Epidural clonidine analgesia for intractable cancer pain. The Epidural Clonidine Study Group

Neuraxial clonidine is not associated with lower post-cesarean opioid consumption or pain scores in parturients on chronic buprenorphine therapy: a retrospective cohort study

PURPOSE

Adequate post-cesarean delivery analgesia can be difficult to achieve for women diagnosed with opioid use disorder receiving buprenorphine. We sought to determine if neuraxial clonidine administration is associated with decreased opioid consumption and pain scores following cesarean delivery in women receiving chronic buprenorphine therapy.

METHODS

This was a retrospective cohort study at a tertiary care teaching hospital of women undergoing cesarean delivery with or without neuraxial clonidine administration while receiving chronic buprenorphine. The primary outcome was opioid consumption (in morphine milligram equivalents) 0-6 h following cesarean delivery. Secondary outcomes included opioid consumption 0-24 h post-cesarean, median postoperative pain scores 0-24 h, and rates of intraoperative anesthetic supplementation. Multivariable analysis evaluating the adjusted effects of neuraxial clonidine on outcomes was conducted using linear regression, proportional odds model, and logistic regression separately.

RESULTS

196 women met inclusion criteria, of which 145 (74%) received neuraxial clonidine while 51 (26%) did not. In univariate analysis, there was no significant difference in opioid consumption 0-6 h post-cesarean delivery between the clonidine (8 [IQR 0, 15]) and control (1 [IQR 0, 8]) groups (P = 0.14). After adjusting for potential confounders, there remained no significant association with neuraxial clonidine administration 0-6 h (Difference in means 2.77, 95% CI [- 0.89 to 6.44], P = 0.14) or 0-24 h (Difference in means 8.56, 95% CI [- 16.99 to 34.11], P = 0.51).

CONCLUSION

In parturients receiving chronic buprenorphine therapy at the time of cesarean delivery, neuraxial clonidine administration was not associated with decreased postoperative opioid consumption, median pain scores, or the need for intraoperative supplementation.

Enhancing fentanyl antinociception and preventing tolerance with α-2 adrenoceptor agonists in rats

Fentanyl (FEN) is a potent opioid analgesic used for pain management. Opioid analgesic tolerance poses a significant challenge to the clinical utility of opioid agonists. Preventing the development of tolerance to opioid analgesia is crucial for improving its efficacy and safety. The noradrenergic system is involved in pain regulation. This study examined the effects of α-2 adrenoceptor (AR) agonists, dexmedetomidine (DEX), and xylazine (XYL) on FEN tolerance and antinociception, and their impact on μ-opioid receptor (MOR) expression in the posterior horn of the spinal cord (SC). Male rats were divided into six groups and treated with different drug combinations for three consecutive days. Analgesia tests and motor performance assessments were conducted, followed by SC analysis using immunohistochemistry (IHC). Analgesia tests revealed the development of FEN tolerance on the second day, but the groups receiving combined drugs did not develop tolerance. Instead, FEN antinociception was enhanced, with a prolonged duration of its effects. None of the drugs caused sedation or motor impairment, and SC morphology appeared normal. MOR expression levels did not differ significantly between the groups based on IHC analysis. These findings suggest that changes in the secondary messenger system may play a role in the early development of FEN tolerance. Combining drugs can prevent tolerance, while enhancing FEN's antinociceptive effects. These results have promising implications for chronic pain management; however, further research is needed to explore the molecular effects of α-2 AR agonists on FEN tolerance. Overall, this study sheds light on the mechanism of FEN tolerance and identifies potential avenues for future research.

Intrathecal pain treatment for severe pain in patients with terminal cancer: A retrospective analysis of treatment-related complications and side effects

OBJECTIVES

Two-thirds of patients with advanced cancer experience pain. Some of these patients have severe pain refractory to oral and parenteral medication, for whom intrathecal pain treatment could be an option. While intrathecal therapy is presently used with good results in clinical practice, the current evidence is limited. Hence, increased knowledge of intrathecal pain treatment is needed. This retrospective study aimed to assess complications and side effects related to intrathecal pain treatment in patients with terminal cancer.

METHODS

A retrospective study on all patients who received intrathecal treatment with morphine and bupivacaine through externalized catheters for cancer-related pain at a single university hospital during a 5-year period.

