Ketamine coadministration attenuates morphine tolerance and leads to increased brain concentrations of both drugs in the rat

Hippocampal nicotinic acetylcholine receptor signaling mediates the anti-allodynic effect of ketamine and morphine on neuropathic pain

The present study investigated the involvement of hippocampal nicotinic acetylcholine receptors (nAChRs) in the anti-allodynic effect of ketamine/morphine on neuropathic pain in adult male Wistar rats. Morphine or ketamine administration decreased the percentage of maximum possible effect (MPE%), indicating an analgesic effect. The most significant decrease occurred with a 5 mg/kg dose of morphine (average MPE% = 98), while a 0.5 mg/kg dose of ketamine resulted in a high response (average MPE% = 91), using decision trees as a machine learning tool. Combining morphine and ketamine improved neuropathic pain (average MPE% = 91). Intra-CA1 microinjection of mecamylamine (2 μg/rat) with morphine (3 mg/kg) reduced neuropathic pain (average MPE% = 94). Co-administration of lower doses of ketamine (0.1 mg/kg, i.p.) and mecamylamine (0.5 or 1 μg/rat) with morphine (3 mg/kg) led to a considerable reduction in pain (average MPE% = 91). Utilizing the generalized least squares (GLS) model enabled the establishment of a continuous relation between drug dose and MPE% as the outcome of interest. There was a 19.60 higher average MPE% for each mg/kg increase in morphine dose. In contrast, there was a 17.05 higher average MPE% for every 0.1 mg/kg increase in ketamine dose. Each 0.1 mg/kg increase in ketamine dose, when combined with morphine (3 mg/kg), led to a 30.85 higher average MPE%. A tenfold impact of increasing mecamylamine dosage on MPE% was observed when paired with morphine. Thus, hippocampal nAChRs play a significant role in mediating the anti-allodynic effect of ketamine and morphine in neuropathic pain.

The Efficacy of Ketamine for Acute and Chronic Pain in Patients with Cancer: A Systematic Review of Randomized Controlled Trials

Managing cancer-related pain poses significant challenges, prompting research into alternative approaches such as ketamine. This systematic review aims to analyze and summarize the impact of ketamine as an adjuvant to opioid therapy for cancer-related pain. We conducted a literature review in MEDLINE, EMBASE, and Scopus from 1 January 1982 to 20 October 2023. Abstracts were screened against inclusion criteria, and eligible studies underwent a full-text review. Data was extracted from the included studies, and a framework analysis approach summarized the evidence regarding ketamine's use in patients with cancer. A total of 21 randomized clinical trials were included, and the quality of all the included studies was good or fair. Significant improvements in pain scores and reduced morphine consumption were consistently observed with intravenous ketamine administration for postoperative pain control, particularly when combined with other analgesics such as morphine. Ketamine was less effective when used as an analgesic for chronic pain management, with several studies on neuropathic pain or chemotherapy-induced neuropathy finding minimal significant effect on reduction of pain scores or morphine requirements. The efficacy of ketamine in pain management appears to depend on factors such as dosage, route of administration, and patient population.

Should Subanesthetic Ketamine be Considered When Managing Opioid Refractory Cancer Pain?

In the cancer pain setting, ketamine has been typically employed as a co-analgesic for opioid refractory and neuropathic pain. One controversial topic is whether subanesthetic ketamine be considered when managing opioid refractory cancer pain. In this "Controversies in Palliative Care" article, three clinicians independently answer this question. Specifically, each clinician provides a synopsis of the key studies that inform their thought processes, share practical advice on their clinical approach, and highlight the opportunities for future research. Three independent clinicians reported a divergence of opinion regarding the usefulness of subanesthetic ketamine for managing opioid refractory cancer pain. All investigators acknowledged the lack of high-quality trials. All agreed on the need for adequately powered trials, the development of standardized methodology, and the exploration of any patient sub-populations that may benefit from ketamine for cancer related pain.

Influence of Intravenous S-Ketamine on the Pharmacokinetics of Oral Morphine in Healthy Volunteers

BACKGROUND

Subanesthetic ketamine may reduce perioperative consumption of opioids. We studied whether intravenous S-ketamine alters the pharmacokinetics of oral morphine in healthy volunteers.

METHODS

In this paired, randomized, double-blind, crossover trial, 12 participants under a 2-hour intravenous S-ketamine (0.57 mg/kg/h) or placebo infusion received oral morphine (0.2 mg/kg) at 30 minutes. Plasma concentrations of ketamine, morphine, and their major metabolites were quantified for 24 hours. The primary end point was area under the curve (AUC) 0-24 of morphine. Other pharmacokinetic variables for morphine and its metabolites were studied as secondary end points. The data were analyzed as between-phase comparisons for each participant using Wilcoxon matched-pairs signed-rank tests ( tmax ) or paired t -tests on log-transformed variables (other variables).

RESULTS

While the AUC 0-24 was similar between the 2 phases, S-ketamine reduced the AUC 0-1.5 of oral morphine by 69% (ratio to control, 0.31; 90% confidence interval [CI], 0.15-0.65; P = .0171) and increased its tmax from 0.5 (range, 0.50-1.5) to 1.0 hour (range, 0.50-4.0; P = .010). The AUC 0-1.5 of morphine-6-glucuronide (M6G) was reduced by 84% (0.16; 90% CI, 0.07-0.37; P = .0025) and maximum plasma concentration ( Cmax ) by 43% (0.57; 90% CI, 0.40-0.81; P = .0155), while its tmax was increased from 1.5 (range, 1.0-2.0) to 4.0 (range, 1.0-8.0; P = .0094) hours by S-ketamine. Similarly, the AUC 0-1.5 of morphine-3-glucuronide (M3G) was reduced by 85% (0.15; 90% CI, 0.05-0.43; P = .0083), and tmax increased from 1.0 (range, 0.5-1.5) to 4.0 hours (range, 1.0-8.0; P = .0063). In addition, the M6G-to-morphine and M3G-to-morphine metabolic AUC ratios were decreased by 47% (0.53; 90% CI, 0.39-0.71; P = .0033) and 52% (0.48; 90% CI, 0.27-0.85; P = .0043) during 0 to 1.5 hours and by 15% (0.85; 90% CI, 0.78-0.92; P = .0057) and 10% (0.90; 90% CI, 0.83-0.98; P = .0468) during 0 to 24 hours, respectively. One participant was excluded from the analyses due to vomiting in the S-ketamine phase.

