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

PURPOSE OF REVIEW: While ketamine's analgesia has mostly been attributed to antagonism of N-methyl-D-aspartate receptors, evidence suggests multiple other pathways are involved in its antidepressant and possibly analgesic activity. These mechanisms and ketamine's role in the nociplastic pain paradigm are discussed. Animal studies demonstrating ketamine's neurotoxicity have unclear human translatability and findings from key rodent and human studies are presented. RECENT FINDINGS: Ketamine's metabolites, and (2R,6R)-hydroxynorketamine in particular, may play a greater role in its clinical activity than previously believed. The activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and the mammalian target of rapamycin by ketamine are mechanisms that are still being elucidated. Ketamine might work best in nociplastic pain, which involves altered pain processing. While much is known about ketamine, new studies will continue to define its role in clinical medicine. Evidence supporting ketamine's neurotoxicity in humans is lacking and should not impede future ketamine clinical trials.

Acute Amiodarone Pulmonary Toxicity.

Amiodarone is an effective antiarrhythmic that frequently is used during the perioperative period. Amiodarone possesses a significant adverse reaction profile. Amiodarone-induced pulmonary toxicity (AIPT) is among the most serious adverse effects and is a leading cause of death associated with its use. Despite significant advances in the understanding of AIPT, its etiology and pathogenesis remain incompletely understood. The diagnosis of AIPT is one of exclusion. The clinical manifestations of AIPT are categorized broadly as acute, subacute, and chronic. Acute AIPT is a rarer and more aggressive form of the disease, most often encountered in cardiothoracic surgery. Acute respiratory distress syndrome (ARDS) is the predominating pattern of amiodarone's acute pulmonary toxicity. The incidence, risk factors, pathogenesis, and diagnosis of acute AIPT are speculative. Early cardiothoracic literature investigating AIPT often attributed amiodarone to the development of postoperative ARDS. Subsequent studies have found no association between amiodarone and acute AIPT and ARDS development. As a drug that is frequently prescribed to a patient population deemed most at risk for this fatal disease, the conflicting evidence on acute AIPT needs further investigation and clarification.

Risk of Gastrointestinal Bleeding With Extended Use of Nonsteroidal Anti-Inflammatory Drug Analgesia After Joint Arthroplasty.

BACKGROUND: Chronic nonsteroidal anti-inflammatory drug (NSAID) use is associated with gastrointestinal bleeding via inhibition of endogenous mucosal protection and platelet aggregation. This study aimed to determine whether extended NSAIDs after joint arthroplasty is associated with increased risk of gastrointestinal bleeding. METHODS: This was a retrospective study examining 28,794 adults who underwent joint arthroplasty by one of 50 surgeons from 2016 to 2018. Episodes of gastrointestinal bleeding within 90 days postoperatively were identified prospectively. Postoperative medications were reported directly by patients with electronic questionnaires. The primary analysis was performed using binary logistic regression. RESULTS: A total of 74 (0.26%) episodes of gastrointestinal bleeding occurred within 90 days (median 8 days) postoperatively. Of 5086 patients with complete data included in the primary analysis, 59.6% had used NSAIDs with median duration of 2 weeks (interquartile range, 0-6 weeks). Patients with gastrointestinal bleeding were significantly older (71.3 vs 67.0 years), required longer hospitalizations (2.1 vs 1.5 days), and more commonly had a history of peptic ulcers (10.8% vs 0.9%). However, there was no positive association between NSAID use and gastrointestinal bleeding. In fact, the odds of gastrointestinal bleeding were lower in patients taking NSAIDs. Gastrointestinal bleeding was associated with anticoagulants, antiplatelet agents, and, to a lesser extent, aspirin. CONCLUSION: NSAIDs were not associated with gastrointestinal bleeding and may be prescribed safely for a majority of patients after joint arthroplasty. The greatest odds of gastrointestinal bleeding occurred in patients with peptic ulcer disease and those who received antiplatelet and anticoagulation agents. Increasing age and bilateral surgery were also associated with gastrointestinal bleeding. LEVEL OF EVIDENCE: Level III.

