Histological findings after long-term infusion of intrathecal ketamine for chronic pain: a case report

Narrative review of intrathecal drug delivery (IDD): indications, devices and potential complications

The management of chronic refractory pain (non-neoplastic and cancer-related pain) remains a therapeutic challenge. The continuous intrathecal (IT) administration of drugs may play an important role in the possible management options. Intrathecal drug delivery devices (IDDDs) may be effective for patients with refractory chronic pain. Therefore, they may be adopted for non-oncologic pain in patients with compression fractures, spondylolisthesis, spondylosis, back surgery failure syndrome and spinal stenosis. Oncologic patients can benefit from these treatments in a variable way according to tumor characteristics, prognosis, periprocedural imaging and risk of disease progression. In this review, we describe the most commonly used drugs (opioids and non-opioids), their pharmacokinetic and pharmacodynamic features and indications of use. The most used drugs are morphine, hydromorphone, fentanyl, methadone, bupivacaine, clonidine, and ketamine. Patient evaluation before the device implantation should be based on clinical examination, medical records assessment and psychometric evaluation. The infusion pumps available on the market are both non-programmable (with continuous IT deliver of drugs) and programmable (with variable deliver of drugs according to their flow rate). Moreover, we describe the procedure of implantation and the potential complications of IT drug delivery (such as bleeding, infection, loss of cerebrospinal fluid, wound seroma, loss of catheter pump propellant).

Repurposing Potential of Ketamine: Opportunities and Challenges

Ketamine is a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor which also interacts with various other receptors that account for its myriad actions. Originally approved as a general anesthetic, it is being explored to be repurposed for numerous other indications such as depressive disorders, suicidal ideation, substance-use disorders, anxiety disorders, chronic pain, refractory status epilepticus, and bronchial asthma exacerbations. Numerous trials are ongoing for the same. The nasal spray of esketamine, a more potent S (+) enantiomer of ketamine, has been approved by the United States Food and Drug Administration (USFDA) for treatment-resistant depression along with the oral antidepressants. However, there are concerns about its safety on long term use, given its psychedelic effects and potential abuse. In this review, we discuss repurposing ketamine for potential therapeutic use and about the safety concerns related to ketamine and esketamine.

Ketamine for pain management

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Ketamine as an adjuvant to opioids for cancer pain

BACKGROUND

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

OBJECTIVES

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

SEARCH METHODS

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

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

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

MAIN RESULTS

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

AUTHORS' CONCLUSIONS

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

Novel polymeric bioerodable microparticles for prolonged-release intrathecal delivery of analgesic agents for relief of intractable cancer-related pain

Intractable cancer-related pain complicated by a neuropathic component due to nerve impingement is poorly alleviated even by escalating doses of a strong opioid analgesic. To address this unmet medical need, we developed sustained-release, bioerodable, hydromorphone (potent strong opioid)- and ketamine (analgesic adjuvant)-loaded microparticles for intrathecal (i.t.) coadministration. Drug-loaded poly(lactic-co-glycolic acid) (PLGA) microparticles were prepared using a water-in-oil-in-water method with evaporation. Encapsulation efficiency of hydromorphone and ketamine in PLGA (50:50) microparticles was 26% and 56%, respectively. Microparticles had the desired size range (20-60 μm) and in vitro release was prolonged at ≥28 days. Microparticles were stable for ≥6 months when stored refrigerated protected from light in a desiccator. Desirably, i.t. injected fluorescent dye-labeled PLGA microparticles in rats remained in the lumbar region for ≥7 days. In a rat model of neuropathic pain, i.t. coinjection of hydromorphone- and ketamine-loaded microparticles (each 1 mg) produced analgesia for 8 h only. Possible explanations include inadequate release of ketamine and/or hydromorphone into the spinal fluid, and/or insufficient ketamine loading to prevent development of analgesic tolerance to the released hydromorphone. As sub-analgesic doses of i.t. ketamine at 24-48 h intervals restored analgesia on each occasion, insufficient ketamine loading appears problematic. We will investigate these issues in future work.

