Neuropathological findings after continuous intrathecal administration of S(+)-ketamine for the management of neuropathic cancer pain

Microglia Promote Inhibitory Synapse Phagocytosis in the Spinal Cord Dorsal Horn and Modulate Pain-Like Behaviors in a Murine Cancer-Induced Bone Pain Model

BACKGROUND

The microglial activation has been implicated in cancer-induced bone pain. Recent studies have revealed that microglia mediate synaptic pruning in the central nervous system, where the cluster of differentiation 47-signal regulatory protein α (CD47-SIRPα) axis creates a "don't eat me" signal and elicits an antiphagocytic effect to protect synapses against elimination. To date, the synaptic phagocytosis in microglia has never been investigated in the murine cancer-induced bone pain model. The present experiments sought to explore whether microglia phagocytize synapses in mice with bone cancer pain as well as the possible mechanisms.

METHODS

Male C3H/HeN mice were used to induce bone cancer pain. Minocycline and S-ketamine were injected into D14. The number of spontaneous flinches (NSF) and paw withdrawal mechanical thresholds (PWMT) were measured on D0, D4, D7, D10, D14, D21, and D28. Hematoxylin and eosin staining presented bone lesions. Western blotting examined the Gephyrin, CD47, and SIRPα expression. Flow cytometry evaluated the proportion of SIRPα + cells in the spine. Immunofluorescence and 3-dimensional reconstruction showed the Gephyrin puncta inside microglial lysosomes.

RESULTS

Mice embedded with tumor cells induced persistent spontaneous pain and mechanical hyperalgesia. Hematoxylin and eosin staining revealed bone destruction and tumor infiltration in marrow cavities. Microglia underwent a responsive and proliferative burst (t = -16.831, P < .001). Western blotting manifested lowered Gephyrin expression in the tumor group (D4, D7, D10, D14, D21, and D28: P < .001). Immunofluorescence and 3-dimensional reconstruction showed larger volumes of Gephyrin puncta inside microglial lysosomes (t = -23.273, P < .001; t = -27.997, P < .001). Treatment with minocycline or S-ketamine exhibited pain relief and antiphagocytic effects (t = -6.191, P < .001, t = -7.083, P < .001; t = -20.767, P < .001, t = -17.080, P < .001; t = 11.789, P < .001, t = 16.777, P < .001; t = 8.868, P < .001, t = 21.319, P < .001). Last but not least, the levels of CD47 and SIRPα proteins were downregulated (D10: P = .004, D14, D21, and D28: P < .001; D10, D14, D21, and D28: P < .001). Flow cytometry and immunofluorescence substantiated reduced microglial SIRPα (t = 11.311, P < .001; t = 12.189, P < .001).

CONCLUSIONS

Microglia-mediated GABAergic synapse pruning in the spinal cord dorsal horn in bone cancer pain mice, which might be associated with the declined CD47-SIRPα signal. Our research uncovered an innovative mechanism that highlighted microglia-mediated synaptic phagocytosis in a murine cancer-induced bone pain model.

Esketamine: Less Drowsiness, More Analgesia

Racemic ketamine is a 1:1 mixture of 2 enantiomers that turn light in opposite direction: Dextrorotatory esketamine is approximately 4 times more affine for the N-methyl-D-aspartate (NMDA) receptor than levorotatory arketamine, which may explain why esketamine is about twice as potent as an analgesic and anesthetic as the racemate. Esketamine has attracted renewed interest in view of the opioid crisis, racemic ketamine's abuse, and esketamine's approval for expanded use. We evaluated the anesthesia literature concerning mental, cardiovascular, cerebral, and antinociceptive effects of esketamine published in English between 1980 and 2022. The review shows that esketamine and racemic ketamine are not "the same" at clinically equivalent analgesic and anesthetic dose: Psychomimetic effects seem to be essentially related to NMDA receptor blockade and esketamine is not devoid of unwanted mental impact. However, it probably involves less cholinergic inhibition. Cognitive disturbances during arousal, awakening, and recovery from the drug are less, and less pronounced with esketamine. The drug allows for an approximately 50% dose reduction in anesthesia and analgesia which goes along with a higher clearance and shorter recovery time as compared to racemic ketamine. In comparison of esketamine with placebo, esketamine shows cardiocirculatory stabilizing and neuroprotective effects which can be seen in anesthesia induction, cardiac surgery, and analgesia and sedation in brain injury. Evidence of esketamine's antinociceptive efficacy is inconsistent, although a recent meta-analysis reports improved pain relief after surgery in a study with short observation time. To better define esketamine's place, direct head-to-head comparison with the racemate at equi-analgesic/anesthetic dose is warranted.

Sustained-Release Esketamine Based Nanoparticle-Hydrogel Delivery System for Neuropathic Pain Management

Introduction

Esketamine, one of the few non-opioid potent analgesics, has demonstrated efficacy in the treatment of various chronic pain, particularly neuropathic pain. However, its potential clinical applications are confined due to its short half-life and severe side effects including delirium, hallucinations, and other psychiatric symptoms. Here, we reported a nanosized drug delivery system for sustained-release esketamine based on polylactic-co-glycolic acid (PLGA) nanoparticles and hyaluronic acid (HA) hydrogel.

Results

In this study, esketamine in the delivery system was continuously released in vitro for at least 21 days, and spinal nerve root administration of the delivery system successfully attenuated (spinal nerve ligation) SNL-induced pain hypersensitivity for at least 14 days. Notably, the excitability of neurons in murine dorsal root ganglion (DRG) was inhibited and the activation of astrocytes in the spinal cord was additionally reduced after administration. Finally, there was no obvious pathophysiological change in the nerves at the administration site after treatment at 14 days.

Conclusion

These results indicate that the sustained-release esketamine based on the nanoparticle-hydrogel delivery system can safely produce a lasting analgesic effect on SNL mice, and its mechanism might be related to modulating the activation of astrocytes in the spinal cord and inhibiting the excitability of neurons in DRG.

Intrathecal Drug Delivery: Advances and Applications in the Management of Chronic Pain Patient

Advances in our understanding of the biology of spinal systems in organizing and defining the content of exteroceptive information upon which higher centers define the state of the organism and its role in the regulation of somatic and automatic output, defining the motor response of the organism, along with the unique biology and spatial organization of this space, have resulted in an increased focus on therapeutics targeted at this extracranial neuraxial space. Intrathecal (IT) drug delivery systems (IDDS) are well-established as an effective therapeutic approach to patients with chronic non-malignant or malignant pain and as a tool for management of patients with severe spasticity and to deliver therapeutics that address a myriad of spinal pathologies. The risk to benefit ratio of IDD makes it a useful interventional approach. While not without risks, this approach has a significant therapeutic safety margin when employed using drugs with a validated safety profile and by skilled practioners. The present review addresses current advances in our understanding of the biology and dynamics of the intrathecal space, therapeutic platforms, novel therapeutics, delivery technology, issues of safety and rational implementation of its therapy, with a particular emphasis upon the management of pain.

