonadherence using different measure definitions. They studied Medicare Part D beneficiaries aged 65 years and older who use multiple oral antidiabetics concurrently and compared those patients with standard coverage with patients with a low-income subsidy.

The patients with standard coverage had cost-sharing requirements in deductible, initial, and coverage gap phrases, while those with low-income subsidies had minimal cost-sharing requirements.

“Different measure definitions generate varying estimates of the effects of cost sharing on concurrent adherence, with conflicting implications for benefit design and policy implications,” the authors wrote.

In unadjusted analyses adherence rates ranged from 37% to 97% depending on measure definition, coverage type, and medication mix.

The researchers used 3 measure definitions:

• “All” considered patients adherent when they used every medication. This measure was the most sensitive to cost-related nonadherence.
• “Average” considered patients adherent when they were adherent to all prescribed medications on average. This was useful for evaluating cost-related nonadherence in the aggregate.
• “Any” considered patients adherent when they used any medication as prescribed. This measure was insensitive to cost-related nonadherence.

Using the All and Average definitions, the researchers found cost sharing had no effect on concurrent adherence for patients using only generic drugs. Only 48%

“When patients face different medication prices, analyses of subgroups using more costly medications are recommended for precise assessments of the effects of cost sharing on adherence and successful implementation of benefit design changes that target adherence improvements,” the authors concluded.