RESULTS

Treatment-related complications were reported in 24 out of 53 patients. The most common complications were catheter dislocation (13%), catheter occlusion (9%), falls due to bupivacaine-related numbness or weakness (9%), and reversible respiratory depression (8%). There were five serious complications, i.e., meningitis or neurological impairment, of which four were reversible. Side effects related to intrathecal drugs, or the implantation procedure were observed in 35 patients. The most common were bupivacaine-related numbness or weakness (57%) and reversible post-dural puncture headache (19%). Systemic opioid doses decreased during the first 3 weeks of intrathecal treatment, from a median daily dose of 681 to 319 oral morphine milligram equivalents. The median treatment duration time was 62 days.

CONCLUSIONS

Complications related to intrathecal treatment are common, but mostly minor and reversible. Side effects are predominantly related to unwanted pharmacological effects from intrathecal drugs. Intrathecal treatment enables the reduction of systemic opioid doses, which indicates a good treatment effect on pain. Hence, intrathecal therapy can be considered a safe pain-relieving treatment in patients with severe refractory cancer-related pain. Future research is warranted on patient acceptability and satisfaction of intrathecal pain treatment.

Efficacy of epidural analgesia for intractable cancer pain: A systematic review

BACKGROUND

Epidural analgesia is a common technique for managing perioperative and obstetric pain. Patients with cancer who cannot tolerate opioids or not responding to conventional treatment may benefit from epidural analgesia. Therefore, this systematic review aimed to analyze the efficacy and safety of epidural analgesia in patients with intractable cancer pain.

METHODS

We searched PubMed, Embase, and the Cochrane Central Register of Controlled Trials to identify studies on patients with cancer who received epidural analgesia. We assessed the quality of all included studies using the risk-of-bias tool or Newcastle-Ottawa scale. The primary outcome was pain relief after epidural analgesia, and the secondary outcome was quality of life, analgesic consumption, and adverse events. The studies were grouped based on the medications used for epidural analgesia. A descriptive synthesis was performed following the Synthesis Without Meta-analysis reporting guideline.

RESULTS

Our systematic review included nine randomized controlled trials (n = 340) and 15 observational studies (n = 926). Two randomized controlled trials suggested that epidural opioids were not superior to systemic opioids in relieving pain. Epidural opioids combined with local anesthetics or adjuvants, including calcitonin, clonidine, ketamine, neostigmine, methadone, and dexamethasone, offered better analgesic effects. No significant difference in pain relief between an intermittent bolus and a continuous infusion of epidural morphine was observed. Epidural opioids had more analgesic effects on nociceptive pain than neuropathic pain. The methods used to evaluate the quality of life and the corresponding results were heterogeneous among studies. Six observational studies demonstrated that some patients could have decreased opioid consumption after epidural analgesia. Adverse events, including complications and drug-related side effects, were reported in 23 studies. Five serious complications, such as epidural abscess and hematoma, required surgical management. The heterogeneity and methodological limitations of the studies hindered meta-analysis and evidence-level determination.

CONCLUSION

Coadministration of epidural opioids, local anesthetics, and adjuvants may provide better pain relief for intractable cancer pain. However, we must assess the patients to ensure that the benefits outweigh the risks before epidural analgesia. Therefore, further high-quality studies are required.

Locus coeruleus inhibition of vibrissal responses in the trigeminal subnucleus caudalis are reduced in a diabetic mouse model

Diabetic neuropathy is the loss of sensory function beginning distally in the lower extremities, which is also characterized by pain and substantial morbidity. Furthermore, the locus coeruleus (LC) nucleus has been proposed to play an important role in descending pain control through the activation of α2-noradrenergic (NA) receptors in the spinal dorsal horn. We studied, on control and diabetic mice, the effect of electrical stimulation of the LC nucleus on the tactile responses in the caudalis division of the spinal trigeminal nucleus (Sp5C), which is involved in the relay of orofacial nociceptive information. Diabetes was induced in young adult C57BL/6J mice with one intraperitoneal injection of streptozotocin (50 mg/kg) daily for 5 days. The diabetic animals showed pain in the orofacial area because they had a decrease in the withdrawal threshold to the mechanical stimulation in the vibrissal pad. LC electrical stimulation induced the inhibition of vibrissal responses in the Sp5C neurons when applied at 50 and 100 ms before vibrissal stimulation in the control mice; however, the inhibition was reduced in the diabetic mice. These effects may be due to a reduction in the tyrosine hydroxylase positive (TH+) fibers in the Sp5C, as was observed in diabetic mice. LC-evoked inhibition was decreased by an intraperitoneal injection of the antagonist of the α2-NA receptors, yohimbine, indicating that it was due to the activation of α2-NA receptors. The decrease in the LC-evoked inhibition in the diabetic mice was partially recovered when clonidine, a non-selective α2-agonist, was injected intraperitoneally. These findings suggest that in diabetes, there is a reduction in the NA inputs from the LC in the Sp5C that may favor the development of chronic pain.