The Options for Neuraxial Drug Administration

Neuraxial drug administration, i.e., the injection of drugs into the epidural or intrathecal space to produce anesthesia or analgesia, is a technique developed more than 120 years ago. Today, it still is widely used in daily practice in anesthesiology and in acute and chronic pain therapy. A multitude of different drugs have been introduced for neuraxial injection, only a part of which have obtained official approval for that indication. A broad understanding of the pharmacology of those agents is essential to the clinician to utilize them in a safe and efficient manner. In the present narrative review, we summarize current knowledge on neuraxial anatomy relevant to clinical practice, including pediatric anatomy. Then, we delineate the general pharmacology of neuraxial drug administration, with particular attention to specific aspects of epidural and intrathecal pharmacokinetics and pharmacodynamics. Furthermore, we describe the most common clinical indications for neuraxial drug administration, including the perioperative setting, obstetrics, and chronic pain. Then, we discuss possible neurotoxic effects of neuraxial drugs, and moreover, we detail the specific properties of the most commonly used neuraxial drugs that are relevant to clinicians who employ epidural or intrathecal drug administration, in order to ensure adequate treatment and patient safety in these techniques. Finally, we give a brief overview on new developments in neuraxial drug therapy.

Pharmacological and clinical implications of local anaesthetic mixtures: a narrative review

Various techniques have been explored to prolong the duration and improve the efficacy of local anaesthetic nerve blocks. Some of these involve mixing local anaesthetics or adding adjuncts. We did a literature review of studies published between 01 May 2011 and 01 May 2021 that studied specific combinations of local anaesthetics and adjuncts. The rationale behind mixing long- and short-acting local anaesthetics to hasten onset and extend duration is flawed on pharmacokinetic principles. Most local anaesthetic adjuncts are not licensed for use in this manner and the consequences of untested admixtures and adjuncts range from making the solution ineffective to potential harm. Pharmaceutical compatibility needs to be established before administration. The compatibility of drugs from the same class cannot be inferred and each admixture requires individual review. Precipitation on mixing (steroids, non-steroidal anti-inflammatory drugs) and subsequent embolisation can lead to serious adverse events, although these are rare. The additive itself or its preservative can have neurotoxic (adrenaline, midazolam) and/or chondrotoxic properties (non-steroidal anti-inflammatory drugs). The prolongation of block may occur at the expense of motor block quality (ketamine) or block onset (magnesium). Adverse effects for some adjuncts appear to be dose-dependent and recommendations concerning optimal dosing are lacking. An important confounding factor is whether studies used systemic administration of the adjunct as a control to accurately identify an additional benefit of perineural administration. The challenge of how best to prolong block duration while minimising adverse events remains a topic of interest with further research required.

A comparison of the pharmacokinetics and NMDAR antagonism-associated neurotoxicity of ketamine, (2R,6R)-hydroxynorketamine and MK-801

With the increasing use of ketamine as an off-label treatment for depression and the recent FDA approval of (S)-ketamine for treatment-resistant depression, there is an increased need to understand the long-term safety profile of chronic ketamine administration. Of particular concern is the neurotoxicity previously observed in rat models following acute exposure to high doses of ketamine, broadly referred to as 'Olney's lesions'. This type of toxicity presents as abnormal neuronal cellular vacuolization, followed by neuronal death and has been associated with ketamine's inhibition of the N-methyl-d-aspartate receptor (NMDAR). In this study, a pharmacological and neuropathological analysis of ketamine, the potent NMDAR antagonist MK-801, and the ketamine metabolite (2R,6R)-hydroxynorketamine [(2R,6R)-HNK)] in rats is described following both single dose and repeat dose drug exposures. Ketamine dosing was studied up to 20 mg/kg intravenously for the single-dose neuropathology study and up to 60 mg/kg intraperitoneally for the multiple-dose neuropathology study. MK-801 dosing was studied up to 0.8 mg/kg subcutaneously for both the single and multiple-dose neuropathology studies, while (2R,6R)-HNK dosing was studied up to 160 mg/kg intravenously in both studies. These studies confirm dose-dependent induction of 'Olney's lesions' following both single dose and repeat dosing of MK-801. Ketamine exposure, while showing common behavioral effects, did not induce wide-spread Olney's lesions. Treatment with (2R,6R)-HNK did not produce behavioral effects, toxicity or any evidence of Olney's lesion formation. Based on these results, future NMDAR-antagonist neurotoxicity studies should strongly consider taking pharmacokinetics more thoroughly into account.

Single dose perioperative intrathecal ketamine as an adjuvant to intrathecal bupivacaine: A systematic review and meta-analysis of adult human randomized controlled trials

STUDY OBJECTIVE

To identify whether adding intrathecal ketamine to intrathecal bupivacaine prolongs the time to first analgesic request in adult humans.

DESIGN

A meta-analysis of randomized controlled trials in humans.

SETTING

The majority of data was obtained in an operating room and postoperative recovery area.

PATIENTS

A total of 750 ASA physical status I and II patients were included in the study. Procedures performed include: cesarean section, lower abdominal surgery, lower limb surgery, and urologic surgery.

INTERVENTIONS

Databases including PubMed, Embase, Web of Science, and Cochrane were searched. Google Scholar was also queried. Multiple reviewers screened the papers for inclusion.

MEASUREMENTS

The primary outcome assessed was time to first analgesic request. Secondary outcomes included onset of sensory blockade, onset of motor blockade, duration of sensory blockade, and duration of motor blockade. Data were extracted to include means, 95% confidence intervals, tests for heterogeneity, and use of the Cochrane Collaboration guidelines to assess for publication bias.

MAIN RESULTS

Eleven randomized controlled trials met inclusion criteria. When comparing intrathecal bupivacaine plus ketamine to intrathecal bupivacaine alone, the time to first analgesic request was prolonged (effect size = 58.23 min (95% CI 37.36 to 79.10) p < 0.0001). Secondary outcomes showed the onset time of sensory blockade was shortened (effect size = -0.87 min (95% CI -1.361 to 0.378) p = 0.0005), the onset time of motor blockade was reduced (effect size = -0.88 min (95% CI -1.77 to 0.013) p = 0.05), the duration of sensory blockade was prolonged (effect size = 39.73 min (95% CI 15.97 to 63.50) p = 0.001), and the duration of motor blockade was prolonged (effect size = 4.02 min (95% CI 3.27 to 4.78) p < 0.0001). Studies were shown to have high heterogeneity. Egger tests for all outcomes were non-significant and funnel plots assessing publication bias were all asymmetrical.

