The variability in CYP3A4 activity determines the metabolic kinetic characteristics of ketamine

Ketamine is a psychotropic drug that can cause significant neurological symptoms and is closely linked to the activity of the CYP3A4 enzyme. This study aimed to examine the diversity of CYP3A4 activity affects the metabolism of ketamine, focusing on genetic variation and drug-induced inhibition. We used a baculovirus-insect cell expression system to prepare recombinant human CYP3A4 microsomes. Then, in vitro enzyme incubation systems were established and used UPLC-MS/MS to detect ketamine metabolite. In rats, we investigated the metabolism of ketamine and its metabolite in the presence of the CYP3A4 inhibitor voriconazole. Molecular docking was used to explore the molecular mechanism of inhibition. The results showed that the catalytic activity of CYP3A4.5, .17, .23, .28, and .29 significantly decreased compared to CYP3A4.1, with a minimum decrease of 3.13%. Meanwhile, the clearance rate of CYP3A4.2, .32, and .34 enhanced remarkably, ranging from 40.63% to 87.50%. Additionally, hepatic microsome incubation experiments revealed that the half-maximal inhibitory concentration (IC50) of voriconazole for ketamine in rat and human liver microsomes were 18.01 ± 1.20 µM and 14.34 ± 1.70 µM, respectively. When voriconazole and ketamine were co-administered, the blood exposure of ketamine and norketamine significantly increased in rats, as indicated by the area under the concentration-time curve (AUC) and maximum concentration (Cmax). The elimination half-life (t1/2Z) of these substances was also prolonged. Moreover, the clearance (CLz/F) of ketamine decreased, while the apparent volume of distribution (Vz/F) increased significantly. This might be attributed to the competition between voriconazole and ketamine for binding sites on the CYP3A4 enzyme. In conclusion, variations in CYP3A4 activity would result in the stratification of ketamine blood exposure.

Sustained antidepressant effect of ketamine through NMDAR trapping in the LHb

Ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist1, has revolutionized the treatment of depression because of its potent, rapid and sustained antidepressant effects2-4. Although the elimination half-life of ketamine is only 13 min in mice5, its antidepressant activities can last for at least 24 h6-9. This large discrepancy poses an interesting basic biological question and has strong clinical implications. Here we demonstrate that after a single systemic injection, ketamine continues to suppress burst firing and block NMDARs in the lateral habenula (LHb) for up to 24 h. This long inhibition of NMDARs is not due to endocytosis but depends on the use-dependent trapping of ketamine in NMDARs. The rate of untrapping is regulated by neural activity. Harnessing the dynamic equilibrium of ketamine-NMDAR interactions by activating the LHb and opening local NMDARs at different plasma ketamine concentrations, we were able to either shorten or prolong the antidepressant effects of ketamine in vivo. These results provide new insights into the causal mechanisms of the sustained antidepressant effects of ketamine. The ability to modulate the duration of ketamine action based on the biophysical properties of ketamine-NMDAR interactions opens up new opportunities for the therapeutic use of ketamine.

Ketamine for Pain Management: A Review of Literature and Clinical Application

Ketamine is a dissociative anesthetic used increasingly as analgesia for different manifestations of pain, including acute, chronic, cancer and perioperative pain as well as pain in the critically ill patient population. Its distinctive pharmacologic properties may provide benefits to individuals suffering from pain, including increased pain control and reduction in opioid consumption and tolerance. Despite wide variability in proposed dosing and method of administration when used for analgesia, it is important all clinicians be familiar with the pharmacodynamics of ketamine in order to appropriately anticipate its therapeutic and adverse effects.

Stereoselective ketamine effect on cardiac output: a population pharmacokinetic/pharmacodynamic modelling study in healthy volunteers

Background

Ketamine has cardiac excitatory side-effects. Currently, data on the effects of ketamine and metabolite concentrations on cardiac output are scarce. We therefore developed a pharmacodynamic model derived from data from a randomised clinical trial. The current study is part of a larger clinical study evaluating the potential mitigating effect of sodium nitroprusside on the psychedelic effects of ketamine.

Methods

Twenty healthy male subjects received escalating esketamine and racemic ketamine doses in combination with either placebo or sodium nitroprusside on four visits: (i) esketamine and placebo, (ii) esketamine and sodium nitroprusside, (iii) racemic ketamine and placebo, and (iv) racemic ketamine and sodium nitroprusside. During each visit, arterial blood samples were obtained and cardiac output was measured. Nonlinear mixed-effect modelling was used to analyse the cardiac output time-series data. Ketamine metabolites were added to the model in a sequential manner to evaluate the effects of metabolites.

Results

A model including an S-ketamine and S-norketamine effect best described the data. Ketamine increased cardiac output, whereas modelling revealed that S-norketamine decreased cardiac output. No significant effects were detected for R-ketamine, metabolites other than S-norketamine, or sodium nitroprusside on cardiac output.

Conclusions

S-Ketamine, but not R-ketamine, increased cardiac output in a dose-dependent manner. In contrast to S-ketamine, its metabolite S-norketamine reduced cardiac excitation in a dose-dependent manner.

Clinical trial registration

Dutch Cochrane Center 5359.

Esketamine: a glimmer of hope in treatment-resistant depression

The motive of this article is to review the pharmacological and clinical aspects of esketamine (ESK), an NMDA-receptor antagonist approved recently by the FDA for treatment-resistant depression (TRD). PubMed/Medline database was searched using keywords 'esketamine' and 'depression', 'S-ketamine' and 'depression', and 'NMDA antagonist' and 'depression'. Individual trials were searched from ClinicalTrials.gov. We included English-language articles evaluating pharmacokinetics and pharmacodynamics of intranasal (IN) esketamine, along with clinical trial data related to its efficacy and safety in patients diagnosed with TRD. Compared to placebo, IN esketamine causes significant and rapid improvement in depression. Dizziness, vertigo, headache, increase in blood pressure are some of its common adverse effects. With the growing number of patients of TRD, additional effective and safe treatment is the need of the hour. Esketamine appears to be an effective therapy when combined with oral antidepressants in patients with TRD. It is of special value due to the rapid onset of its action. Long-term clinical studies are, however, needed to ascertain its safety profile.

Assessment of Relationship of Ketamine Dose With Magnetic Resonance Spectroscopy of Glx and GABA Responses in Adults With Major Depression: A Randomized Clinical Trial

IMPORTANCE

A single subanesthetic dose of ketamine produces an antidepressant response in patients with major depressive disorder (MDD) within hours, but the mechanism of antidepressant effect is uncertain.

OBJECTIVE

To evaluate whether ketamine dose and brain glutamate and glutamine (Glx) and γ-aminobutyric acid (GABA) level responses to ketamine are related to antidepressant benefit and adverse effects.

DESIGN, SETTING, AND PARTICIPANTS

This randomized, parallel-group, triple-masked clinical trial included 38 physically healthy, psychotropic medication-free adult outpatients who were in a major depressive episode of MDD but not actively suicidal. The trial was conducted at Columbia University Medical Center. Data were collected from February 2012 to May 2015. Data analysis was conducted from January to March 2020.

INTERVENTION

Participants received 1 dose of placebo or ketamine (0.1, 0.2, 0.3, 0.4, or 0.5 mg/kg) intravenously during 40 minutes of a proton magnetic resonance spectroscopy scan that measured ventro-medial prefrontal cortex Glx and GABA levels in 13-minute data frames.

MAIN OUTCOMES AND MEASURES

Clinical improvement was measured using a 22-item version of the Hamilton Depression Rating Scale (HDRS-22) 24 hours after ketamine was administered. Ketamine and metabolite blood levels were measured after the scan.

RESULTS

A total of 38 individuals participated in the study, with a mean (SD) age of 38.6 (11.2) years, 23 (60.5%) women, and 25 (65.8%) White patients. Improvement in HDRS-22 score at 24 hours correlated positively with ketamine dose (t36 = 2.81; P = .008; slope estimate, 19.80 [95% CI, 5.49 to 34.11]) and blood level (t36 = 2.25; P = .03; slope estimate, 0.070 [95% CI, 0.007 to 0.133]). The lower the Glx response, the better the antidepressant response (t33 = -2.400; P = .02; slope estimate, -9.85 [95% CI, -18.2 to -1.50]). Although GABA levels correlated with Glx (t33 = 8.117; P < .001; slope estimate, 0.510 [95% CI, 0.382 to 0.638]), GABA response did not correlate with antidepressant effect. When both ketamine dose and Glx response were included in a mediation analysis model, ketamine dose was no longer associated with antidepressant effect, indicating that Glx response mediated the relationship. Adverse effects were related to blood levels in men only (t5 = 2.606; P = .048; estimated slope, 0.093 [95% CI, 0.001 to 0.186]), but Glx and GABA response were not related to adverse effects.

CONCLUSIONS AND RELEVANCE

In this study, intravenous ketamine dose and blood levels correlated positively with antidepressant response. The Glx response correlated inversely with ketamine dose and with antidepressant effect. Future studies are needed to determine whether the relationship between Glx level and antidepressant effect is due to glutamate or glutamine.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01558063.