Stability of Morphine Sulfate-Clonidine and Sufentanil-Clonidine Mixtures

BACKGROUND

Spinal analgesia is recommended for intractable cancer pain. Morphine-clonidine and sufentanil-clonidine are often used in association in intrathecal drug delivery systems, injected by intraabdominal pumps. To refill these pumps and to limit patient transport, it may be necessary to ship the mixtures in polypropylene syringes to peripheral establishments located near patient homes. The purpose of this study is to determine the stability of morphine-clonidine and sufentanil-clonidine mixtures in polypropylene syringes to ensure the best and safest transport conditions and in implantable pumps for intrathecal use.

MATERIALS AND METHODS

The stability study method was conceived according to the International Council for Harmonization guidelines. For polypropylene syringes, four different mixtures of morphine-clonidine and sufentanil-clonidine were assessed over seven days. Two storage temperatures were tested (5 ± 3 °C and 25 ± 2 °C). For implantable pumps, two different mixtures of morphine-clonidine and sufentanil-clonidine were assessed over 28 days and stored at 37 °C.

RESULTS

For the morphine-clonidine mixtures in polypropylene syringes, all mixtures remained stable for five days in both storage conditions (5 ± 3 °C and 25 ± 2 °C) because of relative concentrations systematically positioned between 90% and 110% (95% CIs of the mean of three samples). The two mixtures in implantable pumps remained stable for 28 days. For the sufentanil-clonidine mixtures in polypropylene syringes, cold conservation kept all the preparations stable for seven days, whereas a quick degradation was observed after only two days for ambient storage conditions. This result is similar to that with an implantable pump, in which the concentration is <90% on day 7 for low concentration mixtures. No visual modification, no significant pH modification, and no changes in turbidity assays were observed in either study.

CONCLUSION

This study shows the stability of the morphine-clonidine mixtures in syringes stored at 5 °C for five days and in implantable pumps stored at 37 °C for 28 days. For the sufentanil-clonidine mixtures, the results show stability in syringes for seven days at 5 °C. Pump results show stability of seven days for low concentrations and 28 days for high concentrations.

Topical clonidine for neuropathic pain in adults

BACKGROUND

Clonidine is a presynaptic alpha-2-adrenergic receptor agonist that has been used for many years to treat hypertension and other conditions, including chronic pain. Adverse events associated with systemic use of the drug have limited its application. Topical use of drugs has been gaining interest since the beginning of the century, as it may limit adverse events without loss of analgesic efficacy. Topical clonidine (TC) formulations have been investigated for almost 20 years in clinical trials. This is an update of the original Cochrane Review published in Issue 8, 2015.

OBJECTIVES

The objective of this review was to assess the analgesic efficacy and safety of TC compared with placebo or other drugs in adults aged 18 years or above with chronic neuropathic pain.

SEARCH METHODS

For this update we searched the Cochrane Register of Studies Online (CRSO), MEDLINE (Ovid), and Embase (Ovid) databases, and reference lists of retrieved papers and trial registries. We also contacted experts in the field. The most recent search was performed on 27 October 2021.

SELECTION CRITERIA

We included randomised, double-blind studies of at least two weeks' duration comparing TC versus placebo or other active treatment in adults with chronic neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened references for eligibility, extracted data, and assessed risk of bias. Any discrepancies were resolved by discussion or by consulting a third review author if necessary. Where required, we contacted trial authors to request additional information. We presented pooled estimates for dichotomous outcomes as risk ratios (RRs) with 95% confidence intervals (CIs), and continuous outcomes as mean differences (MDs) with P values. We used Review Manager Web software to perform the meta-analyses. We used a fixed-effect model if we considered heterogeneity as not important; otherwise, we used a random-effects model.  The review primary outcomes were: participant-reported pain relief of 50% or greater; participant-reported pain relief of 30% or greater; much or very much improved on Patient Global Impression of Change scale (PGIC); and very much improved on PGIC. Secondary outcomes included withdrawals due to adverse events; participants experiencing at least one adverse event; and withdrawals due to lack of efficacy. All outcomes were measured at the longest follow-up period. We assessed the certainty of evidence using GRADE and created two summary of findings tables.