CONCLUSIONS

The studies analyzed suggest there may be a benefit to using intrathecal ketamine as an adjunct to bupivacaine. Additional studies are warranted to optimize dosing, clarify the safety and efficacy of this intrathecal drug combination, and examine the various ketamine formulations as intrathecal bupivacaine adjuvants.

Clozapine protects adult neural stem cells from ketamine-induced cell death in correlation with decreased apoptosis and autophagy

Adult neurogenesis, the production of newborn neurons from neural stem cells (NSCs) has been suggested to be decreased in patients with schizophrenia. A similar finding was observed in an animal model of schizophrenia, as indicated by decreased bromodeoxyuridine (BrdU) labelling cells in response to a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist. The antipsychotic drug clozapine was shown to counteract the observed decrease in BrdU-labelled cells in hippocampal dentate gyrus (DG). However, phenotypic determination by immunohistochemistry analysis could not reveal whether BrdU-positive cells were indeed NSCs. Using a previously established cell model for analysing NSC protection in vitro, we investigated a protective effect of clozapine on NSCs.

Primary NSCs were isolated from the mouse subventricular zone (SVZ), we show that clozapine had a NSC protective activity alone, as evident by employing an ATP cell viability assay. In contrast, haloperidol did not show any NSC protective properties. Subsequently, cells were exposed to the non-competitive NMDA-receptor antagonist ketamine. Clozapine, but not haloperidol, had a NSC protective/anti-apoptotic activity against ketamine-induced cytotoxicity. The observed NSC protective activity of clozapine was associated with increased expression of the anti-apoptotic marker Bcl-2, decreased expression of the pro-apoptotic cleaved form of caspase-3 and associated with decreased expression of the autophagosome marker 1A/1B-light chain 3 (LC3-II).

Collectively, our findings suggest that clozapine may have a protective/anti-apoptotic effect on NSCs, supporting previous in vivo observations, indicating a neurogenesis-promoting activity for clozapine. If the data are further confirmed in vivo, the results may encourage an expanded use of clozapine to restore impaired neurogenesis in schizophrenia.

Effect of morphine and a low dose of ketamine on the T cells of patients with refractory cancer pain in vitro

The combination of morphine and ketamine is considered safe and efficacious in many patients. However, a considerable number of immunomodulatory effects have been reported to be produced by both morphine and ketamine. The aim of the present study was to assess the direct effect of morphine and a low dose of ketamine on the T cells of patients with refractory cancer pain in vitro. Venous blood was obtained from patients with refractory cancer pain and peripheral blood mononuclear cells were isolated using the Ficoll-Hypaque density gradient method. Anti-CD3 beads were used to isolate T cells by positive selection. Subsequently, the T cells were treated with vehicle, 200 ng/ml of morphine or 200 ng/ml of morphine + 100 ng/ml ketamine for 24 h, following which the cells were stimulated with anti-CD3 and anti-CD28. Flow cytometric analysis of CD3⁺ T cells, and interleukin (IL)-2 and interferon (IFN)-γ in the supernatant, reverse transcription-quantitative PCR analysis for the detection of IL-2 and IFN-γ and western blotting for the detection of p65 nuclear factor (NF)-κB were performed. In vitro, the CD4⁺ and CD8⁺ T cell counts, CD4⁺/CD8⁺ ratio, secretion of IL-2 and IFN-γ in the supernatant, mRNA expression levels of IL-2 and IFN-γ and expression of p65 NF-κB were significantly decreased following treatment with morphine and morphine + ketamine, compared with results in the control group (all P<0.05). However, there was no significant difference between treatment with morphine and that with morphine + ketamine. Treatment with morphine + ketamine in vitro decreased the immune functions of patients with refractory cancer pain, although the effect of treatment with morphine and a low dose of ketamine did not differ significantly from that with morphine treatment alone.

Effect of Intrathecally Administered Ketamine, Morphine, and Their Combination Added to Bupivacaine in Patients Undergoing Major Abdominal Cancer Surgery a Randomized, Double-Blind Study

Objective

Effective postoperative pain control reduces postoperative morbidity. In this study, we investigated the effects of intrathecal morphine, ketamine, and their combination with bupivacaine for postoperative analgesia in major abdominal cancer surgery.

Study Design

Prospective, randomized, double-blind.

Setting

Academic medical center.

Patients and Methods

Ninety ASA I-III patients age 30 to 50 years were divided randomly into three groups: the morphine group (group M) received 10 mg of hyperbaric bupivacaine 0.5% in 2 mL volume and 0.3 mg morphine in 1 mL volume intrathecally. The ketamine group (group K) received 0.1 mg/kg ketamine in 1 mL volume instead of morphine. The morphine + ketamine group (group K + M) received both 0.3 mg morphine and 0.1 mg/kg ketamine in 1 mL volume intrathecally. Postoperative total morphine consumption, first request of analgesia, visual analog score (VAS), and side effects were recorded.

Results

Total PCA morphine was significantly decreased in group M + K compared with groups M and K. Time to first request of analgesia was prolonged in groups M and M + K compared with group K (P < 0.001). VAS in group M + K was reduced from two to 24 hours, and in group M from 12 and 18 hours postoperation compared with group K, with an overall good analgesia in the three groups. Sedation was significantly higher in group M + K compared with group M until six hours postoperation. No other side effects were observed.

Conclusions

Adding intrathecal ketamine 0.1 mg/kg to morphine 0.3 mg in patients who underwent major abdominal cancer surgery reduced the total postoperative morphine consumption in comparison with either drug alone, with an overall good postoperative analgesia in all groups, with no side effects apart from sedation.

Ketamine for pain management

Supplemental Digital Content is Available in the Text.

Synthesis, absolute configuration and in vitro cytotoxicity of deschloroketamine enantiomers: rediscovered and abused dissociative anaesthetic

Deschloroketamine has been synthesized, the absolute configuration of enantiomers elucidated and the in vitro cytotoxicity of the enantiomers determined using nine different cell lines.