CONCLUSIONS

Intravenous S-ketamine inhibited the metabolism of oral morphine and delayed its absorption, resulting in a net reduction in the exposure to morphine during the first 1.5 hours. Intravenous S-ketamine may delay the absorption and impair the efficacy of orally administered analgesics and other drugs.

An integrative view on the cell-type-specific mechanisms of ketamine's antidepressant actions

Over the past six decades, the use of ketamine has evolved from an anesthetic and recreational drug to the first non-monoaminergic antidepressant approved for treatment-resistant major depressive disorder (MDD). Subanesthetic doses of ketamine and its enantiomer (S)-ketamine (esketamine) directly bind to several neurotransmitter receptors [including N-methyl-d-aspartic acid receptor (NMDAR), κ and μ opioid receptor (KOR and MOR)] widely distributed in the brain and across different cell types, implicating several potential molecular mechanisms underlying the action of ketamine as an antidepressant. This review examines preclinical studies investigating cell-type-specific mechanisms underlying the effects of ketamine on behavior and synapses. Cell-type-specific approaches are crucial for disentangling the critical mechanisms involved in the therapeutic effect of ketamine.

Anaesthesia in Veterinary Oncology: The Effects of Surgery, Volatile and Intravenous Anaesthetics on the Immune System and Tumour Spread

Throughout the course of oncological disease, the majority of patients require surgical, anaesthetic and analgesic intervention. However, during the perioperative period, anaesthetic agents and techniques, surgical tissue trauma, adjuvant drugs for local pain and inflammation and other non-pharmacological factors, such as blood transfusions, hydration, temperature and nutrition, may influence the prognosis of the disease. These factors significantly impact the oncologic patient's immune response, which is the primary barrier to tumour progress, promoting a window of vulnerability for its dissemination and recurrence. More research is required to ascertain which anaesthetics and techniques have immunoprotective and anti-tumour effects, which will contribute to developing novel anaesthetic strategies in veterinary medicine.

Hydrocodone, Oxycodone, and Morphine Metabolism and Drug-Drug Interactions

Awareness of drug interactions involving opioids is critical for patient treatment as they are common therapeutics used in numerous care settings, including both chronic and disease-related pain. Not only do opioids have narrow therapeutic indexes and are extensively used, but they have the potential to cause severe toxicity. Opioids are the classical pain treatment for patients who suffer from moderate to severe pain. More importantly, opioids are often prescribed in combination with multiple other drugs, especially in patient populations who typically are prescribed a large drug regimen. This review focuses on the current knowledge of common opioid drug-drug interactions (DDIs), focusing specifically on hydrocodone, oxycodone, and morphine DDIs. The DDIs covered in this review include pharmacokinetic DDI arising from enzyme inhibition or induction, primarily due to inhibition of cytochrome p450 enzymes (CYPs). However, opioids such as morphine are metabolized by uridine-5'-diphosphoglucuronosyltransferases (UGTs), principally UGT2B7, and glucuronidation is another important pathway for opioid-drug interactions. This review also covers several pharmacodynamic DDI studies as well as the basics of CYP and UGT metabolism, including detailed opioid metabolism and the potential involvement of metabolizing enzyme gene variation in DDI. Based upon the current literature, further studies are needed to fully investigate and describe the DDI potential with opioids in pain and related disease settings to improve clinical outcomes for patients. SIGNIFICANCE STATEMENT: A review of the literature focusing on drug-drug interactions involving opioids is important because they can be toxic and potentially lethal, occurring through pharmacodynamic interactions as well as pharmacokinetic interactions occurring through inhibition or induction of drug metabolism.

Developing non-opioid therapeutics to alleviate pain among persons with opioid use disorder: a review of the human evidence

The opioid crisis remains a major public health concern, causing significant morbidity and mortality worldwide. Pain is frequently observed among individuals with opioid use disorder (OUD), and the current opioid agonist therapies (OAT) have limited efficacy in addressing the pain needs of this population. We reviewed the most promising non-opioid analgesic therapies for opioid-dependent individuals synthesising data from randomised controlled trials in the Medline database from December 2022 to March 2023. Ketamine, gabapentin, serotoninergic antidepressants, and GABAergic drugs were found to be the most extensively studied non-opioid analgesics with positive results. Additionally, we explored the potential of cannabinoids, glial activation inhibitors, psychedelics, cholecystokinin antagonists, alpha-2 adrenergic agonists, and cholinergic drugs. Methodological improvements are required to advance the development of novel analgesic strategies and establish their safety profile for opioid-dependent populations. We highlight the need for greater integration of experimental pain methods and abuse liability assessments, more granular assessments of prior opioid exposure, greater uniformity of pain types within study samples, and a particular focus on individuals with OUD receiving OAT. Finally, future research should investigate pharmacokinetic interactions between OAT and various non-opioid analgesics and perform reverse translation basic experiments, particularly with methadone and buprenorphine, which remain the standard OUD treatment.

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.

Determination of Diffusion Kinetics of Ketamine in Brain Tissue: Implications for in vitro Mechanistic Studies of Drug Actions

Ketamine has been in use for over 50 years as a general anesthetic, acting primarily through blockade of N-methyl-D-aspartate receptors in the brain. Recent studies have demonstrated that ketamine also acts as a potent and rapid-acting antidepressant when administered at sub-anesthetic doses. However, the precise mechanism behind this effect remains unclear. We examined the diffusion properties of ketamine in brain tissue to determine their effects in in vitro studies related to the antidepressant action of ketamine. Brain slices from adult mice were exposed to artificial cerebrospinal fluid (aCSF) containing ∼17 μM ketamine HCl for varying amounts of time. The amount of ketamine within each slice was then measured by tandem high-performance liquid chromatography - mass spectrometry to characterize the diffusion of ketamine into brain tissue over time. We successfully modeled the diffusion of ketamine into brain tissue using a mono-exponential function with a time constant of τ = 6.59 min. This curve was then compared to a one-dimensional model of diffusion yielding a diffusion coefficient of approximately 0.12 cm²⋅s^-1 for ketamine diffusing into brain tissue. The brain:aCSF partition coefficient for ketamine was determined to be approximately 2.76. Our results suggest that the diffusion properties of ketamine have a significant effect on drug concentrations achieved within brain tissue during in vitro experiments. This information is vital to determine the ketamine concentration necessary for in vitro slice preparation to accurately reflect in vivo doses responsible for its antidepressant actions.

