Comparative effectiveness of switching paroxetine formulation for treatment of major depressive disorder: an open-label multicenter study

AIM: To assess the effectiveness and safety of switching the antidepressant formulation from immediate-release (IR) to controlled-release (CR) paroxetine in patients with major depressive disorder (MDD). PATIENTS AND METHODS: A total of 113 outpatients with MDD diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, and treated with a stable dose of IR paroxetine for at least 6 months were enrolled. Patients were then switched to CR paroxetine for 8 weeks. Effectiveness was evaluated by scores on the Himorogi Self-Rating Depression/Anxiety Scales (HSDS/HSAS) and the Clinical Global Impression – Severity (CGI-S). Safety was evaluated based on the reported adverse drug reactions (ADRs). Medication satisfaction and preference were assessed based on questionnaire responses using Likert-type scales. RESULTS: The overall patient HSDS/HSAS scores significantly improved after switching from IR to CR paroxetine (P<0.001). Furthermore, CR paroxetine was superior to IR paroxetine (P<0.001) according to the results of the CGI-S evaluation. ADRs were experienced by 14 (12.4%) patients, including dry mouth, nausea/vomiting, somnolence/drowsiness, and wakefulness/arousal during sleep. Satisfaction and preference for paroxetine improved after switching to the CR formulation (P<0.001; chi-square test). CONCLUSION: These results suggest that switching the treatment from IR to CR paroxetine could improve depressive symptoms and decrease ADRs. However, these results may have been caused by the psychological effect of drug switching. Hence, future studies with blinded evaluation methods are required to confirm and expand our findings.