A Randomized Trial of Manual Phone Calls Versus Automated Text Messages for Peripheral Nerve Block Follow-Ups.

Mobile phone applications (apps) have been used for patient follow-up in the postoperative period, specifically to assess for complications and patient satisfaction. Few studies have evaluated their use in regional anesthesia. The objective of this study was to compare follow-up response rates using manual phone calls versus an automated patient outreach (APO) app for peripheral nerve block patients. We hypothesized that the response rate would be higher in the APO group. A mobile app, "JeffAnesthesia," was developed, which sends notifications to patients to answer survey questions in the app. We randomly assigned patients who received peripheral nerve blocks for postoperative pain to either a manual phone call or an APO app group, with follow-up in each category occurring between postoperative days (POD) 14-21 and 90-100. In total, 60 patients were assigned to the phone call group and 60 patients to the APO app group. Between POD 14-21, 9 (15%) patients were reached in the manual phone call arm, and 16 (26.7%) patients were reached in the APO arm (p = 0.117). At POD 90-100, follow-up was successful with 5 (8.2%) in the manual phone call group vs. 3 (5.0%) patients in the APO app group (p = 0.300). Overall response rate was poor, with comparable response rates between groups. The APO method may reduce time spent by anesthesia staff on follow-up calls, but our data do not suggest this method improves response rates significantly. Further studies are needed to better understand the reasons for the poor response rate and strategies for improvement.

An anesthesiologist-led inpatient buprenorphine initiative.

Hospitalized patients with opioid use disorder who present with acute pain are challenging to manage. Without any treatment, their mortality in the first 28 days after discharge is substantially increased. Unlike extended-release naltrexone, which requires a period of withdrawal, or methadone, which can cause prolonged corrected QT (QTc) and carries a higher risk of respiratory depression, buprenorphine provides potent analgesia with low respiratory risk. Hospitalization provides a unique opportunity for clinicians to perform buprenorphine induction, which could potentially reduce mortality without affecting analgesia. Our acute pain management service uses multimodal analgesia to maintain adequate analgesia and minimize withdrawal during buprenorphine induction in the hospital. With the assistance of narcotics addiction rehabilitation program specialists, we help link patients to outpatient buprenorphine providers and maximize the chance of successful recovery. The primary outcome of this study was to determine the percentage of patients who filled an outpatient buprenorphine prescription after undergoing inpatient induction.

Mepivacaine versus Bupivacaine Spinal Anesthesia for Early Postoperative Ambulation.

BACKGROUND: Early ambulation after total hip arthroplasty predicts early discharge. Spinal anesthesia is preferred by many practices but can delay ambulation, especially with bupivacaine. Mepivacaine, an intermediate-acting local anesthetic, could enable earlier ambulation than bupivacaine. This study was designed to test the hypothesis that patients who received mepivacaine would ambulate earlier than those who received hyperbaric or isobaric bupivacaine for primary total hip arthroplasty. METHODS: This randomized controlled trial included American Society of Anesthesiologists Physical Status I to III patients undergoing primary total hip arthroplasty. The patients were randomized 1:1:1 to 52.5 mg of mepivacaine, 11.25 mg of hyperbaric bupivacaine, or 12.5 mg of isobaric bupivacaine for spinal anesthesia. The primary outcome was ambulation between 3 and 3.5 h. Secondary outcomes included return of motor and sensory function, postoperative pain, opioid consumption, transient neurologic symptoms, urinary retention, intraoperative hypotension, intraoperative muscle tension, same-day discharge, length of stay, and 30-day readmissions. RESULTS: Of 154 patients, 50 received mepivacaine, 53 received hyperbaric bupivacaine, and 51 received isobaric bupivacaine. Patient characteristics were similar among groups. For ambulation at 3 to 3.5 h, 35 of 50 (70.0%) of patients met this endpoint in the mepivacaine group, followed by 20 of 53 (37.7%) in the hyperbaric bupivacaine group, and 9 of 51 (17.6%) in the isobaric bupivacaine group (P < 0.001). Return of motor function occurred earlier with mepivacaine. Pain and opioid consumption were higher for mepivacaine patients in the early postoperative period only. For ambulatory status, 23 of 50 (46.0%) of mepivacaine, 13 of 53 (24.5%) of hyperbaric bupivacaine, and 11 of 51 (21.5%) of isobaric bupivacaine patients had same-day discharge (P = 0.014). Length of stay was shortest in mepivacaine patients. There were no differences in transient neurologic symptoms, urinary retention, hypotension, muscle tension, or dizziness. CONCLUSIONS: Mepivacaine patients ambulated earlier and were more likely to be discharged the same day than both hyperbaric bupivacaine and isobaric bupivacaine patients. Mepivacaine could be beneficial for outpatient total hip arthroplasty candidates if spinal is the preferred anesthesia type.