Neurophysiological response properties of medullary pain-control neurons following chronic treatment with morphine or oxycodone: modulation by acute ketamine

Morphine and oxycodone are two clinically used strong opioids. Chronic treatment with oxycodone as well as morphine can lead to analgesic tolerance and paradoxical hyperalgesia. Here we show that an N-methyl-d-aspartate receptor-dependent pronociceptive change in discharge properties of rostroventromedial medullary neurons controlling spinal nociception has an important role in antinociceptive tolerance to morphine but not oxycodone. Interestingly, chronic oxycodone did not induce pronociceptive changes in the rostroventromedial medulla.

Neuroinflammation, Pain and Depression: An Overview of the Main Findings

Chronic pain is a serious public health problem with a strong affective-motivational component that makes it difficult to treat. Most patients with chronic pain suffer from severe depression; hence, both conditions coexist and exacerbate one another. Brain inflammatory mediators are critical for maintaining depression-pain syndrome and could be substrates for it. The goal of our paper was to review clinical and preclinical findings to identify the neuroinflammatory profile associated with the cooccurrence of pain and depression. In addition, we aimed to explore the regulatory effect of neuronal reorganization on the inflammatory response in pain and depression. We conducted a quantitative review supplemented by manual screening. Our results revealed inflammatory signatures in different preclinical models and clinical articles regarding depression-pain syndrome. We also identified that improvements in depressive symptoms and amelioration of pain can be modulated through direct targeting of inflammatory mediators, such as cytokines and molecular inhibitors of the inflammatory cascade. Additionally, therapeutic targets that improve and regulate the synaptic environment and its neurotransmitters may act as anti-inflammatory compounds, reducing local damage-associated molecular patterns and inhibiting the activation of immune and glial cells. Taken together, our data will help to better elucidate the neuroinflammatory profile in pain and depression and may help to identify pharmacological targets for effective management of depression-pain syndrome.

Impact of ketamine on the behavior and immune system of adult medaka (Oryzias latipes) at environmentally relevant concentrations and eco-risk assessment in surface water

This work for the first time investigated the bioconcentration factor (BCF), toxicity, and eco-risk of KET using adult medaka fish (Oryzias latipes) as model organism after exposure at environmental concentrations (0.05-0.5 μg L^-1) and higher levels (5-100 μg L^-1) for 90 days. The BCF of KET was approximately 1.07- to 10.94- folds. The behavioral functions, including swimming properties, feeding rate, and food preference, were significantly impacted by KET (≥0.05 μg L^-1). After 90-days exposure, KET induced histological abnormalities in liver and kidney tissue at 0.1 and 0.2 μg L^-1, respectively. Additionally, the condition factor, hepatic-somatic index (HSI), and nephric-somatic index (NSI) of medaka were markedly impacted by KET treatment at 0.5, 0.5, and 0.1 μg L^-1, respectively. Morphological inflammation (i.e., haemorrhage and erosion) in the fish body was observed exposed to KET, and the EC₁₀ value was 0.407 μg L^-1. Alterations in the expressions of genes (i.e., cacna1c, oxtr, erk1, and c-fos) and proteins (i.e., OXT and PKA), involved in in calcium ion channels induced by KET, could partly elucidate the underlying mechanism of the toxicity. The inflammatory risk to fish posed by KET in some rivers in southern China was at high level, suggesting the long-term concentration monitoring was required.

KEA-1010, a ketamine ester analogue, retains analgesic and sedative potency but is devoid of Psychomimetic effects

Background

Ketamine, a widely used anaesthetic and analgesic agent, is known to improve the analgesic efficacy of opioids and to attenuate central sensitisation and opioid-induced hyperalgesia. Clinical use is, however, curtailed by unwanted psychomimetic effects thought to be mediated by N-methyl-D-aspartate (NMDA) receptor antagonism. KEA-1010, a ketamine ester-analogue designed for rapid offset of hypnosis through hydrolysis mediated break-down, has been shown to result in short duration sedation yet prolonged attenuation of nociceptive responses in animal models. Here we report on behavioural effects following KEA-1010 administration to rodents.

Methods

KEA-1010 was compared with racemic ketamine in its ability to produce loss of righting reflex following intravenous injection in rats. Analgesic activity was assessed in thermal tail flick latency (TFL) and paw incision models when injected acutely and when co-administered with fentanyl. Tail flick analgesic assessment was further undertaken in morphine tolerant rats. Behavioural aberration was assessed following intravenous injection in rats undergoing TFL assessment and in auditory pre-pulse inhibition models.

Results

KEA-1010 demonstrated an ED₅₀ similar to ketamine for loss of righting reflex following bolus intravenous injection (KEA-1010 11.4 mg/kg [95% CI 10.6 to 12.3]; ketamine (racemic) 9.6 mg/kg [95% CI 8.5–10.9]). Duration of hypnosis was four-fold shorter in KEA-1010 treated animals. KEA-1010 prolonged thermal tail flick responses comparably with ketamine when administered de novo, and augmented morphine-induced prolongation of tail flick when administered acutely. The analgesic effect of KEA-1010 on thermal tail flick was preserved in opioid tolerant rats. KEA-1010 resulted in increased paw-withdrawal thresholds in a rat paw incision model, similar in magnitude yet more persistent than that seen with fentanyl injection, and additive when co-administered with fentanyl. In contrast to ketamine, behavioural aberration following KEA-1010 injection was largely absent and no pre-pulse inhibition to acoustic startle was observed following KEA-1010 administration in rats.