MAIN RESULTS

We included four studies in the review (two new in this update), with a total of 743 participants with painful diabetic neuropathy (PDN). TC (0.1% or 0.2%) was applied in gel form to the painful area two to three times daily. The double-blind treatment phase of three studies lasted 8 weeks to 85 days and compared TC versus placebo. In the fourth study, the double-blind treatment phase lasted 12 weeks and compared TC versus topical capsaicin. We assessed the studies as at unclear or high risk of bias for most domains; all studies were at unclear risk of bias for allocation concealment and blinding of outcome assessment; one study was at high risk of bias for blinding of participants and personnel; two studies were at high risk of attrition bias; and three studies were at high risk of bias due to notable funding concerns. We judged the certainty of evidence (GRADE) to be moderate to very low, downgrading for study limitations, imprecision of results, and publication bias. TC compared to placebo There was no evidence of a difference in number of participants with participant-reported pain relief of 50% or greater during longest follow-up period (12 weeks) between groups (risk ratio (RR) 1.21, 95% confidence interval (CI) 0.78 to 1.86; 179 participants; 1 study; low certainty evidence). However, the number of participants with participant-reported pain relief of 30% or greater during longest follow-up period (8 to 12 weeks) was higher in the TC group compared with placebo (RR 1.35, 95% CI 1.03 to 1.77; 344 participants; 2 studies, very low certainty evidence). The number needed to treat for an additional beneficial outcome (NNTB) for this comparison was 8.33 (95% CI 4.3 to 50.0). Also, there was no evidence of a difference between groups for the outcomes much or very much improved on the PGIC during longest follow-up period (12 weeks) or very much improved on PGIC during the longest follow-up period (12 weeks) (RR 1.06, 95% CI 0.76 to 1.49 and RR 1.82, 95% CI 0.89 to 3.72, respectively; 179 participants; 1 study; low certainty evidence). We observed no evidence of a difference between groups in withdrawals due to adverse events and withdrawals due to lack of efficacy during the longest follow-up period (12 weeks) (RR 0.34, 95% CI 0.04 to 3.18 and RR 1.01, 95% CI 0.06 to 15.92, respectively; 179 participants; 1 study; low certainty evidence) and participants experiencing at least one adverse event during longest follow-up period (12 weeks) (RR 0.65, 95% CI 0.14 to 3.05; 344 participants; 2 studies; low certainty evidence).  TC compared to active comparator There was no evidence of a difference in the number of participants with participant-reported pain relief of 50% or greater during longest follow-up period (12 weeks) between groups (RR 1.41, 95% CI 0.99 to 2.0; 139 participants; 1 study; low certainty evidence). Other outcomes were not reported.

AUTHORS' CONCLUSIONS

This is an update of a review published in 2015, for which our conclusions remain unchanged. Topical clonidine may provide some benefit to adults with painful diabetic neuropathy; however, the evidence is very uncertain. Additional trials are needed to assess TC in other neuropathic pain conditions and to determine whether it is possible to predict who or which groups of people will benefit from TC.

Gadgeteering for Pain Relief: The 2021 John W. Severinghaus Lecture on Translational Science

In this first memorial lecture after John Severinghaus's death in 2021, the author traces his journey as a physician-scientist, using the framework of the hero's journey as described by the author Joseph Campbell 40 to 50 yr ago, and parallels that journey to his own. The author discusses how each were gadgeteers: Severinghaus in a creative engineering way, while the author's approach was asking simple questions translating basic research in pain from animals to humans. The classic hero's journey of departure to achieve a goal, then trials, transformation, and finally, returning with benefits to the individual and others is translated to the common physician-scientist career with motivations progressing from "I will show" to "I wonder if" to "I wonder why." Critical to this journey is self-questioning, openness to new ideas, and realizing that progress occurs through failure as much as success.

