What evidence supports using a booster session of ketamine after an initial course of intravenous ketamine infusions for depression?

Booster Ketamine Sessions After Initial Treatment Course

Repeat-dose intravenous ketamine infusions are the only evidence-based strategy to maintain antidepressant response after an initial treatment course, with data supporting ongoing maintenance infusions at progressively longer intervals rather than isolated "booster" sessions.

Evidence for Maintenance Ketamine Treatment

The concept of a single "booster session" is not well-supported in the literature. Instead, the evidence demonstrates that sustained benefit requires ongoing repeat-dose ketamine administration 1. A systematic review found that no treatment modality other than repeat-dose IV ketamine has demonstrated ability to significantly prolong the acute efficacy of IV ketamine in treatment-resistant depression 1.

Relapse Timeline Without Maintenance Treatment

• Median time to relapse: 2-4 weeks after acute ketamine treatment when no maintenance strategy is employed 1
• Approximately 70% of responders relapsed by 4 weeks following a final infusion in serial treatment studies 2
• This short duration of benefit necessitates a maintenance approach rather than sporadic boosters

Maintenance Dosing Strategies

Real-World VA Health System Data

The most robust real-world evidence comes from 215 patients treated in the VA system 3:

• Initial phase: Infusions every 5 days
• Maintenance phase: Frequency decreased to every 3-4 weeks over the first 5 months
• Total infusions: Mean of 18 infusions over 12 months
• Outcomes: 26% response rate and 15% remission rate at 6 weeks, with improvements sustained through 26 weeks with decreasing infusion frequency

Clinical Response Patterns

Initial treatment series (typically 6-8 infusions over 2-4 weeks):

• Response rates: 67.5% after six infusions 4
• Remission rates: 48.1% after six infusions 4
• Symptoms plateau around session 4, with no significant additional improvement from sessions 4-10 5

Repeated treatment series are feasible and safe:

• Case series demonstrated patients could undergo 2-3 complete treatment series when symptoms worsened 6
• Four of five patients achieved remission after first series, three after second series 6
• Adverse events remained mild and transient with repeated series 6

Practical Algorithm for Maintenance Treatment

Step 1: Complete Initial Induction Series

• 6-8 infusions over 2-4 weeks (typically Monday-Wednesday-Friday schedule)
• Assess response at completion

Step 2: Transition to Maintenance Phase

For responders:

• Begin tapering infusion frequency:
  • Weeks 3-4: Once weekly
  • Weeks 5-8: Every 2 weeks
  • Months 3-6: Every 3-4 weeks
  • Beyond 6 months: Individualize based on symptom monitoring

For non-responders:

• Consider discontinuation after 6-8 infusions if no meaningful improvement

Step 3: Monitor for Symptom Recurrence

• Use standardized scales (PHQ-9, MADRS) at each visit
• If symptoms worsen between scheduled infusions, shorten interval
• If sustained remission achieved, cautiously extend intervals

Step 4: Manage Relapse

• If relapse occurs despite maintenance: Consider repeating full induction series 6
• Subsequent treatment series appear safe and may alter severity of future episodes 6

Critical Caveats

Duration of benefit is limited: The evidence does not support that a single "booster" will provide sustained benefit. The data consistently show that ongoing maintenance infusions are required to sustain response 1.

Long-term safety data are limited: While short-term adverse events are mild and transient 6, 4, the safety of chronic repeated ketamine infusions beyond 12 months requires further study 3.

Suicidal ideation responds rapidly: Even in non-responders to overall depression treatment, suicidal ideation decreased significantly 4, suggesting potential benefit for this specific symptom even when global depression does not fully respond.

Combination with psychotherapy: Emerging evidence suggests combining ketamine with cognitive behavioral therapy may enhance outcomes 7, though high-quality RCT data are lacking.

Bottom Line

Rather than planning isolated "booster sessions," establish a maintenance infusion schedule with progressively longer intervals (starting weekly, extending to every 3-4 weeks) for patients who respond to initial treatment. This approach, supported by real-world VA data 3 and systematic review evidence 1, provides the best strategy for sustaining ketamine's antidepressant effects. Monitor symptoms closely and adjust frequency based on clinical response, recognizing that most patients will require ongoing maintenance rather than occasional boosters.