An Update on Drugs Used for Lumbosacral Epidural Anesthesia and Analgesia in Dogs

This review aims to report an update on drugs administered into the epidural space for anesthesia and analgesia in dogs, describing their potential advantages and disadvantages in the clinical setting. Databases searched include Pubmed, Google scholar, and CAB abstracts. Benefits of administering local anesthetics, opioids, and alpha₂ agonists into the epidural space include the use of lower doses of general anesthetics (anesthetic “sparing” effect), perioperative analgesia, and reduced side effects associated with systemic administration of drugs. However, the potential for cardiorespiratory compromise, neurotoxicity, and other adverse effects should be considered when using the epidural route of administration. When these variables are considered, the epidural technique is useful as a complementary method of anesthesia for preventive and postoperative analgesia and/or as part of a balanced anesthesia technique.

PACAP Protects Adult Neural Stem Cells from the Neurotoxic Effect of Ketamine Associated with Decreased Apoptosis, ER Stress and mTOR Pathway Activation

Ketamine administration is a well-established approach to mimic experimentally some aspects of schizophrenia. Adult neurogenesis dysregulation is associated with psychiatric disorders, including schizophrenia. The potential role of neurogenesis in the ketamine-induced phenotype is largely unknown. Recent results from human genetic studies have shown the pituitary adenylate cyclase-activating polypeptide (PACAP) gene is a risk factor for schizophrenia. Its potential role on the regulation of neurogenesis in experimental model of schizophrenia remains to be investigated. We aimed to determine whether ketamine affects the viability of adult neural stem cells (NSC). We also investigated whether the detrimental effect mediated by ketamine could be counteracted by PACAP. NSCs were isolated from the subventricular zone of the mouse and exposed to ketamine with/without PACAP. After 24 hours, cell viability, potential involvement of apoptosis, endoplasmic reticulum (ER) stress, mTOR and AMPA pathway activation were assessed by quantitative RT-PCR and Western blot analysis. We show that ketamine impairs NSC viability in correlation with increased apoptosis, ER stress and mTOR activation. The results also suggest that the effect of ketamine occurs via AMPA receptor activation. Finally, we show that PACAP counteracted the decreased NSC viability induced by ketamine via the specific activation of the PAC-1 receptor subtype. Our study shows that the NSC viability may be negatively affected by ketamine with putative importance for the development of a schizophrenia phenotype in the ketamine induced animal model of schizophrenia. The neuroprotective effect via PAC-1 activation suggests a potentially novel pharmacological target for the treatment of schizophrenia, via neurogenesis normalization.

Topical versus caudal ketamine/bupivacaine combination for postoperative analgesia in children undergoing inguinal herniotomy

Background:

Multiple studies claim that caudal administration of ketamine causes effective postoperative analgesia. The aim of this study was to assess the clinical effectiveness of ketamine after caudal or topical administration in pediatric patients undergoing inguinal herniotomy.

Patients and Methods:

This randomized, comparative, double-blind study included eighty children (aged 6 months to 6 years) received either 1 ml/kg of 0.25% bupivacaine/ketamine 0.5 mg/kg for caudal analgesia (caudal group) or 0.3 ml/kg of 0.25% bupivacaine/ketamine 0.5 mg/kg sprayed by the surgeon around the spermatic cord and upon the ilioinguinal nerve before wound closure for topical analgesia (topical group). The duration of postoperative analgesia, pain scores, rescue analgesic consumption, sedation score, hemodynamic monitoring, and side-effects were evaluated 48 h postoperative.

Results:

Kaplan–Meier survival analysis of analgesia free time demonstrated a significant advantage of topical ketamine (TK) group over caudal ketamine (CK) group. The duration of postoperative analgesia was longer in TK group than in CK group (28.74 ± 2.88 vs. 21.43 ± 5.01 h, P = 0.000). Fewer children asked for oral analgesics in the topical group (24 of 36, 66.7%) than in the caudal one (28 of 32, 87.5%; P < 0.01). Postoperative pain scores at the 6^th till 48^th h were lower in topical group with comparable analgesic consumption between two groups. In the caudal group, four subjects suffered from retention of urine: Two presented with a residual motor block and two had photophobia.

Conclusion:

Wound instillation of bupivacaine/ketamine is a simple, noninvasive, and effective technique that could be a safe alternative to CK for postoperative analgesia in children undergoing inguinal hernia repair.

Addition of low-dose ketamine to midazolam and low-dose bupivacaine improves hemodynamics and postoperative analgesia during spinal anesthesia for cesarean section

BACKGROUND AND AIMS

Spinal anesthesia for cesarean section (CS) is associated with an incidence of hypotension of 60-94%. This study hypothesizes that intrathecal combination of low-dose ketamine, midazolam, and low-dose bupivacaine improves hemodynamics and postoperative analgesia compared with fentanyl and low-dose bupivacaine during CS.

MATERIAL AND METHODS

Fifty parturients undergoing elective CS were randomized equally to receive ketamine (10 mg), midazolam (2 mg) and 0.5% hyperbaric bupivacaine (8 mg) in group ketamine-midazolam-bupivacaine (KMB) or fentanyl (25 μg) and 0.5% hyperbaric bupivacaine (8 mg) in group fentanyl-bupivacaine (FB). Heart rate (HR), mean arterial blood pressure (MAP), oxygen saturation, sensorimotor block characteristics, pain-free period, side-effects including: hypotension, bradycardia, nausea, vomiting, sedation, pruritus, respiratory depression and dissociative manifestations, Apgar score at 1 and 5 min, and patients' satisfaction visual analog scores (VAS) were recorded. Patients in group KMB were followed for 6 months in order to assess any neurological disorder.

RESULTS

Group KMB showed higher sensory level (P = 0.006), rapid sensory (P = 0.001) and motor (P = 0.005) onsets, prolonged sensory (P = 0.008) and motor (P = 0.002) blocks, and prolonged pain free period (P = 0.002). Ketamine-midazolam stabilized HR and MAP, and significantly reduced incidence of hypotension (P = 0.002), bradycardia (P = 0.013) and vomiting (P = 0.019). Apgar scores at 1 and 5 min were comparable in both groups (P = 0.699 and 0.646 respectively). Patients' satisfaction VAS scores were significantly higher in group KMB (P = 0.001). No patients in KMB group showed dissociative or neurotoxic manifestations.

CONCLUSION

Intrathecal low-dose ketamine combined with midazolam and low-dose bupivacaine stabilizes hemodynamics and prolongs postoperative analgesia without significant side-effects in parturients undergoing CS.

Additives to local anesthetics for peripheral nerve blocks or local anesthesia: a review of the literature

SUMMARY 

A multitude of studies have focused on individual additives to local anesthetics and their effect on quality, onset, duration, spread and selectivity, as well as the potential toxic effects of their use. This review aims to give a broad overview of the current evidence in this developing field, based on beneficial and adverse effects of these drugs. We discuss the limitations of the available data and hope to convey implications and future perspectives for clinicians and researchers alike.

