Predictors of Response to Carbamazepine Extended-Release Capsules Treatment in Bipolar Disorder

Abstract

Predictors of response to psychoactive drugs are valuable in providing practical guidance and in optimizing a treatment regimen. Here we used linear regression analysis to identify treatment-specific predictors of response to therapy with beaded extended-release carbamazepine capsules (CBZ-ERC) (Shire, Wayne, PA, USA) in 600 outpatients with bipolar disorder. Data were obtained from medical charts of subjects who received CBZ-ERC in a private practice setting. Illness severity and improvement were assessed using the Clinical Global Impression-Severity (CGI-S) and Clinical Global Impression-Improvement (CGI-I) scales. We found that increasing baseline CGI-S scores correlated with lower CGI-I scores (R2=0.01, p=0.009); that is, the higher the baseline CGI-S score, the greater the expected degree of improvement. There was also a correlation between increasing CBZ-ERC dose and improvement in CGI-I scores (R2=0.02; p=0.0004). Moreover, we found that increasing carbamazepine (CBZ) blood concentration correlated with decreases in CGI-I scores (R2=0.12; p=0.025), and that there was a correlation between higher total daily CBZ-ERC dose in mg/kg of body weight and decreases in CGI-I scores (R2=0.01; p=0.038). These findings suggest that bipolar patients with more severe baseline symptoms, on higher CBZ-ERC doses, and with higher CBZ blood levels were more likely to respond to CBZ-ERC treatment.