Major depressive disorder (MDD) carries worldwide the largest burden of diseases among mental, neurological, and substance-use disorders measured in Disability Adjusted Life Years (DALYs), according to the World Health Organization (WHO).1 In turn, MDD has the highest DALYs in middle to high income countries, with ischemic cardiac diseases being second.2 Although there are effective treatments for MDD, a large proportion of patients do not achieve remission even after several attempts, and any significant response, when it manifests itself, takes place a delay of a few weeks.3,4 There is always urgency to treat MDD because although patients may have been ill for several weeks, months, and sometimes years, they are often in a crisis situation when they consult. The nature of the crisis may be familial, financial/professional, or the consultation may take place because of intense personal suffering, possibly involving suicidal ideation. Consequently, rapid therapeutic action and high remission rates represent the two major unmet needs for MDD.

In the last few years, considerable attention has been dedicated to the glutamate system as a possible contributor of the antidepressant response. The most striking breakthrough has been the rapid antidepressant response of intravenous ketamine using doses that are about a quarter of the routinely utilized anesthetic dose in children and adults.5,6 Unlike many anesthetic agents, ketamine does not depress cardiovascular and respiratory parameters.7 The primary action of ketamine is to block N-Methyl-D-Aspartate (NMDA) receptors. The antidepressant response to ketamine often manifests itself within a few hours, but is generally maximal after 24 hours.8 Importantly, a single infusion produces in the most subjects a robust decrease of suicidal ideation.9,10 The drawback of this approach is, however, that its benefits generally disappear within a week.6 Consequently, much clinical work remains to be carried out in order to better understand and maintain the antidepressant response of ketamine.

Specific aim #1: The first aim of this proposal is to characterize the antidepressant action of a single dose of ketamine in a truly double-blind paradigm. Indeed, even the low doses of ketamine (0.2-0.5 mg/kg)8,11 produce mild derealization and therefore the use a mere saline solution in prior studies has been inadequate as a control.

To show that the infusion of a low dose of the short-acting benzodiazepine midazolam will serve as an adequate active control for ketamine. It is hypothesized that because midazolam produces marked sedation, it will serve as an adequate control. To determine if the brain-derived neutrophic factor (BDNF) mediates the antidepressant response. In mice, a VAL/MET polymorphism for the BDNF gene, ketamine is devoid of effects. The influence of this polymorphism will be evaluated in patients.

Specific aim #2: The second goal of this proposal is to attempt enhancing and prolonging the antidepressant effect of ketamine by giving it repeatedly at a rate of three infusions per week for two consecutive weeks.

To assess whether ketamine responders will improve further after a six infusions over two weeks. It is hypothesized that ketamine non-responders following a single infusion will not show a significant improvement with repeated infusions of ketamine at a dose of 0.5 mg/kg given three times a week for two weeks, but that in responders repeated ketamine will produce a more robust and sustained antidepressant action than a single infusion. To assess whether the inflammatory status of the depressed patients is altered by the response to ketamine. Pro-inflammatory mediators and cortisol are generally elevated in depression while melatonin is decreased. These anomalies are typically restored with effective treatments. This will be investigated in the light of the rapid antidepressant effect of ketamine.

Specific aim #3: The third goal of this proposal is to prolong the antidepressant effect of ketamine. In this third consecutive phase of the project, ketamine-responsive patients will receive ketamine on a once weekly basis.

1)To demonstrate that the antidepressant effect of ketamine will be sustained over four weeks using a single infusion per week. The antidepressant response to a single infusion of ketamine disappears within 7 days. It is hypothesized that repeated infusions of ketamine, at an interval of one week for four weeks, will maintain the antidepressant effect.

2)To assess how long the antidepressant effect of repeated ketamine infusions will last in follow up. After the first three phases of this project that will last about eight weeks, the average duration of a standard antidepressant medication trial, the responders will be monitored to follow their clinical evolution. It is hypothesized that the responders will show a longer maintenance of their response than after the first infusion in phase one of the project.