Treatment of Neuropathic Pain Directly Due to Cancer: An Update

Simple Summary

This review discusses treatment approaches for providing pain relief to oncological patients affected by pain caused by nerve damage due to the tumor, also known as neuropathic cancer pain. Although being encountered often and causing a relevant burden to these patients, neuropathic cancer pain remains still difficult to diagnose and treat. Strong evidence about the best drugs to be used remain limited, as do therapeutic choices.

Abstract

Neuropathic pain can be defined as pain related to abnormal somatosensory processing in either the peripheral or central nervous system. In this review article, with neuropathic cancer pain (NCP), we refer to pain due to nervous tissue lesions caused by the tumor or its metastases. Nervous tissue damage is the cause of cancer pain in approximately 40% of those experiencing cancer pain. Recognizing a neuropathic pathophysiology in these cases may be difficult and requires specific criteria that are not homogenously applied in clinical practice. The management of this type of pain can be challenging, requiring the use of specific non-opioid adjuvant drugs. The majority of the criteria for NCP diagnosis and management have been based mainly on results from the noncancer population, risking the failure of addressing the specific needs of this population of patients. In this review, we summarize current management options available for NCP and provide some insights on new promising treatments.

Comparison of clonidine and cyproheptadine determination in animal-derived foods by sweeping-micellar electrokinetic chromatography and large volume sample stacking-capillary zone electrophoresis

This study establishes a method for rapid detection of clonidine and cyproheptadine in foods of animal origin. In order to obtain the best detection method, capillary zone electrophoresis (CZE), large volume sample stacking (LVSS), and sweeping-micellar electrokinetic capillary chromatography (sweeping-MEKC) were used respectively. The limits of detection (LODs) of clonidine and cyproheptadine by LVSS-CZE were 0.028 μg mL−1 and 0.034 μg mL−1, and those by sweeping-MEKC were 0.023 μg mL−1 and 0.031 μg mL−1, respectively. Compared with the CZE method, the two online pre-concentration technologies have greatly improved the detection sensitivity and achieved good enrichment results. However, compared with the sweeping-MEKC system, the LVSS system consumed a longer time and was greatly affected by the actual sample matrix. The sweeping-MEKC method was proved to be suitable for real sample analysis. Under the best sweeping-MEKC conditions, clonidine and cyproheptadine could be well separated within 8 min and good linear relationships in the range of 0.1–1.0 μg mL−1 (r 2 > 0.99) were obtained. This method was successfully applied to the determination of clonidine and cyproheptadine in animal-derived foods with the recoveries of 82.3%–90.1% and the relative standard deviations (RSDs) less than 3.11%. The sweeping-MEKC method is simple to operate and has great potential in the rapid detection of clonidine and cyproheptadine in animal-derived foods.

Neuropharmacological basis for multimodal analgesia in chronic pain

Managing chronic pain remains a major unmet clinical challenge. Patients can be treated with a range of interventions, but pharmacotherapy is the most common. These include opioids, antidepressants, calcium channel modulators, sodium channel blockers, and nonsteroidal anti-inflammatory drugs. Many of these drugs target a particular mechanism; however, chronic pain in many diseases is multifactorial and induces plasticity throughout the sensory neuroaxis. Furthermore, comorbidities such as depression, anxiety, and sleep disturbances worsen quality of life. Given the complexity of mechanisms and symptoms in patients, it is unsurprising that many fail to achieve adequate pain relief from a single agent. The efforts to develop novel drug classes with better efficacy have not always proved successful; a multimodal or combination approach to analgesia is an important strategy in pain control. Many patients frequently take more than one medication, but high-quality evidence to support various combinations is often sparse. Ideally, combining drugs would produce synergistic action to maximize analgesia and reduce side effects, although sub-additive and additive analgesia is still advantageous if additive side-effects can be avoided. In this review, we discuss pain mechanisms, drug actions, and the rationale for mechanism-led treatment selection.Abbreviations: COX - cyclooxygenase, CGRP - calcitonin gene-related peptide, CPM - conditioned pain modulation, NGF - nerve growth factor, NNT - number needed to treat, NMDA - N-methyl-d-aspartate, NSAID - nonsteroidal anti-inflammatory drugs, TCA - tricyclic antidepressant, SNRI - serotonin-noradrenaline reuptake inhibitor, QST - quantitative sensory testing.