Pharmacokinetics of an intravenous constant rate infusion of a morphine-lidocaine-ketamine combination in Holstein calves undergoing umbilical herniorrhaphy

OBJECTIVE

To describe the pharmacokinetics of morphine, lidocaine, and ketamine associated with IV administration of a constant rate infusion (CRI) of a morphine-lidocaine-ketamine (MLK) combination to calves undergoing umbilical herniorrhaphy.

ANIMALS

20 weaned Holstein calves with umbilical hernias.

PROCEDURES

Calves were randomly assigned to receive a CRI of an MLK solution (0.11 mL/kg/h; morphine, 4.8 μg/kg/h; lidocaine, 2.1 mg/kg/h; and ketamine, 0.42 mg/kg/h) for 24 hours (MLK group) or 2 doses of flunixin meglumine (1.1 mg/kg, IV, q 24 h) and a CRI of saline (0.9% NaCl) solution (0.11 mL/kg/h) for 24 hours (control group). For all calves, the CRI was begun after anesthesia induction. Blood samples were obtained immediately before and at predetermined times for 120 hours after initiation of the assigned treatment. Noncompartmental analysis was used to estimate pharmacokinetic parameters for the MLK group.

RESULTS

During the CRI, steady-state serum concentrations were achieved for lidocaine and ketamine, but not morphine. Mean terminal half-life was 4.1, 0.98, and 1.55 hours and area under the concentration-time curve was 41, 14,494, and 7,426 h•μg/mL for morphine, lidocaine, and ketamine, respectively. After the CRI, the mean serum drug concentration at steady state was 6.3, 616.7, and 328 ng/mL for morphine, lidocaine, and ketamine, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

During the CRI of the MLK solution, steady-state serum concentrations were achieved for lidocaine and ketamine, but not morphine, likely owing to the fairly long half-life of morphine. Kinetic analyses of MLK infusions in cattle are necessary to establish optimal dosing protocols.

Recovery of horses from general anesthesia after induction with propofol and ketamine versus midazolam and ketamine

OBJECTIVE To evaluate quality of recovery from general anesthesia in horses after induction with propofol and ketamine versus midazolam and ketamine. DESIGN Prospective randomized crossover study. ANIMALS 6 healthy adult horses. PROCEDURES Horses were premedicated with xylazine (1.0 mg/kg [0.45 mg/lb], IV), and general anesthesia was induced with midazolam (0.1 mg/kg [0.045 mg/lb], IV) or propofol (0.5 mg/kg [0.23 mg/lb], IV), followed by ketamine (3.0 mg/kg [1.36 mg/lb], IV). Horses were endotracheally intubated, and anesthesia was maintained with isoflurane. After 60 minutes, horses were given romifidine (0.02 mg/kg [0.009 mg/lb], IV) and allowed to recover unassisted. Times to first movement, sternal recumbency, and standing and the number of attempts to stand were recorded. Plasma concentrations of propofol or midazolam were measured following induction and immediately before recovery. Recovery quality was scored by 3 graders with a recovery rubric and a visual analog scale. RESULTS Number of attempts to stand was significantly lower when horses received propofol (median, 2; range, 1 to 3) than when they received midazolam (median, 7.5; range, 3 to 16). For both the recovery rubric and visual analog scale, recovery quality was significantly better when horses received propofol than when they received midazolam. Plasma drug concentration at recovery, as a percentage of the concentration at induction, was significantly lower when horses received propofol than when they received midazolam. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that for horses undergoing short (ie, 60 minutes) periods of general anesthesia, recovery quality may be better following induction with propofol and ketamine, compared with midazolam and ketamine.

Enantioselective capillary electrophoresis for pharmacokinetic analysis of methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in equines anesthetized with ketamine and isoflurane

An enantioselective assay for the determination of methadone and its main metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in equine plasma based on capillary electrophoresis with highly sulfated γ-cyclodextrin as chiral selector and electrokinetic analyte injection is described. The assay is based on liquid/liquid extraction of the analytes at alkaline pH from 0.1 mL plasma followed by electrokinetic sample injection of the analytes from the extract across a buffer plug without chiral selector. Separation occurs cationically at normal polarity in a pH 3 phosphate buffer containing 0.16% (w/v) of highly sulfated γ-cyclodextrin. The developed assay is precise (intra- and interday RSD < 4% and < 7%, respectively), is capable to determine enantiomer levels of methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in plasma down to 2.5 ng/mL, and was successfully applied to monitor enantiomer drug and metabolite levels in plasma of a pony that was anesthetized with racemic ketamine and isoflurane and received a bolus of racemic methadone and a bolus followed by constant rate infusion of racemic methadone. The data suggest that the assay is well suited for pharmacokinetic purposes.

The pharmacokinetics of ketamine following intramuscular injection to F344 rats

Ketamine is a glutamate N-methyl-D-aspartate receptor antagonist that is a rapid-acting dissociative anesthetic. It has been proposed as an adjuvant treatment along with other drugs (atropine, midazolam, pralidoxime) used in the current standard of care (SOC) for organophosphate and nerve agent exposures. Ketamine is a pharmaceutical agent that is readily available to most clinicians in emergency departments and possesses a broad therapeutic index with well-characterized effects in humans. The objective of this study was to determine the pharmacokinetic profile of ketamine and its active metabolite, norketamine, in F344 rats following single or repeated intramuscular administrations of subanesthetic levels (7.5 mg/kg or 30 mg/kg) of ketamine with or without the SOC. Following administration, plasma and brain tissues were collected and analyzed using a liquid chromatography-mass spectrometry method to quantitate ketamine and norketamine. Following sample analysis, the pharmacokinetics were determined using non-compartmental analysis. The addition of the current SOC had a minimal impact on the pharmacokinetics of ketamine following intramuscular administration and repeated dosing at 7.5 mg/kg every 90 minutes allows for sustained plasma concentrations above 100 ng/mL. The pharmacokinetics of ketamine with and without the SOC in rats supports further investigation of the efficacy of ketamine co-administration with the SOC following nerve agent exposure in animal models.

Effect of Ketamine on Cocaine-Induced Immunotoxicity in Rats

The abuse of cocaine (COC) with ketamine (KET) is currently popular among young drug abusers and has been associated with increased risk of human immunodeficiency virus (HIV) infection. The effect of subacute exposure to COC and KET alone and in combination on the immune system was assessed in adult male Sprague-Dawley (SD) rats. To simulate the route and mode of human exposure, rats were treated with COC alone (5 mg/kg, IV), KET alone (100 mg/kg, PO) or KET followed immediately by COC (same doses and routes of administration) once-a-day for 7 consecutive days. Rats were sacrified 30 minutes following the last treatment. Total circulating leukocyte and lymphocyte counts were decreased with relative neutrophilia, whereas immunoglobulin M (Ig M) antibody response to sheep erythrocytes (SRBCs) was increased in animals treated with COC. Moreover, treatment with COC alone increased serum interleukin-10 (IL-10) concentration; however, it did not affect serum interferon gamma (INF-γ) concentration. Spleen histology showed hyperplasia of white pulp whereas thymus gland demonstrated mild cortical degeneration. On the other hand, KET treatment did not produce any significant change of any of these parameters. However, when coadministered with COC, significant reduction of bodyweight, spleen/bodyweight, and thymus/bodyweight ratios with degeneration of splenic white pulp and thymic cortex occurred. Moreover, the primary immunoglobulin response to SRBC and serum IL-10 concentration were decreased without significant change in serum IFN-γ or circulating leukocytic counts. COC caused a significant increase in serum corticosterone concentration that KET effectively prevented. On the other hand, a significant increase in plasma and tissue concentrations of norcocaine (NC) resulted following KET and COC administration in combination. Daily SKF-525A pretreatment at a dose of 30 mg/kg, IP, for 7 days 1 hour prior to KET and COC in combination effectively reversed the effects of this combination on body weight, organ/bodyweight ratios, histopathology, and serum Ig M and IL-10 concentrations without affecting leukocytic counts. On the other hand, SKF-525A pretreatment did not change the immunomodulatory effects of COC compared to non-pretreated animals. The results suggest that COC-induced immunomodulation most likely occurred through neuroendocrinal mechanisms. On the other hand, enhanced oxidative metabolism of COC in the presence of KET-induced immunosuppression.

Single-dose infusion ketamine and non-ketamine N-methyl-d-aspartate receptor antagonists for unipolar and bipolar depression: a meta-analysis of efficacy, safety and time trajectories

BACKGROUND

Ketamine and non-ketamine N-methyl-d-aspartate receptor antagonists (NMDAR antagonists) recently demonstrated antidepressant efficacy for the treatment of refractory depression, but effect sizes, trajectories and possible class effects are unclear.

METHOD

We searched PubMed/PsycINFO/Web of Science/clinicaltrials.gov until 25 August 2015. Parallel-group or cross-over randomized controlled trials (RCTs) comparing single intravenous infusion of ketamine or a non-ketamine NMDAR antagonist v. placebo/pseudo-placebo in patients with major depressive disorder (MDD) and/or bipolar depression (BD) were included in the analyses. Hedges' g and risk ratios and their 95% confidence intervals (CIs) were calculated using a random-effects model. The primary outcome was depressive symptom change. Secondary outcomes included response, remission, all-cause discontinuation and adverse effects.

