Objective: The objective of this study was to evaluate the relationship between compliance with an antipsychotic medication regimen and risk of hospitalization in a cohort of California Medicaid patients with schizophrenia.
Methods: Compliance behavior was estimated by using a retrospective review of California Medicaid pharmacy refill and medical claims for 4,325 outpatients for whom antipsychotics were prescribed for treatment of schizophrenia from 1999 to 2001. Compliance behavior was estimated by using four different definitions: gaps in medication therapy, medication consistency and persistence, and a medication possession ratio. Patients were followed for one year and had an average of 19.1 dispensing events. Logistic regression models using each compliance estimate were used to determine the odds of hospitalization.
Results: Risk of hospitalization was significantly correlated with compliance. With all definitions, lower compliance was associated with a greater risk of hospitalization over and above any other risk factors for hospitalization. For example, the presence of any gap in medication coverage was associated with increased risk of hospitalization, including gaps as small as one to ten days (odds ratio [OR]=1.98). A gap of 11 to 30 days was associated with an OR of 2.81, and a gap of more than 30 days was associated with an OR of 3.96.
Conclusions: This study showed a direct correlation between estimated partial compliance and hospitalization risk among patients with schizophrenia across a continuum of compliance behavior.