Nonanaesthetic Effects of Ketamine a Review Article Pdf

Ketamine, a nonselective NMDA receptor adversary, is used widely in medicine as an coldhearted amanuensis. However, ketamine'due south mechanisms of action lead to widespread physiological effects, some of which are at present coming to the forefront of research for the treatment of diverse medical disorders. This newspaper aims at reviewing recent information on key nonanesthetic uses of ketamine in the electric current literature. MEDLINE, CINAHL, and Google Scholar databases were queried to notice articles related to ketamine in the handling of depression, pain syndromes including astute pain, chronic pain, and headache, neurologic applications including neuroprotection and seizures, and alcohol and substance apply disorders. It tin be concluded that ketamine has a potential function in the treatment of all of these weather condition. However, enquiry in this expanse is even so in its early stages, and larger studies are required to evaluate ketamine'south efficacy for nonanesthetic purposes in the general population.

1. Introduction

Ketamine has been used as an anesthetic drug for over 65 years [ane]. An enantiomeric, lipid-soluble phencyclidine derivative, ketamine is one of the well-nigh ordinarily used drugs in anesthesia. As a nonselective NMDA receptor antagonist, it has equal affinity for different NMDA receptor types. NMDA is a subgroup of ionotropic glutamate receptors, forth with AMPA and kainite. Ketamine is inexpensive and therefore widely used in developing countries. It additionally has item utility for anesthesia induction in hemodynamically unstable patients [ii].

Ketamine administration has long been known to mediate a wide diversity of pharmacological effects, including dissociation, analgesia, sedation, catalepsy, and bronchodilation. Though ketamine is known almost widely for its coldhearted backdrop, recent enquiry has uncovered multiple novel uses for this drug, including neuroprotection, combatting inflammation and tumors, and treatment of depression, seizures, chronic pain, and headache [three–5]. Racemic ketamine, a mixture of (South)- and (R)-ketamine (Figure one), is normally used in this inquiry, though both (Due south)-ketamine and (R)-ketamine alone are besides subjects of report. While (S)-ketamine carries roughly 3- to 4-fold greater say-so equally an coldhearted, it also carries a greater chance of psychotogenic side effects [6]. Nevertheless, ketamine has an all-encompassing side-effect profile and a potential for corruption that cannot exist ignored, which has historically led to its abstention in favor of other agents, and its safety is an surface area of ongoing research [iii]. Additionally, there are a multifariousness of agin reactions that take been associated with ketamine apply which must be considered, including self-resolving sinus tachycardia, neuropsychiatric effects, intestinal hurting, liver injury, and dose-dependent urogenital pathology including ulcerative cystitis [7–ix]. Currently, there are roughly 800 or more clinical trials exploring aspects of nonanesthetic uses of ketamine registered on ClinicalTrials.gov, illustrating the extensive ongoing interest in this area.

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The nonanesthetic clinical uses of ketamine take been the focus of extensive recent research, some of the almost applicative and prevalent of which are explored hither. For this scoping study, nosotros sought to utilize the Arksey and O'Malley methodological framework to provide a broad overview of the field, with attention to ongoing research and electric current cognition gaps [ten]. Relevant literature from 2010 through the present was queried through the MEDLINE, CINAHL, and Google Scholar databases. Keywords included "ketamine" combined with terms including "not-coldhearted uses," "depression," "headache," "neuroprotection," "pain," "pain syndromes," "chronic hurting," "booze utilise disorder," "substance use disorder," and "seizure." Watch research from prior to 2010 was too incorporated. Relevant original articles including randomized trials, retrospective studies, review articles, instance reports, and preclinical animal studies were included. This paper will discuss some of the nearly common and promising nonanesthetic uses of ketamine, including its utility in the treatment of depression, hurting syndromes including headaches, neurologic disorders including seizures, and alcohol/substance employ disorders.

2. Ketamine and Depression

Despite the high prevalence of low, which affects roughly 1 in 5 people over their lifetime, currently available pharmacologic treatments, the most commonly utilized of which are selective serotonin reuptake inhibitors (SSRIs), have limited efficacy [11]. SSRIs reach adequate upshot in as piddling equally 30% of patients [12], while having a high burden of side effects ranging from nausea and headaches to weight gain and sexual dysfunction [13]. Pharmacologic treatment of depression has also historically been limited by the fact that conventional antidepressants typically take weeks to attain upshot [14]. Nearly all antidepressants target monoaminergic systems, and research on new molecular targets (including corticotropin-releasing factor i antagonists, neurokinin 1 antagonists, and vasopressin V1b antagonists) has not nevertheless led to alternative treatments [15]. Low is known to be associated with alterations in glutamatergic neurotransmission and dysfunctional activity of the resting country network [sixteen]. Additionally, depression is thought to be acquired by enhanced subcortical and limbic activity, which affects cognition and emotion regulation [15]. Ketamine offers a promising alternative to conventional antidepressants due to its rapid onset and apparent efficacy. More than broadly, ketamine appears to accept efficacy in treating multiple internalizing disorders including depression, anxiety, and obsessive-compulsive disorder [17–19].

Ketamine is thought to affect these encephalon areas straight through modification of glutamatergic neurotransmission [20], although it has likewise been shown to mediate its furnishings through modulation of dopaminergic neurotransmission [21] and serotonergic neurotransmission [20]. Ketamine also indirectly acts through several other neurochemical pathways. Information technology induces upregulation of the mammalian target of rapamycin (mTOR) pathway, shifting activity away from subcortical and limbic regions and toward the medial and lateral prefrontal cortex [15], and has the potential to opposite the mTOR signaling pathway impairment that is seen in major depressive disorder (MDD) [22]. Ketamine additionally upregulates the expression of glutamate transporters, specifically EAAT2 and EAAT3, in the rat hippocampus [23]. Modulation of hippocampal plasticity is another mechanism by which ketamine is thought to mediate its antidepressant effects [14], the mechanism of which may be related to EAAT3 regulation of AMPA receptor trafficking and redistribution [23].