Conclusions

KEA-1010 provides antinociceptive efficacy in acute thermal and mechanical pain models that augments standard opioid analgesia and is preserved in opioid tolerant rodents. The NMDA channel affinity and psychomimetic signature of the parent compound ketamine is largely absent for KEA-1010.

Additive and subadditive antiallodynic interactions between μ-opioid agonists and N-methyl D-aspartate antagonists in male rhesus monkeys

μ-Opioid agonists are clinically effective analgesics, but also produce undesirable effects such as sedation and abuse potential that limit their clinical utility. Glutamatergic systems also modulate nociception and N-methyl D-aspartate (NMDA) receptor antagonists have been proposed as one useful adjunct to enhance the therapeutic effects and/or attenuate the undesirable effects of μ-opioid agonists. Whether NMDA antagonists enhance the antiallodynic effects of μ-agonists in preclinical models of thermal hypersensitivity (i.e. capsaicin-induced thermal allodynia) are unknown. The present study determined the behavioral effects of racemic ketamine, (+)-MK-801, (-)-nalbuphine, and (-)-oxycodone alone and in fixed proportion mixtures in assays of capsaicin-induced thermal allodynia and schedule-controlled responding in rhesus monkeys. Ketamine, nalbuphine, and oxycodone produced dose-dependent antiallodynia. MK-801 was inactive up to doses that produced undesirable effects. Ketamine, but not MK-801, enhanced the potency of μ-agonists to decrease rates of operant responding. Ketamine and nalbuphine interactions were additive in both procedures. Ketamine and oxycodone interactions were additive or subadditive depending on the mixture. Furthermore, oxycodone and MK-801 interactions were subadditive on antiallodynia and additive on rate suppression. These results do not support the broad clinical utility of NMDA receptor antagonists as adjuncts to μ-opioid agonists for thermal allodynic pain states.

[Ketamine in the therapy of chronic pain and depression]

Although ketamine has been known and clinically applied for a long time, questions still arise around the many possible indications in which the anesthetic and analgesic substance could be used. In particular, these questions relate to new indications in which ketamine is used in low subanesthetic doses.The mechanism of action at the NMDA receptor clearly distinguishes ketamine from all other analgesics. Possible applications include the prevention of chronic postoperative pain as well as the treatment of neuropathic pain. With the treatment of refractory depression completely new therapeutic areas for ketamine could be established.

Perioperative intravenous ketamine for acute postoperative pain in adults

BACKGROUND

Inadequate pain management after surgery increases the risk of postoperative complications and may predispose for chronic postsurgical pain. Perioperative ketamine may enhance conventional analgesics in the acute postoperative setting.

OBJECTIVES

To evaluate the efficacy and safety of perioperative intravenous ketamine in adult patients when used for the treatment or prevention of acute pain following general anaesthesia.

SEARCH METHODS

We searched CENTRAL, MEDLINE and Embase to July 2018 and three trials registers (metaRegister of controlled trials, ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP)) together with reference checking, citation searching and contact with study authors to identify additional studies.

SELECTION CRITERIA

We sought randomised, double-blind, controlled trials of adults undergoing surgery under general anaesthesia and being treated with perioperative intravenous ketamine. Studies compared ketamine with placebo, or compared ketamine plus a basic analgesic, such as morphine or non-steroidal anti-inflammatory drug (NSAID), with a basic analgesic alone.

DATA COLLECTION AND ANALYSIS

Two review authors searched for studies, extracted efficacy and adverse event data, examined issues of study quality and potential bias, and performed analyses. Primary outcomes were opioid consumption and pain intensity at rest and during movement at 24 and 48 hours postoperatively. Secondary outcomes were time to first analgesic request, assessment of postoperative hyperalgesia, central nervous system (CNS) adverse effects, and postoperative nausea and vomiting. We assessed the evidence using GRADE and created a 'Summary of findings' table.

MAIN RESULTS

We included 130 studies with 8341 participants. Ketamine was given to 4588 participants and 3753 participants served as controls. Types of surgery included ear, nose or throat surgery, wisdom tooth extraction, thoracotomy, lumbar fusion surgery, microdiscectomy, hip joint replacement surgery, knee joint replacement surgery, anterior cruciate ligament repair, knee arthroscopy, mastectomy, haemorrhoidectomy, abdominal surgery, radical prostatectomy, thyroid surgery, elective caesarean section, and laparoscopic surgery. Racemic ketamine bolus doses were predominantly 0.25 mg to 1 mg, and infusions 2 to 5 µg/kg/minute; 10 studies used only S-ketamine and one only R-ketamine. Risk of bias was generally low or uncertain, except for study size; most had fewer than 50 participants per treatment arm, resulting in high heterogeneity, as expected, for most analyses. We did not stratify the main analysis by type of surgery or any other factor, such as dose or timing of ketamine administration, and used a non-stratified analysis.Perioperative intravenous ketamine reduced postoperative opioid consumption over 24 hours by 8 mg morphine equivalents (95% CI 6 to 9; 19% from 42 mg consumed by participants given placebo, moderate-quality evidence; 65 studies, 4004 participants). Over 48 hours, opioid consumption was 13 mg lower (95% CI 10 to 15; 19% from 67 mg with placebo, moderate-quality evidence; 37 studies, 2449 participants).Perioperative intravenous ketamine reduced pain at rest at 24 hours by 5/100 mm on a visual analogue scale (95% CI 4 to 7; 19% lower from 26/100 mm with placebo, high-quality evidence; 82 studies, 5004 participants), and at 48 hours by 5/100 mm (95% CI 3 to 7; 22% lower from 23/100 mm, high-quality evidence; 49 studies, 2962 participants). Pain during movement was reduced at 24 hours (6/100 mm, 14% lower from 42/100 mm, moderate-quality evidence; 29 studies, 1806 participants), and 48 hours (6/100 mm, 16% lower from 37 mm, low-quality evidence; 23 studies, 1353 participants).Results for primary outcomes were consistent when analysed by pain at rest or on movement, operation type, and timing of administration, or sensitivity to study size and pain intensity. No analysis by dose was possible. There was no difference when nitrous oxide was used. We downgraded the quality of the evidence once if numbers of participants were large but small-study effects were present, or twice if numbers were small and small-study effects likely but testing not possible.Ketamine increased the time for the first postoperative analgesic request by 54 minutes (95% CI 37 to 71 minutes), from a mean of 39 minutes with placebo (moderate-quality evidence; 31 studies, 1678 participants). Ketamine reduced the area of postoperative hyperalgesia by 7 cm² (95% CI -11.9 to -2.2), compared with placebo (very low-quality evidence; 7 studies 333 participants). We downgraded the quality of evidence because of small-study effects or because the number of participants was below 400.CNS adverse events occurred in 52 studies, while 53 studies reported of absence of CNS adverse events. Overall, 187/3614 (5%) participants receiving ketamine and 122/2924 (4%) receiving control treatment experienced an adverse event (RR 1.2, 95% CI 0.95 to 1.4; high-quality evidence; 105 studies, 6538 participants). Ketamine reduced postoperative nausea and vomiting from 27% with placebo to 23% with ketamine (RR 0.88, 95% CI 0.81 to 0.96; the number needed to treat to prevent one episode of postoperative nausea and vomiting with perioperative intravenous ketamine administration was 24 (95% CI 16 to 54; high-quality evidence; 95 studies, 5965 participants).

