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Keywords:

  • antipsychotics;
  • costs;
  • olanzapine;
  • optimal matching;
  • propensity score;
  • quetiapine;
  • resource utilization;
  • schizophrenia

ABSTRACT

Objective:  Compare annual health-care costs and resource utilization associated with olanzapine versus quetiapine for treating schizophrenia in a Medicaid population.

Methods:  Adult schizophrenia patients were selected from deidentified Pennsylvania Medicaid claims database (1999–2003). Included patients were continuously enrolled and initiated with olanzapine or quetiapine monotherapy after a 90-day washout period. Treatment costs were calculated for 1-year post-therapy initiation and inflation adjusted to year 2003. To control for selection bias, olanzapine and quetiapine patients were 1:1 matched using an optimal matching algorithm on propensity score, which was generated using logistic regression controlling for demographics, prior drug therapy, utilization, and costs. Treatment costs for the matched cohorts were compared directly, as well as using a difference-in-difference analysis.

Results:  A total of 6929 patients treated with olanzapine and 2321 with quetiapine met inclusion criteria. Quetiapine patients appeared more severe at baseline. After propensity score matching, 2321 patient pairs had similar baseline characteristics, including total costs. Compared with matched quetiapine patients, for the 1-year postindex period, olanzapine patients had similar drug costs ($6131 vs. $6014, P = 0.326), lower medical costs ($9897 vs. $11,218, P = 0.0128), and lower total health-care costs ($16,028 vs. $17,232, P = 0.0279). Lower psychiatric hospitalization costs account for most of the total cost difference. Difference-in-difference regression analysis confirmed olanzapine's economic advantage. Further adjusting for baseline variations, the total cost advantage of olanzapine patients was $962 (P = 0.032), and was mostly because of reduced psychiatric hospitalization costs of $992 (P = 0.004).

Conclusion:  Schizophrenia patients treated with olanzapine had lower total costs than quetiapine patients, mostly attributable to reductions in psychiatric hospitalization costs.