The relationship between antipsychotic medication adherence and patient outcomes among individuals diagnosed with bipolar disorder: a retrospective study

BACKGROUND Reducing hospitalizations and emergency room visits is important to improve patient outcomes. This observational study examined the association between adherence to antipsychotics and risk of hospitalizations and emergency room (ER) visits among patients with bipolar disorder. METHODS Claims data from commercial healthcare plans (Pharmetrics; January 2000 to December 2006) for patients with bipolar disorder receiving an antipsychotic prescription were examined. Adherence was analyzed over a 12-month follow-up period after the receipt of first prescription of an antipsychotic. Adherence to antipsychotics was measured by the medication possession ratio (MPR). The MPR was calculated as the number of days that an antipsychotic medication was filled as compared with the total number of days during the follow-up period. Logistic stepwise regressions examined the association between achievement of various adherence goals and patient outcomes (hospitalization or ER visit for mental health or any reason). RESULTS In total, 7,769 patients with bipolar disorder were included. The mean MPR was 0.417, with 61.7% of individuals having an MPR < 0.50, and 78.7% an MPR < 0.75. As adherence improved, the risk of hospitalization or ER visit declined. A significant reduction in the risk of hospitalization (odds ratio (OR) 0.85, 95% confidence interval (CI) 0.75 to 0.98) or an ER visit (OR 0.84, 95% CI 0.74 to 0.96) for any cause was associated with an MPR >or= 0.75. An MPR >or= 0.80 was associated with a significant reduction in the risk of a mental health-related hospitalization (OR 0.82, 95% CI 0.70 to 0.95), while an MPR >or= 0.90 was associated with a significant reduction in risk of a mental health-related ER visit (OR 0.71, 95% CI 0.54 to 0.91). CONCLUSION Patients with lower antipsychotic adherence were at greater risk of hospitalizations and ER visits. Thus, any efforts to increase adherence, even in small increments, can be helpful in decreasing these risks.