Preoperative Aspirin Does Not Increase Transfusion or Reoperation in Isolated Valve Surgery.

OBJECTIVE: Preoperative aspirin has been studied in patients undergoing isolated coronary artery bypass graft surgery. However, there is a paucity of clinical data available evaluating perioperative aspirin in other cardiac surgical procedures. This study was designed to investigate the effects of aspirin on bleeding and transfusion in patients undergoing non-emergent, isolated, heart valve repair or replacement. DESIGN: Retrospective, cohort study. SETTING: Academic medical center. PARTICIPANTS: A total of 694 consecutive patients having non-emergent, isolated, valve repair or replacement surgery at an academic medical center were identified. INTERVENTIONS: Of the 488 patients who met inclusion criteria, 2 groups were defined based on their preoperative use of aspirin: those taking (n = 282), and those not taking (n = 206) aspirin within 5 days of surgery. MEASUREMENTS AND MAIN RESULTS: Binary logistic regression was used to examine relationships among demographic and clinical variables. No significant difference was found between the aspirin and non-aspirin groups with respect to the percentage receiving red blood cell (RBC) transfusion, mean RBC units transfused in those who required transfusion, massive transfusion of RBC, or amounts of fresh frozen plasma, cryoprecipitate, or platelets. Aspirin was not associated with an increase in the rate of re-exploration for bleeding (5.3% v 6.3%, p = 0.478). Major adverse cardiocerebral events (MACE), 30-day mortality, and 30-day readmission rates were not statistically different between the aspirin-and non-aspirin-treated groups. CONCLUSIONS: Preoperative aspirin therapy in elective, isolated, valve surgery did not result in an increase in transfusion or reoperation for bleeding and was not associated with reduced readmission rate, MACE, or 30-day mortality.

A Randomized Controlled Trial Comparing Adductor Canal Catheter and Intraarticular Catheter After Primary Total Knee Arthroplasty.

BACKGROUND: Multimodal analgesia, including peripheral nerve blocks, is recommended for postoperative pain relief after total knee arthroplasty (TKA). To date, no randomized controlled trial has compared the efficacy of adductor canal catheters (ACCs) and intraarticular catheters (IACs) in patients undergoing TKA. METHODS: A prospective, randomized control trial was performed in 96 primary, unilateral TKA patients comparing ACC with IAC between April, 2014 and August, 2015. Primary outcome measured was numeric pain scores before and after the first physical therapy session on postoperative day 1. Secondary outcomes were oxycodone consumption at 24 and 48 hours, total opioid consumption in morphine equivalents at 24 and 48 hours, active and passive range of motion during physical therapy, patient satisfaction, and length of stay. RESULTS: Results demonstrated that the ACC provided significantly better pain control on postoperative day 1 (P = .02) compared with the IAC. ACC trended toward significantly reduced oxycodone consumption at 24 hours postoperatively compared to IAC (25.64 vs 34.67 mg, P = .057). However, total opioid consumption was equivalent between the groups at 24 hours (32.24 vs 38.55 P = .185) or 48 hours (45.2 vs 52.0, P = .330). CONCLUSION: ACC should be considered as part of a multimodal pain regimen after primary, unilateral TKA and provides a better option for pain control after discharge.