RESULTS

A total of 14 RCTs (nine ketamine studies: n = 234; five non-ketamine NMDAR antagonist studies: n = 354; MDD = 554, BD = 34), lasting 10.0 ± 8.8 days, were meta-analysed. Ketamine reduced depression significantly more than placebo/pseudo-placebo beginning at 40 min, peaking at day 1 (Hedges' g = -1.00, 95% CI -1.28 to -0.73, p < 0.001), and loosing superiority by days 10-12. Non-ketamine NMDAR antagonists were superior to placebo only on days 5-8 (Hedges' g = -0.37, 95% CI -0.66 to -0.09, p = 0.01). Compared with placebo/pseudo-placebo, ketamine led to significantly greater response (40 min to day 7) and remission (80 min to days 3-5). Non-ketamine NMDAR antagonists achieved greater response at day 2 and days 3-5. All-cause discontinuation was similar between ketamine (p = 0.34) or non-ketamine NMDAR antagonists (p = 0.94) and placebo. Although some adverse effects were more common with ketamine/NMDAR antagonists than placebo, these were transient and clinically insignificant.

CONCLUSIONS

A single infusion of ketamine, but less so of non-ketamine NMDAR antagonists, has ultra-rapid efficacy for MDD and BD, lasting for up to 1 week. Development of easy-to-administer, repeatedly given NMDAR antagonists without risk of brain toxicity is of critical importance.

Chronic Administration of the N-Methyl-D-Aspartate Receptor Antagonist Ketamine Improves Rett Syndrome Phenotype

BACKGROUND

Rett syndrome (RTT) is a neurological disorder caused by mutation of the X-linked MECP2 gene, which results in the progressive disruption of excitatory and inhibitory neuronal circuits. To date, there is no effective treatment available for the disorder. Studies conducted in RTT patients and murine models have shown altered expression of N-methyl-D-aspartate receptors (NMDARs). Genetic deletion of the NMDAR subunit, GluN2A, in mice lacking Mecp2 is sufficient to prevent RTT phenotypes, including regression of vision.

METHODS

We performed a systematic, randomized preclinical trial of chronic administration of low-dose (8 mg/kg, intraperitoneal) ketamine, an NMDAR antagonist, starting either early in development or at the onset of RTT phenotype in Mecp2-null mice.

RESULTS

Daily exposure to ketamine ameliorated RTT symptoms and extended the life span of treated Mecp2-null mice without adverse side effects. Furthermore, significant improvement was observed in cortical processing and connectivity, which were fully restored to a wild-type level, particularly when treatment was started at the onset of regression.

CONCLUSIONS

Our findings provide strong evidence that targeting NMDA receptors can be a safe and effective treatment for RTT.

Effects of ketamine and lidocaine in combination on the sevoflurane minimum alveolar concentration in alpacas

This study investigated the effects of ketamine and lidocaine in combination on the minimum alveolar concentration of sevoflurane (MACSEVO) in alpacas. Eight healthy, intact male, adult alpacas were studied on 2 separate occasions. Anesthesia was induced with SEVO, and baseline MAC (MACB) determination began 45 min after induction. After MACB determination, alpacas were randomly given either an intravenous (IV) loading dose (LD) and infusion of saline or a loading dose [ketamine = 0.5 mg/kg body weight (BW); lidocaine = 2 mg/kg BW] and an infusion of ketamine (25 μg/kg BW per minute) in combination with lidocaine (50 μg/kg BW per minute), and MACSEVO was re-determined (MACT). Quality of recovery, time-to-extubation, and time-to-standing, were also evaluated. Mean MACB was 1.88% ± 0.13% and 1.89% ± 0.14% for the saline and ketamine + lidocaine groups, respectively. Ketamine and lidocaine administration decreased (P < 0.05) MACB by 57% and mean MACT was 0.83% ± 0.10%. Saline administration did not change MACB. Time to determine MACB and MACT was not significantly different between the treatments. The quality of recovery, time-to-extubation, and time-to-standing, were not different between groups. The infusion of ketamine combined with lidocaine significantly decreased MACSEVO by 57% and did not adversely affect time-to-standing or quality of recovery.

The absolute bioavailability of racemic ketamine from a novel sublingual formulation

AIM

The principal study objective was to investigate the pharmacokinetic characteristics of a new sublingual ketamine wafer and to establish its absolute bioavailability and local tolerability.

METHODS

The study was of open label, two way randomized crossover design in eight healthy male volunteers. Each participant received either a single 10 mg intravenous dose as a constant rate 30 min infusion or a 25mg sublingual dose of ketamine wafer in two treatment periods with a 7 day wash out. Pharmacokinetic blood sampling and local tolerability and safety assessments were carried out during 24 h following both dosing occasions. Plasma concentrations were analyzed by non-compartmental methods and local tolerability was assessed using modified Likert scales.

RESULTS

The median (90% CI lower, upper limit) absolute bioavailability of sublingual ketamine was 29% (27, 31%). The first quantifiable plasma ketamine concentration was observed within 5 min for all eight participants for both routes of administration and the median (min–max) time of the peak plasma concentration was 0.75 h (0.25–1.0 h) after sublingual administration. The ketamine wafer had very good local tolerability.

CONCLUSION

Sublingual administration of the ketamine wafer resulted in rapid absorption. The ketamine wafer has comparable bioavailability with other oral transmucosal formulations of ketamine but with markedly reduced inter-subject variability, warranting further evaluation as an analgesic adjunct.

Urine metabolomics in rats after administration of ketamine

In this study, we developed a urine metabonomic method, based on gas chromatography–mass spectrometry (GC-MS), to evaluate the effect of ketamine on rats. Pattern recognition analysis, including both principal component analysis and partial least squares discriminate analysis revealed that ketamine (50 mg/kg) induced metabolic perturbations. Compared with the control group, at day 7, the level of alanine, butanoic acid, glutamine, butanedioic, trimethylsiloxy, L-aspartic acid, D-glucose, cholesterol, acetamide, and oleic acid of the ketamine group was increased, while the level of 2,3,4-trihydroxybutyric acid, benzeneacetic acid, threitol, ribitol, xylitol, and glycine decreased. At day 14, the level of alanine, ethanedioic acid, L-proline, glycerol, tetradecanoic acid, l-serine, l-phenylalanine, L-aspartic acid, d-glucose, cholesterol, heptadecanoic acid, and acetamide in rat urine of the ketamine group was increased, while the 2,3,4-trihydroxybutyric acid, benzeneacetic acid, d-ribose, threitol, ribitol, glycine, pyrazine, and oleic acid levels decreased. Our results indicate that metabonomic methods based on GC-MS may be useful to elucidate ketamine abuse, through the exploration of biomarkers.

Influence of prior determination of baseline minimum alveolar concentration (MAC) of isoflurane on the effect of ketamine on MAC in dogs

The objective of this study was to determine if prior measurement of the minimum alveolar concentration (MAC) of isoflurane influences the effect of ketamine on the MAC of isoflurane in dogs. Eight mixed-breed dogs were studied on 2 occasions. Anesthesia was induced and maintained using isoflurane. In group 1 the effect of ketamine on isoflurane MAC was determined after initially finding the baseline isoflurane MAC. In group 2, the effect of ketamine on isoflurane MAC was determined without previous measure of the baseline isoflurane MAC. In both groups, MAC was determined again 30 min after stopping the CRI of ketamine. Plasma ketamine concentrations were measured during MAC determinations. In group 1, baseline MAC (mean ± SD: 1.18 ± 0.14%) was decreased by ketamine (0.88 ± 0.14%; P < 0.05). The MAC after stopping ketamine was similar (1.09 ± 0.16%) to baseline MAC and higher than with ketamine (P < 0.05). In group 2, the MAC with ketamine (0.79 ± 0.11%) was also increased after stopping ketamine (1.10 ± 0.17%; P < 0.05). The MAC values with ketamine were different between groups (P < 0.05). Ketamine plasma concentrations were similar between groups during the events of MAC determination. The MAC of isoflurane during the CRI of ketamine yielded different results when methods of same day (group-1) versus separate days (group-2) are used, despite similar plasma ketamine concentrations with both methods. However, because the magnitude of this difference was less than 10%, either method of determining MAC is deemed acceptable for research purposes.

[Perioperative intensive-medical investigations regarding compatibility of the ketamine-azaperone-general anesthesia in pigs]

was observed. Perioperatively oxygen saturation was persistently high and mean arterial pressure was steady, too. An additional Ketamine administration caused a short tachycardia during operation. After restoration of total mobility, respiratory and heart rate stayed within the reference ranges again. All EMG values in between those caused by pain stimuli were significantly below the borderline of a muscle activity in conformity with a clinically visible complete muscle relaxation. Cortisol increased simultaneously with Ketamine and Azaperone before operation, but it remained at this level until the end of the determinations, parallel to the course of Norketamine, close to the maximum before anesthesia. The complex intensive-medical monitoring confirms that under real surgical conditions the counter-regulatory effects of both drugs equalize the respective cardiovascular and respiratory side effects. It is concluded also that the increase of cortisol is likely to be more a side effect of Ketamine/Norketamine than the expression of distress by surgical interventions or by wake-up reactions, and that an intoxication by additional Ketamine dosage or motoric disorders (i.e., catalepsis) can be excluded as undesired side effects of both drugs.