Efficacy of an intrathecal multidrug infusion for pain control in older adults and in end-stage malignancies: A report of three cases

The aim of the present study was to explore the effectiveness of an alternative method to manage pain based on a time-limited intrathecal (IT) infusion of an analgesic medication mixture. Three patients (69, 64 and 94 years of age) with intractable and poorly controlled pain due to bed sores, pelvic metastatic mass, and thoracic vertebra and rib fractures, respectively, were treated. Daily doses of opioids could not be increased due to side effects. An IT catheter (20 G) was placed by percutaneous approach in the lumbar area while advancing toward the thoracic region, and was then tunnelled and fixed subcutaneously. It was connected to an external infusion pump with a mixture of bupivacaine 1 mg⁄mL, naloxone 0.02 ng⁄mL, ketamine 100 µg⁄mL, morphine 0.01 mg⁄mL and clonidine 0.75 µg⁄mL. The starting rate was 1 mL⁄h. The pain was mostly controlled at a rate of <1 mL⁄h. Opioid consumption was reduced dramatically. The catheter was kept in place for one month in the first and third patients, and for six months in the second patient, until his death. Major side effects, such as hypotension, constipation, muscle weakness, sphincter dysfunction, and cognitive or mood deterioration, were not observed with this approach. One patient experienced a urinary tract infection followed by sepsis and meningitis, which was cured by antibiotics. The catheter was removed in this patient. IT infusion with a low-concentration multidrug mixture could be considered as an alternative modality for intractable pain relief in older adults or in malignancies.

Ketamine: use in anesthesia

The role of ketamine anesthesia in the prehospital, emergency department and operating theater settings is not well defined. A nonsystematic review of ketamine was performed by authors from Australia, Europe, and North America. Results were discussed among authors and the final manuscript accepted. Ketamine is a useful agent for induction of anesthesia, procedural sedation, and analgesia. Its properties are appealing in many awkward clinical scenarios. Practitioners need to be cognizant of its side effects and limitations.

Ketamine as an adjuvant to opioids for cancer pain

BACKGROUND

This is an update of the original review published in Issue 1, 2003. Ketamine is a commonly used anaesthetic agent, and in subanaesthetic doses is also given as an adjuvant to opioids for the treatment of cancer pain, particularly when opioids alone prove to be ineffective. Ketamine is known to have psychotomimetic (including hallucinogenic), urological and hepatic adverse effects.

OBJECTIVES

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

SEARCH METHODS

Studies were originally identified from MEDLINE (1966 to 2002), EMBASE (1980 to 2002), CancerLit (1966 to 2002), The Cochrane Library (Issue 1, 2001); by handsearching reference lists from review articles, trials, and chapters from standard textbooks on pain and palliative care. The manufacturer of ketamine (Pfizer Parke-Davis) provided search results from their in-house database, PARDLARS.An improved and updated search of the following was performed in May 2012: CENTRAL, MEDLINE & OVID MEDLINE R, EMBASE.

SELECTION CRITERIA

Randomized controlled trials (RCTs) of adult patients with cancer and pain being treated with an opioid, and receiving either ketamine (any dose and any route of administration) or placebo or an active control. Studies having a group size of at least 10 participants who completed the trial.

DATA COLLECTION AND ANALYSIS

Two independent review authors identified four RCTs for possible inclusion in the review, and 32 case studies/case series reports. Quality and validity assessment was performed by three independent review authors, and two RCTs were excluded because of inappropriate study design. Patient-reported pain intensity and pain relief was assessed using visual analogue scales (VAS), verbal rating scales or other validated scales, and adverse effects data were collated. For the update three RCTs were identified for possible inclusion in the review.

