Background: Major depressive disorder is a prevalent, disabling, and often chronic or recurrent psychiatric condition. About 35% of patients fail to respond to conventional treatment approaches and are considered to have treatment-resistant depression (TRD). Objective: We compared the safety and effectiveness of different stimulation levels of adjunctive vagus nerve stimulation (VNS) therapy for the treatment of TRD. Methods: In a multicenter, double blind study, 331 patients with TRD were randomized to one of three dose groups: LOW (0.25 mA current, 130 μs pulse width), MEDIUM (0.5-1.0 mA, 250 μs), or HIGH (1.25-1.5 mA, 250 μs). A highly treatment-resistant population (>97% had failed to respond to ≥6 previous treatments) was enrolled. Response and adverse effects were assessed for 22 weeks (end of acute phase), after which output current could be increased, if clinically warranted. Assessments then continued until Week 50 (end of long-term phase). Results: VNS therapy was well tolerated. During the acute phase, all groups showed statistically significant improvement on the primary efficacy endpoint (change in Inventory of Depressive Symptomatology-Clinician Administered Version [IDS-C]), but not for any between-treatment group comparisons. In the long-term phase, mean change in IDS-C scores showed continued improvement. Post-hoc analyses demonstrated a statistically significant correlation between total charge delivered per day and decreasing depressive symptoms; and analysis of acute phase responders demonstrated significantly greater durability of response at MEDIUM and HIGH doses than at the LOW dose. Conclusions: TRD patients who received adjunctive VNS showed significant improvement at study endpoint compared with baseline, and the effect was durable over 1 year. Higher electrical dose parameters were associated with response durability.
- Dose response
- Treatment durability
- Treatment-resistant depression
- VNS efficacy
- Vagus nerve stimulation