Ketamine in the Past, Present, and Future: Mechanisms, Metabolites, and Toxicity

The metabolic clock of ketamine abuse in rats by a machine learning model

Ketamine has recently become an anesthetic drug used in human and veterinary clinical medicine for illicit abuse worldwide, but the detection of illicit abuse and inference of time intervals following ketamine abuse are challenging issues in forensic toxicological investigations. Here, we developed methods to estimate time intervals since ketamine use is based on significant metabolite changes in rat serum over time after a single intraperitoneal injection of ketamine, and global metabolomics was quantified by ultra-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF-MS). Thirty-five rats were treated with saline (control) or ketamine at 3 doses (30, 60, and 90 mg/kg), and the serum was collected at 21 time points (0 h to 29 d). Time-dependent rather than dose-dependent features were observed. Thirty-nine potential biomarkers were identified, including ketamine and its metabolites, lipids, serotonin and other molecules, which were used for building a random forest model to estimate time intervals up to 29 days after ketamine treatment. The accuracy of the model was 85.37% in the cross-validation set and 58.33% in the validation set. This study provides further understanding of the time-dependent changes in metabolites induced by ketamine abuse.

Nitrous oxide for the treatment of complex regional pain syndrome: a randomized blinded trial

INTRODUCTION

Complex Regional Pain Syndrome (CRPS) is a debilitating neuropathic condition often refractory to conventional treatments. N-methyl-D-aspartate (NMDA) receptor antagonists have a well-established role in the development and modulation of chronic neuropathic pain. Nitrous oxide is widely used and generally safe anesthetic gas with NMDA receptor antagonist activity. We therefore tested the hypothesis that brief periods of nitrous oxide exposure reduce pain in patients with CRPS.

METHODS

Patients with a diagnosis of CRPS were randomized to either 2 hours of nitrous oxide exposure on three alternating days (Nitrous Oxide) versus a placebo air/oxygen mixture (Air-Oxygen). Our primary outcome was patient-reported pain scores at 1 week and 1 month. Secondary and exploratory outcomes were physical and mental health (PRMOIS-29 v2 survey), specific neuropathic pain symptoms (McGill short-form questionnaire), and opioid consumption.

RESULTS

44 patients participated in the study; 20 were randomized to Nitrous Oxide and 24 were assigned to Air-Oxygen. Pain scores did not differ significantly, with the estimated difference in means (Nitrous Oxide-Air-Oxygen) of -0.57 (95% CI: -1.42 to 0.28) points, p=0.19. There were also no differences detected in secondary outcomes, with the estimated difference in mean Z-scores for physical health (Nitrous Oxide-Air-Oxygen) of 0.13 (95% CI: -0.16 to 0.43), mental health 0.087 (95% CI: -0.31 to 0.48), and Patient Global Impression of Change score -0.7 (95% CI: -1.85 to 0.46).

CONCLUSIONS

Compared with air/oxygen, 2 hours of nitrous oxide/oxygen exposure for three sessions did not provide meaningful therapeutic potential for patients with chronic CRPS. Our results do not support using nitrous oxide for the treatment of CRPS.

Observational study of the effect of ketamine infusions on sedation depth, inflammation, and clinical outcomes in mechanically ventilated patients with SARS-CoV-2

Severely ill patients with COVID-19 are challenging to sedate and often require high-dose sedation and analgesic regimens. Ketamine can be an effective adjunct to facilitate sedation of critically ill patients but its effects on sedation level and inflammation in COVID-19 patients have not been studied. This retrospective, observational cohort study evaluated the effect of ketamine infusions on inflammatory biomarkers and clinical outcomes in mechanically ventilated patients with SARS-CoV-2 infection. A total of 186 patients were identified (47 received ketamine, 139 did not). Patients who received ketamine were significantly younger than those who did not (mean (standard deviation) 59.2 (14.2) years versus 66.3 (14.4) years; P = 0.004), but there was no statistically significant difference in body mass index (P = 0.25) or sex distribution (P = 0.91) between groups. Mechanically ventilated patients who received ketamine infusions had a statistically significant reduction in Richmond Agitation-Sedation Scale score (-3.0 versus -2.0, P < 0.001). Regarding inflammatory biomarkers, ketamine was associated with a reduction in ferritin (P = 0.02) and lactate (P = 0.01), but no such association was observed for C-reactive protein (P = 0.27), lactate dehydrogenase (P = 0.64) or interleukin-6 (P = 0.87). No significant association was observed between ketamine administration and mortality (odds ratio 0.971; 95% confidence interval 0.501 to 1.882; P = 0.93). Ketamine infusion was associated with improved sedation depth in mechanically ventilated COVID-19 patients and provided a modest anti-inflammatory benefit but did not confer benefit with respect to mortality or intensive care unit length of stay.