A unmarried subanesthetic dose (0.5 mg/kg) of intravenous (IV) ketamine hydrochloride has been shown to have a rapid antidepressant effect, which begins as early on as two hours after ketamine administration, peaks at 24 hours, and lasts for up to vii–14 days [24, 25]. This effect has been noted in both unipolar and bipolar depression [26], although outcome duration may be shorter in patients with bipolar disorder [27]. Promisingly, efficacy from ketamine is seen in people with handling-resistant depression, who have failed multiple antidepressant regimens [28, 29]. In 1 report of 67 patients (including 45 women), IV ketamine administered at 0.v mg/kg twice per calendar week has been shown to achieve rapid-onset and sustained antidepressant effect for a 15-mean solar day period [30].

Broadly there are 2 generations of studies evaluating ketamine for unipolar depression: (1) studies on safety/efficacy of one subanesthetic dose of 4 ketamine and (2) studies on alternating drug commitment routes, MDD relapse prevention, and mechanistic assay [15]. The first study on single-dose Four ketamine in vii patients with mood disorders was published in 2000 past Berman et al. and plant a meaning but transient improvement of depression severity with a unmarried subanesthetic dose of 4 ketamine (0.5 mg/kg) [31]. While the improvement to depression symptoms was transient, this improvement did exceed the elimination half-life of ketamine [15]. A larger replication study with 18 subjects was published by the Intramural Research Program of the National Institute of Mental Health (NIMH) in 2006 and too found that subanesthetic ketamine (0.v mg/kg) has a pregnant antidepressant effect [17]. This clinical trial has largely been credited with launching the field of enquiry into ketamine'due south antidepressant effects [32]. Multiple open-label instance series have demonstrated similar results with a single ketamine infusion [33]. Subsequent research has shown that a regimen of serial Iv ketamine (0.5 mg/kg) infusions achieves a greater response rate, without more than meaning side effects [33, 34]. Other routes of ketamine administration have as well been examined. For example, intranasal ketamine hydrochloride (50 mg) has been shown to mediate an antidepressant outcome, though the magnitude of the effect may exist less than that of IV ketamine [35]. Intranasal esketamine (which is the S(+) enantiomer of ketamine) in combination with an oral antidepressant was recently canonical by the Food and Drug Assistants for the treatment of treatment-resistant low, though the long-term effects of this regimen remain preliminary [36]. Nevertheless, when used for its antidepressant effect in mice, (R)-ketamine appears to have more than stiff and persistent effects than (S)-ketamine, every bit well as no psychotomimetic side effects [6].

IV ketamine may have increased utility in specialized populations, such as the military, cancer patients, and patients with Alzheimer'south disease. In active duty armed forces populations, long-term psychiatric admission for suicidality may create unique problems including separating the patient from his or her support network and leading to administrative obstacles in returning to duty [37]. In one written report on 10 soldiers in the U.s.a., a single dose of IV ketamine (0.two mg/kg) was found to significantly subtract suicidality and hopelessness [37]. Ketamine appears to be a apace efficacious antidepressant and antisuicidal pharmacologic agent which may be well suited for this detail population and others in which long-term psychiatric hospitalization creates pregnant challenges, though information technology is possible that the particular applications for the US armed services may non translate to broader armed forces apply effectually the world. Iv ketamine (0.5 mg/kg) has besides demonstrated utility in treating acute-onset depression and suicidal ideation in i study of 39 newly diagnosed cancer patients [38]. Furthermore, ketamine may take unique utility in treating depression associated with Alzheimer's disease, as ketamine appears to have neuroprotective properties against soluble amyloid-beta protein-mediated toxicity, co-ordinate to ane study utilizing 15 mg/kg intraperitoneal ketamine in mice [39].

The rapid-onset antisuicidal properties of ketamine are maybe mediated by enhancing neuroplasticity [15, 24, 40]. This event is fifty-fifty seen in patients who are nonresponders to the antidepressant effect of ketamine [41]. Comeback in suicidal ideation occurs as early as within 40 minutes of subanesthetic dose ketamine administration (0.5 mg/kg) and may last as long as 10 days, according to one study of 57 patients [42]. While change in depressive symptom severity correlates with modify in suicidal ideation, even when depressive symptom severity is controlled for, the antisuicidal effect of ketamine persists [43]. Ketamine has been demonstrated to effectively treat anhedonia independent of depressive symptoms, and this upshot can final upward to 14 days [44]. It has been theorized that reducing anhedonia is the mechanism by which ketamine reduces suicidal thoughts [45]. Ketamine has as well been shown to take anxiolytic and procognitive effects in a rat model of depression, using doses between v and 30 mg/kg [46]. Additionally, when used as the anesthetic during electroconvulsive therapy (ECT), ketamine decreases Hamilton Depression Rating Calibration scores before and more significantly than when propofol is used [47]. Yet, while meta-analysis of 16 articles with 346 patients has demonstrated superior treatment effect in patients with depression who receive ketamine in ECT over other anesthetics, these patients were also noted to have more side effects and longer recovery times [48].