Selective antinociceptive effects of a combination of the N-methyl-D-aspartate receptor peptide antagonist [Ser(1)]histogranin and morphine in rat models of pain

Numerous rather than a few analgesic endogenous neuropeptides are likely to work in concert in vivo in ameliorating pain. Identification of effective neuropeptide combinations would also facilitate the development of gene or cell-based analgesics. In this study, opioid peptides endomorphin-1 (EM-1) and endomorphin-2 (EM-2) and the peptide histogranin analogue [Ser¹]histogranin (SHG), which possess activity as an N-methyl-d-aspartate (NMDA) receptor antagonist, were intrathecally (i.t.) injected alone and in combination in rat models of acute and persistent pain. None of the peptides when injected alone altered hind paw responses of uninjured rats to acute noxious stimulation. EM-1 and EM-2 showed divergent efficacies in the persistent pain models. For example, EM-1 injected alone was antinociceptive in rats with neuropathic pain, whereas EM-2 demonstrated no efficacy. Demonstration of synergism was also divergent across the models. For example, while SHG combined with EM-1 did not alter the efficacy of EM-1 in rats with neuropathic pain, SHG significantly increased the efficacy of EM-1 in the formalin test. By contrast, the potency and efficacy of the peptides alone and combinations were much less than those of the reference analgesic morphine. Furthermore, morphine combined with the clinically used NMDA receptor antagonist ketamine showed synergism across a broad range of pain states. While the current set of neuropeptides could serve as a basis for analgesic therapeutics, there could be other neuropeptides with greater efficacy and potency and broader therapeutic application.

Evaluation of the analgesic effect of ketamine as an additive to intrathecal bupivacaine in patients undergoing cesarean section

OBJECTIVE

Nowadays, conventional analgesic agents, which are widely used for pain relief after cesarean section, provide suboptimal analgesia with occasional serious side effects. We designed a randomized, double-blind, placebo-controlled study to evaluate the analgesic efficacy of intrathecal ketamine added to bupivacaine after cesarean section.

METHODS

Sixty patients scheduled for cesarean section under spinal anesthesia were randomly allocated to one of the two groups to receive either bupivacaine 10 mg combined with 0.1 mg/kg ketamine, or bupivacaine 10 mg combined with 0.5 mL distilled water intrathecally. The time to the first analgesic request, analgesic requirement in the first 24 hours after surgery, onset times of sensory and motor blockades, the durations of sensory and motor blockades, and the incidences of adverse effects such as hypotension, ephedrine requirement, bradycardia, and hypoxemia, were recorded.

RESULTS

Patients who received ketamine had a significantly prolonged duration of anesthesia compared with those who did not in the control group [95% confidence intervals (CI) 195-217; p = 0.001]. The mean time to the first analgesic request was also significantly longer in ketamine group (95% CI 252.5-275; p < 0.001). The total analgesic consumption in the 24 hours following surgery significantly lessened in the ketamine group compared with that of the control group (95% CI 2-2.5; p < 0.001). The two groups did not differ significantly in intraoperative and postoperative side effects.

CONCLUSION

Intrathecal ketamine 0.1 mg/kg co-administered with spinal bupivacaine elongated the time to the first analgesic request and lessened the total analgesic consumption in the first 24 postoperative hours in comparison with bupivacaine alone in the control group following elective cesarean delivery.

Intrathecal drug administration in chronic pain syndromes

Chronic pain may recur after initial response to strong opioids in both patients with cancer and patients without cancer or therapy may be complicated by intolerable side effects. When minimally invasive interventional pain management techniques also fail to provide satisfactory pain relief, continuous intrathecal analgesic administration may be considered. Only 3 products have been officially approved for long-term intrathecal administration: morphine, baclofen, and ziconotide. The efficacy of intrathecal ziconotide for the management of patients with severe chronic refractory noncancer pain was illustrated in 3 placebo-controlled trials. A randomized study showed this treatment option to be effective over a short follow-up period for patients with pain due to cancer or AIDS. The efficacy of intrathecal opioid administration for the management of chronic noncancer pain is mainly derived from prospective and retrospective noncontrolled trials. The effect of intrathecal morphine administration in patients with pain due to cancer was compared with oral or transdermal treatment in a randomized controlled trial, which found better pain control and fewer side effects with intrathecal opioids. Other evidence is derived from cohort studies. Side effects of chronic intrathecal therapy may either be technical (catheter or pump malfunction) or biological (infection). The most troublesome complication is, however, the possibility of granuloma formation at the catheter tip that may induce neurological damage. Given limited studies, the evidence for intrathecal drug administration in patients suffering from cancer-related pain is more compelling than that of chronic noncancer pain.

Ketamine for pain in adults and children with cancer: a systematic review and synthesis of the literature

OBJECTIVE

Chronic cancer pain is often refractory and difficult to treat. Ketamine is a medication with evidence of efficacy in the treatment of chronic pain.

DESIGN

This article presents a synthesis of the data on ketamine for refractory cancer pain in adults and children.

RESULTS

There are five randomized, double-blind, controlled trials of ketamine use in cancer pain that demonstrate improvement in pain for some patients. There are six prospective, uncontrolled trials in cancer pain that also demonstrate improvement in pain scores for some patients. There are no randomized, controlled trials in children with cancer pain, although there are a few studies reflecting improved pain control with ketamine for children with cancer pain. Adverse events for adults on ketamine are most commonly somnolence, feelings of insobriety, nausea/vomiting, hallucinations, depersonalization/derealization, and drowsiness. However, when ketamine is combined with benzodiazepines, feelings of insobriety, hallucinations, and depersonalization/derealization are not reported. Children on ketamine have had few reported adverse effects, which include sedation, anorexia, urinary retention, and myoclonic movements. Recommended ketamine infusion dosages are from 0.05 to 0.5 mg/kg/h (intravenous or subcutaneous). Recommended oral dosages of ketamine are 0.2-0.5 mg/kg/dose two to three times daily with a maximum of 50 mg/dose three times daily.

CONCLUSIONS

Despite limitations in the breadth and depth of data available, there is evidence that ketamine may be a viable option for treatment-refractory cancer pain.

Diverse roles of neurotensin agonists in the central nervous system

Neurotensin (NT) is a tridecapeptide that is found in the central nervous system (CNS) and the gastrointestinal tract. NT behaves as a neurotransmitter in the brain and as a hormone in the gut. Additionally, NT acts as a neuromodulator to several neurotransmitter systems including dopaminergic, sertonergic, GABAergic, glutamatergic, and cholinergic systems. Due to its association with such a wide variety of neurotransmitters, NT has been implicated in the pathophysiology of several CNS disorders such as schizophrenia, drug abuse, Parkinson's disease (PD), pain, central control of blood pressure, eating disorders, as well as, cancer and inflammation. The present review will focus on the role that NT and its analogs play in schizophrenia, endocrine function, pain, psychostimulant abuse, and PD.