Ex vivo percutaneous absorption of ketamine, bupivacaine, diclofenac, gabapentin, orphenadrine, and pentoxifylline: comparison of versatile cream vs. reference cream

This ex vivo human percutaneous absorption study evaluated a set of six model drugs (ketamine hydrochloride, bupivacaine hydrochloride, diclofenac sodium, gabapentin, orphenadrine citrate, pentoxifylline) from two popular formulations for topically applied compounding preparations. The compounded preparations used in this study were Versatile cream and a reference cream. Each formulation was applied to human trunk skin mounted on Franz Diffusion Cells, 50 mg/chamber (or 28.2 mg/cm2). Serial dermal receiver solutions were collected for 48 hours. Analysis of the resultant data supports the concept that the Versatile base formulation provides improved characteristics relative to the reference base. This is of key importance where the patient does not show clinical improvement when a conventional topical delivery vehicle is used in the formulation. From the results, it is reasonable to anticipate that, relative to the reference formulation, the Versatile formulation provides enhanced transdermal delivery of some analgesic medications.

Pharmacokinetics of ketamine and xylazine in young and old Sprague-Dawley rats

To compare the pharmacokinetics of coadministered intraperitoneal ketamine and xylazine in young (8 to 10 wk; n = 6) and old rats (2 to 2.4 y; n = 6), blood samples obtained at 15 and 30 min and 1, 2, and 4 h after drug administration were analyzed by HPLC-tandem mass spectrometry. In both groups, the withdrawal reflex was absent during anesthesia and was present at 1.1 (± 0.2) and 2.6 (± 0.7) h after drug administration in young and old rats, respectively, with the first voluntary movement at 1.5 ± 0.2 and 4.9 ± 1.0 h. Drug availability of ketamine and xylazine was 6.0 and 6.7 times greater, respectively, in old than young rats. The rate constant of elimination of both drugs was greatly decreased and the elimination half-life was significantly greater in old compared with young rats. In conclusion, age and associated factors affect the availability of ketamine and xylazine when coadministered to attain clinical anesthesia, changing the pharmacokinetics of these drugs and prolonging anesthesia duration and recovery times with aging. Compared with their young counterparts, aged rats required much higher doses to attain a similar level of anesthesia. Finally, the long half-life of both ketamine and xylazine, when coadministered to old rats, may be a factor in research protocols because residual plasma concentrations could still be present for as long as 3 and 5 d, respectively, after administration.

[Effect of sub-anaesthetic doses of ketamine in the postoperative period in a patient with uncontrolled depression]

Recent studies indicate that the intravenous infusion of ketamine hydrochloride (an N-methyl-D-aspartate receptor antagonist) leads to a rapid reduction in depressive symptoms. A 42 year-old woman with breast cancer and major depression resistant to medical treatment received a 90 minute intravenous infusion of 0.3 mg/kg ketamine for 5 consecutive days. A significant reduction from 22 to 13 (-41%) was observed in the symptoms assessed using the Hamilton scale, with the effect maintained for 14 days. The possible therapeutic mechanism is discussed.

Quantitative study of controlled substance bedside wasting, disposal and evaluation of potential ecologic effects

Drugs in wastewater arise from many sources. For health care, these include excretion and direct disposal (bedside wasting). The present study reports on the dispensing and wasting of 15 controlled substances (CS) at two health care facilities in Albany, NY over a nearly two year period. The study considered measures of ecotoxicity, drug metabolism, excretion and disposal of these CS. Potential alternatives to flushing of CS into wastewaters from healthcare facilities are discussed. Drug medication and waste collection records (12,345) included: numbers of drugs dispensed, returned and wasted. Overall, 8528 g of 15 CS were wasted. Three (midazolam, acetaminophen-codeine and fentanyl) accounted for 87.5% of the total wasted. Wasting varied by hospital, 14 CS at the academic medical center hospital and 8 at the surgical care center were wasted. Liquids were more frequently wasted than tablets or pills. Some combination drugs (acetaminophen (APAP)-codeine) were frequently (50% of drug dispensed) wasted while others were less wasted (APAP-hydrocodone-6.3%; APAP-oxycodone-1.3%). The 8 CS judged more hazardous to aquatic life were: APAP-codeine, APAP-hydrocodone, APAP-oxycodone, alprazolam, diazepam, fentanyl, midazolam, and testosterone. Ketamine, morphine, oxycodone and zolpidem were of lesser acute toxicity based on available LC50 values. These CS might provide a therapeutically equivalent alternative to the more environmentally harmful drugs. In health care facilities, professionals dispose of CS by bedside wasting into water or other receptacles. This can be avoided by returning CS to the hospital's pharmacy department, thence to a licensed distributor. Study of this process of drug wasting can identify opportunities for process improvements. We found 3 CS (APAP-codeine, midazolam and testosterone) where ½ to 1/3 of the drug was wasted and 5 others with 30 to 13% wasted. Knowledge of the adverse impacts from the release of highly toxic drugs into the environment might influence CS selection and disposal alternatives.

[Toxicokinetics of ketamine in rabbits]

OBJECTIVE

To investigate the toxicokinetics profiles of ketamine and its main metabolite norketamine in rabbits.

METHODS

The rabbits were administered orally the hydrochloride of ketamine with a dose of 0.15 g/kg. The serum and urine samples were collected before administration and at different time points after drug administration. The concentrations of ketamine and norketamine were determined by GC-NPD and GC-MS. Compartment model and toxicokinetics parameters were simulated and calculated by WinNorLin program. Changes of important vital signs of rabbits were recorded during the experiment.

RESULTS

The mean serum concentration-time profile of ketamine and norketamine were fitted to a two-compartment open model with first order kinetics. The kinetic equation of ketamine and norketamine were p(t) = 121.760 e(-0.0025t) +0.980 e(-0.002t) +4.579 e(-0.021 t) and p(t) = 640.919 e(-0.03 t) +1.023 e(-0.001 t) +9.784 e (-0.031 t), respectively. The peak time and the peak concentration of ketamine in serum were (40.950 +/- 12.098) min and (9.015 +/- 1.344) microg/mL, respectively. The elimination half-time of ketamine in rabbits was (430.370 +/- 28.436) min. The serum and urine showed a middle relation in concentrations of ketamine during 30-240 min after drug administration. After oral administration ketamine to rabbits, the toxic symptom on the rabbits occurred at 30 min and disappeared after 120 min.

CONCLUSION

The toxicokinetics parameters and kinetic equation of ketamine and norketamine in rabbits may provide the theoretical basis for forensic identification of reasonable specimen collection and inferring the time of oral administration ketamine from the ketamine concentration in serum.

Pharmacodynamic profiles of ketamine (R)- and (S)- with 5-day inpatient infusion for the treatment of complex regional pain syndrome

BACKGROUND

Ketamine might be effective in blocking central sensitization of pain transmission neurons through its effect on NMDA receptors in refractory Complex Regional Pain Syndrome (CRPS) patients. At higher doses, ketamine infusions can be associated with significant risks; outpatient therapy requires return visits for a 10-day period with variable efficacy and duration.

OBJECTIVE

This study determined the efficacy of a 5-day moderate dose, continuous racemic ketamine infusion. The pharmacodynamic responses to racemic ketamine and norketamine were examined.

DESIGN

Observational study

METHODS

In this study, ketamine was titrated from 10-40 mg/hour in 16 CRPS patients, and maintained for 5 days. Pain was assessed daily. Ketamine and norketamine concentrations were obtained on Day 1 before starting the infusion; at 60 to 90 minutes, 120 to 150 minutes, 180 to 210 minutes, and 240 to 300 minutes after the initiation of the infusion on Days 2, 3, 4, and 5; and on Day 5 at 60 minutes after the conclusion of the infusion. The plasma concentrations of (R)-ketamine, (S)-ketamine, (R)-norketamine and (S)-norketamine were determined using an enantioselective liquid chromatography - mass spectrometry method.

RESULTS

Ketamine and norketamine infusion rates stabilized 5 hours after the start of the infusion. The subjects showed no evidence of significant tachycardia, arterial oxygen desaturation, or hallucinatory responses. Subjects generally experienced minimal pain relief on day one followed by significant relief by day 3. Mean pain scores decreased from the 8-9 to 3-5 ranges; however, the analgesic response to ketamine infusion was not uniform. On Day 5, there was little or no change in the pain measure assessed as the worst pain experienced over the last 24 hours in 37% of the subjects. (R)- and (S)-ketamine concentrations peaked at 240-300 min. (R)- and (S)-norketamine concentrations were lower and peaked on Day 2 of the infusion, as opposed to Day 1 for (R)- and (S)-ketamine. Significant pain relief was achieved by the second day of infusion and correlated with the maximum plasma levels of ketamine and norketamine. Pain relief continued to significantly improve over the 5-day infusion at concentrations of 200-225 ng/mL for (R)- and (S)-ketamine, and 90-120 ng/mL for (R)- and (S)-norketamine.

CONCLUSIONS

A 5-day ketamine infusion for the treatment of severe CRPS provided significant (p <0.05) pain relief by Day 3 compared to baseline. The pain relief experienced on Day 2 of the infusion continued to improve over the 5-day infusion period and correlated with the maximum plasma levels of ketamine and norketamine. We speculate that downstream metabolites of ketamine and norketamine might be playing a role in its therapeutic efficacy.

