title: Cost-sharing and adherence to antihypertensives for low and high adherers.
abstract: OBJECTIVE
  To examine how the influence of cost-sharing on adherence to antihypertensive drugs varies across adherence levels.
  
  
  METHODS
  Cross-sectional study using medical and pharmacy claims and benefits data on 83,893 commercially insured patients with hypertension from the 2000-2001 Medstat MarketScan Database.
  
  
  METHODS
  We measured drug adherence using the medication possession ratio (MPR) for antihypertensive drugs over 9 months. Drug cost-sharing was measured as either copayments or coinsurance. Other patient characteristics included age, sex, comorbidity, health plan type, and county-level sociodemographics. We compared adherence for different cost-sharing categories with a bivariate test of equal medians and simultaneous quantile regressions predicting different percentiles of drug adherence.
  
  
  RESULTS
  Median MPR was high (>80%) across all cost-sharing categories. Among the poorest adherers, the regression-adjusted MPR was 8 to 9 points lower among patients with the highest drug cost-sharing compared with patients with the lowest cost-sharing (copayment $5 or less). The effects of cost-sharing were smaller at the median (2-3 points lower) and nonsignificant at higher levels of adherence. Other significant factors influencing adherence at low adherence levels were drug class and comorbidity.
  
  
  CONCLUSIONS
  Cost-sharing had a substantial negative association with adherence among low adherers and little association at higher adherence levels. At a clinical level, physicians should closely monitor adherence to antihypertensive drugs, particularly for patients with multiple comorbidities and those taking multiple drugs. At a health system level, current benefit designs should encourage adherence while limiting the cost burden of drugs for patients with multiple chronic conditions taking multiple drugs.
authors.affiliation: Health Economics Resource Ctr, Palo Alto VA Healthcare System, Menlo Park, CA 94025, USA. jean.yoon@va.gov
authors.forename: Jean
authors.initials: J
authors.lastname: Yoon
authors.forename: Susan L
authors.initials: SL
authors.lastname: Ettner
mesh_terms: D000293:Adolescent; D000328:Adult; D000959:Antihypertensive Agents / Q000191:economics* / Q000627:therapeutic use; D015897:Comorbidity; D017047:Cost Sharing; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007345:Insurance Claim Review; D008297:Male; D055118:Medication Adherence; D008875:Middle Aged; D012044:Regression Analysis; D014481:United States
chemical_list: D000959:Antihypertensive Agents