Comparing caudal and intravenous ketamine for supplementation of analgesia after Salter innominate osteotomy

PURPOSE

Previous studies claim that caudal administration of ketamine causes effective analgesia. The aim of this study was to assess the clinical effectiveness of ketamine after caudal or intravascular administration in pediatric patients that underwent orthopedic surgery to distinguish between local and systemic analgesia.

METHODS

After the induction of general anesthesia, 36 patients, aged 18 months to 10 years, assigned to undergo orthopedic surgery, received a caudal injection of bupivacaine and were randomly blinded into two groups: one group received 1 mg/kg S(+)-ketamine as the caudal group and the other group received 1 mg/kg S(+)-ketamine as the intravascular group. Postsurgical measurements included the effectiveness of postsurgical analgesia, which was assessed by using the observational pain scale (OPS), duration of analgesia, sedation score, and hemodynamic and respiratory monitoring.

RESULTS

The mean time to first analgesia was clearly longer in the caudal ketamine group (13.35 h) than in the intravenous ketamine (9.93 h) group (P < 0.01). During the 24-h observation time, fewer children asked for additional analgesic drugs in the caudal group (8 of 18, 44.4 %) than in the intravenous group (12 of 18, 66.6 %; P = 0.01). The times to first micturation and spontaneous leg movements and the incidence of nausea and vomiting were similar in the two groups. The OPS and sedation scores after operation showed no obvious differences between the groups at any time.

CONCLUSION

Although caudal ketamine provides good postsurgical analgesia due to its potential neurotoxicity and only small clinical differences with intravenous ketamine, the administration of intravenous ketamine might be a reasonable option to potentially extend the postsurgical analgesic effect of the caudal administration of local anesthetics in children undergoing Salter osteotomy.

Recent developments in paediatric neuraxial blocks

Paediatric anaesthesia and paediatric regional anaesthesia are intertwined. Almost all surgeries unless contradicted could be and should be supplemented with a regional block. The main objective of this review is to elaborate on the recent advances of the central neuraxial blocks, such as application of ultrasound guidance and electrical stimulation in the pursuit of safety and an objective end point. This review also takes account of the traditional technique and understand the benefits as well the risk of each as compared with the recent technique. The recent trends in choosing the most appropriate peripheral block for a given surgery thereby sparing the central neuroaxis is considered. A penile block for circumcision or a sciatic block for unilateral foot surgery, rather than caudal epidural would have a better risk benefit equation. Readers will find a special mention on the recent thoughts on continuous epidural analgesia in paediatrics, especially its rise and fall, yet its unique importance. Lastly, the issue of block placements under sedation or general anaesthesia with its implication in this special population is dealt with. We conducted searches in MEDLINE (PubMed) and assessed the relevance of the abstracts of citations identified from literature searches. The search was carried out in English, for last 10 years, with the following key words: Recent advances in paediatric regional anaesthesia; ultrasound guidance for central neuraxial blocks in children; role of electrical stimulation in neuraxial blocks in children; complications in neuraxial block. Full-text articles of potentially relevant abstracts were retrieved for further review.

Bayesian enhanced meta-analysis of post-operative analgesic efficacy of additives for caudal analgesia in children

BACKGROUND

The authors calculated the effect size for post-operative analgesia of three additives, clonidine, neostigmine, and tramadol to bupivacaine, ropivacaine, or levobupivacaine used for single-dose caudal extradural blockade in children.

METHODS

A meta-analysis was performed for three end points of efficacy: the increase of time until administration of analgesic drugs, the proportion of patients requiring analgesic drugs during the initial 24 post-operative hours, and the amounts of post-operative analgesic drugs. A Bayesian inference supporting direct statements about the probability of the magnitude of an effect was used to compare the effects size.

RESULTS

Neostigmine increased the duration of analgesia by 9.96 h (95% confidence interval: 7.75 to 12.16), as compared with 3.68 h (2.65 to 4.7) with clonidine and 4.45 (2.84 to 6.07) with tramadol. There is a 95% probability that neostigmine increases the duration of post-operative analgesia by more than 8 h, clonidine by more than 2.8 h, and tramadol by more than 3.25 h, as compared with local anesthetics alone. The odds ratios for the proportion of patients requiring analgesic drugs were 0.22 [0.13 to 0.37] for clonidine and 0.28 [0.10 to 0.75] for neostigmine. With tramadol, there was no statistically significant difference. All three additives reduced the amounts of post-operative analgesic drugs. Neostigmine and tramadol increase the probability for post-operative nausea or vomiting (PONV).

CONCLUSIONS

Neostigmine provides the longest post-operative analgesia. With clonidine, the duration of analgesia is shorter and sedation is increased, but the probability for PONV could be decreased.

Combinations of intrathecal gamma-amino-butyrate receptor agonists and N-methyl-d-aspartate receptor antagonists in rats with neuropathic spinal cord injury pain

Underlying below-level cutaneous hypersensitivity observed following spinal cord injury (SCI) is a concurrent loss of inhibition with an increase in excitation in the spinal dorsal horn. Thus, a dual pharmacological approach, increasing spinal γ-aminobutyrate (GABA) inhibition and decreasing N-methyl-d-aspartate (NMDA) receptor-mediated excitation, could be more beneficial than either approach alone. The current study evaluated the antinociceptive effects of lumbar intrathecal (i.t.) administration of GABA receptor agonists and NMDA receptor antagonists alone and in combination in rats with neuropathic SCI pain. Rats developed markedly decreased hind paw withdrawal thresholds following an acute thoracic spinal cord compression, indicative of below-level hypersensitivity. Separately, i.t. GABA(A) receptor agonist muscimol and GABA(B) receptor agonist baclofen demonstrated dose-dependent antinociception, whereas i.t. NMDA receptor antagonist ketamine and the endogenous peptide [Ser¹]histogranin, a putative NMDA receptor antagonist, demonstrated no efficacy. The combination of baclofen and ketamine resulted in a supra-additive (synergistic) antinociception whereas the combinations with muscimol were merely additive. Intrathecal pretreatment with the GABA(B) receptor antagonist CGP 35348 prevented the antinociceptive effect of the baclofen and ketamine combination. The data indicate that blocking spinal NMDA receptors alone is not sufficient to ameliorate SCI hypersensitivity, whereas a combined approach, simultaneous activation of spinal GABA(B) receptors and NMDA receptor blockade with ketamine, leads to significant antinociception. By engaging diverse pain modulating systems at the spinal level, combination drug treatment may be a useful approach in treating neuropathic SCI pain.

