Medication adherence and use of generic drug therapies.
OBJECTIVE
To assess whether lower copayments charged for generic drugs explain the improved drug adherence associated with use of generics.


METHODS
We analyzed 2001-2004 healthcare claims data from 45 large employers. Study subjects were age > or = 18 years, had 1 or more of 5 study conditions (hypercholesterolemia, hypertension, hypothyroidism, seizure disorders, type 2 diabetes), and new use of generic-only or brand-only drug therapy for that condition. We measured adherence as the medication possession ratio (MPR), and adequate adherence as MPR > or = 80%. Logistic regressions were conducted to assess adequate adherence, adjusting for copayments.


RESULTS
We identified 327,629 new users of drug therapy. The proportion starting generic therapies ranged from 9% (hypothyroidism) to 45% (hypertension). After 1 year, 66.2% of individuals with hypothyroidism achieved an MPR > or = 80% compared with 53.4% with hypertension, 53.2% with hypercholesterolemia, 52.0% with diabetes, and 42.2% with seizure disorders. Generics were associated with greater adherence than brands in patients with hypercholesterolemia or diabetes (P <.05). Lower adherence was seen in patients with hypertension or hypothyroidism (P <.05). There was no difference in seizure disorders. The likelihood of achieving an MPR =80% with $0 copayments compared with $1 to $9 ranged from an adjusted odds ratio (AOR) of 1.32 for seizure disorders (95% confidence interval [CI] = 1.41, 1.43) to an AOR of 1.45 for hypothyroidism (95% CI = 1.43, 1.48).


CONCLUSIONS
Generic prescribing was associated with modestly improved adherence in 2 of 5 study conditions. Copayments of $0 were associated with improved adherence across all conditions.
Briesacher
Becky A
BA
Division of Geriatric Medicine, University of Massachusetts, Worcester, MA 01605, USA. becky.briesacher@umassmed.edu
Andrade
Susan E
SE
Fouayzi
Hassan
H
Chan
K Arnold
KA
D016001:Confidence Intervals; D016208:Databases, Factual; D016568:Drugs, Generic / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D007349:Insurance, Health, Reimbursement / Q000191:economics / Q000706:statistics & numerical data*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio; D014481:United States; D016903:Drug Monitoring
D016568:Drugs, Generic