title: Effects of generic substitution on refill adherence to statin therapy: a nationwide population-based study.
abstract: BACKGROUND
  Several countries have introduced generic substitution, but few studies have assessed its effect on refill adherence. This study aimed to analyse whether generic substitution influences refill adherence to statin treatment.
  
  
  METHODS
  Between 1 July 2006 and 30 June 2007, new users of simvastatin (n = 108,806) and atorvastatin (n = 7,464) were identified in the Swedish Prescribed Drug Register . The present study included atorvastatin users as an unexposed control group because atorvastatin was patent-protected and thus not substitutable. We assessed refill adherence using continuous measure of medication acquisition (CMA). To control for potential confounders, we used analysis of covariance (ANCOVA). Differences in CMA associated with generic substitution and generic substitution at first-time statin purchase were analysed.
  
  
  RESULTS
  Nine of ten simvastatin users were exposed to generic substitution during the study period, and their adherence rate was higher than that of patients without substitution [84.6% (95% CI 83.5-85.6) versus 59.9% (95% CI 58.4-61.4), p < 0.001]. CMA was higher with increasing age (60-69 years 16.7%, p < 0.0001 and 70-79 years 17.8%, p < 0.0001, compared to 18-39 years) and secondary prevention (12.8%, p < 0.0001). CMA was lower among patients who were exposed to generic substitution upon initial purchase, compared to those who were exposed to a generic substitution subsequently [80.4% (95% CI 79.4-90.9) versus 89.8% (88.7-90.9), p < 0.001]. This difference decreased when those with only one statin purchase were excluded.
  
  
  CONCLUSIONS
  Statin refill adherence was higher among patients who exposed to generic substitution compared to those who were not. Increasing age and previous cardiovascular disease affected refill adherence.
authors.affiliation: Section of Social Medicine and Epidemiology, Department of Public Health and Community Medicine, Institute of Medicine, The Sahlgrenska Academy at University of Gothenburg, PO Box 453, 405 30, Gothenburg, Sweden. henrik.trusell@gmail.com.
authors.forename: Henrik
authors.initials: H
authors.lastname: Trusell
authors.affiliation: Section of Social Medicine and Epidemiology, Department of Public Health and Community Medicine, Institute of Medicine, The Sahlgrenska Academy at University of Gothenburg, PO Box 453, 405 30, Gothenburg, Sweden. karolina.a.sundell@gu.se.|Nordic School of Public Health, Gothenburg, Sweden. karolina.a.sundell@gu.se.
authors.forename: Karolina Andersson
authors.initials: KA
authors.lastname: Sundell
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000069059:Atorvastatin / Q000627:therapeutic use*; D002318:Cardiovascular Diseases / Q000517:prevention & control; D011307:Drug Prescriptions; D057915:Drug Substitution; D016568:Drugs, Generic; D005260:Female; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000627:therapeutic use*; D008297:Male; D055118:Medication Adherence; D008875:Middle Aged; D012042:Registries; D055502:Secondary Prevention; D019821:Simvastatin / Q000627:therapeutic use*; D013548:Sweden; D055815:Young Adult
chemical_list: D016568:Drugs, Generic; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D000069059:Atorvastatin; D019821:Simvastatin