MAIN RESULTS

Three new studies were identified by the updated search. All three were excluded from the review. Two studies were eligible for inclusion in the original review and both concluded that ketamine improves the effectiveness of morphine in the treatment of cancer pain. However, pooling of the data was not appropriate because of the small total number of participants (30), and the presence of clinical heterogeneity. Some patients experienced hallucinations on both ketamine plus morphine and morphine alone and were treated successfully with diazepam. No other serious adverse effects were reported.

AUTHORS' CONCLUSIONS

Since the last version of this review three new studies were identified but excluded from the review. Current evidence is insufficient to assess the benefits and harms of ketamine as an adjuvant to opioids for the relief of cancer pain. More RCTs are needed.

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.

Intrathecal analgesia

Since the first use of intrathecal (IT) drug infusion systems in the early 1980s, these delivery systems have undergone numerous revisions making them more tolerable, easier to program, and longer lasting. Concurrent with technological advances, the indications for IT pump placement have also been continuously evolving, to the point where the most common indication is now noncancer pain. This article provides an evidence-based review of the indications, efficacy, and complications of IT drug therapy for the most commonly administered spinal analgesics.

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.

Intrathecal analgesia

Since the first use of intrathecal (IT) drug infusion systems in the early 1980s, these delivery systems have undergone numerous revisions making them more tolerable, easier to program, and longer lasting. Concurrent with technological advances, the indications for IT pump placement have also been continuously evolving, to the point where the most common indication is now noncancer pain. This article provides an evidence-based review of the indications, efficacy, and complications of IT drug therapy for the most commonly administered spinal analgesics.

Continuous extradural analgesia in a cow with complex regional pain syndrome

A chronic pain syndrome, similar to the complex regional pain syndrome (CRPS) described in human beings, was diagnosed in a cow with persisting severe pelvic limb lameness. Diagnosis was based on the disproportionate relationship between the severity and duration of pain and the lesion, the failure of conventional analgesic and surgical therapy and the presence of characteristic clinical features. Multimodal therapy, i.e. a mixture of methadone, ketamine and bupivacaine was administered continuously for 17 days via an extradural catheter to counteract nociceptive hypersensitization. Doses were adjusted daily after assessing the effect, using a composite pain score. Physiotherapy was also performed. The diagnosis of CRPS in cattle is unusual. In this case, treatment was successful and the cow was discharged mildly lame and in improving physical condition. Long-term extradural analgesia proved to be safe and effective in the treatment of this syndrome, which was nonresponsive to conventional therapy.

Iontophoretic administration of S(+)-ketamine in patients with intractable central pain: A placebo-controlled trial

The efficacy of 50 and 75 mg S(+)-ketamine administered daily by an iontophoresis-assisted transdermal drug delivery system was tested against placebo in a randomized, double-blind design in 33 patients with central neuropathic pain. At baseline and 1 week after the start of treatment subjects were evaluated with standard measures of efficacy: pain intensity measured by visual analog scale (VAS), health status (Pain Disability Index and EQ-5D) and quality of life (SF-36). Safety assessment included incidence and intensity of adverse events. No significant differences in pain scores (VAS) were observed between the ketamine groups and placebo during the course of the trial. Corrected for baseline levels, daily 50 mg S(+)-ketamine did not improve patient's health status or quality of life compared with placebo treatment. However, daily 75 mg S(+)-ketamine showed significant improvements on the Pain Disability Index, on the EQ-5D, and on the SF-36 except for the role-physical functioning and general health perception. Iontophoretic administration of S(+)-ketamine was well tolerated with a low incidence of adverse events (mild and transient in nature, resolving spontaneously). Iontophoretic administration of S(+)-ketamine was not more effective than placebo treatment in reducing pain scores in patients with severe central neuropathic pain. However, iontophoretic administration of 75 mg S(+)-ketamine improved the health status and the quality of life in these patients.