While ketamine has many clinically promising features, information technology has a number of drawbacks to consider. I of these is result elapsing: the antidepressant effect of ketamine lasts on boilerplate only 1-2 weeks [49]. There is substantial variation in the duration of handling response, with many patients reporting less than one week of depressive symptom improvement from a single ketamine infusion [27]. However, a ketamine maintenance infusion regimen, in which infusions of ketamine 0.5 mg/kg are administered upwards to every 2 weeks, has shown promising results in a study of viii patients [fifty]. Due to poor bioavailability resulting from high offset-pass hepatic metabolism, ketamine is typically administered by injection, which is a drawback for medications that require ongoing dosing [21, 51]. Iv administration every 2-3 days requiring hospital or dispensary visits is impractical. However, alternative routes of administration offer promising alternatives (for instance, very-low-dose sublingual ketamine has been shown to improve mood, noesis, and sleep, when x mL of a 10 mg/mL solution is administered sublingually for v minutes and swallowed) [24]. Another drawback of ketamine is that, as a derivative of phencyclidine (PCP) [11], ketamine causes a transient increase in psychotomimetic symptoms [fifteen, 41] and dissociative symptoms, though these return to baseline by four hours posttransfusion [41]. Ketamine has corruption and addiction potential [1, 37] and causes cerebral deficits, which accept been shown to be reversible with cessation of ketamine utilise [fifteen]. However, concerningly, chronic recreational ketamine employ has also been shown to produce cognitive and melancholia deficits including depression [52], which raises concern most the utilise of ketamine every bit an option for long-term antidepressant therapy. Other potential adverse furnishings of ketamine include transient tachycardia and hypertension [ane]. There are too concerns about neurotoxicity, bladder toxicity, and tolerance with repeated ketamine infusion use [34].

As a result of these drawbacks, many clinicians and researchers view IV ketamine infusions not every bit an terminate-all replacement for conventional antidepressants, but a promising new direction for antidepressant therapy that warrants further research and an endeavour to develop "ketamine-like" drugs that practice non carry the side effects that currently limit the employ of ketamine [1, 25, 32]. For example, the possible antidepressant effects of other glutamatergic modulators, including riluzole, dextromethorphan, nitrous oxide, and GLYX-13 (rapastinel), are currently being examined [53].

3. Ketamine and Pain Syndromes

Ketamine has been widely used to manage acute and chronic pain, both alone and as an offshoot to opiates. The primary analgesic mechanism of ketamine is through NMDA receptor animosity, though ketamine has also been shown to deed on opioid, nicotinic, and muscarinic receptors. Ketamine's anti-inflammatory qualities may too contribute to its efficacy in hurting relief [54, 55]. While ketamine'due south issue on astute pain is driven primarily by inhibition of NMDA receptors and prevention of wind-upward, ketamine is thought to mediate its outcome on chronic hurting through desensitization of upregulated NMDA receptors [56–58]. Routes of ketamine administration for analgesia include parenteral, oral, sublingual, topical, and intranasal [54]. Information technology appears that administration of high-dose ketamine over a short time class (42–480 mg daily for 1–10 days) produces analgesia more than effectively than lower doses for longer durations (such as 18 mg daily for 90 days) [59]. The level of evidence and consensus for the utility of ketamine in hurting direction varies between types of pain.

three.1. Acute Pain

Ketamine appears to reduce analgesic requirement in the setting of acute pain. For example, in 160 patients undergoing cesarean section, a single postoperative intravenous ketamine bolus (0.25 mg/kg) was shown to reduce the severity of postoperative pain and decrease analgesic requirements [60]. As a result, ketamine can preclude opioid tolerance [61] and may reduce the charge per unit of opioid-induced hyperalgesia post-obit surgery [62], while also mitigating adverse effects linked to opiates such as respiratory suppression, oversedation, and hypotension [63]. In addition its opioid-sparing effects, ketamine has been shown to reduce nausea and airsickness in the perioperative period at doses of <0.v mg/kg [64]. While ketamine has generally been shown to reduce intraoperative opioid requirements in both opioid-naïve and opioid-dependent populations [62, 65], this is somewhat controversial. Some studies have demonstrated decreased boilerplate hurting scores when continuous ketamine (0.two mg/kg/hr) is used intraoperatively, but no subtract in overall opioid requirement [66]. Furthermore, other studies show no departure in postoperative hurting levels or postoperative opioid requirement in postsurgical patients when ketamine is used, including several studies that demonstrated no do good to the utilize of ketamine infusion in patients undergoing spinal surgery [67, 68].

Because of its efficacy in treating acute pain, ketamine has utility in the acute care setting. Ketamine has well-established utility in the emergency department (ED) as brusk-term analgesia for indications such as acute long bone fractures, trauma victims, and opioid-dependent patients with acute pain, which in one report was administered as ketamine xv mg Four in one case followed by a continuous ketamine infusion at 20 mg/60 minutes for 1 hr [69]. When used alone for hurting management in the ED setting, depression-dose ketamine (<i mg/kg) provides comparable pain relief to opiates, with the benefit of producing less respiratory low [70]. Ketamine has also been shown to decrease opioid consumption for astute pain in ED patients, in a written report of 30 patients with severe hurting where ketamine xv mg Four and hydromorphone 0.v mg 4 were administered together [63].

3.two. Chronic Pain

The role of intraoperative ketamine in the reduction of chronic postoperative pain development is unclear. Some reports suggest that ketamine decreases the rate of chronic postoperative hurting when administered as a 0.15–1 mg/kg preincisional loading dose followed past intraoperative infusion [71], and intravenous ketamine has been shown in meta-analysis of 40 papers including 1388 participants to significantly reduce chronic hurting incidence following certain types of surgery [72]. This effect may be mediated through a reduction in master and secondary hyperalgesia in the postoperative period, which decreases the incidence of chronic pain [73]. However, in that location appears to exist a reduction in astute pain but not chronic pain evolution following amputation, thoracotomy, or mastectomy with the use of ketamine as a coanalgesic agent [74]. Epidural ketamine and intravenous ketamine have not been shown to decrease the incidence of development of chronic postthoracotomy pain [75–77]. Additionally, meta-analysis has likewise not shown intravenous and epidural ketamine to significantly reduce the rate of persistent postsurgical hurting (PPSP) at three or half dozen months [78].