Stereoselective pharmacokinetics of ketamine and norketamine after racemic ketamine or S-ketamine administration in Shetland ponies sedated with xylazine

The pharmacokinetics of ketamine and norketamine enantiomers after administration of intravenous (IV) racemic ketamine (R-/S-ketamine; 2.2 mg/kg) or S-ketamine (1.1 mg/kg) to five ponies sedated with IV xylazine (1.1mg/kg) were compared. The time intervals to assume sternal and standing positions were recorded. Arterial blood samples were collected before and 1, 2, 4, 6, 8 and 13 min after ketamine administration. Arterial blood gases were evaluated 5 min after ketamine injection. Plasma concentrations of ketamine and norketamine enantiomers were determined by capillary electrophoresis and were evaluated by non-linear least square regression analysis applying a monocompartmental model. The first-order elimination rate constant was significantly higher and elimination half-life and mean residence time were lower for S-ketamine after S-ketamine compared to R-/S-ketamine administration. The maximum concentration of S-norketamine was higher after S-ketamine administration. Time to standing position was significantly diminished after S-ketamine compared to R-/S-ketamine. Blood gases showed low-degree hypoxaemia and hypercarbia.

Relationship between ketamine-induced psychotic symptoms and NMDA receptor occupancy: a [(123)I]CNS-1261 SPET study

RATIONALE

Ketamine induces effects resembling both positive and negative psychotic symptoms of schizophrenia. These are thought to arise through its action as an uncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor.

OBJECTIVES

We used [(123)I]CNS-1261 to study ketamine binding to NMDA receptors in healthy human controls in vivo and its relationship to positive and negative psychotic symptom induction.

MATERIALS AND METHODS

Ten healthy controls underwent two single-photon emission tomography scans with [(123)I]CNS-1261. On each occasion, they received a bolus infusion of either ketamine or saline. The Brief Psychiatric Rating Scale (BPRS) was administered at the end of each scan. Predefined regions of interest were used to estimate change in volume of distribution of [(123)I]CNS-1261 following ketamine administration. Two normalised-to-cortex binding indices were also used in order to study effects of ketamine on NMDA receptor availability by region, after correction for global and nonspecific effects.

RESULTS

Ketamine-induced reduction in [(123)I]CNS-1261 volume of distribution in all regions showed the strongest correlation with BPRS negative subscale (p < 0.01). With the normalised-to-cortex measures, NMDA receptor binding in middle inferior frontal cortex showed a significant correlation with BPRS negative subscale (BI1 r = 0.88, BI2 r = 95.9, p < 0.001).

CONCLUSIONS

[(123)I]CNS-1261 binding was modulated by ketamine, a drug known to compete for the same site on the NMDA receptor in vitro. Ketamine may induce negative symptoms through direct inhibition of the NMDA receptor, and positive symptoms may arise through a different neurochemical pathway.

Comparison of subcutaneous and intramuscular ketamine-medetomidine with and without reversal by atipamezole in Dutch belted rabbits (Oryctolagus cuniculus)

Forty male Dutch belted rabbits (Oryctolagus cuniculus) enrolled in a minimally invasive pharmacokinetics study were used to compare the efficacy of an anesthetic combination delivered through 2 injection routes. Rabbits were randomly assigned to 4 groups (n = 10/group) to determine the sedative and physiologic effects of ketamine (25 mg/kg)-medetomidine (0.5 mg/kg) given either intramuscularly (IM) or subcutaneously (SC). Palpebral, pedal, ear pinch, and righting reflexes, as well as cardiopulmonary parameters (heart rate, respiratory rate, and arterial blood oxyhemoglobin saturation), were recorded every 5 min. In addition, the reversal effects of an intravenous dose of atipamezole (1 mg/kg), an alpha 2 adrenoreceptor antagonist, were assessed by comparing the return of the righting reflex in rabbits given the reversal agent with those that recovered spontaneously. Compared with the IM route, SC ketamine-medetomidine effectively induced chemical restraint with less than a 2-min difference in onset of anesthesia and markedly less resistance (for example, fl inching, kicking, and so forth) during the injection. In all groups, the anesthetic regimen, regardless of the route of administration, provided an adequate level of anesthesia. Reversal with atipamezole improved arterial hemoglobin oxygen saturation for both the SC and IM groups; however, an enhanced rate of recovery from anesthesia was clinically apparent only for animals given the combination by the IM route.

Modeling the norketamine metabolite in children and the implications for analgesia

BACKGROUND

Norketamine, a metabolite of ketamine, is an analgesic with a potency one-third that of ketamine. The aim of this study was to describe norketamine pharmacokinetics in children in order to predict time-concentration profiles for this metabolite after racemic ketamine single dose and infusion administration. The possible analgesic potential resulting from norketamine concentration may then be predicted using simulation.

METHODS

Ketamine and norketamine data were available from two sources: (i) children presenting for procedural sedation in an emergency department given ketamine 1-1.5 mg.kg(-1) IV as a bolus dose; and (ii) a literature search of those studies describing ketamine and norketamine time-concentration profiles after either IV or IM single-dose ketamine in adults and children. A population pharmacokinetic analysis was undertaken using nonlinear mixed effects models (NONMEM). A two-compartment (central, peripheral) linear disposition model was used to fit the parent drug. An additional metabolite compartment was linked to the central compartment by series of intermediate compartments to account for norketamine delayed formation. Norketamine volume of distribution was fixed equivalent to central volume. Simulation was used to predict norketamine time-concentration profiles in children given either ketamine as an i.v. bolus 2 mg.kg(-1) or as an analgesic infusion 0.2 mg.kg(-1).h(-1) for 24 h.

RESULTS

The analysis comprised 621 observations from 70 subjects. There were 57 children (age 8.3, sd: 3.5 years, range: 1.5-14; weight 32.5, sd: 15.6 kg, range: 10.8-74.8) and 13 adults. Population parameter estimates for the parent drug, standardized to a 70 kg person using allometric models were central volume (V1) 22 (BSV 89.6%) l.70 kg(-1), peripheral volume of distribution (V2) 129 (30.9%) l.70 kg(-1), clearance other than that metabolized to norketamine (CLother) 47.8 (37.7%) l.h(-1).70 kg(-1) and intercompartment clearance (Q) 216 (54.5%) l.h(-1).70 kg(-1). The norketamine formation clearance (CL2M) was 12.4 (127%) l.h(-1).70 kg(-1), elimination clearance (CLM) was 13.5 (145%) l.h(-1).70 kg(-1), and the rate constant for intermediate compartments was 26.5 (59.1%) h(-1).

CONCLUSIONS

Ketamine has a longer elimination half-life (2.1 h) than norketamine (1.13 h). Simulation suggested that norketamine contributes to analgesia for 4 h after 2 mg.kg(-1) i.v. bolus, provided the assumption that a norketamine concentration above 0.1 mg.l(-1) contributes analgesia is true. Similarly, the norketamine metabolite may contribute to analgesia for 1.5 h after low-dose infusion (0.2 mg.kg(-1).h(-1)) cessation.

Ketamine disposition in children presenting for procedural sedation and analgesia in a children's emergency department

BACKGROUND

The aim of this study was to describe ketamine pharmacokinetics in children to simulate time-concentration profiles to predict duration of concentrations associated with anesthesia, arousal and analgesia.

METHODS

Children presenting for painful procedures in the Emergency Dept were given ketamine 1-1.5 mgxkg(-1) i.v. Blood was assayed for ketamine on 3-6 occasions (median 3) over the subsequent 14-152 min (median 28.5). A population pharmacokinetic analysis was undertaken by using nonlinear mixed effects models (NONMEM). Simulation was used to predict time-concentration profiles in this cohort

RESULTS

There were 188 observations from 54 children (age 8.3 sd 3.5 years, weight 32.5 sd 15.6 kg). A two-compartment (central, peripheral) linear disposition model fitted data better than a one-compartment model. Population parameter estimates and their between subject variability (BSV), standardized to a 70-kg person using allometric models, were central volume (V1) 38.7 (BSV 64%) l.70 kg(-1), peripheral volume of distribution (V2) 102 (51.7%) l.70 kg(-1), clearance (CL) 90 (38.1%) l.h(-1) 70 kg(-1) and intercompartment clearance (Q) 215 (19%) l.h(-1) 70 kg(-1). At 10 min half of the children given 1 mgxkg(-1) will have a serum concentration below 0.75 mgxl(-1). This is a concentration associated with 'awakening' in adults. However, almost all the children will still have a serum concentration above 0.1 mgxl(-1), a level associated with analgesia in adults.

CONCLUSIONS

Ketamine 1 mgxkg(-1) i.v. provides satisfactory serum concentrations for children undergoing sedation for painful procedures of <5-min duration and produces concentrations associated with analgesic effect for more than 10 min. Clearance increases with decreasing age in children. The relationship between serum concentration and effect is poorly defined in children.