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

Questions have been raised about the potential neurotoxicity of the neuraxial use of ketamine although ketamine and its active enantiomer S(+)-ketamine have been used intrathecally and epidurally (caudally) for the management of perioperative pain and in a variety of chronic pain syndromes. Clinical experience following neuraxial administration of S(+)-ketamine has been documented without reference to local central nervous system toxicity following this approach. In addition, there are no preclinical safety data regarding stability, compatibility, and neurotoxicity on intrathecal use of single S(+)-ketamine or combinations of S(+)-ketamine, morphine, bupivacaine, and clonidine. In the present case, the continuous intrathecal administration of S(+)-ketamine, in combination with morphine, bupivacaine, and clonidine resulted in adequate pain relief in a patient suffering from intractable neuropathic cancer pain. However, postmortem observation of the spinal cord and nerve roots revealed severe histological abnormalities including central chromatolysis, nerve cell shrinkage, neuronophagia, microglial upregulation, and gliosis. Based on our results, neuraxial administration of S (+)-ketamine cannot be recommended for clinical practise before a systematic study of toxicology of neuraxial S(+)-ketamine in animals or humans has been performed.

Long-term intrathecal S(+)-ketamine in a patient with cancer-related neuropathic pain

Neuropathic pain sometimes needs invasive pain therapy. We present the case of a patient with cancer-related neuropathic pain untreatable with conventional pain therapy after tumour-embolization. The patient was treated successfully with intrathecal (i.t.) administration of S(+)-ketamine, in addition to morphine. Plasma concentrations of S(+)-ketamine were measured regularly throughout the treatment. Continuous i.t. administration of S(+)-ketamine over a period of 3 months demonstrated low plasma levels and no unwanted side-effects.

Investigation of the potentiation of the analgesic effects of fentanyl by ketamine in humans: a double-blinded, randomised, placebo controlled, crossover study of experimental pain[ISRCTN83088383]

BACKGROUND: Despite preclinical evidence suggesting a synergistic interaction between ketamine and opioids promoting analgesia, several clinical trials have not identified dosing regimens capable of eliciting a benefit in the co-administration of ketamine with opioids. METHODS: Ten healthy volunteers participated in a double blinded, randomised, placebo controlled, crossover laboratory study in order to determine whether a low dose of ketamine potentiated the antinociceptive effect of fentanyl without causing an increase in sedative effects. A battery of tests was used to assess both nociception and sedation including electrical current, pressure, thermal stimuli, psychometric tests, and both subjective and objective scores of sedation. Target controlled infusions of the study drugs were used. Ketamine and fentanyl were administered alone and in combination in a double-blinded randomised crossover design. Saline was used as the control, and propofol was used to validate the tests of sedation. Cardiovascular and respiratory parameters were also assessed. RESULTS: The electrical current pain threshold dose response curve of fentanyl combined with ketamine was markedly steeper than the dose response curve of fentanyl alone. While a ketamine serum concentration of 30 ng/ml did not result in a change in electrical pain threshold when administered alone, when it was added to fentanyl, the combination resulted in greater increase in pain threshold than that of fentanyl administered alone. When nociception was assessed using heat and pressure stimuli, ketamine did not potentiate the anti-nociceptive effect of fentanyl. There was no difference between the sedative effect of fentanyl and fentanyl in combination with ketamine as assessed by both subjective and objective measures of sedation. Cardiovascular and respiratory parameters were unaffected by the study drugs at the doses given. CONCLUSION: A serum concentration of ketamine that did not alter indices of sedation potentiated the antinociceptive effect of fentanyl. This potentiation of antinociception occurred without an increase in sedation suggesting that low steady doses of ketamine (30-120 ng/ml) might be combined with mu opioid agonists to improve their analgesic effect in a clinical setting. (296 words).

Evaluation of analgesia provided by the administration of epidural ketamine in dogs with a chemically induced synovitis

OBJECTIVE

To determine if epidural ketamine provides analgesia in dogs with a chemically induced synovitis.

STUDY DESIGN

Prospective randomized experimental trial.

ANIMALS

Thirty-two healthy, adult mongrel dogs (13-30 kg).