Phase I: the double-blind crossover. After patients will have been deemed eligible to participate in the study, blood will be drawn for genotyping and various assays (BDNF Val/Met, BDNF, morning melatonin and salivary cortisol, C-reactive protein, IL-1β, IL-2, IL-6, IL-8, IL-12, IFN-γ, TNF-α, and anti-inflammatory factors IL-4 and IL-10, as previously done in our laboratory).101-102 They will be randomized to receive intravenously either 0.5 mg/kg of ketamine (the readily available racemic mixture) or 30 µg/kg of midazolam as a 250 ml infusion (prepared in our unit) over 40 minutes, given by a research nurse in the presence of a study physician. Their antidepressant drug regimen will not be altered throughout the study. A clinician will evaluate their clinical status prior to the infusion, using the Montgomery-Asberg Depression Rating Scale (MADRS)103 and the Clinical Global Intensity-Severity (CGI-S)104 and the patients will rate themselves using the Quick Inventory Depressive Symptoms-Self-report (QIDS-SR)105 and a self-report questionnaire rating suicidality. The patients will be assessed using the Brief Psychiatric Rating Scale-positive symptom scale106 at baseline (before the infusion), time 0 (immediately after infusion is complete), then at 60 and 120 minutes post time 0. The CGI-Improvement (CGI-I)104 will be used to obtain a clinical evaluation of overall change of their condition after two hours before discharging the patients two hours after the infusion. The patients will come in the next day for an evaluation using the MADRS, CGIs, and the QIDS-SR and will be asked to guess what drug they received. Four days after the infusion, the patients will repeat the QIDS-SR at home, and they will come in for an evaluation at day 7. If the patients did not respond, or if they returned to 80% of their MADRS score before the infusion, they will receive either ketamine or midazolam to complete the crossover protocol. If the patients are maintaining more than a 20% improvement of their baseline MADRS score, they will be asked to come in on a weekly basis for an assessment, and will be asked to complete a QIDS-SR twice a week (at days 10, 14, 18, 21, and so on) in order to assess how long the therapeutic effect lasts. Patients who have not response to their second infusion or those found to have relapsed during the weekly follow-up visits, will continue into phase II. Patients who are unable, ineligible, or unwilling to enter phase II will be given a recommended treatment plan and returned to their family physician with a consultation plan, or additional/alternative treatment options at the discretion of the study physician. In order to obtain an objective measure of their activity level and of the pattern of their sleep-wake cycle, patients will wear an actimeter watch for several days during screening and throughout the protocol. The data will be downloaded weekly during the visits. Phase II: the repeated treatment over two weeks. Once patients are deemed not to have responded to the second infusion or have lost their improvement (relapsing to a MADRS score over 80% of their baseline score prior to the second infusion), they will receive repeated ketamine infusions (0.5 mg/kg). They will be given 3 infusions per week for two weeks. On visit 6 of phase 2 the patients will be assessed using the Brief Psychiatric Rating Scale-positive symptom scale106 at baseline (before the infusion), time 0 (immediately after infusion is complete), then at 60 and 120 minutes post time 0. Their clinical status will be assessed prior to each infusion using the MADRS, the CGI-S, the CGI-I, and they will rate themselves using the QIDS-SR and a self-report questionnaire rating suicidality. Patients will be assessed two to three days after the sixth infusion. The ratings throughout phase II will help determine whether repeated administration produces a greater and sustained improvement than a single infusion. Biological assays will be repeated at the end of Phase II. Phase III: the repeated treatment over four weeks and the naturalistic follow-up.

Two to three days after the sixth infusion, patients not achieving a 50% improvement of their MADRS score, when compared to their baseline score prior to the first of the six infusions, will be taken out of the study and offered to be treated in our Research Unit using additional pharmacological and/or psychotherapeutic approaches. Patients improving by 50% or more on the MADRS scale will receive ketamine once a week for four weeks. They will be assessed using the same scales as mentioned above prior to each infusion. Patients will be assessed two to three days after the fourth weekly infusion. The ratings throughout phase III will help determine whether repeated administration of ketamine is effective to maintain the beneficial action of a relatively more intense regimen of ketamine.

Monitoring of the patients reaching more than 80% or more of their MADRS score, when compared to their baseline score prior to the last four infusions, will cease and will be offered to be treated in our Research Unit using additional pharmacological and/or psychotherapeutic approaches. Patients maintaining more than 20% improvement will be assessed weekly to determine how long the therapeutic effects of ketamine last. Biological assays will be repeated at the end of Phase III.