AUTHORS' CONCLUSIONS

Perioperative intravenous ketamine probably reduces postoperative analgesic consumption and pain intensity. Results were consistent in different operation types or timing of ketamine administration, with larger and smaller studies, and by higher and lower pain intensity. CNS adverse events were little different with ketamine or control. Perioperative intravenous ketamine probably reduces postoperative nausea and vomiting by a small extent, of arguable clinical relevance.

Ketamine for pain management

Supplemental Digital Content is Available in the Text.

Consensus Guidelines on the Use of Intravenous Ketamine Infusions for Chronic Pain From the American Society of Regional Anesthesia and Pain Medicine, the American Academy of Pain Medicine, and the American Society of Anesthesiologists

BACKGROUND

Over the past 2 decades, the use of intravenous ketamine infusions as a treatment for chronic pain has increased dramatically, with wide variation in patient selection, dosing, and monitoring. This has led to a chorus of calls from various sources for the development of consensus guidelines.

METHODS

In November 2016, the charge for developing consensus guidelines was approved by the boards of directors of the American Society of Regional Anesthesia and Pain Medicine and, shortly thereafter, the American Academy of Pain Medicine. In late 2017, the completed document was sent to the American Society of Anesthesiologists' Committees on Pain Medicine and Standards and Practice Parameters, after which additional modifications were made. Panel members were selected by the committee chair and both boards of directors based on their expertise in evaluating clinical trials, past research experience, and clinical experience in developing protocols and treating patients with ketamine. Questions were developed and refined by the committee, and the groups responsible for addressing each question consisted of modules composed of 3 to 5 panel members in addition to the committee chair. Once a preliminary consensus was achieved, sections were sent to the entire panel, and further revisions were made. In addition to consensus guidelines, a comprehensive narrative review was performed, which formed part of the basis for guidelines.

RESULTS

Guidelines were prepared for the following areas: indications; contraindications; whether there was evidence for a dose-response relationship, or a minimum or therapeutic dose range; whether oral ketamine or another N-methyl-D-aspartate receptor antagonist was a reasonable treatment option as a follow-up to infusions; preinfusion testing requirements; settings and personnel necessary to administer and monitor treatment; the use of preemptive and rescue medications to address adverse effects; and what constitutes a positive treatment response. The group was able to reach consensus on all questions.

CONCLUSIONS

Evidence supports the use of ketamine for chronic pain, but the level of evidence varies by condition and dose range. Most studies evaluating the efficacy of ketamine were small and uncontrolled and were either unblinded or ineffectively blinded. Adverse effects were few and the rate of serious adverse effects was similar to placebo in most studies, with higher dosages and more frequent infusions associated with greater risks. Larger studies, evaluating a wider variety of conditions, are needed to better quantify efficacy, improve patient selection, refine the therapeutic dose range, determine the effectiveness of nonintravenous ketamine alternatives, and develop a greater understanding of the long-term risks of repeated treatments.

Ketamine Pharmacokinetics and Pharmacodynamics Are Altered by P-Glycoprotein and Breast Cancer Resistance Protein Efflux Transporters in Mice

To understand the systemic impact of breast cancer resistance protein (Bcrp) and P-glycoprotein (Pgp) deletion, untargeted metabolomics was performed on cerebral spinal fluid (CSF) and plasma of wild-type (WT) and Pgp and Bcrp double-knockout (dKO) rats anesthetized with ketamine-xylazine. We unexpectedly found elevated ketamine levels in both CSF and plasma of dKO versus WT rats. Therefore, the effect of these transporters was investigated on the 1) oral and intraperitoneal serum pharmacokinetics (PK) of ketamine, using a liquid chromatography method (high-performance liquid chromatography with ultraviolet detection), and 2) the anesthetic effect of ketamine using a duration of loss-of-righting reflex (dLORR) test in WT, Bcrp knockout (KO), Pgp KO, and Pgp/Bcrp dKO mice. The PK data demonstrated a significantly increased oral bioavailability and serum exposure of ketamine in dKO > Pgp KO > Bcrp KO mice compared with WT mice. Intraperitoneal ketamine-induced dLORR was significantly longer in dKO > Pgp KO > Bcrp KO > WT mice compared with WT mice. Inhibition of Bcrp and Pgp in WT mice using the dual Pgp/Bcrp inhibitor elacridar increased the ketamine-induced dLORR compared with vehicle-treated mice. The ketamine intracellular concentration was significantly decreased in Madin-Darby canine kidney II BCRP/PGP cells compared with the parental cells. In total, these results demonstrate that ketamine appears to be a dual Pgp/Bcrp substrate whose PK and pharmacodynamics are affected by Pgp and Bcrp-mediated efflux.