Ketamine, an Old-New Drug: Uses and Abuses

Ketamine as an old-new drug has a variety of clinical implications. In the last 30 years, ketamine has become popular for acute use in humans. Ketamine in standard doses is principally utilized for the induction and maintenance of surgical procedures. Besides its use in anesthesia and analgesia, recent studies have shown that ketamine has found a place in the treatment of asthma, epilepsy, depression, bipolar affective disorders, alcohol and heroin addiction. Ketamine primarily functions as a noncompetitive antagonist targeting the N-methyl-D-aspartate (NMDA) receptor, but its mechanism of action is complex. It is generally regarded as safe, with low doses and short-term use typically not leading to significant adverse effects. Also, ketamine is known as a powerful psychostimulant. During the past decade, ketamine has been one of the commonly abused drugs.

Real-world study of intranasal ketamine for use in patients with refractory chronic migraine: a retrospective analysis

INTRODUCTION

Subanesthetic ketamine infusion has been used for managing refractory headache in inpatient or outpatient infusion settings. Intranasal ketamine may be an alternative option for outpatient care.

METHODS

A retrospective study was conducted at a single tertiary headache center to assess the clinical effectiveness and tolerability of intranasal ketamine in patients with refractory chronic migraine. Candidates who received intranasal ketamine between January 2019 and February 2020 were screened through an electronic medical record query. Manual chart reviews and structured telephone interviews were conducted on obtaining informed consent.

RESULTS

Of 242 subjects screened, 169 (79.9% women) of median (IQR) age 44 (22) years were interviewed. They reported a median (IQR) of 30 (9) monthly headache days and tried 4 (1) classes of preventive medications. Overall, they used 6 (6) sprays per day, with a median (IQR) of spray use of 10 (11) days per month. Intranasal ketamine was reported as 'very effective' in 49.1% and the quality of life was considered 'much better' in 35.5%. At the time of the interview, 65.1% remained current intranasal ketamine users and 74.0% reported at least one adverse event.

CONCLUSION

In this descriptive study, intranasal ketamine served as an acute treatment for refractory chronic migraine by reducing headache intensity and improving quality of life with relatively tolerable adverse events. Most patients found intranasal ketamine effective and continued to use it despite these adverse events. Given the potential for overuse, it should be reserved for those clearly in need of more effective rescue treatment with appropriate safety precautions. Well-designed prospective placebo-controlled trials are necessary to demonstrate the efficacy and safety of intranasal ketamine in patients with migraine.

Twelve-year outcomes of bedside laser photocoagulation for severe retinopathy of prematurity

Purpose

The purpose of this study is to evaluate the 12-year outcomes of bedside laser photocoagulation (LP) for severe retinopathy of prematurity (ROP) under sedation combined with ocular surface anesthesia in neonatal intensive care units (NICU).

Design

The study is a retrospective case series.

Methods

Infants treated with bedside LP for severe ROP from April 2009 to September 2021 were included. All LP treatments were performed under sedation and surface anesthesia at the bedside in NICU. Data were recorded for clinical and demographic characteristics, total laser spots, duration of treatment, proportion of total regression of ROP, proportion of recurrence, and adverse events.

Results

A total of 364 infants (715 eyes) were included, with a mean gestational age of 28.6 ± 2.4 weeks (range: 22.6-36.6 weeks) and a mean birth weight of 1,156.0 ± 339.0 g (range: 480-2,200 g). The mean number of laser spots was 832 ± 469, and the mean duration of treatment was 23.5 ± 5.3 min per eye. Of all the eyes, 98.3% responded to LP with complete regression of ROP. ROP recurred in 15 (2.1%) eyes after the initial LP. Additional LP was performed in seven (1.0%) eyes. No patient exhibited mistaken LP of other ocular tissues, and there were no serious ocular adverse effects. None of them needed endotracheal intubation.

Conclusions

Bedside LP treatment is effective and safe for premature infants with severe ROP under sedation and surface anesthesia in NICU, especially for infants whose general condition is unstable and not suitable for transport.

What Do We Know about Nociplastic Pain?

