Attrition factors in clinical trials of comorbid bipolar and substance-related disorders

Background: This study analyzed and defined specific factors that account for attrition in clinical research for patients with bipolar and substance-related disorders. Methods: Data were analyzed from two completed studies: an open-label trial of lamotrigine in patients with bipolar disorder (BPD) and cocaine-related disorder, and a placebo-controlled trial of quetiapine in patients with BPD and alcohol-related disorders. Correlations and Independent sample t-tests were performed to assess the impact of baseline characteristics including on length of study participation. Significance was set at the p = 0.05 level. Results: In the lamotrigine-treated patients, the presence of an amphetamine-related disorder, in addition to cocaine-related disorders, was associated with a shorter time in the study. In the quetiapine-treated patients higher scores on the Addiction Severity Index Legal subscale were associated with shorter length in the study. The presence of panic disorder was associated with shorter time in both studies. Limitations: Although the data were taken from the two largest clinical trials, to date, in patients with BPD and substance-related disorders, the sample sizes were relatively modest. In addition, the baseline assessments were somewhat different in the two studies limiting our ability to make conclusions on differences between patients with BPD and cocaine use versus alcohol use. Conclusions: This study adds to an emerging literature on the significance of panic disorder in patients with BPD.