(R,S)-Ketamine metabolites (R,S)-norketamine and (2S,6S)-hydroxynorketamine increase the mammalian target of rapamycin function.

BACKGROUND: Subanesthetic doses of (R,S)-ketamine are used in the treatment of neuropathic pain and depression. In the rat, the antidepressant effects of (R,S)-ketamine are associated with increased activity and function of mammalian target of rapamycin (mTOR); however, (R,S)-ketamine is extensively metabolized and the contribution of its metabolites to increased mTOR signaling is unknown. METHODS: Rats (n = 3 per time point) were given (R,S)-ketamine, (R,S)-norketamine, and (2S,6S)-hydroxynorketamine and their effect on the mTOR pathway determined after 20, 30, and 60 min. PC-12 pheochromocytoma cells (n = 3 per experiment) were treated with escalating concentrations of each compound and the impact on the mTOR pathway was determined. RESULTS: The phosphorylation of mTOR and its downstream targets was significantly increased in rat prefrontal cortex tissue by more than ~2.5-, ~25-, and ~2-fold, respectively, in response to a 60-min postadministration of (R,S)-ketamine, (R,S)-norketamine, and (2S,6S)-hydroxynorketamine (P < 0.05, ANOVA analysis). In PC-12 pheochromocytoma cells, the test compounds activated the mTOR pathway in a concentration-dependent manner, which resulted in a significantly higher expression of serine racemase with ~2-fold increases at 0.05 nM (2S,6S)-hydroxynorketamine, 10 nM (R,S)-norketamine, and 1,000 nM (R,S)-ketamine. The potency of the effect reflected antagonistic activity of the test compounds at the α7-nicotinic acetylcholine receptor. CONCLUSIONS: The data demonstrate that (R,S)-norketamine and (2S,6S)-hydroxynorketamine have potent pharmacological activity both in vitro and in vivo and contribute to the molecular effects produced by subanesthetic doses of (R,S)-ketamine. The results suggest that the determination of the mechanisms underlying the antidepressant and analgesic effects of (R,S)-ketamine requires a full study of the parent compound and its metabolites.

Randomized Controlled Trial of Enhanced Recovery After Surgery Protocols in Live Kidney Donors: ERASKT Study.

Background: Enhanced recovery after surgery (ERAS) pathways represent a comprehensive approach to optimizing perioperative management and reducing hospital stay and cost. In living donor kidney transplantation, key impediments to postoperative discharge include pain, and opioid associated complications such as nausea, vomiting, and the return of gastrointestinal function. Methods: In this randomized controlled trial, living kidney transplantation donors were assigned to either the ERAS or control group. The ERAS group patients received 15 preoperative, 17 intraoperative, 19 postoperative element intervention. The control group received standard care. The ERAS group received a multimodal opioid sparing pain management including an intraoperative transverse abdominis plane block. Our primary outcome measure was postoperative opioid consumption. The secondary outcome measures were postoperative pain scores, first oral intake, and hospital length of stay. Results: There were no significant differences in demographics between the 2 groups. The ERAS group had a statistically significant reduction in total postoperative opioid consumption calculated in intravenous morphine equivalents (24.2 ±â€…20.2 versus 71 ±â€…39.5 mg, P < 0.01). Postoperative pain scores were significantly lower (P < 0.001) from 1 h postoperatively to 48 h. Surgical time was 45 min shorter (P = 0.037). Intraoperative PlasmaLyte administration was lower (PlasmaLyte: 1444 ±â€…907 versus 2168 ±â€…1347 mL, P = 0.049). Time to tolerating regular diet was shorter by 2 h (P < 0.008), and length of hospital stay was decreased by 10.1 h. Conclusions: The ERAS group experienced superior postoperative analgesia and a shorter length of hospital stay compared with controls.

