Factors Associated with Adherence to Treatment with Olanzapine and Other Atypical Antipsychotic Medications in Patients with Schizophrenia

Objectives: Poor treatment response is an important factor contributing to lack of treatment adherence. The goals of this research were to determine whether improvements in Positive and Negative Syndrome Scale (PANSS) symptom domains predict the likelihood of staying on treatment and whether differential responses to treatment with various atypical antipsychotics in specific symptom domains account for differences in discontinuation rates or treatment adherence.

Methods: We conducted a post-hoc analysis of pooled data from 5 randomized, double-blind, 24- to 28-week clinical trials in 1103 olanzapine-treated and 1090 risperidone-, quetiapine-, ziprasidone-, or aripiprazole-treated adult patients with schizophrenia. The 5 PANSS factors were tested as potential predictors of treatment adherence for all treatment groups combined. Treatment differences in the 5 PANSS factors and individual items were assessed between olanzapine and the other atypical antipsychotics combined. Secondary analyses repeated for the 21 Heinrichs Quality of Life Scale (QLS) items.

Results: Improvement in PANSS positive factor was the strongest predictor of treatment adherence, irrespective of medication (based on standardized scores, hazard ratio [HR], 1.58; 95% confidence interval [CI], +1.40 to +1.79; P < .001). Improvement in PANSS hostility (HR, 1.23; 95% CI, +1.11 to +1.37; P < .001) and depressive (HR, 1.15; 95% CI, +1.05 to +1.27; P = .002) factors was also a significant predictor; negative and disorganized thoughts factors were not. All QLS items had significant predictive effects. Olanzapine-treated patients showed significantly greater improvements than all other groups at week 24 on all 5 PANSS factors (P = .028 for negative; P < .001 for all others) and on 3 QLS items.

Conclusion: Significant improvement in positive symptoms, regardless of treatment, followed by significant improvement in hostility and depressive symptoms, may best predict treatment adherence. Olanzapine-treated patients experienced significantly greater improvements in these specific symptoms than patients treated with the other atypical antipsychotics examined. These findings may further explain why olanzapine-treated patients continue treatment more often.