Treatment adherence among patients with bipolar or manic disorder taking atypical and typical antipsychotics

OBJECTIVE: This retrospective claims-based study evaluated treatment adherence among patients with bipolar or manic disorder treated with atypical and typical antipsychotics. METHOD: Claims data for 18,158 antipsychotic treatment episodes in 15,224 commercially insured patients with bipolar or manic disorder (ICD-9-CM criteria), from January 1999 through August 2003, were evaluated. Overall adherence was measured by adherence intensity (medication possession ratio) and treatment duration (length of treatment episodes). Treatment-related factors that may affect medication adherence were also investigated. Pairwise comparisons of the individual atypicals and a combined group of leading typical antipsychotics were undertaken using multiple regression analysis adjusting for differing patient characteristics. RESULTS: Adherence intensity with quetiapine was 3% greater than with the typicals combined (p=.002) and was greater than with risperidone or olanzapine by 4% (p<.001) and 2% (p=.001), respectively. Olanzapine (2%, p<.001) and ziprasidone (3%, p=.001) showed significantly greater adherence intensity than risperidone. Risperidone (p=.002), olanzapine (p=.055), and the typicals (p=.021) demonstrated negative associations between dose and adherence intensity, while quetiapine showed a nonsignificant trend for a positive association (p=.074). Quetiapine and risperidone had significantly longer treatment durations than the typicals combined (1.05 and 1.00 months, respectively, p<.001) and longer treatment durations than olanzapine (0.75 and 0.79 months, respectively, p<.001) or ziprasidone (0.78 months, p=.002 and 0.69 months, p=.003, respectively). Shorter treatment durations were associated with switching to other antipsychotics or remaining on or switching to other psychotropics (e.g., traditional mood stabilizers) only. All of the atypicals except ziprasidone were associated with a significantly lower likelihood of switching compared with the typicals (p<.05). CONCLUSIONS: The claims-based findings of this study suggest that, for bipolar or manic disorder, quetiapine therapy may be associated with better treatment adherence than typical or some atypical antipsychotics. Estimated differences, however, were relatively small, particularly for adherence intensity.