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.

Intravenous versus oral acetaminophen for pain and quality of recovery after ambulatory spine surgery: a randomized controlled trial.

INTRODUCTION: As ambulatory spine surgery increases, efficient recovery and discharge become essential. Multimodal analgesia is superior to opioids alone. Acetaminophen is a central component of multimodal protocols and both intravenous and oral forms are used. While some advantages for intravenous acetaminophen have been touted, prospective studies with patient-centered outcomes are lacking in ambulatory spine surgery. A substantial cost difference exists. We hypothesized that intravenous acetaminophen would be associated with fewer opioids and better recovery. METHODS: Patients undergoing ambulatory spine surgery were randomized to preoperative oral placebo and intraoperative intravenous acetaminophen or preoperative oral acetaminophen. All patients received general anesthesia and multimodal analgesia. The primary outcome was 24-hour opioid use in intravenous morphine milligram equivalents (MMEs), beginning with arrival to the postanesthesia care unit (PACU). Secondary outcomes included pain, Quality of Recovery (QoR)-15 scores, postoperative nausea and vomiting, recovery time, and correlations between pain catastrophizing, QoR-15, and pain. RESULTS: A total of 82 patients were included in final analyses. Demographics were similar between groups. For the primary outcome, the median 24-hour MMEs did not differ between groups (12.6 (4.0, 27.1) vs 12.0 (4.0, 29.5) mg, p=0.893). Postoperative pain ratings, PACU MMEs, QoR-15 scores, and recovery time showed no differences. Spearman's correlation showed a moderate negative correlation between postoperative opioid use and QoR-15. CONCLUSION: Intravenous acetaminophen was not superior to the oral form in ambulatory spine surgery patients. This does not support routine use of the more expensive intravenous form to improve recovery and accelerate discharge. TRIAL REGISTRATION NUMBER: NCT04574778.

In Vivo Study of the Inflammatory Tissue Response Surrounding a Novel Extended-Wear Kink-Resistant Insulin Infusion Set Prototype Compared With a Commercial Control Over Two Weeks of Wear Time.

BACKGROUND: Infusion set function remains the limiting factor of insulin pump therapy due to nonmetabolic complications. Here, we tested an investigational extended-wear infusion set prototype with a soft, angled, wire-reinforced cannula with three additional side holes, and compared failure mechanisms and tissue response with a commercial Teflon control. METHODS: A total of 48 Teflon and 48 prototype infusion sets were inserted subcutaneously every other day for 14 days in 12 swine and infused with dilute insulin. After two weeks, tissue around cannulas was excised, and occlusions, leaks, and kinks were determined. Tissue was processed and stained to assess the total area of inflammation (TAI) and the inflammatory layer thickness (ILT) around the cannulas. Data were analyzed using Fisher's exact, analysis of variance-general linear model, Kruskal-Wallis, and post hoc tests. RESULTS: On average, the TAI surrounding the investigational cannula was 52.6% smaller than around the commercial control. The ILT was 66.3% smaller around investigational cannulas. Kinks occurred in 2.1% (investigational) vs 32.4% (commercial) cannulas (P < .001). There was no difference in occlusion alarms and leaks onto skin. CONCLUSIONS: The data suggest that the infusion set prototype elicits less inflammation over an extended wear time and is resistant to kinking, compared with a commercial Teflon device. This is consistent with previously published data on the impact of cannula material/angle on the inflammatory tissue response. We highlight the following important aspects of infusion set design: (1) secure skin adhesion, (2) reliable cannula insertion, (3) automatic removal of the stylet, (4) cannula material/design that resists kinking, and (5) minimization of local tissue inflammation.

Stereoselective and regiospecific hydroxylation of ketamine and norketamine.