METHODS

(Part I) Synovitis was induced in the right stifle of 16 dogs and allowed to develop for 12 hours. Epidural injection at the lumbosacral space of either ketamine (2 mg kg(-1); n = 8) or placebo (n = 8) was performed. Limb use and pain were measured using a force platform and numerical rating scale (NRS). Assessments were performed before and at 12, 14, 16, 18, 20, and 24 hours after the induction of synovitis. (Part II) Epidural injection of either ketamine (n = 8) or placebo (n = 8) was performed immediately before the induction of synovitis. Analgesia was assessed as in Part I. Assessments occurred before and at 2, 4, 6, 8, and 12 hours after the induction of synovitis.

RESULTS

(Part I) Vertical ground reaction forces (VGRF) significantly decreased and NRS scores of total pain significantly increased after the induction of synovitis in all dogs (p < 0.05). No significant differences in VGRF or NRS scores were measured between treatment groups at any assessment period. (Part II) Dogs that received ketamine had significantly lower NRS scores 2 hours after treatment (p < 0.05). NRS scores did not differ between groups at any other evaluation. VGRF did not differ significantly between treatment groups at any assessment period.

CONCLUSION

Epidural ketamine at a dose of 2 mg kg(-1) administered after the development of synovitis does not provide significant levels of analgesia. Administration of ketamine before the induction of synovitis significantly decreased the NRS score 2 hours post-induction.

CLINICAL RELEVANCE

Administration of epidural ketamine before tissue injury may provide analgesia of short duration in dogs.

Polyanalgesic Consensus Conference 2003: an update on the management of pain by intraspinal drug delivery-- report of an expert panel

Intraspinal drug infusion using fully implantable pump and catheter systems is a safe and effective therapy for selected patients with chronic pain. The options for this approach are increasing, as drugs that are commercially available for systemic administration are adapted to this use and other drugs that are in development specifically for intraspinal administration become available. In 2000 a Polyanalgesic Consensus Conference was organized to evaluate the existing literature and develop guidelines for drug selection. The major outcome of this effort, an algorithm for drug selection, was based on the best available evidence at the time. Rapid changes have occurred in the science and practice of intraspinal infusion and a Polyanalgesic Consensus Conference 2003 was organized to pursue the following goals: 1) to review the literature on intraspinal drug infusion since 1999, 2) to revise the 2000 drug-selection algorithm, 3) to develop guidelines for optimizing drug dosage and concentration, 4) to create a process for documenting minimum evidence supporting the use of a drug for intraspinal infusion, and 5) to clarify issues pertaining to compounding of drugs. Based on the best available evidence and expert opinion, consensus recommendations were developed in all these areas. The panel's conclusions may provide a foundation for clinical practice and a rational basis for new research.

Treatment of neuropathic cancer pain with continuous intrathecal administration of S +-ketamine

The effective treatment of patients suffering from neuropathic cancer pain remains a clinical challenge. When patients experience either insufficient analgesia or problematic side-effects after opioid administration, intrathecal administration of morphine and other medications such as bupivacaine and clonidine may offer significant advantages. Additionally, ketamine, a non-competitive N-methyl-D-Aspartate-receptor antagonist is able to alter pain perception at the spinal level. Because of the potential neurotoxicity after neuraxial use of racemic ketamine, intrathecal administration of the preservative-free active compound, S (+)-ketamine may be a valuable alternative. In this paper, we present a patient with severe neuropathic cancer pain successfully treated by continuous intrathecal infusion of morphine, bupivacaine, clonidine and S (+)-ketamine. Moreover, quality of life measurements before and 3 weeks after the start of spinal treatment revealed an improvement in pain relief and a higher overall quality of life. No clinical signs of neurologic deficit were observed during spinal treatment with S (+)-ketamine. However, the continuous intrathecal administration of S (+)-ketamine should be considered as the last resort because there are no preclinical safety data with relevant concentrations on intrathecal use of S (+)-ketamine.