Endogenous Opiates and Behavior: 2016

This paper is the thirty-ninth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2016 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Chronic morphine exposure potentiates p-glycoprotein trafficking from nuclear reservoirs in cortical rat brain microvessels

The rates of opioid prescription and use have continued to increase over the last few decades resulting in a greater number of opioid tolerant patients. Treatment of acute pain from surgery and injury is a clinical challenge for these patients. Several pain management strategies including prescribing increased opioids are used clinically with limited success; all currently available strategies have significant limitations. Many opioids are a substrate for p-glycoprotein (p-gp), an efflux transporter at the blood-brain barrier (BBB). Increased p-gp is associated with a decreased central nervous system uptake and analgesic efficacy of morphine. Our laboratory previously found that acute peripheral inflammatory pain (PIP) induces p-gp trafficking from the nucleus to the luminal surface of endothelial cells making up the BBB concomitant with increased p-gp activity and decreased morphine analgesic efficacy. In the current study, we tested whether PIP-induced p-gp trafficking could contribute to decreased opioid efficacy in morphine tolerant rats. A 6-day continuous dosing of morphine from osmotic minipumps was used to establish morphine tolerance in female rats. PIP induced p-gp trafficking away from nuclear stores showed a 2-fold increase in morphine tolerant rats. This observation suggests that p-gp trafficking contributes to the decreased morphine analgesic effects in morphine tolerant rats experiencing an acute pain stimulus. Attenuating p-gp trafficking during an acute pain stimulus could improve pain management by increasing the amount of opioid that could reach CNS analgesic targets and decrease the need for the dose escalation that is a serious challenge in pain management.

Interactions of (2S,6S;2R,6R)-Hydroxynorketamine, a Secondary Metabolite of (R,S)-Ketamine, with Morphine

Ketamine and its primary metabolite norketamine attenuate morphine tolerance by antagonising N-methyl-d-aspartate (NMDA) receptors. Ketamine is extensively metabolized to several other metabolites. The major secondary metabolite (2S,6S;2R,6R)-hydroxynorketamine (6-hydroxynorketamine) is not an NMDA antagonist. However, it may modulate nociception through negative allosteric modulation of α7 nicotinic acetylcholine receptors. We studied whether 6-hydroxynorketamine could affect nociception or the effects of morphine in acute or chronic administration settings. Male Sprague Dawley rats received subcutaneous 6-hydroxynorketamine or ketamine alone or in combination with morphine, as a cotreatment during induction of morphine tolerance, and after the development of tolerance induced by subcutaneous minipumps administering 9.6 mg morphine daily. Tail flick, hot plate, paw pressure and rotarod tests were used. Brain and serum drug concentrations were quantified with high-performance liquid chromatography-tandem mass spectrometry. Ketamine (10 mg/kg), but not 6-hydroxynorketamine (10 and 30 mg/kg), enhanced antinociception and decreased rotarod performance following acute administration either alone or combined with morphine. Ketamine efficiently attenuated morphine tolerance. Acutely administered 6-hydroxynorketamine increased the brain concentration of morphine (by 60%), and brain and serum concentrations of 6-hydroxynorketamine were doubled by morphine pre-treatment. This pharmacokinetic interaction did not, however, lead to altered morphine tolerance. Co-administration of 6-hydroxynorketamine 20 mg/kg twice daily did not influence development of morphine tolerance. Even though morphine and 6-hydroxynorketamine brain concentrations were increased after co-administration, the pharmacokinetic interaction had no effect on acute morphine nociception or tolerance. These results indicate that 6-hydroxynorketamine does not have antinociceptive properties or attenuate opioid tolerance in a similar way as ketamine.

Chronic Opioid Therapy Modifies QST Changes After Ketamine Infusion in Chronic Pain Patients

The long-term effects of opioids on sensitization processes are believed to be mediated through the N-methyl-D-aspartate receptor. Quantitative sensory testing (QST) changes observed after a ketamine infusion have been previously described but the effect that chronic opioids will have is not known. The results of this prospective randomized factorial trial compared the thermal QST changes observed after a .05 mg/kg ketamine infusion or a saline placebo in chronic pain subjects who were either opioid-naive or were chronically using opioids for chronic noncancer pain are presented. No baseline QST differences were noted between the 4 groups at baseline. Comparison of changes preinfusion with postinfusion QST measurements resulted in decreased average change in temporal summation response between opioid subjects who received a placebo compared with those who received a ketamine infusion (-5.22, SD = 9.96 vs 13.81, SD = 19.55; P = .004). Additionally, the average change in temporal summation was decreased among subjects who received a ketamine infusion and were not chronically using opioids compared with subjects who were using chronic opioids and received a placebo infusion (-1.91, SD = 13.25 vs 13.81, SD = 19.55; P = .007). The results indicate that low-dose ketamine infusions produce subtle changes in QST phenotypes that are modified by the chronic use of opioids. This illustrates the potential diagnostic and therapeutic value of ketamine in the setting of chronic opioid use.

PERSPECTIVE

The presented data further our understanding of modulation of sensory perception in the setting of chronic opioid use and the role of the N-methyl-D-aspartate receptor. The use of low-dose ketamine infusions may be useful for the treatment as well as diagnosis of opioid-related neuropathic conditions.

Spinal analgesia for severe cancer pain: A retrospective analysis of 60 patients

Background and aims

Pain is highly prevalent in advanced cancer, and in some patients refractory to conventional opioid treatment. For these patients, invasive methods of pain relief should be considered. Spinal administration of opioids has been shown to be an effective alternative in refractory cancer pain. The aim of this retrospective study was to collect information on the use of spinal analgesia for cancer pain in Helsinki University Hospital.

Methods

A retrospective patient chart study of all cancer patients with spinal analgesia, either intrathecal or epidural, in a single academic center during a five year period (n = 60).

