Effect of increased cost-sharing on oral hypoglycemic use in five managed care organizations: how much is too much

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Meyers Primary Care Institute

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Adolescent; Adult; Aged; Chronic Disease; *Cost Sharing; Databases, Factual; Diabetes Mellitus, Type 2; Episode of Care; Financing, Personal; Humans; Hypoglycemic Agents; Managed Care Programs; Middle Aged; Patient Compliance; *Prescription Fees; Regression Analysis; Self Administration; United States


Health Services Research | Primary Care


BACKGROUND: For patients with a chronic disease, increased cost-sharing for medications may lead to unintended consequences, including reduced use of medications essential for control of their disease.

OBJECTIVE: The objective of this study was toestimate the effects of small ($1-6 per 30-day supply), moderate ($7-10), and large (>$10) increases in medication cost-sharing on 12-month trends in oral hypoglycemic (OH) use among adults with type 2 diabetes.

METHODS: We conducted a quasiexperimental study using a time series with comparison group design. Data were obtained from computerized membership, benefit, and pharmacy dispensing data of 5 managed care organizations (MCOs). A total of 13,110 12-month episodes of OH use and a medication cost-sharing increase ("intervention") were matched with 13,110 that had no increase. The dependent variable was OH average daily dose (ADD) standardized to each episode's mean OH ADD in the 6-month preintervention period. The principal independent variable was change in cost per 30-day OH supply between the 6-month pre- and postintervention periods. Effects of changes in cost-sharing on OH ADD were estimated using segmented time series regression.

RESULTS: Episodes with >$10 increase in cost-sharing had significantly (alpha=0.05) decreased OH ADD in the postintervention period. At 6 months after this increase, OH ADD had decreased by 18.5% from that predicted from the preintervention trend. Episodes with a $1 to $10 increase in cost-sharing and those with no increase in cost-sharing had significant linear increases in OH use over the 12-month period.

CONCLUSIONS: Large increases in medication cost-sharing were associated with immediate and persistent reductions in OH use. Small and moderate increases had little effect on OH use in the 6-month period after the increase.


Med Care. 2005 Oct;43(10):951-9.

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Medical care

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