Interventional Therapies for Pain in Cancer Patients: a Narrative Review

PURPOSE OF REVIEW

Pain is a prevalent symptom in the lives of patients with cancer. In light of the ongoing opioid epidemic and increasing awareness of the potential for opioid abuse and addiction, clinicians are progressively turning to interventional therapies. This article reviews the interventional techniques available to mitigate the debilitating effects that untreated or poorly treated pain have in this population.

RECENT FINDINGS

A range of interventional therapies and technical approaches are available for the treatment of cancer-related pain. Many of the techniques described may offer effective analgesia with less systemic toxicity and dependency than first- and second-line oral and parenteral agents. Neuromodulatory techniques including dorsal root ganglion stimulation and peripheral nerve stimulation are increasingly finding roles in the management of oncologic pain. The goal of this pragmatic narrative review is to discuss interventional approaches to cancer-related pain and the potential of such therapies to improve the quality of life of cancer patients.

Factors mediating pain-related risk for opioid use disorder

Pain is a complex experience with far-reaching organismal influences ranging from biological factors to those that are psychological and social. Such influences can serve as pain-related risk factors that represent susceptibilities to opioid use disorder. This review evaluates various pain-related risk factors to form a consensus on those that facilitate opioid abuse. Epidemiological findings represent a high degree of co-occurrence between chronic pain and opioid use disorder that is, in part, driven by an increase in the availability of opioid analgesics and the diversion of their use in a non-medical context. Brain imaging studies in individuals with chronic pain that use/abuse opioids suggest abuse-related mechanisms that are rooted within mesocorticolimbic processing. Preclinical studies suggest that pain states have a limited impact on increasing the rewarding effects of opioids. Indeed, many findings indicate a reduction in the rewarding and reinforcing effects of opioids during pain states. An increase in opioid use may be facilitated by an increase in the availability of opioids and a decrease in access to non-opioid reinforcers that require mobility or social interaction. Moreover, chronic pain and substance abuse conditions are known to impair cognitive function, resulting in deficits in attention and decision making that may promote opioid abuse. A better understanding of pain-related risk factors can improve our knowledge in the development of OUD in persons with pain conditions and can help identify appropriate treatment strategies. This article is part of the special issue on 'Vulnerabilities to Substance Abuse.'.

Non-opioid Analgesics and Emerging Therapies

Pain is a common and debilitating symptom of cancer. Cancer-related pain can occur at any point along the continuum from diagnosis to treatment to survivorship¹. A systematic review published in 2016 estimated the prevalence of cancer pain to be 55% in those undergoing antineoplastic treatment, 66.4% in advanced cancer, and 39.3% in the post-treatment population. Thirty-eight percent of cancer patients in this pooled analysis experienced moderate to severe pain².

A Practical Approach to Using Adjuvant Analgesics in Older Adults

The adjuvant analgesics are a large and diverse group of drugs that were developed for primary indications other than pain and are potentially useful analgesics for one or more painful conditions. The "adjuvant" designation reflects their early use as opioid co-analgesics for cancer pain. During the past 3 decades, their role in pain management has changed with the advent of many new entities, emerging data from numerous analgesic trials, and growing clinical experience. Many of these drugs are now used as primary analgesics for specific types of chronic pain. With proper patient selection and cautious administration, they can potentially contribute meaningfully to the management of chronic pain in older adults. A practical approach categorizes the many adjuvant analgesics by broad indications: multipurpose drugs and drugs that target neuropathic pain, musculoskeletal pain, and cancer pain, respectively. This article reviews the status of the evidence supporting the analgesic potential of the adjuvant analgesics and discusses best practices in terms of drug selection and dosing. J Am Geriatr Soc 68:691-698, 2020.

Interventional Techniques to Management of Cancer-Related Pain: Clinical and Critical Aspects

Interventional techniques to manage cancer-related pain may be efficient treatment modalities in patients unresponsive or unable to tolerate systemic opioids. However, indication and selection of the right technique demand knowledge, which is still incipient among clinicians. The present article summarizes the current evidence regarding the five most essential groups of interventional techniques to treat cancer-related pain: Neuraxial analgesia, minimally invasive procedures for vertebral pain, sympathetic blocks for abdominal cancer pain, peripheral nerve blocks, and percutaneous cordotomy. Furthermore, indication, mechanism, drug agents, contraindications, and complications of the main techniques of each group are discussed.

Selective deficiencies in descending inhibitory modulation in neuropathic rats: implications for enhancing noradrenergic tone

Supplemental Digital Content is Available in the Text.

