The Impact of Cost-Sharing on Adherence to Antihypertensive Drugs for Low and High Adherers Jean Yoon UCLA Department of Health Services

Adherence and Cost-Sharing Cost-sharing one policy lever to affect adherence to drugs Modest effects for antihypertensive drugs ▫Elasticity of demand to for antihypertensive and anticholesterol drugs* Low adhering patients at higher risk of uncontrolled hypertension Unknown whether they respond differently to cost-sharing than high adhering patients * P Landsman et al, 2005

Research Question and Hypothesis Research Question: Does price responsiveness to drugs differ for low and high utilizers of prescription drugs? ▫Hypothesis: Adherence among low utilizers will be more affected by cost-sharing to drugs than high utilizers  Experience more side effects  Have financial barriers  Less knowledge about drugs

Methods: Data source Medstat MarketScan Database Privately insured adults ,893 patients with drug claim for antihypertensive drug during index period (Jan-June 2000) and diagnosis of hypertension in classes of antihypertensives

Dependent Variable: Drug Adherence Adherence measured with continuous medication possession ratio (MPR) ▫Days supply for rx within class summed and divided over 9 month period following index rx ▫MPR ranges 0%-120% ▫If switch drug classes, days supply summed across drug classes

Main Independent Variable: Drug Cost-Sharing Cost-sharing for brand name drugs ▫$5 or less copayment ▫$6-12 copayment ▫>$12 copayment ▫10% coinsurance ▫20% coinsurance

Other Independent Variables Patient demographics County demographics Health plan attributes Antihypertensive drug class Risk prevention Comorbidity

Statistical Analyses Bivariate test of equal medians of adherence by patient characteristics Multivariable regressions using OLS and simultaneous quantile regressions predicting adherence Quantile regression predicts quantile/percentile rather than mean ▫Allows for covariates to vary at different percentiles

Quantile Regression Detail MPR i = X i  θ + ε θ i MPR = adherence X =vector of covariates θ any quantile between 0 and 1.0 Quant θ (ε θ i |X i ) = 0

Simultaneous Quantile Regression Set θ equal to 0.10, 0.5, 0.75 Obtain 3 sets of coefficients for different quantiles of adherence Bootstrapped standard errors Wald test of differences of coefficients between quantiles

Sample Characteristics Median adherence 86.3% Mean age 52 years 51% Female 48.5 % Active employees 54% at least one major comorbidity

Adherence to Antihypertensive Drugs By Cost-Sharing Group Cost-Sharing Median Adherence* Copayment <=$588.9 Copayment $ Copayment >$ Coinsurance 10%85.4 Coinsurance 20%86.1 * P-value <0.0001

Adherence to Drugs by Cost-Sharing in Regression Models Cost SharingMeanPercentile Copayment <=$5-- Copayment $ *-8.0 *-2.9 *0.3 Copayment >$12-2.9*-9.1 *-2.2*-0.1 Coinsurance 10%-3.8*-9.6*-2.6 *-0.4 Coinsurance 20%-2.6*-8.2*-2.2*-0.8 * P-value <0.01

Conclusion Adherence levels relatively high for antihypertensive drugs Price responsiveness much greater at lower levels compared to higher levels of adherence ▫Side effects of drugs ▫Income ▫Education Vulnerable patients most at risk for lower adherence and poorer health under higher cost-sharing arrangements

Limitations Adherence measured using supply of drugs filled which may overstate actual adherence Comorbidity measured using claims data may be undermeasured

Policy Implications Trend towards placing burden of increasing costs onto patients Adverse consequences for low adherers Financial arrangements should protect most vulnerable patients ▫Design appropriate patient incentives

Acknowledgements Thomson Reuters provided data for this study through their dissertation support program This research was funded by an AHRQ Dissertation Grant Susan Ettner provided valuable feedback on this study