Results

Forty-four patients were treated with intrathecal (IT) and sixteen with epidural (EP) technique. The most common indication for spinal analgesia was pain refractory to systemic analgesics. Good analgesia was achieved in 50% and 70% of the patients in the EP and IT groups, respectively. The median daily systemic opioid doses prior to spinal analgesia were 874.5 mg and 730.5 mg as oral morphine equivalents in the IT and EP groups, respectively. The systemic opioid could be discontinued or significantly reduced in 83% of the patients. Morphine was used in all IT infusions and most EP infusions, mostly combined with bupivacaine 10mg (IT) or 66mg (EP). The median starting doses of morphine were 3 mg/day (IT) and 19 mg/day (EP) and were increased during titration 27% to 3.8 mg/day (IT) and 91% to 36.2 mg/day (EP). Clonidine (median 0.015 mg/day IT and 0.15 mg/day EP) and/or ketamine were used as adjuvants. The average titration time to stable analgesia was 7–9 days. Numbness in lower limbs was reported by 24% of the IT group. On average, catheters were placed 98 and 61 days before death in IT and EP groups, respectively. No serious complications occurred. Catheter dislocation occurred in 27% of all sixty patients during follow-up. Treatment was discontinued in 10 patients because of catheter dislocation (n =7) or local infection (n = 3).

Conclusions and implications

Spinal administration of opioids is a safe and effective method of pain management in patients with severe cancer pain and can greatly reduce the need of systemic opioids. We are implementing closer collaboration with oncologists to provide spinal analgesia to more patients and earlier to reduce suffering. Catheter dislocation led to discontinuation of spinal analgesia in 17% of the patients and we are evaluating new ways to prevent catheter dislocation. The initial median spinal opioid dose was too low in both groups, and we are now using higher initial doses. A common adverse effect was numbness of the lower limbs, regardless of the relatively low doses of spinal bupivacaine. We now use lower doses and introduce the intrathecal catheter higher at L1–2 to reduce motor blockade at the level of conus.

As an initial intrathecal infusions we suggest: morphine dose calculated using an oral to intrathecal ratio of 1:100 (unless the patient is elderly or already drowsy), clonidine dose 30μg/day and bupivacaine dose 7.5 mg/day.

Ketamine as an adjuvant to opioids for cancer pain

BACKGROUND

This is an update of a review first published in 2003 and updated in 2012.Ketamine is a commonly used anaesthetic agent, and in subanaesthetic doses is also given as an adjuvant to opioids for the treatment of refractory cancer pain, when opioids alone or in combination with appropriate adjuvant analgesics prove to be ineffective. Ketamine is known to have psychomimetic (including hallucinogenic), urological, and hepatic adverse effects.

OBJECTIVES

To determine the effectiveness and adverse effects of ketamine as an adjuvant to opioids for refractory cancer pain in adults.

SEARCH METHODS

For this update, we searched MEDLINE (OVID) to December 2016. We searched CENTRAL (CRSO), Embase (OVID) and two clinical trial registries to January 2017.

SELECTION CRITERIA

The intervention considered by this review was the addition of ketamine, given by any route of administration, in any dose, to pre-existing opioid treatment given by any route and in any dose, compared with placebo or active control. We included studies with a group size of at least 10 participants who completed the trial.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the search results and performed 'Risk of bias' assessments. We aimed to extract data on patient-reported pain intensity, total opioid consumption over the study period; use of rescue medication; adverse events; measures of patient satisfaction/preference; function; and distress. We also assessed participant withdrawal (dropout) from trial. We assessed the quality of the evidence using GRADE (Grading of Recommendations Assessment, Development and Evaluation).

MAIN RESULTS

One new study (185 participants) was identified by the updated search and included in the review. We included a total of three studies in this update.Two small studies, both with cross-over design, with 20 and 10 participants respectively, were eligible for inclusion in the original review. One study with 20 participants examined the addition of intrathecal ketamine to intrathecal morphine, compared with intrathecal morphine alone. The second study with 10 participants examined the addition of intravenous ketamine bolus in two different doses to ongoing morphine therapy, compared with placebo. Both of these studies reported reduction in pain intensity and reduction in morphine requirements when ketamine was added to opioid for refractory cancer pain. The new study identified by the updated search had a parallel group design and 185 participants. This placebo-controlled study examined rapid titration of subcutaneous ketamine to high dose (500 mg) in participants who were using different opioids. There were no differences between groups for patient-reported pain intensity.Pooling of the data from the three included trials was not appropriate because of clinical heterogeneity.The study examining intrathecal drug administration reported no adverse events related to ketamine. In the study using intravenous bolus administration, ketamine caused hallucinations in four of 10 participants. In the rapid dose escalation/high-dose subcutaneous ketamine study, there was almost twice the incidence of adverse events in the ketamine group, compared to the placebo group, with the most common adverse events being needle site irritation and cognitive disturbance. Two serious adverse events (bradyarrhythmia and cardiac arrest) thought to be related to ketamine were also reported in this trial.For all three studies there was an unclear risk of bias overall. Using GRADE, we judged the quality of the evidence to be very low due to study limitations and imprecision due to the small number of participants in all comparisons.

AUTHORS' CONCLUSIONS

Current evidence is insufficient to assess the benefits and harms of ketamine as an adjuvant to opioids for the relief of refractory cancer pain. The evidence was of very low quality, meaning that it does not provide a reliable indication of the likely effect, and the likelihood that the effect will be substantially different is high. Rapid dose escalation of ketamine to high dose (500 mg) does not appear to have clinical benefit and may be associated with serious adverse events. More randomised controlled trials (RCTs) examining specific low-dose ketamine clinical regimens in current use are needed.