Descending noradrenergic pathways modulate spontaneous but not evoked thalamic neuronal hyperexcitability in neuropathic pain states. Spinal clonidine inhibits evoked and spontaneous firing, whereas reboxetine selectively inhibits evoked firing.

Pontine noradrenergic neurones form part of a descending inhibitory system that influences spinal nociceptive processing. Weak or absent descending inhibition is a common feature of chronic pain patients. We examined the extent to which the descending noradrenergic system is tonically active, how control of spinal neuronal excitability is integrated into thalamic relays within sensory-discriminative projection pathways, and how this inhibitory control is altered after nerve injury. In vivo electrophysiology was performed in anaesthetised spinal nerve–ligated (SNL) and sham-operated rats to record from wide dynamic range neurones in the ventral posterolateral thalamus (VPL). In sham rats, spinal block of α₂-adrenoceptors with atipamezole resulted in enhanced stimulus-evoked and spontaneous firing in the VPL, and produced conditioned place avoidance. However, in SNL rats, these conditioned avoidance behaviours were absent. Furthermore, inhibitory control of evoked neuronal responses was lost, but spinal atipamezole markedly increased spontaneous firing. Augmenting spinal noradrenergic tone in neuropathic rats with reboxetine, a selective noradrenergic reuptake inhibitor, modestly reinstated inhibitory control of evoked responses in the VPL but had no effect on spontaneous firing. By contrast, clonidine, an α₂ agonist, inhibited both evoked and spontaneous firing, and exhibited increased potency in SNL rats compared with sham controls. These data suggest descending noradrenergic inhibitory pathways are tonically active in sham rats. Moreover, in neuropathic states, descending inhibitory control is diminished, but not completely absent, and distinguishes between spontaneous and evoked neuronal activity. These observations may have implications for how analgesics targeting the noradrenergic system provide relief.

Strategies to Treat Chronic Pain and Strengthen Impaired Descending Noradrenergic Inhibitory System

Gabapentinoids (gabapentin and pregabalin) and antidepressants (tricyclic antidepressants and serotonin noradrenaline reuptake inhibitors) are often used to treat chronic pain. The descending noradrenergic inhibitory system from the locus coeruleus (LC) to the dorsal horn of the spinal cord plays an important role in the analgesic mechanisms of these drugs. Gabapentinoids activate the LC by inhibiting the release of γ-aminobutyric acid (GABA) and inducing the release of glutamate, thereby increasing noradrenaline levels in the spinal cord. Antidepressants increase noradrenaline levels in the spinal cord by inhibiting reuptake, and accumulating noradrenaline inhibits chronic pain through α₂-adrenergic receptors in the spinal cord. Recent animal studies, however, revealed that the function of the descending noradrenergic inhibitory system is impaired in chronic pain states. Other recent studies found that histone deacetylase inhibitors and antidepressants restore the impaired noradrenergic descending inhibitory system acting on noradrenergic neurons in the LC.

Monoamines as Drug Targets in Chronic Pain: Focusing on Neuropathic Pain

Monoamines are involved in regulating the endogenous pain system and indeed, peripheral and central monoaminergic dysfunction has been demonstrated in certain types of pain, particularly in neuropathic pain. Accordingly, drugs that modulate the monaminergic system and that were originally designed to treat depression are now considered to be first line treatments for certain types of neuropathic pain (e.g., serotonin and noradrenaline (and also dopamine) reuptake inhibitors). The analgesia induced by these drugs seems to be mediated by inhibiting the reuptake of these monoamines, thereby reinforcing the descending inhibitory pain pathways. Hence, it is of particular interest to study the monoaminergic mechanisms involved in the development and maintenance of chronic pain. Other analgesic drugs may also be used in combination with monoamines to facilitate descending pain inhibition (e.g., gabapentinoids and opioids) and such combinations are often also used to alleviate certain types of chronic pain. By contrast, while NSAIDs are thought to influence the monoaminergic system, they just produce consistent analgesia in inflammatory pain. Thus, in this review we will provide preclinical and clinical evidence of the role of monoamines in the modulation of chronic pain, reviewing how this system is implicated in the analgesic mechanism of action of antidepressants, gabapentinoids, atypical opioids, NSAIDs and histaminergic drugs.