In that location is moderate testify that ketamine effectively reduces chronic noncancer pain [59]. A contempo systematic review and meta-analysis of 7 studies showed short-term analgesic do good from Iv ketamine in patients with chronic pain, which appears to occur in a dose-response human relationship [79]. In a study of 49 patients, ketamine infusion was shown to decrease visual analog calibration (VAS) scores in patients with intractable chronic hurting, in whom ketamine 0.5 mg/kg was administered over 30–45 minutes, followed by either continuation at this dose in subsequent infusions every 3-iv weeks, or increase in the dose upwards to the highest tolerated dose providing analgesia [80]. Daily oral ketamine (upward to 64 mg/day) has also been shown to be safe and opioid-sparing in patients with chronic pain [81]. The combination of subcutaneous ketamine infusion and sublingual ketamine lozenges appears to reduce opioid use in patients with chronic nonmalignant hurting [82]. In one retrospective study of 51 patients with refractory chronic hurting, oral ketamine treatment (starting at 0.5 mg/kg/solar day, then increased in 15 to 20 mg increments as needed) led to the resolution of pain in 44% of patients, reduced opioid requirements past an average of 62%, and was ineffective in merely 22% of patients [83]. These results are especially promising because of the limitations of currently available treatments for chronic hurting, with only thirty–forty% of patients with chronic pain achieving adequate to good relief [84]. Ketamine infusions (administered as infusions of 0.1–0.3 mg/kg/hour for 4–8 hours/mean solar day, up to 16 hours over three consecutive days) have too been shown to significantly reduce hurting intensity in children and adolescents with chronic pain, with the largest do good seen in patients with CRPS [85]. All the same, the utility of ketamine in treating chronic pain is non universally accepted. For example, in i study of 36 patients, ketamine was shown non to amend long-term pain scores in patients who take chronic opiates, or to finer reduce opiate requirements [86].

The utility of ketamine has been validated in neuropathic pain [87], specially in complex regional pain syndrome (CRPS). CRPS causes pregnant morbidity, and fourscore% of patients with CRPS are severely disabled [88]. Many patients with CRPS are unresponsive to traditional therapeutic approaches, and ketamine has been shown to reduce hurting levels in some of these handling-refractory patients [89]. When studied in mice, ketamine (administered subcutaneously at a dose of 2 mg/kg/day for 7 days) appears to decrease nociceptive sensitization in the chronic stage of CRPS, but not the astute stage [55]. When CRPS blazon one (CRPS-ane) alone was studied using a cohort of 10 patients, S(+)-ketamine infusion (using the following regimen per 70 kg: min 0–5: ane.five mg, min 20–25: three.0 mg, min forty–45: iv.5 mg, min sixty–65: 6.0 mg, min 80–85: 7.5 mg, min 100–105: 9.0 mg, and min 120–125: x.five mg) appears to reduce pain levels for 10 weeks or longer, therefore demonstrating a disease-modulatory function [56]. Despite the efficacy of ketamine as an analgesic in this population, functional improvement of affected limbs was not shown in one study of 5 patients who received anesthetic doses of ketamine over x days [90]. Though ketamine appears to exist safe and effective in treating CRPS, farther studies are warranted to evaluate dosing, timing, and routes of administration of ketamine for optimal efficacy in CRPS handling [91]. For example, 10% ketamine cream applied 3 times daily in combination with oral palmitoylethanolamide has been shown in a case report to effectively treat refractory CRPS hurting [92], but larger, controlled studies are warranted.

There are boosted chronic pain atmospheric condition in which a small-scale number of studies have shown promising results from ketamine, and farther research is warranted. Ketamine infusions appear to be effective equally an offshoot with gabapentin for managing chronic neuropathic pain in spinal string injury patients, with a duration of efficacy lasting two weeks afterward infusion termination, according to a study in twoscore patients, who received lxxx mg IV ketamine over 5 hours daily for i week and gabapentin 300 mg 3 times daily [93]. In patients with phantom limb pain, ketamine also appears to mediate curt-term analgesic effects [94]. S-ketamine has been shown to reduce chronic pancreatitis pain in a study of x patients when administered as an infusion of 2μg/kg/min for 3 hours, though this effect disappeared following the end of infusion [95]. Ketamine may also have utility in scenarios where opioids lonely often accept inadequate efficacy, including vasoocclusive episodes in patients with sickle cell disease. Few studies take examined the role of low-dose ketamine in the treatment of sickle cell pain, though the majority of reported cases accept shown that ketamine effectively reduces pain intensity and opioid requirements in patients with sickle cell pain [96]. The data on this topic are limited, and further studies are warranted to validate this finding [97]. Additionally, since hurting disorders are highly correlated with suicidal ideation and attempts, the antisuicidal backdrop of ketamine may brand ketamine a useful treatment option in patients with concomitant pain and suicidal ideation [forty].