Ketamine-induced neuronal cell death in the perinatal rhesus monkey

Ketamine is widely used as a pediatric anesthetic. Studies in developing rodents have indicated that ketamine-induced anesthesia results in brain cell death. Additional studies are needed to determine if ketamine anesthesia results in brain cell death in the nonhuman primate and if so, to begin to define the stage of development and the duration of ketamine anesthesia necessary to produce brain cell death. Rhesus monkeys (N = 3 for each treatment and control group) at three stages of development (122 days of gestation and 5 and 35 postnatal days [PNDs]) were administered ketamine intravenously for 24 h to maintain a surgical anesthetic plane, followed by a 6-h withdrawal period. Similar studies were performed in PND 5 animals with 3 h of ketamine anesthesia. Animals were subsequently perfused and brain tissue processed for analyses. Ketamine (24-h infusion) produced a significant increase in the number of caspase 3-, Fluoro-Jade C- and silver stain-positive cells in the cortex of gestational and PND 5 animals but not in PND 35 animals. Electron microscopy indicated typical nuclear condensation and fragmentation in some neuronal cells, and cell body swelling was observed in others indicating that ketamine-induced neuronal cell death is most likely both apoptotic and necrotic in nature. Ketamine increased N-methyl-D-aspartate (NMDA) receptor NR1 subunit messenger RNA in the frontal cortex where enhanced cell death was apparent. Earlier developmental stages (122 days of gestation and 5 PNDs) appear more sensitive to ketamine-induced neuronal cell death than later in development (35 PNDs). However, a shorter duration of ketamine anesthesia (3 h) did not result in neuronal cell death in the 5-day-old monkey.

Improved postoperative analgesia with coadministration of preoperative epidural ketamine and midazolam

STUDY OBJECTIVE

To assess postoperative pain regulation and pharmacokinetic effects of preoperative administration of ketamine and midazolam.

DESIGN

Double-blind, randomized clinical study.

SETTING

University hospital.

PATIENTS

46 ASA physical status I and II patients (age, 26-58 yrs), scheduled for gastrectomy.

INTERVENTIONS

Patients were randomly assigned to three treatment groups: a preoperative epidural injection of 10 mL (1) ketamine (0.5 mg/kg) solution (Ket group); (2) ketamine (0.5 mg/kg) plus midazolam (0.05 mg/kg) solution (KM group); or (3) normal saline solution (Ctr group).

MEASUREMENTS

Analgesic effects were evaluated by Visual Analog Scale (VAS) pain scores at rest, time to first request for analgesic (TFA), and morphine consumption during the initial postoperative time of 48 hours. Plasma concentration of ketamine in the Ket group and the KM group was measured by high-performance liquid chromatography, and the elimination half-life of ketamine was calculated.

MAIN RESULTS

Compared with the Ctr group, the Ket and KM groups had lower VAS pain scores, longer TFA, and lower morphine consumption. The KM group had the longest TFA and the lowest morphine consumption of the three groups. The KM group also had higher plasma concentrations of ketamine 90 to 240 minutes after injection, and a longer elimination half-life of ketamine, than did the Ket group.

CONCLUSIONS

Preoperative epidural coadministration of a low dose of ketamine with midazolam is more effective in relieving postoperative pain than using ketamine alone. In addition, epidural midazolam prolongs the elimination of ketamine.

Pharmacokinetics of intramuscular ketamine in young ostriches premedicated with romifidine

Ketamine is a short-acting dissociative anaesthetic for chemical restraint and surgical anaesthesia in domestic and non-domestic animals. The present study was designed to determine the pharmacokinetics of a single dose of ketamine (10 mg/kg) after intramuscular (i.m.) administration to young ostriches premedicated with romifidine. Ketamine was rapidly absorbed after i.m. administration. Maximal ketamine concentration (C(max)) of 2.93 +/- 0.61 microg/ml was reached at 12.5 +/- 2.50 min and thereafter ketamine concentrations decreased rapidly. The elimination half-life (t(1/2 z)) obtained was 62.37 +/- 17.37 min and mean residence time (MRT) was 77.33 +/- 19.12 min. The area under the curve (AUC) was 114.19 +/- 15.76 microg x min/ml.

The effects of ketamine on the minimum alveolar concentration of isoflurane in cats

OBJECTIVES

To determine the minimum alveolar concentration (MAC) of isoflurane during the infusion of ketamine.

STUDY DESIGN

Prospective, experimental trial.

ANIMALS

Twelve adult spayed female cats weighing 5.1 +/- 0.9 kg.

METHODS

Six cats were anesthetized with isoflurane in oxygen, intubated and attached to a circle-breathing system with mechanical ventilation. Catheters were placed in a peripheral vein for the infusion of fluids and ketamine, and the jugular vein for blood sampling for the measurement of ketamine concentrations. An arterial catheter was placed to allow blood pressure measurement and sampling for the measurement of PaCO2, PaO2 and pH. PaCO2 was maintained between 29 and 41 mmHg (3.9-5.5 kPa) and body temperature was kept between 37.8 and 39.3 degrees C. Following instrumentation, the MAC of isoflurane was determined in triplicate using a tail clamp method. A loading dose (2 mg kg(-1) over 5 minutes) and an infusion (23 microg kg(-1) minute(-1)) of ketamine was started and MAC was redetermined starting 30 minutes later. Two further loading doses and infusions were used, 2 mg kg(-1) and 6 mg kg(-1) with 46 and 115 microg kg(-1) minute(-1), respectively and MAC was redetermined. Cardiopulmonary measurements were taken before application of the noxious stimulus. The second group of six cats was used for the measurement of steady state plasma ketamine concentrations at each of the three infusion rates used in the initial study and the appropriate MAC value determined from the first study.

RESULTS

The MAC decreased by 45 +/- 17%, 63 +/- 18%, and 75 +/- 17% at the infusion rates of 23, 46, and 115 microg kg(-1) minute(-1). These infusion rates corresponded to ketamine plasma concentrations of 1.75 +/- 0.21, 2.69 +/- 0.40, and 5.36 +/- 1.19 microg mL(-1). Arterial blood pressure and heart rate increased significantly with ketamine. Recovery was protracted.

CONCLUSIONS AND CLINICAL RELEVANCE

The MAC of isoflurane was significantly decreased by an infusion of ketamine and this was accompanied by an increase in heart rate and blood pressure. Because of the prolonged recovery in our cats, further work needs to be performed before using this in patients.

Pharmacodynamic effects and pharmacokinetic profile of a long-term continuous rate infusion of racemic ketamine in healthy conscious horses

Ketamine (KET) possesses analgesic and anti-inflammatory activity at sub-anesthetic doses, suggesting a benefit of long-term KET treatment in horses suffering from pain, inflammatory tissue injury and/or endotoxemia. However, data describing the pharmacodynamic effects and safety of constant rate infusion (CRI) of KET and its pharmacokinetic profile in nonpremedicated horses are missing. Therefore, we administered to six healthy horses a CRI of 1.5 mg/kg/h KET over 320 min following initial drug loading. Cardiopulmonary parameters, arterial blood gases, glucose, lactate, cortisol, insulin, nonesterified fatty acids, and muscle enzyme levels were measured, as were plasma concentrations of KET and its metabolites using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Levels of sedation and muscle tension were scored. Respiration and heart rate significantly increased during the early infusion phase. Glucose and cortisol significantly varied both during and after infusion. During CRI all horses scored 0 on sedation. All but one horse scored 0 on muscle tension, with one mare scoring 1. All other parameters remained within or close to physiological limits without significant changes from pre-CRI values. The mean plasma concentration of KET during the 1.5 mg/kg/h KET CRI was 235 ng/mL. The decline of its plasma concentration-time curve of both KET and norketamine (NKET) following the CRI was described by a two-compartmental model. The metabolic cascade of KET was NKET, hydroxynorketamine (HNK), and 5,6-dehydronorketamine (DHNK). The KET median elimination half-lives (t1/2alpha and t1/2beta) were 2.3 and 67.4 min, respectively. The area under the KET plasma concentration-time curve (AUC), elimination was 76.0 microg.min/mL. Volumes of C1 and C2 were 0.24 and 0.79 L/kg, respectively. It was concluded that a KET CRI of 1.5 mg/kg/h can safely be administered to healthy conscious horses for at least 6 h, although a slight modification of the initial infusion rate regimen may be indicated. Furthermore, in the horse KET undergoes very rapid biotransformation to NKET and HNK and DHNK were the major terminal metabolites.

Antinociceptive effects, metabolism and disposition of ketamine in ponies under target-controlled drug infusion

Ketamine is widely used as an anesthetic in a variety of drug combinations in human and veterinary medicine. Recently, it gained new interest for use in long-term pain therapy administered in sub-anesthetic doses in humans and animals. The purpose of this study was to develop a physiologically based pharmacokinetic (PBPk) model for ketamine in ponies and to investigate the effect of low-dose ketamine infusion on the amplitude and the duration of the nociceptive withdrawal reflex (NWR). A target-controlled infusion (TCI) of ketamine with a target plasma level of 1 microg/ml S-ketamine over 120 min under isoflurane anesthesia was performed in Shetland ponies. A quantitative electromyographic assessment of the NWR was done before, during and after the TCI. Plasma levels of R-/S-ketamine and R-/S-norketamine were determined by enantioselective capillary electrophoresis. These data and two additional data sets from bolus studies were used to build a PBPk model for ketamine in ponies. The peak-to-peak amplitude and the duration of the NWR decreased significantly during TCI and returned slowly toward baseline values after the end of TCI. The PBPk model provides reliable prediction of plasma and tissue levels of R- and S-ketamine and R- and S-norketamine. Furthermore, biotransformation of ketamine takes place in the liver and in the lung via first-pass metabolism. Plasma concentrations of S-norketamine were higher compared to R-norketamine during TCI at all time points. Analysis of the data suggested identical biotransformation rates from the parent compounds to the principle metabolites (R- and S-norketamine) but different downstream metabolism to further metabolites. The PBPk model can provide predictions of R- and S-ketamine and norketamine concentrations in other clinical settings (e.g. horses).

