Clozapine use reduced psychiatric hospitalization and emergency room visits in patients with bipolar disorder independent of improved treatment regularity in a three-year follow-up period.

OBJECTIVES: The efficacy of clozapine in bipolar disorder remains to be systemically examined. In the current study, we sought to disentangle the effect of clozapine from that of improved treatment regularity and to compare the effect of clozapine with the effect of regular treatment for bipolar disorder by exploring the complete 10-year clozapine prescription data from a Taiwanese total population health claims database. METHODS: In the period between 2000 and 2009, 3,874 (3.3%) out of the 117,785 patients identified as having bipolar disorder in a Taiwanese total population health claims database were ever prescribed clozapine. Among them, 920 patients with bipolar disorder who had good pre-clozapine medication compliance and received at least two clozapine prescriptions were further categorized according to their clozapine medication possession ratio (MPR) as regular users (MPR ≥ 0.8; n = 476) and irregular users (MPR < 0.8; n = 444). Using a mirror-image design, we compared the numbers of emergency room (ER) visits, hospitalizations and hospital days, and the average durations of a single hospitalization during the pre- and post-clozapine mirror periods with a follow-up time of up to three years, controlling for time-variant course confounders. RESULTS: The patterns of change in outcome indices from the pre-clozapine period to the post-clozapine period differed significantly between the two clozapine-user groups. Clinical outcome indices improved only in regular users, while they deteriorated in irregular users. Over the three-year follow-up period, the irregular users consistently had a higher adjusted risk for increased numbers of ER visits [odds ratio (OR): 2.06-2.43], hospitalizations (OR: 2.52-3.22), and total hospital days (OR: 2.42-2.91) when compared to the regular users. Thus, effects of clozapine were consistently demonstrated in one- to three-year mirror comparison periods. CONCLUSIONS: Clozapine, when used with high treatment regularity (MPR > 0.8), was effective in reducing the numbers of ER visits, hospitalizations, and total hospital days in patients with bipolar disorder with previous frequent hospitalizations and ER visits despite regular pre-clozapine treatment for bipolar disorder. However, high early attrition and suboptimal treatment compliance need to be rectified in order to optimize the outcome of clozapine treatment in bipolar disorders.