Ketamine in chronic pain management: an evidence-based review

Ketamine has diverse effects that may be of relevance to chronic pain including: N-methyl-D-aspartic acid, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, gamma-aminobutyric acid(A) receptors; inhibition of voltage gated Na(+) and K(+) channels and serotonin, dopamine re-uptake. Ketamine has been in clinical practice for over 30 yr; however, there has been little formal research on the effectiveness of ketamine for chronic pain management. In this review we evaluate the available clinical data as a basis for defining the potential use of ketamine for chronic pain. Literature referenced in this review was obtained from a computer search of EMBASE and MEDLINE from 1966 through August, 2002. Search terms included ketamine, ketalar, pain, painful, analgesic, and analgesia. Abstracts were screened for relevance and publications relating to chronic pain use were obtained. Levels of evidence were stratified according to accepted guidelines (level I-IV). For central pain, there is level II and level IV evidence of efficacy for parenteral and oral ketamine. For complex regional pain syndromes, there is only level IV evidence of efficacy of epidural ketamine. For fibromyalgia, there is level II evidence of pain relief, reduced tenderness at trigger points, and increased endurance. For ischemic pain, a level II study reported a potent dose-dependent analgesic effect, but with a narrow therapeutic window. For nonspecific neuropathic pain, level II and level IV studies reported divergent results with questionable long-term effects on pain. For phantom limb pain and postherpetic neuralgia, level II and level II studies provided objective evidence of reduced hyperpathia and pain relief was usually substantial either after parenteral or oral ketamine. Acute on chronic episodes of severe neuropathic pain represented the most frequent use of ketamine as a "third line analgesic," often by IV or subcutaneous infusion (level IV). In conclusion, the evidence for efficacy of ketamine for treatment of chronic pain is moderate to weak. However, in situations where standard analgesic options have failed ketamine is a reasonable "third line" option. Further controlled studies are needed.

Ketamine as adjuvant to opioids for cancer pain. A qualitative systematic review

Ketamine is increasingly being used as an adjuvant to opioids in the treatment of refractory cancer pain. This systematic review examines the available evidence. Randomized, controlled trials, with or without crossover, were included. Studies were identified from MEDLINE, EMBASE, CANCERLIT, the Cochrane Library, handsearched reference lists from review articles and chapters from standard textbooks on pain and palliative care and reference lists from papers retrieved. Four randomized, controlled studies were identified. Two were excluded due to poor quality. Both included studies concluded that ketamine improves morphine treatment in cancer pain. Quantitative meta-analysis was not possible. The available evidence is not sufficient to conclude that ketamine improves the effectiveness of opioid treatment in cancer pain. High quality, randomized, controlled trials with larger numbers of patients and standardized, clinically relevant routes of administration of ketamine are needed.

Intrathecal morphine for chronic benign pain

In the treatment of chronic benign pain, the administration of an intrathecal opioid produces a potent analgesia without interfering with the motor and sensory functions of the lower extremities. An intrathecal opioid should be considered only when pain control with conventional oral and systemic administration is inadequate or is associated with unmanageable side effects. A trial period and a psychological evaluation are mandatory prior to implantation of a permanent device. About 40% of the patients need surgical revision for various complications. Hormonal changes may influence sexual behaviour. Catheter granulomas can form with high concentrations of morphine. Adjuvant drugs such as bupivacaine, clonidine and ketamine might be necessary to deal with the development of tolerance to morphine. The sophistication of available technology for intrathecal infusion today far exceeds our knowledge of the potential neurological effects of this treatment modality.

Toxicity of intravenous anaesthetics

Intravenous anaesthetic agents are generally remarkably safe. However, it is clear that propofol infusion syndrome is a real, albeit rare, entity. This often lethal syndrome of metabolic acidosis, acute cardiomyopathy and skeletal myopathy is strongly associated with infusions of propofol at rates of 5 mg/kg/hour and greater for more than 48 hours. There is evidence to support the hypothesis that the syndrome is caused by the failure of free fatty acid metabolism due to inhibition of free fatty acid entry into the mitochondria and also specific sites in the mitochondrial respiratory chain. The syndrome therefore mimics the mitochondrial myopathies. Midazolam causes seizure-like activity in very-low-birthweight premature infants requiring the drug prior to tracheal intubation or during prolonged positive pressure ventilation. This can be successfully reversed with the specific benzodiazepine antagonist flumazenil. Midazolam can also cause paradoxical reactions, including increased agitation, poor co-operation and aggressive or violent behaviour, which has been successfully managed with flumazenil.