Though ketamine has anecdotally been reported to effectively treat cancer pain, when studied systematically, ketamine has non been found to be useful in the treatment of hurting from advanced cancer as an adjunct to opioids, though difficulty in designing studies in the context of palliative care may contribute to these results [98, 99]. Ketamine can be considered as an adjuvant therapy in patients with cancer who accept failed standard therapy, though optimal dosing is unclear [100].

three.iii. Headache

Chronic migraine affects 1% of the population within the United States, creating a meaning economical brunt, and treatment options for refractory cases are limited [101, 102]. Due to its efficacy in the treatment of chronic pain, it has been hypothesized that ketamine might be a useful addition to headache and migraine control regimens. For instance, while triptans effectively relieve acute migraine hurting in 43–76% of cases [103], ketamine could play an of import role in pain control for triptan nonresponders. Ketamine could also play a role in migraine management for patients in whom triptans are contraindicated, such as patients with cardiovascular diseases. The actions of ketamine on glutamate NDMA bounden sites at the level of the secondary somatosensory cortex, insula, and anterior cingulate cortex have been associated with modulation of affective pain processing and the decrease of allodynia and central sensitization. These effects associated with chronic pain might also exist the ground of the mechanism of consequence on headache pain [101, 104]. It is useful to take these mechanisms into business relationship when considering memantine, a noncompetitive glutamatergic NMDA antagonist, which has been previously shown to exist an effective treatment for chronic and refractory migraine [101, 105].

Minimal evidence exists surrounding the utilize of ketamine in chronic headache treatment. Individual cases suggest that ketamine administered 4 (using an initial infusion rate of 0.1 mg/kg/hour, and then increased by 0.1 mg/kg/60 minutes every 3-4 hours until a goal pain score 3/10 was reached and maintained for 8 hours, then downtitrated) in inpatient management of refractory migraine consistently reduces curt-term pain severity, although no chronic relief has been observed [101]. A large review including 77 patients has demonstrated similar results, with intravenous ketamine administration (starting at an infusion rate of 0.1 mg/kg/hr, increased as needed at six-60 minutes intervals to a maximum infusion charge per unit of ane mg/kg/hr) causing acute but not long-term improvement to refractory headache [106]. When considering alternate methods of delivery, randomized controlled trials and instance studies of intranasal ketamine'due south effects on migraine with aura have demonstrated that 25 mg intranasal ketamine reduces the severity, and in some cases the duration, of the associated aura [107, 108]. This further reinforces the potential of the use of drugs with action on glutaminergic pathways, such as ketamine, as headache modulators [107].

Ketamine has also been investigated in combination with other drug regimens. Magnesium sulfate, which binds to NMDA channels, might be administered concomitantly with ketamine to produce a heightened upshot. When given intravenously to 2 chronic cluster headache patients, this combination (ketamine 0.v mg/kg over 2 hours and magnesium sulfate 3000 mg over 30 minutes) was shown to produce immediate hurting relief, a subtract in suicidal ideation, and a decrease in attack frequency and intensity for up to six weeks [109]. Evidence exists that levels of kynurenic acid, an NMDA receptor adversary, are decreased in cluster headache patients, providing further back up for the theory that NMDA receptors are overactive in these patients and that a focus on therapeutic options targeting these receptors is warranted [109, 110].

Unfortunately, there are also several pieces of contradictory evidence against the utilize of ketamine for the treatment of primary headache [111]. Modest randomized studies have shown no improvement in acute headache hurting outcomes with IV ketamine (0.2-0.3 mg/kg) when compared to both placebo and prochlorperazine, while also inducing increased side effects [111–113]. Additionally, virtually investigations of this use of ketamine are reported as small case series, and further report is required in order to make informed conclusions on the efficacy of ketamine in the treatment of headache. The current trunk of literature has led to the conclusion by some experts that there is not sufficient testify for the widespread apply of ketamine in headache patients [111, 114].

three.four. Drawbacks

Ketamine has multiple drawbacks as a treatment for pain. Ketamine may accept limited utility as a treatment for chronic pain syndromes given the potential risks associated with repeated IV administration of ketamine, including its neurotoxicity and potential to impair long-term retentivity [115]. While these risks take not yet been formally studied in a controlled way, the outcome of frequent (defined as more often than twice per month) recreational ketamine utilize was shown in a report of 37 patients to cause long-lasting impairments in episodic and semantic memory [116]. Furthermore, both sensitization and tolerance are possible consequences of repeated ketamine utilize, and while the duration required to observe these effects from intermittent ketamine use has not been extensively studied in humans, in mouse studies sensitization has been shown to occur over the course of weeks and is clearly evident by v weeks of weekly administration of intraperitoneal ketamine (20 mg/kg or 50 mg/kg, in mice) [117]. Ketamine also has been known to cause hepatic toxicity due to mitochondrial impairment, urological toxicity including ulcerative cystitis, and immediate risks including tachyarrhythmias, hallucinations, and flashbacks [88, 118, 119]. Psychedelic effects are also associated with ketamine [59], and benzodiazepine coadministration may be required to care for its psychosis-like effects [58].

Most studies on the utility of ketamine in hurting direction take minor sample sizes, and treatment effect may therefore be overestimated [72]. This suggests the need for larger trials evaluating the use of ketamine in pain command. Further enquiry is too required to characterize the office of ketamine in cancer-related hurting [120], including the office of oral ketamine in palliative care [121]. Furthermore, while ketamine infusions have been well studied, alternative routes of ketamine assistants accept been evaluated less extensively. For instance, open up studies of ii% topical ketamine preparations have suggested a therapeutic effect on chronic hurting without adverse effects locally or systemically, though further enquiry is needed to elucidate its efficacy [122]. The South-enantiomer of ketamine too appears to accept a ii- to threefold more than potent analgesic result than (R)-ketamine [123], and the utility of using (Southward)-ketamine lonely equally a treatment for pain warrants boosted study.