Bifunctional peptide-based opioid agonist/nociceptin antagonist ligand for dual treatment of nociceptive and neuropathic pain

Drugs able to treat both nociceptive and neuropathic pain effectively without major side effects are lacking. We developed a bifunctional peptide-based hybrid (KGNOP1) that structurally combines a mu-opioid receptor agonist (KGOP1) with antinociceptive activity and a weak nociceptin receptor antagonist (KGNOP3) with anti-neuropathic pain activity. We investigated KGNOP1-related behavioral effects after intravenous administration in rats by assessing thermal nociception, cold hyperalgesia in a model of neuropathic pain induced by chronic constriction injury of the sciatic nerve, and plethysmography parameters including inspiratory time (TI) and minute ventilation (VM) in comparison to the well-known opioid analgesics, tramadol and morphine. Time-course and dose-dependent effects were investigated for all behavioral parameters to determine the effective doses 50% (ED50). Pain-related effects on cold hyperalgesia were markedly increased by KGNOP1 as compared to KGNOP3 and tramadol (ED50: 0.0004, 0.32, and 12.1 μmol/kg, respectively), whereas effects on thermal nociception were significantly higher with KGNOP1 as compared to morphine (ED50: 0.41 and 14.7 μmol/kg, respectively). KGNOP1 and KGOP1 produced a larger increase in TI and deleterious decrease in VM in comparison to morphine and tramadol (ED50(TI): 0.63, 0.52, 12.2, and 50.9 μmol/kg; ED50(VM): 0.57, 0.66, 10.6, and 50.0 μmol/kg, respectively). Interestingly, the calculated ratios of anti-neuropathic pain/antinociceptive to respiratory effects revealed that KGNOP1 was safer than tramadol (ED50 ratio: 5.44 × 10 vs 0.24) and morphine (ED50 ratio: 0.72 vs 1.39). We conclude that KGNOP1 is able to treat both experimental neuropathic and nociceptive pain, more efficiently and safely than tramadol and morphine, respectively, and thus should be a candidate for future clinical developments.

Concurrent bullatine A enhances morphine antinociception and inhibits morphine antinociceptive tolerance by indirect activation of spinal κ-opioid receptors

ETHNOPHARMACOLOGICAL RELEVANCE

Bullatine A, a C₂₀-diterpenoid alkaloid and one of the major effective ingredients in Aconiti brachypodi Radix (Xue-shang-yi-zhi-hao), can block pain hypersensitivity in a variety of rodent models through expression of spinal microglial dynorphin A.

AIM OF THE STUDY

To assess the interaction between bullatine A and morphine on antinociception in acute nociception and pain hypersensitivity states, with the exogenous synthetic dynorphin A as a comparison MATERIALS AND METHODS: Spinal nerve ligation-induced neuropathic rats and naïve mice were used for assessing the acute and chronic interactions of bullatine A/dynorphin A with morphine.

RESULTS

Single subcutaneous injection of bullatine A or dynorphin A(1-17) did not either alter formalin- and thermally (hot-plate and water immersion tests)-induced acute nociception or potentiate morphine antinociception in naïve mice. In contrast, bullatine A dose-dependently inhibited formalin-induced tonic pain with the efficacy of 54% inhibition and the half-effective dose of 0.9mg/kg. Concurrent bullatine A additively enhanced morphine antinociception. In neuropathic rats, the antinociceptive effects of multiple bidaily intrathecal injections of bullatine A and dynorphin A remained consistent over 13 days, whereas morphine produced progressive and complete tolerance to antinociception, which was completely inhibited by concurrent bullatine A and dynorphin A. A single intrathecal injection of bullatine A and dynorphin A immediately reversed established morphine tolerance in neuropathic rats, although the blockade was a less degree in the thermally induced mouse acute nociceptive tests. The inhibitory effects of bullatine A and dynorphin A on morphine tolerance were immediately and completely attenuated by intrathecal dynorphin A antibody and/or selective κ-opioid receptor antagonist GNTI.

CONCLUSION

These results suggest that bullatine A produces antinociception without induction of tolerance and inhibits morphine antinociceptive tolerance, and provide pharmacological basis for concurrent bullatine A and morphine treatment for chronic pain and morphine analgesic tolerance.

Laparoscopic surgery: a narrative review of pharmacotherapy in pain management

Laparoscopic surgery is widespread, and an increasing number of surgeries are performed laparoscopically. Early pain after laparoscopy can be similar or even more severe than that after open surgery. Thus, proactive pain management should be provided. Pain after laparoscopic surgery is derived from multiple origins; therefore, a single agent is seldom sufficient. Pain is most effectively controlled by a multimodal, preventive analgesia approach, such as combining opioids with non-opioid analgesics and local anaesthetics. Wound and port site local anaesthetic injections decrease abdominal wall pain by 1-1.5 units on a 0-10 pain scale. Inflammatory pain and shoulder pain can be controlled by NSAIDs or corticosteroids. In some patient groups, adjuvant drugs, ketamine and α2-adrenergic agonists can be helpful, but evidence on gabapentinoids is conflicting. In the present review, the types of pain that need to be taken into account while planning pain management protocols and the wide range of analgesic options that have been assessed in laparoscopic surgery are critically assessed. Recommendations to the clinician will be made regarding how to manage acute pain and how to prevent persistent postoperative pain. It is important to identify patients at the highest risk for severe and prolonged post-operative pain, and to have a proactive strategy in place for these individuals.

BK channels in microglia are required for morphine-induced hyperalgesia

Although morphine is a gold standard medication, long-term opioid use is associated with serious side effects, such as morphine-induced hyperalgesia (MIH) and anti-nociceptive tolerance. Microglia-to-neuron signalling is critically involved in pain hypersensitivity. However, molecules that control microglial cellular state under chronic morphine treatment remain unknown. Here we show that the microglia-specific subtype of Ca²⁺-activated K⁺ (BK) channel is responsible for generation of MIH and anti-nociceptive tolerance. We find that, after chronic morphine administration, an increase in arachidonic acid levels through the μ-opioid receptors leads to the sole activation of microglial BK channels in the spinal cord. Silencing BK channel auxiliary β3 subunit significantly attenuates the generation of MIH and anti-nociceptive tolerance, and increases neurotransmission after chronic morphine administration. Therefore, microglia-specific BK channels contribute to the generation of MIH and anti-nociceptive tolerance.

Long-term use of opioids can lead to a paradoxical increase in pain sensitivity. Here, Hayashi et al. link activation of potassium channels on microglia with morphine-induced hyperalgesia and anti-nociceptive tolerance in mice.