Ketamine as an adjuvant to opioids for cancer pain

BACKGROUND

Ketamine is a commonly used anaesthetic agent, and in subanaesthetic doses is also given as an adjuvant to opioids for the treatment of cancer pain, particularly when opioids alone prove to be ineffective. Ketamine is known to have hallucinogenic side effects. To date no systematic review of the benefits and harms of adjuvant ketamine for cancer pain has been undertaken.

OBJECTIVES

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

SEARCH STRATEGY

Studies were identified from MEDLINE (1966-2001), EMBASE (1980-2001), CancerLit (1966-2001), the Cochrane Library (Issue 1, 2001); by handsearching reference lists from review articles, trials, and chapters from standard textbooks on pain and palliative care. The manufacturer of ketamine (Pfizer Parke-Davis) provided search results from their in-house database, PARDLARS.

SELECTION CRITERIA

RCTs of adult patients with cancer and pain being treated with an opioid, and receiving either ketamine (any dose and any route of administration) or placebo or an active control.

DATA COLLECTION AND ANALYSIS

Two independent reviewers identified four RCTs for possible inclusion in the review, and 32 case studies/case series reports. Quality and validity assessment was performed by three independent reviewers, and two RCTs were excluded because of inappropriate study design. Patient reported pain intensity and pain relief was assessed using visual analog scales, verbal rating scales or other validated scales, and adverse effects data were collated.

MAIN RESULTS

Two trials were eligible for inclusion in the review and both concluded that ketamine improves the effectiveness of morphine in the treatment of cancer pain. However, pooling of the data was not appropriate because of the small total number of patients (30), and the presence of clinical heterogeneity. Some patients experienced hallucinations on both ketamine plus morphine and morphine alone and were treated successfully with diazepam. No other serious adverse effects were reported.

REVIEWER'S CONCLUSIONS

Current evidence is insufficient to assess the benefits and harms of ketamine as an adjuvant to opioids for the relief of cancer pain. More randomized controlled trials are needed.

Analgesia and analgesic techniques

In recent years, there has been a great increase in our understanding of pain mechanisms and our awareness of pain in small animals. Despite increased knowledge, many animals still go undertreated or untreated. Small exotic animals are a unique group of patients, and can prove challenging for the practitioner concerned with their welfare. This article reviews the process of nociception and how one can intervene in the pain pathway. Newer analgesic drugs are discussed, along with some novel administration techniques that can be adapted for small mammals. Ketamine has been regarded primarily as a chemical restraining agent, but new information reveals that it may have an important place in pain management.

Targeting the N-methyl-D-aspartate receptor for chronic pain management. Preclinical animal studies, recent clinical experience and future research directions

A 1967-1999 MEDLINE search of published reports evaluating the role of the glutamate N-methyl-D-aspartate (NMDA) receptor in pain identified 378 animal studies and 132 human studies. There is convincing evidence in these studies that the NMDA receptor mediates prolonged nociceptive behaviors in animal models and various chronic pain symptoms in the clinical population. Administration of older compounds, such as ketamine, dextromethorphan, and amantadine, which are now known to act as NMDA receptor antagonists, have recently been shown to alleviate chronic pain. For years, the pharmaceutical industry has been attempting to produce novel compounds that modulate NMDA receptor activity; however, the adverse effects associated with this class of drugs have prevented their widespread clinical use. Collaborative studies between basic researchers, clinical scientists, and clinicians are needed to delineate characteristics of NMDA receptor antagonism that predict optimal analgesic activity and an acceptable toxicity profile in patients with chronic pain.