four. Neurologic Applications of Ketamine

4.i. Neuroprotection

In add-on to mediating coldhearted effects, the noncompetitive animosity of NMDA by ketamine has recently been postulated to play a role in neuroprotection. Ketamine was previously idea to increase intracranial force per unit area (ICP) [4] and therefore would be contraindicated in cases where ICP may already exist elevated (such as trauma and neurosurgical patients). This determination was based on a few small studies with limited scope, just did result in an FDA package insert warning [124]. Several more contempo studies challenged and disproved this theory [4, 124]. These reports of cases linking ketamine induction to elevated ICP may non have adequately taken ventilation into account; in one example of reported elevated ICP after ketamine induction, the patient was spontaneously breathing after induction, and ICP was noted to subtract dramatically with initiation of transmission hyperventilation [125]. Therefore, hypercarbia is the more likely underlying cause of ICP acme rather than use of ketamine induction, and in patients who undergo ketamine induction and normocarbia is maintained using mechanical ventilation, ascent in ICP is not seen [four].

Several mechanisms of action behind ketamine's neuroprotective qualities take been proposed. Ketamine has anti-inflammatory properties and is thought to reduce microglial activation and reduce cytokines TNF and IL-6, although studies have not been able to evidence any differences in plasma inflammatory markers after ketamine administration [5, 124, 126]. It is known that unlike other coldhearted drugs including propofol, ketamine does non provide neuroprotection via inhibition of TLR-four-NF-κB-dependent signaling [127]. Through its NMDA inhibition, ketamine reduces glutamate excitotoxicity by preventing excitatory amino acid receptor stimulation, and this reduction has been proven through the use of MRI, in one report of 24 infants [124, 126]. Excitotoxicity, defined equally the excessive stimulation of neurons causing neuronal injury, has been suggested as the underlying procedure behind several types of central nervous system pathology [124]. Ketamine reduces neuronal death and injury through the blockade of calcium entry into vulnerable immature neurons [126, 128]. NMDA receptor activation is also thought to cause the loss of mitochondrial membrane potential and apoptosis through military camp response element bounden protein shutoff, a procedure that NMDA inhibition by ketamine would also forbid [124]. Finally, it is well documented that ketamine protects confronting ischemic injury by reducing cell swelling and preserving cellular energy post-obit anoxia-hypoxia injury, while also increasing neuronal viability and preserving cellular morphology [129–131]. It is hypothesized that inhibition of P-CREB dephosphorylation in the infarct surface area by low-dose ketamine is responsible for a decrease in infarct volume, edema ratio, and neurologic deficit [132]. These are all processes known to be induced by cerebral injury such equally stroke and trauma, which gives ketamine promising clinical implications [iv].

Ketamine appears to be benign in neuroprotection following multiple types of neural injury. Studies take shown that ketamine reduces focal ischemia and hemorrhagic necrosis volumes also as chronic cerebral hypoperfusion [4, v, 133–135]. In beast studies, outcomes following incomplete cognitive ischemia were improved with ketamine assistants, thought to exist related to reduced plasma catecholamine levels [5]. Additionally, ketamine causes an increase in claret menstruation regionally and globally and reduces resistance in the cerebrovasculature [4, 136, 137]. Ketamine provides some measure of cardiovascular stimulation as well, which may contribute to cerebral perfusion [138]. For example, ketamine might have utility as a hemodynamic agent in traumatic brain injury (TBI) patients with hypovolemia, every bit it is well documented that ketamine can crusade an peak in center rate, systolic blood pressure, and cardiac index [124]. Studies have shown that ketamine also inhibits spreading depolarizations, which cause depression of neuronal activeness. These tiresome potential changes propagate in brains with previously existing ischemic harm to cause or increase damage, and their prevention could better outcomes in TBI, subarachnoid hemorrhage, and cancerous stroke cases [124, 139, 140]. In TBI specifically, which involves increased inflammation, autophagy, edema, and ischemia, ketamine produces several beneficial effects. At subanesthetic doses in animal models, information technology prevents IL-six and TNF-α release, reduces deficits in dendrites, and possibly activates the mTOR signaling pathway to downregulate autophagic protein production [141]. This has been translated to clinical TBI inquiry: in one report of 115 brain-injured patients, ketamine assistants (with a median dose of 200 mg) was plant to reduce the occurrence of the isoelectric spreading depolarizations that are seen in traumatized human cortex [139]. In some other study of 66 patients with aneurysmal subarachnoid hemorrhage, (S)-ketamine infusion (with a mean dose of 2.8 ± 1.4 mg/kg/hr) significantly decreased the incidence of spreading depolarizations [142]. While the role of ketamine in spinal cord injury has been shown in animal models [143, 144], this has not yet been translated to man enquiry.

Ketamine's neuroprotective effects take also been proven clinically through functional assessment. In homo cardiac surgery patients, single-dose ketamine (0.5 mg/kg) administration at surgery induction has been associated with reduced postoperative delirium and cognitive dysfunction, results which are attributed to the reduction in systemic inflammation secondary to ketamine usage [iv, 5, 138]. In animal models, ketamine has reduced impaired cognitive behavior caused by cell expiry in the cortex and hippocampus [129, 145] and has attenuated functional deficits in memory and beliefs caused by TBI [141].

While multiple studies support ketamine'due south potential for neuroprotection, some others provide inconclusive prove. Ketamine'due south furnishings on neurologic injury following cardiopulmonary featherbed have been studied in both adults and children, with no resulting show for either neuroprotection or neurotoxicity [126, 146]. A review of neuroprotective agents administered in the perioperative menstruum reveals that intravenous ketamine is associated with no pregnant difference or change in new postoperative cognitive deficits or bloodshed and concludes that there is currently not enough evidence to prove that ketamine has a neuroprotective effect [138, 146, 147].