Xylazine, Ketamine and their Combination for Lumbar Epidural Analgesia in Water Buffalo Calves (Bubalus bubalis)

The study was conducted to evaluate the effects of xylazine individually (0.05 mg/kg), ketamine individually (2.5 mg/kg), and a combination of xylazine and ketamine (0.05 mg/kg and 2.5 mg/kg) after lumbar epidural administration in water buffalo calves. Fifteen non-descript, male water buffalo calves of 6-8 months of age weighing between 55 and 75 kg were randomly placed in three groups (groups A, B and C). The agents were administered at the first lumbar epidural space. Clinico-physiological parameters, such as analgesia, ataxia, sedation, salivation, heart rate, respiratory rate and rectal temperature were studied. Other haematological and biochemical parameters monitored were haemoglobin, packed cell volume, total leukocyte count, plasma glucose, cortisol, protein albumin, globulin, blood urea nitrogen (BUN), creatinine, alanineamino transferase (ALT), sodium, potassium and chloride. The onset of analgesia (mean +/- SEM) was faster in group C (3.2 +/- 0.20 min) compared with that of group B (4.6 +/- 0.22 min) and group A (34.0 +/- 1.86 min). Analgesia of the thorax, flank, inguinal region, hind limbs, perineum and tail was complete in group C, but mild to moderate in groups A and B. Ataxia was severe in group C and mild in groups A and B. Mild to deep sedation was produced by groups A and C animals. Group B animals failed to produce sedation. Longer duration and greater depth of analgesia was produced in animals of group C. Heart rate, respiratory rate and rectal temperature decreased in groups A and C. The haematological parameters decreased in all the groups. The biochemical parameters like glucose, cortisol, BUN, creatinine, and ALT increased in all the animals. However, total proteins and albumin decreased in the three groups. The plasma electrolytes sodium, potassium and chloride did not show any significant change. The results of this study indicated a possible synergistic analgesic interaction between epidurally administered xylazine and ketamine, without causing any marked systemic effects in water buffalo calves.

Urinary excretion rates of ketamine and norketamine following therapeutic ketamine administration: method and detection window considerations

Ketamine is widely used in veterinary medicine. Its medical application in humans is limited to children because in adults it induces severe psychedelic episodes. In recent years, teenagers have abused ketamine as a recreational and "club drug" because of its hallucinogenic and stimulant effects. Ketamine is also misused as a "date-rape" drug (to induce amnesia in unsuspecting victims). Sensitive gas chromatography-mass spectrometry-negative chemical ionization (GC-MS-NCI) and liquid chromatography-mass spectrometry-atmospheric pressure chemical ionization (LC-MS-APCI) methods were applied for the simultaneous quantification of ketamine and its major metabolite, norketamine, in urine. Urine samples were collected from hospitalized children who had received ketamine as an anesthetic. Individual urine samples were collected up to 16 days after drug administration. Using the GC-MS-NCI method, ketamine was detected in the urine of the children from only the day of drug administration up to 2 days after drug administration. Its concentrations ranged from 29 to 1410 ng/mL. Norketamine (measured in concentrations of 0.1-1442 ng/mL) was detected up to 14 days. Using the LC-MS-APCI method, norketamine was detected up to 6 days after drug administration, ranging in concentrations of 2-1559 ng/mL, while ketamine was detected up to 11 days (2-1204 ng/mL). In the urine taken from one child, ketamine was not detected through the entire 16-day period using both methods. The detection window for the analytes is highly dependent on the method used for determination and varies between individuals.

Evaluation of ketamine systemic absorption from topical preparations. Short Communication

The aim of this study was to evaluate the systemic absorption of the topically administered ketamine using different vehicles and additives, in order to develop a transdermal therapeutic system (TTS) of this drug. After the application of different ketamine preparations (1% in hydrogel, o/w cream, or organogel) the ketamine appeared in the blood. The lowest level could be observed with o/w cream, while the highest concentration was achieved by means of the hydrogel system, however this difference was not significant. Further studies are going to be performed with higher drug concentrations for the characterization of the differences in the pharmacodynamics of the drug with different vehicles and to evaluate the correlation between the in vitro and in vivo absorption.

Pharmacokinetics and clinical effects of a subanesthetic continuous rate infusion of ketamine in awake horses

OBJECTIVE

To determine the pharmacokinetics and clinical effects of a subanesthetic, continuous rate infusion of ketamine administered to healthy awake horses.

ANIMALS

8 adult horses.

PROCEDURES

Ketamine hydrochloride was administered to 2 horses, in a pilot study, at rates ranging from 0.4 to 1.6 mg/kg/h for 6 hours to determine an appropriate dose that did not cause adverse effects. Ketamine was then administered to 6 horses for a total of 12 hours (3 horses at 0.4 mg/kg/h for 6 hours followed by 0.8 mg/kg/h for 6 hours and 3 horses at 0.8 mg/kg/h for 6 hours followed by 0.4 mg/kg/h for 6 hours). Concentration of ketamine in plasma, heart rate, respiratory rate, blood pressure, physical activity, and analgesia were measured prior to, during, and following infusion. Analgesic testing was performed with a modified hoof tester applied at a measured force to the withers and radius.

RESULTS

No signs of excitement and no significant changes in the measured physiologic variables during infusion rates of 0.4 and 0.8 mg of ketamine/kg/h were found. At 6 hours following infusions, heart rate and mean arterial pressure were decreased, compared with preinfusion measurements. An analgesic effect could not be demonstrated during or after infusion. Pharmacokinetic variables for 0.4 and 0.8 mg/kg/h infusions were not significantly different.

CONCLUSIONS AND CLINICAL RELEVANCE

Ketamine can be administered to awake horses at 0.4 or 0.8 mg/kg/h without adverse behavioral effects. The observed pharmacokinetic values are different than those reported for single-dose IV bolus administration of this drug.

Behavioral effects of ketamine and toxic interactions with psychostimulants

Background

The anesthetic drug ketamine (KT) has been reported to be an abused drug and fatal cases have been observed in polydrug users. In the present study, considering the possibility of KT-enhanced toxic effects of other drugs, and KT-induced promotion of an overdose without making the subject aware of the danger due to the attenuation of several painful subjective symptoms, the intraperitoneal (i.p.) KT-induced alterations in behaviors and toxic interactions with popular co-abused drugs, the psychostimulants cocaine (COC) and methamphetamine (MA), were examined in ICR mice.

Results

A single dose of KT caused hyperlocomotion in a low (30 mg/kg, i.p.) dose group, and hypolocomotion followed by hyperlocomotion in a high (100 mg/kg, i.p.) dose group. However, no behavioral alterations derived from enhanced stress-related depression or anxiety were observed in the forced swimming or the elevated plus-maze test. A single non-fatal dose of COC (30 mg/kg, i.p.) or MA (4 mg/kg, i.p.) caused hyperlocomotion, stress-related depression in swimming behaviors in the forced swimming test, and anxiety-related behavioral changes (preference for closed arms) in the elevated plus-maze test. For the COC (30 mg/kg) or MA (4 mg/kg) groups of mice simultaneously co-treated with KT, the psychostimulant-induced hyperlocomotion was suppressed by the high dose KT, and the psychostimulant-induced behavioral alterations in the above tests were reversed by both low and high doses of KT. For the toxic dose COC (70 mg/kg, i.p.)- or MA (15 mg/kg, i.p.)-only group, mortality and severe seizures were observed in some animals. In the toxic dose psychostimulant-KT groups, KT attenuated the severity of seizures dose-dependently. Nevertheless, the mortality rate was significantly increased by co-treatment with the high dose KT.

Conclusion

Our results demonstrated that, in spite of the absence of stress-related depressive and anxiety-related behavioral alterations following a single dose of KT treatment, and in spite of the KT-induced anticonvulsant effects and attenuation of stress- and anxiety-related behaviors caused by COC or MA, the lethal effects of these psychostimulants were increased by KT.

Ketamine displaces the novel NMDA receptor SPET probe [123I]CNS-1261 in humans in vivo

[(123)I]CNS-1261 [N-(1-naphthyl)-N'-(3-iodophenyl)-N-methylguanidine] is a high-affinity SPET ligand with selectivity for the intra-channel PCP/ketamine/MK-801 site of the N-methyl-d-aspartate (NMDA) receptor. This study evaluated the effects of ketamine (a specific competitor for the intra-channel PCP/ketamine/MK-801 site) on [(123)I]CNS-1261 binding to NMDA receptors in vivo. Ten healthy volunteers underwent 2 bolus-plus-infusion [(123)I]CNS-1261 scans, one during placebo and the other during a ketamine challenge. Ketamine administration led to a significant decrease in [(123)I]CNS-1261 V(T) in most of the brain regions examined (P<.05). [(123)I]CNS-1261 appears to be a specific ligand in vivo for the intra-channel PCP/ketamine/MK-801 NMDA binding site.