The objective was to determine the cytochrome P450s (CYPs) responsible for the stereoselective and regiospecific hydroxylation of ketamine [(R,S)-Ket] to diastereomeric hydroxyketamines, (2S,6S;2R,6R)-HK (5a) and (2S,6R;2R,6S)-HK (5b) and norketamine [(R,S)-norKet] to hydroxynorketamines, (2S,6S;2R,6R)-HNK (4a), (2S,6R;2R,6S)-HNK (4b), (2S,5S;2R,5R)-HNK (4c), (2S,4S;2R,4R)-HNK (4d), (2S,4R;2R,4S)-HNK (4e), (2S,5R;2R,5S)-HNK (4f). The enantiomers of Ket and norKet were incubated with characterized human liver microsomes (HLMs) and expressed CYPs. Metabolites were identified and quantified using LC/MS/MS and apparent kinetic constants estimated using single-site Michaelis-Menten, Hill or substrate inhibition equation. 5a was predominantly formed from (S)-Ket by CYP2A6 and N-demethylated to 4a by CYP2B6. 5b was formed from (R)- and (S)-Ket by CYP3A4/3A5 and N-demethylated to 4b by multiple enzymes. norKet incubation produced 4a, 4c and 4f and minor amounts of 4d and 4e. CYP2A6 and CYP2B6 were the major enzymes responsible for the formation of 4a, 4d and 4f, and CYP3A4/3A5 for the formation of 4e. The 4b metabolite was not detected in the norKet incubates. 5a and 4b were detected in plasma samples from patients receiving (R,S)-Ket, indicating that 5a and 5b are significant Ket metabolites. Large variations in HNK concentrations were observed suggesting that pharmacogenetics and/or metabolic drug interactions may play a role in therapeutic response.

Lidocaine infusions for refractory chronic migraine: a retrospective analysis.

INTRODUCTION: Patients with refractory chronic migraine have poor quality of life. Intravenous infusions are indicated to rapidly 'break the cycle' of pain. Lidocaine infusions may be effective but evidence is limited. METHODS: The records of 832 hospital admissions involving continuous multiday lidocaine infusions for migraine were reviewed. All patients met criteria for refractory chronic migraine. During hospitalization, patients received additional migraine medications including ketorolac, magnesium, dihydroergotamine, methylprednisolone, and neuroleptics. The primary outcome was change in headache pain from baseline to hospital discharge. Secondary outcomes measured at the post-discharge office visit (25-65 days after treatment) included headache pain and the number of headache days, and percentage of sustained responders. Percentage of acute responders, plasma lidocaine levels, and adverse drug effects were also determined. RESULTS: In total, 609 patient admissions met criteria. The mean age was 46±14 years; 81.1% were female. Median pain rating decreased from baseline of 7.0 (5.0-8.0) to 1.0 (0.0-3.0) at end of hospitalization (p<0.001); 87.8% of patients were acute responders. Average pain (N=261) remained below baseline at office visit 1 (5.5 (4.0-7.0); p<0.001). Forty-three percent of patients were sustained responders at 1 month. Headache days (N=266) decreased from 26.8±3.9 at baseline to 22.5±8.3 at the post-discharge office visit (p<0.001). Nausea and vomiting were the most common adverse drug effects and all were mild. CONCLUSION: Lidocaine infusions may be associated with short-term and medium-term pain relief in refractory chronic migraine. Prospective studies should confirm these results.

Enantioselective pharmacokinetics of (R)- and (S)-ketamine after a 5-day infusion in patients with complex regional pain syndrome.