Conversely, ketamine has also been shown to cause apoptotic cell expiry in neurons, specifically in the frontal cerebral cortex and hippocampal region, besides as long-term deficits in cerebral processing [124, 128, 139, 148–150]. In animal models, ketamine at anesthetic doses is observed to collapse cortical neuron growth cones [151]. Cell injury caused by ketamine seems to be dose- and time-dependent [129, 150], secondary to an induced abnormal cell wheel reentry leading to apoptosis [129, 152]. This window of neurotoxicity seems to be focused during early brain development and meaning synaptogenesis [149], particularly toward the end of pregnancy and in the early postpartum menstruation. In mice and rats, the window of greatest vulnerability to neurotoxic agents is the first 2-3 weeks after nascency, and in humans, the time of greatest vulnerability spans from midgestation to two-3 years of life [149]. In human forebrains, NMDA receptor expression peaks during gestational weeks xx–22, which coincides with the showtime of the brain growth spurt which lasts into the postnatal menstruation [153]. In neonatal mice, high-dose ketamine causes astringent degeneration of parietal cortical cells with resultant learning and memory deficits at 2 months [154]. Long-term neurofunctional outcomes are also impaired after three daily doses of ketamine, with increased numbers of apoptotic cells in the hippocampus and later defects in learning and retention [149, 155]. Promisingly, one study has shown the potential of ketamine to counteract its own neurotoxic effects by inducing the production of the action-dependent neuroprotective protein (ADNP); pretreatment with a subanesthetic dose of ketamine before sedation might upregulate the product of this protein and provide a neuroprotective effect in rats [151]. Other approaches to mitigating the risk of ketamine-induced neuronal apoptosis are being investigated; for instance, clozapine has been shown to improve the viability of mouse neuronal stalk cells that are exposed to ketamine [156].

The juxtaposition of ketamine'due south neurotoxic and neuroprotective effects provides an interesting puzzler. These effects seem to vary not only by acute dosage and cumulative usage over time, only also by the state of the brain (absence versus presence of baneful stimuli) during the time of ketamine introduction [149]. Some have concluded based on the existing evidence that the neuroprotective effects of ketamine are largely dependent on the utilize of lower doses, as higher doses can result in ketamine-induced toxicities [129, 157]. Further study is clearly required, specifically in the areas of ongoing brain development in pediatric populations as well every bit in the time period surrounding surgery [149]. Additionally, further study is required in human models, as much of the current evidence is based on animate being models. Ketamine clearly has a great amount of promise every bit a neuroprotective agent, although the exact parameters of its use require further elucidation.

four.2. Seizures

While benzodiazepine monotherapy is the preferred handling for isolated seizures and in that location is no broadly accepted office for ketamine as a treatment for isolated seizures, ketamine has the potential to play a part in the handling of status epilepticus (SE), in which seizure activeness persists for longer than five minutes [158]. The utility of ketamine in treating status epilepticus may be explained by the fact that sensitivity to GABA agonists decreases with seizure duration, but this is not as profound with NMDA receptor antagonism [159], and synaptic NMDA receptors may even be upregulated in prolonged seizures [160] and therefore stand for an platonic pharmacologic target. Ketamine also appears to reduce glutamate uptake and may be protective against glutamate-induced neurotoxicity in the setting of seizure [161]. Ketamine appears to work synergistically with benzodiazepines to treat SE, and dual therapy using midazolam and ketamine (4.5 mg/kg midazolam with 45 mg/kg ketamine) has been shown to treat SE more effectively than either agent lone [162]. Furthermore, ketamine (10 mg/kg) in combination with a benzodiazepine (diazepam i mg/kg) and either valproate (30 mg/kg) or brivaracetam (10 mg/kg) has been shown to be both more effective and less toxic than benzodiazepine monotherapy for the treatment of SE [163].

Ketamine has a promising role in the handling of refractory status epilepticus (RSE), which is defined as seizure activity that does non answer to 2 antiepileptic drugs at appropriate doses, and is seen in around 30% of cases of status epilepticus [164, 165]. Four Ketamine appears to finer terminate RSE (when administered as a 0.v mg/kg IV bolus followed by a continuous infusion gradually uptitrated to ane.5 mg/kg/hour) [166], and while most studies evaluating the use of IV ketamine in status epilepticus are in adults, ketamine besides appears to be both safe and effective in children with refractory status epilepticus, at a mean dose of twoscoreμm/kg/infinitesimal [167]. Since RSE is conventionally treated using anesthetics which require intubation, utilizing ketamine in the treatment of RSE can prevent the need for intubation and spare patients the associated risks [168]. RSE carries significant morbidity and mortality, with up to 90% of individuals with RSE suffering severe morbidity and up to xix% of individuals with SE lasting greater than 30 minutes experiencing death [169], making novel handling options like ketamine valuable. Ketamine infusion (with a maximum dose range of 25–175μm/kg/minute) with or without propofol has also been shown in a study of 67 patients to effectively command superrefractory status epilepticus (SRSE), in which seizures persist for at to the lowest degree 24 hours afterward anesthetics are initiated [170]. Ketamine (either as a 1.i–4 mg/kg bolus or as 1.0-1.i mg/kg/hour infusion) as well appears to be protective in cases with both RSE and traumatic encephalon injury, according to a retrospective review of a accomplice of 11 patients [165].

