Ketamine
Recently, researchers have identified ketamine as a potential therapeutic option for depression and SI. A single ketamine infusion treatment has a rapid response, minimal AEs, and potentially long-lasting efficacy with SI, which would make it ideal for the treatment of acutely suicidal patients.4 Ketamine is an N-methyl-D-aspartate receptor (NMDAR) inhibitor that also has been found to be a weak μ- and κ-opioid receptor agonist and an inhibitor of the reuptake of serotonin, dopamine, and norepinephrine. Inhibition of the NMDAR results in analgesia, and ketamine is approved for the induction of anesthesia, pain relief, and sedation.12
Although AEs such as hallucinations and sedation create the potential for dangerous recreational use, ketamine is safely used in health care settings for a variety of indications. Effects are noted within 5 minutes of administration if given by infusion, and the main effects can last between 20 and 40 minutes.
Ketamine has a complex pharmacology and plays a role in other cell signaling mechanisms, but the significance of these additional mechanisms in the therapeutic effects of ketamine have only recently been elucidated. Preclinical studies indicate a probable NMDAR inhibition-independent mechanism responsible for the antidepressant response to ketamine.13,14 The complex associations with rapamycin signaling, eukaryotic elongation factor 2 dephosphorylation, increased synthesis of brain-derived neurotrophic factor, and activation of glutamatergic AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors have been linked to its rapid antidepressant effect and ketamine’s induction of synaptogenesis within the limbic system.13,14
Clinical Research
Ketamine was studied as an adjunctive treatment to psychotherapy for addictions as far back as the 1970s.15 The available reports indicate a universally positive result, with increased rates of remission and decreased rates of relapse attributed to ketamine’s ability to alter one’s thought processes by reinforcing limbic-cortex interactions that facilitate the growth of more positive cognitive schemas and improved emotional attitudes about the self in support of the recovery process.15
Neurobiologic studies have shown that treatment with ketamine has a direct and immediate effect on neuronal pathways of the limbic system. It is known to regulate the mind’s reaction to positive stimuli by reversing the depressed subject’s blunted reaction to positive faces.16 This rapid normalization of the positive faces test is unique to ketamine infusion and is not seen in tests with traditional antidepressants.
In 2000, the first placebo-controlled trial using ketamine for treatment resistant depression (TRD) demonstrated the rapid antidepressant effects of a single dose of ketamine, but this study only looked at these effects for 1 week.17 In multiple double blind, placebo-controlled trials since then, IV infusion of ketamine was shown to be an effective intervention for TRD.13,18,19 More recently, a published investigation involving the treatment of MDD showed that ketamine in conjunction with a selective serotonin reuptake inhibitor (SSRI) accelerated and enhanced the effectiveness of the SSRI in reducing depressive symptoms.20
Based on the rapid resolution of depressive symptoms using ketamine, researchers have looked at its effect on suicidality as a secondary measure. A case study of a patient with severe depressive episodes and multiple previous suicidal attempts reported that the patient responded to a single dose of ketamine, described the experience as “being reborn,” and maintained complete remission of SI for the 6-month study period.21 In a larger study, 133 TRD patients received a single IV dose of ketamine with significant reductions in SI independent of depressive and anxiety symptoms.22
Depression Treatment
These results have led to an excitement for ketamine therapy as a novel treatment of depression, and off-label use by treatment centers now exists in several countries to aid those with TRD.23 This off-label use continues to be controversial, as research has yet to determine the safest most effective route and duration of treatment and whether the ketamine treatment AEs will exceed any accrued therapeutic benefit.13
The American Psychological Association Council of Research Task Force on Novel Biomarkers and Treatment critically examined the clinical evidence of ketamine use and has raised important concerns about the use of ketamine in the outpatient setting, administered in the absence of consensus therapeutic monitoring guidelines, and ambitiously marketed as a panacea for TRD.13,24 A study showed permanent impairment of brain function for both groups compared with monkeys treated with saline infusions.25 In 2016, the FDA gave fast-track approval for an intranasal ketamine that would make the treatment more easily available in the outpatient setting, but this could lead to certain patients developing a dependency on ketamine or engaging in its diversion for recreational use. There are case reports and anecdotes in the literature of patients and research subjects developing drug-seeking behaviors and overuse of ketamine.24 Additionally, the comorbidities associated with TRD and SI have not been fully evaluated. For instance, there is evidence that depressed patients with obsessive compulsive disorder may have worse outcomes that include delayed onset SI.26
There also is concern for the use of ketamine for chronic opioid users. The combination of ketamine with opioids may increase the response to the opioid in an otherwise drug tolerant patient, leading to risk of death by overdose in patients who have not increased their usual dose.27 However, this effect was noted only when ketamine and opioids were administered together, and the effect does not seem to last postinfusion.27
The challenges in treatment of TRD include finding an effective formulation—IV infusion of ketamine requires cardiovascular monitoring and is administered by anesthesiologists. The short duration of action for depression requires repeated infusions, and the frequency and quantity of infusions have not been determined. Efforts to find other NMDAR inhibitors (eg, memantine, nitrous oxide, D-cycloserine, and others) that match ketamine’s antidepressant efficacy but with easier delivery methods and fewer risks have thus far been unsuccessful.13 It is now believed that ketamine’s unique ability to activate intracellular signaling pathways linked to synaptic plasticity gives it the antidepressant function. Recent studies have further narrowed ketamine’s antidepressant function to the R- enantiomer of the ketamine metabolite, hydroxynorketamine.14 The nasal spray for ketamine is the S- enantiomer, which has better bioavailability but may have less antidepressant efficacy compared with the racemic mixture used in ketamine infusions.