Intrathecal clonidine in the neonatal rat: dose-dependent analgesia and evaluation of spinal apoptosis and toxicity

BACKGROUND

Neuraxial clonidine is used for perioperative analgesia in children of all ages. Preclinical studies in the postnatal rat allow comparison of the relative toxicity and safety of spinal analgesics throughout postnatal development.

METHODS

Rat pups aged 3, 7, or 21 postnatal (P) days were briefly anesthetized for intrathecal injections of saline or clonidine. At each age, the maximum tolerated, antinociceptive (increased hindlimb mechanical withdrawal threshold) and antihyperalgesic (hindpaw carrageenan inflammation) doses were determined. Lumbar spinal cord sections were assessed for apoptosis and cell death (histology, activated caspase-3 immunohistochemistry, Fluoro-Jade C staining), histopathology (hematoxylin and eosin staining), and increased glial reactivity (microglial and astrocytic markers). P3 intrathecal ketamine sections served as positive controls. In additional groups, thermal latency and mechanical withdrawal threshold were measured at P35.

RESULTS

Intrathecal clonidine produces age- and dose-dependent analgesia in rat pups. Maximal doses of clonidine did not alter the degree or distribution of apoptosis or increase glial reactivity in the neonatal spinal cord. No spinal histopathology was seen 1 or 7 days after injection at any age. Intrathecal clonidine did not produce persistent changes in reflex sensitivity to mechanical or thermal stimuli at P35.

CONCLUSIONS

Intrathecal clonidine in the postnatal rat did not produce signs of spinal cord toxicity, even at doses much larger than required for analgesia. The therapeutic ratio (maximum tolerated dose/antihyperalgesic dose) was >300 at P3, >30 at P7, and >10 at P21. These data provide additional information to inform the clinical choice of spinal analgesic drug in early life.

Caudal blocks

Caudal anesthesia is the single most important pediatric regional anesthetic technique. The technique is relatively easy to learn (1), has a remarkable safety record (2), and can be used for a large variety of procedures. The technique has been reviewed in the English (3) and French (4) literature, as well as in German guidelines (5) and in pediatric anesthesia textbooks (6).

Duloxetine in patients with central neuropathic pain caused by spinal cord injury or stroke: a randomized, double-blind, placebo-controlled trial

The mechanisms underlying central neuropathic pain are poorly understood. Pain inhibitory mechanisms including sertononergic and norepinephrine systems may be dysfunctional. In this randomized, double-blinded, placebo-controlled trial we evaluated the effects of duloxetine on pain relief (spontaneous pain and evoked pain), tolerability, health status, and quality of life in patients with central pain related to cerebrovascular lesions or spinal cord lesions. At baseline and eight weeks following start of treatment subjects were evaluated with standard measures of efficacy: pain intensity (primary efficacy variable), quantitative sensory testing, health status and quality of life (secondary efficacy variables). Forty-eight patients received escalating doses of either duloxetine (60 and 120mg/day) or matching placebo capsules. In both groups, patients started with 1 capsule per day. If pain relief was insufficient, patients were titrated to a higher dose. A trend towards a decrease in mean pain score after eight weeks was observed for duloxetine treatment (p=0.056). Duloxetine alleviated dynamic (p=0.035) and cold allodynia (p<0.001) significantly better than placebo. Tactile pain and pressure pain thresholds did not improve significantly. The duloxetine group showed a significant improvement for the bodily pain domain of the SF36 (p=0.035). No significant differences were observed in the other domains of the SF36, the Pain Disability Index, and the EQ-5D. While this trial showed no significant effect on pain intensity, duloxetine revealed a biologic effect. It would be worthwhile to suspend our judgement and to perform more studies to evaluate the role of duloxetine in modulation of the symptoms of central neuropathic pain.

Efficacy and adverse effects of ketamine as an additive for paediatric caudal anaesthesia: a quantitative systematic review of randomized controlled trials

BACKGROUND

The aim of this quantitative systematic review was to assess the efficacy and adverse effects of ketamine added to caudal local anaesthetics in comparison with local anaesthetics alone in children undergoing urological, lower abdominal, or lower limb surgery.

METHODS

The systematic search, data extraction, critical appraisal, and pooled data analysis were performed according to the PRISMA statement. All randomized controlled trials (RCTs) were included in this meta-analysis and relative risk (RR), mean difference (MD), and the corresponding 95% confidence intervals (CIs) were calculated using the Revman(®) statistical software for dichotomous and continuous outcomes.

RESULTS

Thirteen RCTs (published between 1991 and 2008) including 584 patients met the inclusion criteria. There was a significant longer time to first analgesic requirements in patients receiving ketamine in addition to a local anaesthetic compared with a local anaesthetic alone (MD: 5.60 h; 95% CI: 5.45-5.76; P<0.00001). There was a lower RR for the need of rescue analgesia in children receiving a caudal regional anaesthesia with ketamine in addition to local anaesthetics (RR: 0.71; 95% CI: 0.44-1.15; P=0.16).

CONCLUSIONS

Caudally administered ketamine, in addition to a local anaesthetic, provides prolonged postoperative analgesia with few adverse effects compared with local anaesthetics alone. There is a clear benefit of caudal ketamine, but the uncertainties about neurotoxicity relating to the dose of ketamine, single vs repeated doses and the child's age, still need to be clarified for use in clinical practice.

The neurological safety of epidural parecoxib in rats

Epidural injection of cyclooxygenase-2 inhibitors has been suggested as a useful therapeutic modality in pain management in animal studies and clinical settings. Direct epidural administration of parecoxib, a highly selective cyclooxygenase-2 inhibitor, may have advantages over its parenteral administration regarding required dose, side effects, and efficacy. However, no animal studies have been performed to investigate the possible neurotoxicity of epidurally injected parecoxib. Therefore, the present study was performed to assess the neurotoxicity of epidurally injected parecoxib in rats. Rats (n=45) were randomly divided into three groups: normal saline group (group N, n=15), ethanol group (group E, n=15), and parecoxib group (group P, n=15). 0.3 mL of epidural parecoxib (6 mg) and the same volume of epidural ethanol or normal saline were injected into the epidural space. Neurologic assessment was performed 3, 7 and 21 days after the injection by pinch toe testing. Histologic changes were evaluated for vacuolation of the dorsal funiculus, chromatolytic changes of the motor neurons, neuritis, and meningeal inflammation. All rats in groups N and P showed normal response to pinch-toe testing and had a normal gait at each observation point. Histological examination showed no evidence suggestive of neuronal body or axonal lesions, gliosis, or myelin sheet damage in group N or P at any time. However, all rats in group E showed sensory-motor dysfunction, behavioral change, or histopathological abnormalities. No neurotoxicity on the spinal cord or abnormalities in sensorimotor function or behavior was noted in rats that received epidural parecoxib.