In the context of chemical warfare, ketamine may have a role in neuroprotection and reducing neuroinflammation induced past organophosphorus nerve agents, which are known to crusade seizures, status epilepticus, and encephalon harm. Ketamine in combination with atropine, with or without a benzodiazepine, appears to have utility in reducing the effects of organophosphorus nervus agents including soman, which could have utility in field conditions [171]. A report in guinea pigs exposed to soman showed that (Due south)-ketamine and atropine provided comparable protection against decease and seizure-related brain damage, only at doses 2-3 times lower than racemic ketamine and atropine [172].

While a promising treatment for RSE and SRSE, ketamine has several notable drawbacks. It appears that ketamine alone may not be an constructive treatment for status epilepticus that has lasted for over one 60 minutes [158]. Adverse reactions to ketamine accept likewise been reported, including psychiatric symptoms like hallucinations and delirium, increased saliva secretion, and arrhythmias, though these are noted to exist treatable and self-limited [173]. Major complications have not been reported [174]. Ketamine-induced neurotoxicity has been described, primarily using animal models [164]. Cerebellar syndrome including cerebellar atrophy has been reported with loftier-dose ketamine [175].

In that location is limited prospective data on the handling of SE and RSE using ketamine, and this topic warrants further research [176, 177]. While a racemic mixture of (S)- and (R)-ketamine is typically used, it has been shown that (S)-ketamine is more speedily eliminated, leading to faster recovery of psychomotor faculties [123]. Whether (Due south)-ketamine is superior to racemic ketamine in the treatment of seizures warrants further study. While the benefits of ketamine in treating RSE and SRSE are promising, utilise of ketamine has not been widely adopted, perchance considering ketamine has not been integrated into management algorithms [178]. Therefore, integration of ketamine into treatment protocols warrants further consideration past neurologic societies and guideline creators. Furthermore, other novel uses of ketamine for seizure disorders are currently existence investigated; for example, recently a instance was reported in which low-dose 4 ketamine was used in an epileptic patient with postoperative worsening of his seizure burden, with successful improvement in seizures and abstention of oversedation or intubation [179]. However, it has also been recently called into question whether ketamine may induce seizure in some cases, with one recent case of new-onset seizure being reported following intramuscular ketamine assistants in a pediatric patient, which certainly warrants further consideration as well [180].

In that location are clear benefits to early administration of ketamine for SE, including limiting the adverse events from polypharmacy and fugitive intubation [178], and earlier administration of ketamine for SE and RSE has been advocated [174, 178, 181]. Furthermore, early on assistants of ketamine may prevent neuronal necrosis, making it a useful medication to use early on in SE [182].

4.3. Ketamine and Alcohol and Substance Use Disorders

There is ongoing research surrounding the role of ketamine in treating alcohol and substance use disorders. It is idea that in addition to modulating glutamatergic neurotransmission, ketamine may mediate downstream effects on neuronal connectivity and plasticity through brain-derived neurotrophic factor and other factors to improve dopamine signaling, thereby treating drug-related synaptic deficits [183]. In a study of 111 alcohol-dependent patients, relapse rates were significantly lower at one year in patients who received intramuscular ketamine [184], though this sentinel trial lacked both randomization and blinding [185]. A written report of 58 opioid-dependent patients found that subanesthetic ketamine infusion (0.5 mg/kg/hour) significantly improves immediate and short-term (48-hour) withdrawal symptoms in patients who undergo precipitated opioid withdrawal [186]. In a study of 55 cocaine-dependent patients, patients who received a single forty-infinitesimal ketamine infusion (0.five mg/kg) in conjunction with a mindfulness-based relapse prevention programme had a significantly lower relapse rate than patients who received the same mindfulness programme in conjunction with a midazolam infusion [187]. Based on these promising results, it is possible that ketamine may fill a major gap in habit treatment, as there are currently no FDA-approved medications for the treatment of cocaine utilize disorder [187]. Ketamine has likewise been shown to care for heroin dependence in a dose-dependent way, with one study on 70 detoxified heroin-dependent patients demonstrating that patients who received college doses of intramuscular ketamine (2.0 mg/kg) had a significantly higher rate of forbearance at two years [188]. However, the use of ketamine in alcohol and substance employ disorders is complicated by its psychotogenic, dissociative properties and conventional Four administration route, which could pose particular challenges in patients with addiction or mental illnesses [189].

5. Conclusions

Ketamine has emerged as a promising pharmacologic agent with diverse indications, but controversy surrounds it, as a result of its toxicities, psychedelic side furnishings, and abuse potential. Every bit an antidepressant, ketamine has the do good of beingness significantly faster acting than conventional agents while also having antisuicidal properties, though its long-term use is limited by toxicity and impracticality of Four infusions. In the treatment of migraines, ketamine appears to effectively reduce acute headache symptoms, while not modulating the disease land of chronic migraines. Ketamine appears to be neuroprotective and may play a role in management of TBI, subarachnoid hemorrhage, and strokes. In the treatment of pain, ketamine appears to reduce the analgesic requirement for treatment of acute pain and likewise has a articulate role in the management of CRPS, though again its apply is limited by its side-effect profile and toxicity, including neurotoxicity and memory damage, when used long term. Ketamine may besides play a office in drug detoxification and alcohol and drug relapse prevention. The role of ketamine in the management of seizures including SE and RSE is as well promising. In general, ketamine has multiple nonanesthetic uses that are cartoon attending, simply because many studies evaluating its utility have alien results and sample sizes are typically modest, further research studies including large-scale prospective studies are required to elucidate its role in the field of medicine.

Disclosure

Abby Pribish and Nicole Wood are co-beginning authors.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Copyright

Copyright © 2020 Abby Pribish et al. This is an open access commodity distributed under the Artistic Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Source: https://www.hindawi.com/journals/arp/2020/5798285/

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