Nociplastic pain is a recently distinguished type of pain, distinct from neuropathic and nociceptive pain, and is well described in the literature. It is often mistaken for central sensitization. Pathophysiology has not been clearly established with regard to alteration of the concentration of spinal fluid elements, the structure of the white and gray matter of the brain, and psychological aspects. Many different diagnostic tools, i.e., the painDETECT and Douleur Neuropathique 4 questionnaires, have been developed to diagnose neuropathic pain, but they can also be applied for nociplastic pain; however, more standardized instruments are still needed in order to assess its occurrence and clinical presentation. Numerous studies have shown that nociplastic pain is present in many different diseases such as fibromyalgia, complex regional pain syndrome type 1, and irritable bowel syndrome. Current pharmacological and nonpharmacological treatments for nociceptive and neuropathic pain are not entirely suitable for treating nociplastic pain. There is an ongoing effort to establish the most efficient way to manage it. The significance of this field has led to several clinical trials being carried out in a short time. The aim of this narrative review was to discuss the currently available evidence on pathophysiology, associated diseases, treatment possibilities, and clinical trials. It is important that physicians widely discuss and acknowledge this relatively new concept in order to provide optimized pain control for patients.

The clinical toxicology of ketamine

INTRODUCTION

Ketamine is a pharmaceutical drug possessing both analgesic and anaesthetic properties. As an anaesthetic, it induces anaesthesia by producing analgesia with a state of altered consciousness while maintaining airway tone, respiratory drive, and hemodynamic stability. At lower doses, it has psychoactive properties and has gained popularity as a recreational drug.

OBJECTIVES

To review the epidemiology, mechanisms of toxicity, pharmacokinetics, clinical features, diagnosis and management of ketamine toxicity.

METHODS

Both OVID MEDLINE (January 1950-April 2023) and Web of Science (1900-April 2023) databases were searched using the term "ketamine" in combination with the keywords "pharmacokinetics", "kinetics", "poisoning", "poison", "toxicity", "ingestion", "adverse effects", "overdose", and "intoxication". Furthermore, bibliographies of identified articles were screened for additional relevant studies. These searches produced 5,268 non-duplicate citations; 185 articles (case reports, case series, pharmacokinetic studies, animal studies pertinent to pharmacology, and reviews) were considered relevant. Those excluded were other animal investigations, therapeutic human clinical investigations, commentaries, editorials, cases with no clinical relevance and post-mortem investigations.

EPIDEMIOLOGY

Following its introduction into medical practice in the early 1970s, ketamine has become a popular recreational drug. Its use has become associated with the dance culture, electronic and dubstep dance events.

MECHANISM OF ACTION

Ketamine acts primarily as a non-competitive antagonist on the glutamate N-methyl-D-aspartate receptor, causing the loss of responsiveness that is associated with clinical ketamine dissociative anaesthesia.

PHARMACOKINETICS

Absorption of ketamine is rapid though the rate of uptake and bioavailability is determined by the route of exposure. Ketamine is metabolized extensively in the liver. Initially, both isomers are metabolized to their major active metabolite, norketamine, by CYP2B6, CYP3A4 and CYP2C9 isoforms. The hydroxylation of the cyclohexan-1-one ring of norketamine to the three positional isomers of hydroxynorketamine occurs by CYP2B6 and CYP2A6. The dehydronorketamine metabolite occurs either by direct dehydrogenation from norketamine via CYP2B6 metabolism or non-enzymatic dehydration of hydroxynorketamine. Norketamine, the dehydronorketamine isomers, and hydroxynorketamine have pharmacological activity. The elimination of ketamine is primarily by the kidneys, though unchanged ketamine accounts for only a small percentage in the urine. The half-life of ketamine in humans is between 1.5 and 5 h.

CLINICAL FEATURES

Acute adverse effects following recreational use are diverse and can include impaired consciousness, dizziness, irrational behaviour, hallucinations, abdominal pain and vomiting. Chronic use can result in impaired verbal information processing, cystitis and cholangiopathy.

DIAGNOSIS

The diagnosis of acute ketamine intoxication is typically made on the basis of the patient's history, clinical features, such as vomiting, sialorrhea, or laryngospasm, along with neuropsychiatric features. Chronic effects of ketamine toxicity can result in cholangiopathy and cystitis, which can be confirmed by endoscopic retrograde cholangiopancreatography and cystoscopy, respectively.

MANAGEMENT

Treatment of acute clinical toxicity is predominantly supportive with empiric management of specific adverse effects. Benzodiazepines are recommended as initial treatment to reduce agitation, excess neuromuscular activity and blood pressure. Management of cystitis is multidisciplinary and multi-tiered, following a stepwise approach of pharmacotherapy and surgery. Management of cholangiopathy may require pain management and, where necessary, biliary stenting to alleviate obstructions. Chronic effects of ketamine toxicity are typically reversible, with management focusing on abstinence.

CONCLUSIONS

Ketamine is a dissociative drug employed predominantly in emergency medicine; it has also become popular as a recreational drug. Its recreational use can result in acute neuropsychiatric effects, whereas chronic use can result in cystitis and cholangiopathy.