Pharmacotherapy for acute pain in children: current practice and recent advances

INTRODUCTION

Acute pain in children may be undertreated. Improved understanding of developmental neurobiology and paediatric pharmacokinetics should facilitate better management of pharmacotherapy. The objective of this review is to discuss current paediatric practice and recent advances with these analgesic agents by using an evidence-based approach.

AREAS COVERED

Using PubMed an extensive literature review was conducted on the commonly used analgesic agents in children from 2000 to April 2010.

EXPERT OPINION

A multimodal analgesic regimen provides better pain control and functional outcome in children. The choice of pharmacological treatment is determined by the severity and type of pain. However, more research and evidence is required to determine the optimal drug combinations.

Combining ketamine with astrocytic inhibitor as a potential analgesic strategy for neuropathic pain ketamine, astrocytic inhibitor and pain

BACKGROUND

Neuropathic pain is an intractable clinical problem. Intrathecal ketamine, a noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist, is reported to be useful for treating neuropathic pain in clinic by inhibiting the activity of spinal neurons. Nevertheless, emerging studies have disclosed that spinal astrocytes played a critical role in the initiation and maintenance of neuropathic pain. However, the present clinical therapeutics is still just concerning about neuronal participation. Therefore, the present study is to validate the coadministration effects of a neuronal noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine and astrocytic cytotoxin L-α-aminoadipate (LAA) on spinal nerve ligation (SNL)-induced neuropathic pain.

RESULTS

Intrathecal ketamine (10, 100, 1000 μg/kg) or LAA (10, 50, 100 nmol) alleviated SNL-induced mechanical allodynia in a dose-dependent manner respectively. Phosphorylated NR1 (pNR1) or glial fibrillary acidic protein (GFAP) expression was down-regulated by intrathecal ketamine (100, 1000 μg/kg) or LAA (50, 100 nmol) respectively. The combination of ketamine (100 μg/kg) with LAA (50 nmol) showed superadditive effects on neuropathic pain compared with that of intrathecal administration of either ketamine or LAA alone. Combined administration obviously relieved mechanical allodynia in a quick and stable manner. Moreover, down-regulation of pNR1 and GFAP expression were also enhanced by drugs coadministration.

CONCLUSIONS

These results suggest that combining NMDAR antagonist ketamine with an astrocytic inhibitor or cytotoxin, which is suitable for clinical use once synthesized, might be a potential strategy for clinical management of neuropathic pain.

Ketamine induces apoptosis via the mitochondrial pathway in human lymphocytes and neuronal cells

BACKGROUND

Ketamine has been shown to have neurotoxic properties, when administered neuraxially. The mechanism of this local toxicity is still unknown. Therefore, we investigated the mechanism of cytotoxicity in different human cell lines in vitro.

METHODS

We incubated the following cell types for 24 h with increasing concentrations of S(+)-ketamine and racemic ketamine: (i) human Jurkat T-lymphoma cells overexpressing the antiapoptotic B-cell lymphoma 2 protein, (ii) cells deficient of caspase-9, caspase-8, or Fas-associated protein with death domain and parental cells, and (iii) neuroblastoma cells (SHEP). N-Methyl-d-aspartate (NMDA) receptors and caspase-3 cleavage were identified by immunoblotting. Cell viability and apoptotic cell death were evaluated flowcytometrically by Annexin V and 7-aminoactinomycin D double staining. Mitochondrial metabolic activity and caspase-3 activation were measured.

RESULTS

Ketamine, in a concentration-dependent manner, induced apoptosis in lymphocytes and neuroblastoma cell lines. Cell lines with alterations of the mitochondrial pathway of apoptosis were protected against ketamine-induced apoptosis, whereas alterations of the death receptor pathway did not reduce apoptosis. S(+)-Ketamine and racemic ketamine induced the same percentage of cell death in Jurkat cells, whereas in neuroblastoma cells, S(+)-ketamine was slightly less toxic.

CONCLUSIONS

Ketamine at millimolar concentrations induces apoptosis via the mitochondrial pathway, independent of death receptor signalling. At higher concentrations necrosis is the predominant mechanism. Less toxicity of S(+)-ketamine was observed in neuroblastoma cells, but this difference was minor and therefore unlikely to be mediated via the NMDA receptor.

The clinical and laboratorial evaluation of transdermal ketamine, fentanyl, clonidine or their combination in chronic low back pain

OBJECTIVES: chronic low back pain may result in central sensitization, with involvement of different receptors. The aim of this study was to evaluate the analgesic action of transdermal (T) ketamine (a NMDA antagonist), clonidine (an α2-agonist), fentanyl (an opioid agonist), or their combination in chronic low back pain. METHODS: after the institutional approval and informed consent signature, 54 patients were prospectively randomized into 6 groups. Each patient had two of the T preparations applied in different arms. The effect of either T ketamine (1 mg/h), T clonidine (25 µg/h) or T fentanyl (25 µg/h), combined with T placebo (CloG, KetG and FenG); or the combination of T ketamine and clonidine (Ket-CloG), T fentanyl and ketamine (Fen-KetG), or T fentanyl and clonidine (Fen-CloG) was searched for pain and adverse effects. Pain was evaluated by: 1) VAS pain scores, and 2) noradrenaline plasma levels at 0-h (just prior to T application), 3- and 6-h after the T application of two medications, by HPLC. RESULTS: clinically, the pain VAS score at 6-h was smaller in comparison to the 0-h in all groups (p<0.02), and lower when compared to the Fen-CloG and Fen-KetG at the 6-h in relation to the administration of each correspondent T drug alone (p<0.05). The laboratorial data revealed that administration of T fentanyl alone (FenG) resulted in plasma noradrenaline decrease at 6-h (p<0.01), while the association of T fentanyl with clonidine resulted in plasma noradrenaline decrease at 3- and 6-h as compared to the others (p<0.01). The combination of both T ketamine and clonidine (Ket-CloG) did not result in a better analgesic profile and resulted in excessive sedation during the evaluation (p<0.02). CONCLUSIONS: all the studied drugs resulted in clinical analgesia (VAS) at 6-h. However, T fentanyl analgesia was corroborated by lower plasma noradrenaline levels at 6-h when applied alone or at 3-h when combined with T clonidine.