Pharmacokinetic and Pharmacodynamic Characteristics of??Medications Used for Moderate Sedation

The ability to deliver safe and effective moderate sedation is crucial to the ability to perform invasive procedures. Sedative drugs should have a quick onset of action, provide rapid and clear-headed recovery, and be easy to administer and monitor. A number of drugs have been demonstrated to provide effective sedation for outpatient procedures but since each agent has its own limitations, a thorough knowledge of the available drugs is required to choose the appropriate drug, dose and/or combination regimen for individual patients. Midazolam, propofol, ketamine and sevoflurane are the most frequently used agents, and all have a quick onset of action and rapid recovery. The primary drawback of midazolam is the potential for accumulation of the drug, which can result in prolonged sedation and a hangover effect. The anaesthetics propofol and sevoflurane have recently been used for sedation in procedures of short duration. Although effective, these agents require monitored anaesthesia care. Ketamine is an effective agent, particularly in children, but there is concern regarding emergence reactions. AQUAVAN injection (fospropofol disodium), a phosphorylated prodrug of propofol, is an investigational agent possessing a unique and distinct pharmacokinetic and pharmacodynamic profile. Compared with propofol emulsion, AQUAVAN is associated with a slightly longer time to peak effect and a more prolonged pharmacodynamic effect. Advances in the delivery of sedation, including the development of new sedative agents, have the potential to further improve the provision of moderate sedation for a variety of invasive procedures.

Effect of intravenous administration of ketamine on the minimum alveolar concentration of isoflurane in anesthetized dogs

OBJECTIVE

To determine the effect of 6 plasma ketamine concentrations on the minimum alveolar concentration (MAC) of isoflurane in dogs.

ANIMALS

6 dogs.

PROCEDURE

In experiment 1, the MAC of isoflurane was measured in each dog and the pharmacokinetics of ketamine were determined in isoflurane-anesthetized dogs after IV administration of a bolus (3 mg/kg) of ketamine. In experiment 2, the same dogs were anesthetized with isoflurane in oxygen. A target-controlled IV infusion device was used to administer ketamine and to achieve plasma ketamine concentrations of 0.5, 1, 2, 5, 8, and 11 microg/mL by use of parameters obtained from experiment 1. The MAC of isoflurane was determined at each plasma ketamine concentration, and blood samples were collected for ketamine and norketamine concentration determination.

RESULTS

Actual mean +/- SD plasma ketamine concentrations were 1.07 +/- 0.42 microg/mL, 1.62 +/- 0.98 microg/mL, 3.32 +/- 0.59 microg/mL, 4.92 +/- 2.64 microg/mL, 13.03 +/- 10.49 microg/mL, and 22.80 +/- 25.56 microg/mL for target plasma concentrations of 0.5, 1, 2, 5, 8, and 11 microg/mL, respectively. At these plasma concentrations, isoflurane MAC was reduced by 10.89% to 39.48%, 26.77% to 43.74%, 25.24% to 84.89%, 44.34% to 78.16%, 69.62% to 92.31%, and 71.97% to 95.42%, respectively. The reduction in isoflurane MAC was significant, and the response had a linear and quadratic component. Salivation, regurgitation, mydriasis, increased body temperature, and spontaneous movements were some of the adverse effects associated with the high plasma ketamine concentrations.

CONCLUSIONS AND CLINICAL RELEVANCE

Ketamine appears to have a potential role for balanced anesthesia in dogs.

Pharmacokinetics of ketamine and its metabolite, norketamine, after intravenous administration of a bolus of ketamine to isoflurane-anesthetized dogs

OBJECTIVE

To determine the pharmacokinetics of ketamine and norketamine in isoflurane-anesthetized dogs. Animals-6 dogs.

PROCEDURE

The minimum alveolar concentration (MAC) of isoflurane was determined in each dog. Isoflurane concentration was then set at 0.75 times the individual's MAC, and ketamine (3 mg/kg) was administered IV. Blood samples were collected at various times following ketamine administration. Blood was immediately centrifuged, and the plasma separated and frozen until analyzed. Ketamine and norketamine concentrations were measured in the plasma samples by use of liquid chromatography-mass spectrometry. Ketamine concentration-time data were fitted to compartment models. Norketamine concentration-time data were examined by use of noncompartmental analysis.

RESULTS

The MAC of isoflurane was 1.43 +/- 0.18% (mean +/- SD). A 2-compartment model best described the disposition of ketamine. The apparent volume of distribution of the central compartment, the apparent volume of distribution at steady state, and the clearance were 371.3 +/- 162 mL/kg, 4,060.3 +/- 2,405.7 mL/kg, and 58.2 +/- 17.3 mL/min/kg, respectively. Norketamine rapidly appeared in plasma following ketamine administration and had a terminal half-life of 63.6 +/- 23.9 minutes. A large variability in plasma concentrations, and therefore pharmacokinetic parameters, was observed among dogs for ketamine and norketamine.

CONCLUSIONS AND CLINICAL RELEVANCE

In isofluraneanesthetized dogs, a high variability in the disposition of ketamine appears to exist among individuals. The disposition of ketamine may be difficult to predict in clinical patients.

A streamlined method to predict hepatic clearance using human liver microsomes in the presence of human plasma

INTRODUCTION

Human liver microsomal incubations are often used to predict the metabolic lability of new chemical entities. The clearance values are scaled-up from in vitro data and mathematically corrected for plasma protein binding, or in some cases the free fraction ratio of plasma to microsomes, using well-established scaling methods such as the well-stirred model. This can be time consuming for multiple compounds since it requires separate experiments to determine in vitro lability, and free fraction.

METHODS

We attempted to streamline clearance predictions by combining experiments into one. Firstly, we combined the free fraction experiments into one free fraction ratio by measuring the partitioning of compound between plasma and microsomes, and by applying this experimental ratio to clearance predictions found that it performed at least as well as free fractions determined separately. We also incubated compounds with plasma added to the incubation mixture and compared the predicted clearances to values determined using traditional mathematical protein binding corrections.

RESULTS

Consistently, incubations with added plasma resulted in CL predictions closer to literature values than incubations only mathematically corrected for protein binding. For example, incorporating plasma into a ketamine incubation resulted in a CL value of 15.1 mL/min/kg, compared with a value of 10.2 using mathematical binding corrections. The literature value is 16.4 mL/min/kg.

DISCUSSION

This work characterizes this new method and compares it to the traditional microsomal incubation method using several literature compounds, and suggests that streamlining the methods may generate quality data faster and with less resource investment.

The use and assessment of ketamine–medetomidine–butorphanol combinations for field anaesthesia in wild European badgers (Meles meles)

OBJECTIVE

To evaluate the effectiveness of four ketamine-based anaesthetics in badgers using a quantitative anaesthesia assessment technique.

STUDY DESIGN

Prospective randomized 'blinded' experimental trial.

METHODS

The quality of induction, of anaesthesia (at 5-minute intervals) and of recovery were assessed in 93 badgers, given either one of three ketamine (K)-medetomidine (M)-butorphanol (B) combinations: group A - M K B at 20/40/80 microg kg(-1); group B - M K B at 20/40/60 microg kg(-1); and group C - M K B at 20/60/40 microg kg(-1), or ketamine (K) alone at 2 mg kg(-1) (group D). The assessor was ignorant of the combination administered. Physiological variables (heart and respiratory rates and rectal temperature) were measured at 5-minute intervals during anaesthesia. Gingival mucus membrane colour was also recorded.

RESULTS

Induction to anaesthesia was most rapid with ketamine (2 mg kg(-1)) although induction quality did not differ between techniques. Ketamine used alone gave the poorest score for anaesthesia quality. Heart rate (HR) and scores for gingival mucus membrane colour were higher in animals anaesthetized with ketamine alone. Rectal temperature did not differ significantly between the techniques at any time during anaesthesia. Ketamine used alone produced the poorest quality of recovery.

CONCLUSION AND CLINICAL RELEVANCE

The M-K-B combinations investigated overcame several side effects associated with ketamine anaesthesia, but at the expense of more variable induction times, lower HRs, and poorer mucus membrane coloration.

Characterization of the stereoselective biotransformation of ketamine to norketaminevia determination of their enantiomers in equine plasma by capillary electrophoresis

A robust CE method for the simultaneous determination of the enantiomers of ketamine and norketamine in equine plasma is described. It is based upon liquid-liquid extraction of ketamine and norketamine at alkaline pH from 1 mL plasma followed by analysis of the reconstituted extract by CE in the presence of a pH 2.5 Tris-phosphate buffer containing 10 mg/mL highly sulfated beta-CD as chiral selector. Enantiomer plasma levels between 0.04 and 2.5 microg/mL are shown to provide linear calibration graphs. Intraday and interday precisions evaluated from peak area ratios (n = 5) at the lowest calibrator concentration are < 8 and < 14%, respectively. The LOD for all enantiomers is 0.01 microg/mL. After i.v. bolus administration of 2.2 mg/kg racemic ketamine, the assay is demonstrated to provide reliable data for plasma samples of ponies under isoflurane anesthesia, of ponies premedicated with xylazine, and of one horse that received romifidine, L-methadone, guaifenisine, and isoflurane. In animals not premedicated with xylazine, the ketamine N-demethylation is demonstrated to be enantioselective. The concentrations of the two ketamine enantiomers in plasma are equal whereas S-norketamine is found in a larger amount than R-norketamine. In the group receiving xylazine, data obtained do not reveal this stereoselectivity.