INTRODUCTION: This study determined the pharmacokinetics and pharmacodynamics of (R)- and (S)-ketamine and (R)- and (S)-norketamine following a 5-day moderate dose, as a continuous (R,S)-ketamine infusion in complex regional pain syndrome (CRPS) patients. MATERIALS AND METHODS: Ketamine was titrated to 10-40 mg/h and maintained for 5 days. (R)- and (S)-Ketamine and (R)- and (S)-norketamine pharmacokinetic and pharmacodynamic studies were performed. Blood samples were obtained on Day 1 preinfusion, and at 60-90, 120-150, 180-210, and 240-300 min after the start of the infusion, on Days 2, 3, 4, 5, and on Day 5 at 60 min after the end of infusion. The plasma concentrations of (R)- and (S)-ketamine and (R)- and (S)-norketamine were determined using enantioselective liquid chromatography-mass spectrometry. RESULTS: Ketamine and norketamine levels stabilized 5 h after the start of the infusion. (R)-Ketamine clearance was significantly lower resulting in higher steady-state plasma concentrations than (S)-ketamine. The first-order elimination for (S)-norketamine was significantly greater than that of (R)-enantiomer. When comparing the pharmacokinetic parameters of the patients who responded to ketamine treatment with those who did not, no differences were observed in ketamine clearance and the first-order elimination of norketamine. CONCLUSION: The results indicate that (R)- and (S)-ketamine and (R)- and (S)-norketamine plasma concentrations do not explain the antinociceptive activity of the drug in patients suffering from CRPS.

Advances in translational neuropathic research: example of enantioselective pharmacokinetic-pharmacodynamic modeling of ketamine-induced pain relief in complex regional pain syndrome.

Historically, complex regional pain syndrome (CRPS) was poorly defined, which meant that scientists and clinicians faced much uncertainty in the study, diagnosis, and treatment of the syndrome. The problem could be attributed to a nonspecific diagnostic criteria, unknown pathophysiologic causes, and limited treatment options. The two forms of CRPS still are painful, debilitating disorders whose sufferers carry heavy emotional burdens. Current research has shown that CRPS I and CRPS II are distinctive processes, and the presence or absence of a partial nerve lesion distinguishes them apart. Ketamine has been the focus of various studies involving the treatment of CRPS; however, currently, there is incomplete data from evidence-based studies. The question as to why ketamine is effective in controlling the symptoms of a subset of patients with CRPS and not others remains to be answered. A possible explanation to this phenomenon is pharmacogenetic differences that may exist in different patient populations. This review summarizes important translational work recently published on the treatment of CRPS using ketamine.

Effect of difelikefalin, a selective kappa opioid receptor agonist, on respiratory depression: A randomized, double-blind, placebo-controlled trial.

Difelikefalin, a selective kappa opioid receptor agonist designed to limit central nervous system (CNS) penetration, is under development for the treatment of pruritus. Its hydrophilic, small-peptidic structure limits CNS entry, minimizing potential CNS-mediated adverse events (AEs). This study assessed the effect of difelikefalin on key relevant measures of respiratory depression in healthy volunteers. This single-center, randomized, double-blind, placebo-controlled, three-way crossover study enrolled healthy, nonsmoking volunteers. Subjects were randomized to 1 of 3 treatment sequences of difelikefalin (1.0 or 5.0 mcg/kg i.v.) or placebo on sequential days with an intervening 24 (±2) h washout period. The primary end points included incidence of increased end-tidal carbon dioxide (ETCO2 ) greater than or equal to 10 mm Hg versus baseline or a level greater than 50 mm Hg sustained greater than or equal to 30 seconds, and incidence of reduction in saturation of peripheral oxygen (SpO2 ) to less than 92% sustained greater than or equal to 30 seconds. Secondary end points included incidence of reduced respiratory rate and other safety assessments. Fifteen subjects were randomized and completed the study. No subject on placebo or difelikefalin met the increased ETCO2 or reduced SpO2 primary end point criteria for respiratory depression. All respiratory measures in each group remained near baseline values during 4-h postdose observations. No subject met the reduced respiratory rate criterion or experienced clinically significant changes in ETCO2 , SpO2 , or respiratory rate. The most commonly reported treatment-emergent AEs (TEAEs; ≥20% of subjects) were paresthesia, hypoesthesia, and somnolence in the difelikefalin arms. All TEAEs were mild and resolved without intervention. Difelikefalin 1.0 and 5.0 mcg/kg i.v. did not produce respiratory depression.