Introduction
Intravenous (IV) ketamine infusion has emerged as one of the most extensively studied rapid-acting antidepressant interventions available to clinicians today. Since the landmark 2000 study by Berman and colleagues demonstrating significant antidepressant effects within hours of a single subanesthetic dose, IV ketamine has accumulated a robust evidence base supporting its use in treatment-resistant depression (TRD). This protocol document outlines the standard clinical approach to IV ketamine infusion therapy, drawing from published literature, consensus guidelines, and established clinical practice.
Patient Selection and Pre-Treatment Evaluation
Inclusion Criteria
Candidates for IV ketamine infusion typically present with moderate-to-severe major depressive disorder that has failed to respond to at least two adequate trials of antidepressant medications from different pharmacological classes. Clinicians should document prior treatment history thoroughly, including medication names, maximum doses achieved, duration of trials, and reasons for discontinuation. For detailed guidance on identifying appropriate candidates, see the patient selection criteria framework.
Pre-Treatment Assessment
Before initiating ketamine therapy, a comprehensive evaluation should include baseline vital signs (blood pressure, heart rate, respiratory rate, oxygen saturation), a complete metabolic panel, thyroid function tests, and a urine drug screen. A thorough psychiatric history must assess for active psychotic symptoms, poorly controlled hypertension, elevated intracranial pressure, and a personal history of substance use disorder involving ketamine or phencyclidine (PCP). Cardiovascular history warrants particular attention, as ketamine produces sympathomimetic effects that transiently elevate blood pressure and heart rate.
Standard Dosing Protocol
Induction Series
The most widely replicated dosing regimen involves administering ketamine at 0.5 mg/kg of ideal body weight, infused intravenously over 40 minutes. This subanesthetic dose has demonstrated the most favorable risk-benefit profile across randomized controlled trials. The induction series typically consists of six infusions administered over two to three weeks, with sessions scheduled two to three times per week on non-consecutive days.
Some clinicians employ a flexible dosing approach, initiating therapy at 0.5 mg/kg and titrating in increments of 0.1 mg/kg per session based on clinical response and tolerability, up to a ceiling of approximately 0.75-1.0 mg/kg. Dose adjustments should be guided by both the degree of antidepressant response and the severity of dissociative side effects experienced during prior infusions.
Maintenance Phase
Patients who demonstrate a clinically meaningful response during the induction series typically transition to a maintenance protocol. Initial maintenance infusions are commonly scheduled at weekly intervals, with gradual extension to biweekly or monthly sessions as clinical stability permits. The optimal maintenance frequency should be individualized based on duration of antidepressant effect following each infusion.
Infusion Procedure and Monitoring
Environment and Setup
Infusions should be conducted in a quiet, dimly lit clinical environment equipped for continuous cardiopulmonary monitoring. The patient is positioned in a comfortable semi-reclined chair or bed. An IV catheter is placed in a peripheral vein, and the ketamine solution is prepared by diluting the appropriate dose in 100 mL of normal saline (0.9% NaCl).
Intra-Infusion Monitoring
Continuous monitoring during the infusion should include pulse oximetry, automated blood pressure measurements at five-minute intervals, and continuous heart rate monitoring. The infusion should be paused or terminated if systolic blood pressure exceeds 180 mmHg, diastolic blood pressure exceeds 110 mmHg, heart rate exceeds 120 beats per minute, or oxygen saturation falls below 92%. An emergency cart with resuscitation equipment and airway management supplies must be immediately accessible.
Common Side Effects
Patients frequently experience dissociative symptoms, including perceptual distortions, derealization, and a sense of floating or detachment. Nausea occurs in approximately 10-15% of patients and can be managed with ondansetron 4 mg IV administered prophylactically. Transient elevations in blood pressure of 15-25% above baseline are expected and typically resolve within 30 minutes of infusion completion. Pretreatment with clonidine 0.1 mg orally may be considered for patients with labile blood pressure responses.
Post-Infusion Recovery
Patients should remain in the clinical setting for a minimum of 60 minutes following infusion completion for observation. Discharge criteria include return of vital signs to within 10% of baseline, resolution of significant dissociative symptoms, ability to ambulate without assistance, and absence of nausea or vomiting. All patients must be accompanied by a responsible adult and are instructed not to drive, operate heavy machinery, or make important legal or financial decisions for the remainder of the day.
Outcome Measurement
Standardized depression rating scales should be administered at each visit. Commonly used instruments include the Patient Health Questionnaire-9 (PHQ-9), the Quick Inventory of Depressive Symptomatology (QIDS-SR16), and the Montgomery-Asberg Depression Rating Scale (MADRS). A response is generally defined as a 50% or greater reduction in baseline scores, while remission thresholds vary by instrument. Suicidal ideation should be assessed independently using validated tools such as the Columbia Suicide Severity Rating Scale (C-SSRS).
Clinical Considerations
Concurrent use of benzodiazepines may attenuate the antidepressant efficacy of ketamine, and clinicians should consider tapering or holding benzodiazepine doses on infusion days when clinically safe. Lamotrigine has shown preliminary evidence of extending the duration of antidepressant response between infusions. Long-term safety data regarding repeated ketamine exposure remain limited, and clinicians should monitor for potential hepatotoxicity, urological symptoms, and cognitive effects with ongoing treatment.
References
- MedlinePlus: Ketamine Injection Drug Information — National Library of Medicine patient medication information for IV ketamine including dosing and precautions
- DailyMed: FDA Drug Label Information — National Library of Medicine database of official FDA drug labeling for ketamine (Ketalar)
- ASA: American Society of Anesthesiologists — Professional society providing clinical guidelines for ketamine administration and monitoring standards
- PubMed: Ketamine: A Review of Clinical Pharmacokinetics and Pharmacodynamics — Comprehensive pharmacokinetic and pharmacodynamic review for IV ketamine dosing optimization
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