title: Drug copayment and adherence in chronic heart failure: effect on cost and outcomes.
abstract: OBJECTIVE
  To measure the association among prescription copayment, drug adherence, and subsequent health outcomes among patients with chronic heart failure (CHF).
  
  
  METHODS
  Retrospective cohort study.
  
  
  METHODS
  Database of a large, national health insurance plan.
  
  
  METHODS
  Patients with CHF receiving commercial and Medicare supplemental benefits.
  
  
  RESULTS
  We estimated adherence to therapy with beta-blockers or angiotensin-converting enzyme (ACE) inhibitors in 2002 by using the medication possession ratio, an estimate of the proportion of days a patient was exposed to a drug while taking a drug regimen. For 2003, we measured the annualized total cost of health care and identified hospitalizations with a diagnostic code for CHF. We used a two-stage regression approach to model the association among copayment, adherence, and patient outcomes. For patients taking ACE inhibitors, a $10 increase in copayment was associated with a 2.6% decrease in the medication possession ratio (95% confidence interval [CI] 2.0-3.1%). This change in adherence was associated with a predicted 0.8% decrease in medical costs (95% CI -4.2-2.5%) but a predicted 6.1% increase in the risk of hospitalization for CHF (95% CI 0.5-12.0%). Among patients taking beta-blockers, a $10 increase in copayment was associated with a 1.8% decrease in the medication possession ratio (95% CI 1.4-2.2%). This change in adherence was associated with a predicted 2.8% decrease in medical costs (95% CI -5.9-0.1%) and a predicted 8.7% increase in the risk of hospitalization for CHF (95% CI 3.8-13.8%).
  
  
  CONCLUSIONS
  Among patients with CHF, higher drug copayments were associated with poorer adherence. The change was relatively small and did not affect predicted total health care costs, but it was sufficient to increase the predicted risk of hospitalization for CHF.
authors.affiliation: Division of Epidemiology, i3 Drug Safety, Auburndale, Massachusetts 02466, USA. alex.cole@i3drugsafety.com
authors.forename: J Alexander
authors.initials: JA
authors.lastname: Cole
authors.forename: Heather
authors.initials: H
authors.lastname: Norman
authors.forename: Lisa B
authors.initials: LB
authors.lastname: Weatherby
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Walker
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000191:economics* / Q000627:therapeutic use; D000368:Aged; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000191:economics* / Q000627:therapeutic use; D002908:Chronic Disease; D015331:Cohort Studies; D003669:Deductibles and Coinsurance; D005260:Female; D017048:Health Care Costs; D006333:Heart Failure / Q000188:drug therapy* / Q000191:economics; D006760:Hospitalization / Q000639:trends; D006801:Humans; D008297:Male; D006278:Medicare; D008875:Middle Aged; D018803:Models, Economic; D010349:Patient Compliance; D011306:Prescription Fees; D012189:Retrospective Studies; D016896:Treatment Outcome; D014481:United States
chemical_list: D000319:Adrenergic beta-Antagonists; D000806:Angiotensin-Converting Enzyme Inhibitors