The impact of cost sharing on antidepressant use among older adults in British Columbia

Abstract

Objective: Antidepressant therapies are underused among older adults and could be further curtailed by patient cost-sharing requirements. The authors studied the effects of two sequential cost-sharing policies in a large, stable population of all British Columbia seniors: change from full prescription coverage to 10-25 dollars copayments (copay) in January 2002 and replacement with income-based deductibles and 25% coinsurance in May 2003.

Methods: PharmaNet data were used to calculate monthly dispensing of antidepressants (in imipramine-equivalent milligrams) among all British Columbia residents age 65 and older beginning January 1997 through December 2005. Monthly rates of starting and stopping antidepressants were calculated. Population-level patterns over time were plotted, and the effects of implementing cost-sharing policies on antidepressant use, initiation, and stopping were examined in segmented linear regression models.

Results: Implementation of the copay policy was not associated with significant changes in level of antidepressant dispensing or the rate of dispensing growth. Subsequent implementation of the income-based deductible policy also did not lead to a significant change in dispensing level but led to a significant (p=.02) decrease in the rate of growth of antidepressant dispensing. The copay policy was associated with a significant (p=.01) drop in the frequency of antidepressant initiation among persons with depression. Income-based deductibles reduced the rate of increase in antidepressant initiation over time. Implementation of the copay and income-based deductible policies did not have significant effects on stopping rates.

Conclusions: Introducing new forms of medication cost sharing appears to have the potential to reduce some use and initiation of antidepressant therapy by seniors. The clinical consequences of such reduced use need to be clarified.

Figure 1

Antidepressants dispensed per 1,000 seniors per month in British Columbia between January 1997 and July 2006^{a a} Antidepressant utilization is expressed in imipramine-equivalent milligrams. The median daily dose during this period was 45 imipramine-equivalent milligrams.

Figure 2

Number of seniors in British Columbia initiating antidepressant use per 1,000 seniors per month between July 1997 and July 2005

Figure 3

Proportion of depressed seniors in British Columbia who discontinued their antidepressant medications in each month between January 1998 and July 2005