Efficacy of analgesic and sub-dissociative dose ketamine for acute pain in the emergency department

BACKGROUND

Acute pain accounts for over 70% of Emergency Department (ED) visits. Sub-dissociative dose ketamine (0.1-0.6 mg/kg) is safe and effective for the management of acute pain in the ED. However, the optimal dose of intravenous ketamine that provides effective analgesia and minimizes the risk of adverse effects has yet to be identified. The objective of this study was to describe an effective analgesia dose range of IV ketamine for acute pain in the ED.

METHODS

This multi-center, retrospective cohort study evaluated adult patients who received analgesic and sub-dissociative dose ketamine for the management of acute pain between May 5, 2018, and August 30, 2021, in 21 emergency departments at academic, community, and critical access hospitals across four states. Patients were excluded if they received ketamine for an indication other than pain, such as procedural sedation or intubation, or for whom there was incomplete documentation for the primary outcome. Patients who received a ketamine dose <0.3 mg/kg were stratified into the low-dose group, and those who received a dose of 0.3 mg/kg or higher to the high-dose group. The primary outcome was change in pain scores within 60 min using a standard 11-point numeric rating scale (NRS). Secondary outcomes included incidence of adverse effects and use of rescue analgesics. Continuous variables were compared between dose groups using student t-test or Wilcoxon Rank-Sum test. Linear regression was used to assess the association between the change in NRS pain scores within 60 min and dose after adjusting for baseline pain, requiring an additional dose of ketamine, and receiving an opioid.

RESULTS

From 3796 patient encounters screened for receipt of ketamine, 384 patients met inclusion criteria including 258 in the low-dose group, and 126 in the high-dose group. The primary reason for exclusion was incomplete documentation of pain scores, or ketamine used for sedation. Median baseline pain scores were 8.2 in the low-dose group and 7.8 in the high-dose group (difference 0.5; 95% CI 0 to 1, p = 0.04). Both groups demonstrated significant reductions in their mean NRS pain scores within 60 min following the first administration of IV ketamine. There were no differences in the change in pain scores between both groups (-2.2 vs -2.6, mean difference 0.4, 95% CI -0.4 to 1.1, p = 0.34). Use of rescue analgesics (40.7% vs 36.5%, p = 0.43) and adverse effects were similar between groups, including early discontinuation of the ketamine infusion (37.2% vs. 37.3%, p = 0.99). Overall, the most common adverse effects were agitation (7.3%) and nausea (7.0%).

CONCLUSION

The analgesic efficacy and safety of high-dose sub-dissociative ketamine (≥0.3 mg/kg) was not superior to low-dose (< 0.3 mg/kg) for the management of acute pain in the ED. Low-dose ketamine <0.3 mg/kg is an effective and safe pain management strategy in this population.

Narrative Review: Low-Dose Ketamine for Pain Management

Pain is the leading cause of medical consultations and occurs in 50-70% of emergency department visits. To date, several drugs have been used to manage pain. The clinical use of ketamine began in the 1960s and it immediately emerged as a manageable and safe drug for sedation and anesthesia. The analgesic properties of this drug were first reported shortly after its use; however, its psychomimetic effects have limited its use in emergency departments. Owing to the misuse and abuse of opioids in some countries worldwide, ketamine has become a versatile tool for sedation and analgesia. In this narrative review, ketamine's role as an analgesic is discussed, with both known and new applications in various contexts (acute, chronic, and neuropathic pain), along with its strengths and weaknesses, especially in terms of psychomimetic, cardiovascular, and hepatic effects. Moreover, new scientific evidence has been reviewed on the use of additional drugs with ketamine, such as magnesium infusion for improving analgesia and clonidine for treating psychomimetic symptoms. Finally, this narrative review was refined by the experience of the Pain Group of the Italian Society of Emergency Medicine (SIMEU) in treating acute and chronic pain with acute manifestations in Italian Emergency Departments.

Acute Pain Management Pearls: A Focused Review for the Hospital Clinician

Acute pain management is a challenging area encountered by inpatient clinicians every day. While patient care is increasingly complex and costly in this realm, the availability of applicable specialists is waning. This narrative review seeks to support diverse hospital-based healthcare providers in refining and updating their acute pain management knowledge base through clinical pearls and point-of-care resources. Practical guidance is provided for the design and adjustment of inpatient multimodal analgesic regimens, including conventional and burgeoning non-opioid and opioid therapies. The importance of customized care plans for patients with preexisting opioid tolerance, chronic pain, or opioid use disorder is emphasized, and current recommendations for inpatient management of associated chronic therapies are discussed. References to best available guidelines and literature are offered for further exploration. Improved clinician attention and more developed skill sets related to acute pain management could significantly benefit hospitalized patient outcomes and healthcare resource utilization.