Antipsychotic adherence and its correlation to health outcomes for chronic comorbid conditions

To examine the relationship between adherence to antipsychotics and adherence to medications for cardiometabolic conditions (diabetes, hypertension, and hyperlipidemia) and subsequent health care utilization and expenditures in patients with schizophrenia and preexisting cardiometabolic conditions.

Medstat MarketScan Medicaid databases from 2004 to 2008 were used to identify a retrospective cohort of schizophrenia patients (ICD-9-CM codes 295.1-295.3, 295.6, or 295.9) with preexisting cardiometabolic medication use who had initiated antipsychotic treatments. Patients who initiated a second-generation antipsychotic between July 1, 2004, and December 31, 2006, were identified as the new user cohort. Comorbid conditions were identified if patients had at least 1 inpatient or 2 outpatient claims for hypertension, hyperlipidemia, and/or diabetes (ICD-9-CM codes 401.xx to 405.xx inclusive, 272.xx inclusive, and 250.xx inclusive, respectively) and were using medication to manage these conditions prior to antipsychotic initiation. Adherence to cardiometabolic medications was compared between adherent and nonadherent patients taking antipsychotics using the proportion of days covered over 8 quarters categorized as phases of treatment to reflect initiation (1, days 1-90), continuation (2-4, days 91-360), and maintenance (5-8, days 361-520). Proportion of days covered values ≥ 0.80 were deemed adherent. Prior period antipsychotic adherence was used to predict cardiometabolic medication adherence, health care utilization, and expenditures using generalized estimating equations and negative binomial regressions.

The final population represented 1,006 patients. Antipsychotic adherence during continuation was a significant predictor of medication adherence for hypertension (odds ratio [OR] = 2.40, 95% CI = 1.67-3.44), diabetes (OR = 2.28, 95% CI = 1.43-3.67), and hyperlipidemia (OR = 2.16, 95% CI = 1.11-4.20) during maintenance. Antipsychotic adherence during continuation resulted in significantly lower emergency room use (OR = 0.67, 95% CI = 0.52-0.87), lower inpatient use (OR = 0.77, 95% CI = 0.56-1.06, not significant), and significantly higher outpatient ($996, 95% CI = $663-$1,330), medication ($652, 95% CI = $542-$762), and total health ($1,371, 95% CI = $490-$2,252) expenditures during maintenance.

Antipsychotic adherence was associated with better adherence to cardiometabolic medications and a potential reduction in emergency room and inpatient service utilization. Clinicians should consider adherence to both antipsychotic and cardiometabolic medications when caring for patients with schizophrenia and comorbid conditions.