Dexmedetomidine attenuates persistent postsurgical pain by upregulating K+-Cl- cotransporter-2 in the spinal dorsal horn in rats

Background

Dexmedetomidine (DEX) could have an analgesic effect on pain transmission through the modulation of brain-derived neurotrophic factor (BDNF). In addition, KCC2-induced shift in neuronal Cl− homeostasis is crucial for postsynaptic inhibition mediated by GABAA receptors. Accumulating evidence shows that nerve injury, peripheral inflammation and stress activate the spinal BDNF/TrkB signal, which results in the downregulation of KCC2 transport and expression, eventually leads to GAGAergic disinhibition and hyperalgesia. The aim of this experiment was to explore the interaction between DEX and KCC2 at a molecular level in rats in the persistent postsurgical pain (PPSP).

Methods

PPSP in rats was evoked by the skin/muscle incision and retraction (SMIR). Mechanical hypersensitivity was assessed with the Dynamic Plantar Aesthesiometer. Western blot and immunofluorescence assay were used to assess the expressions of related proteins.

Results

In the first part of our experiment, the results revealed that the BDNF/TrkB-KCC2 signal plays a critical role in the development of SMIR-evoked PPSP; the second part showed that intraperitoneal administrations of 40 µg/kg DEX at 15 min presurgery and 1 to 3 days post-surgery significantly attenuated SMIR-evoked PPSP. Simultaneously, SMIR-induced KCC2 downregulation was partly reversed, which coincided with the inhibition of the BDNF/TrkB signal in the spinal dorsal horn. Moreover, intrathecal administrations of KCC2 inhibitor VU0240551 significantly reduced the analgesic effect of DEX on SMIR-evoked PPSP.

Conclusion

The results of our study indicated that DEX attenuated PPSP by restoring KCC2 function through reducing BDNF/TrkB signal in the spinal dorsal horn in rats, which provides a new insight into the treatment of chronic pain in clinical postsurgical pain management.

Comparison of Morphine and Clonidine as Adjuvants in Paravertebral Block

BACKGROUND

General anesthesia (GA) has been considered as the gold standard for breast cancer surgery. The problem of postoperative pain as well as the high incidence of nausea and vomiting has led to the search for a better modality for pain management with fewer side effects. In the last few years, paravertebral block (PVB) has gained immense popularity either in combination with GA or by itself for the anesthetic management of patients undergoing breast surgery.

CONTEXT

Paravertebral block in breast surgery.

AIMS

This study aims to evaluate the efficacy and duration of postoperative analgesia provided by ultrasound (USG)-guided PVB with bupivacaine and morphine versus bupivacaine and clonidine in patients undergoing modified radical mastectomy (MRM).

SUBJECT AND METHODS

In the study, 70 patients who were scheduled for MRM were enrolled and randomly divided into Group M (n = 35) and Group C (n = 35). Both groups received USG-guided PVB at T2-T3 after administering GA. Group M received 2 mg/kg 0.5% bupivacaine with 0.05 mg/kg morphine and Group C received 2 mg/kg 0.5% bupivacaine with 1 μg/kg clonidine in the block. Postoperatively, pain intensity was recorded using the visual analog scale (VAS) (0-10 scale) at 1, 2, 6, 18, and 24 h duration when patients were resting and during a standardized movement. Modified Post Anaesthesia Discharge Scoring System was assessed at 1, 2, 6, 18 and 24 h after surgery.

RESULTS

In this study conducted on 70 patients, VAS scores (both at rest and on movement) were found comparable at postoperative 1, 2, 6, 18, and 24 h (P > 0.05). There was no statistical difference in comparing postanesthesia discharging scoring in both the groups. No incidence of postoperative nausea and vomiting was seen in any group.

CONCLUSIONS

Morphine and clonidine in PVB are equally effective, and there is no superiority of one agent over the other. Hence, both drugs may be used with equal efficacy as adjuvants to bupivacaine in PVB for providing postoperative analgesia.

Intrathecal clonidine as an adjuvant for neuraxial anaesthesia during caesarean delivery: a systematic review and meta-analysis of randomised trials

BACKGROUND

Clonidine is used as adjuvant to local anaesthetics for spinal anaesthesia. Its potential harm and benefits have not been systematically reviewed in obstetrics, and medical regulatory authorities do not recommend its intrathecal administration. The aim of this study was to assess the safety and efficacy of intrathecal clonidine for caesarean delivery.

METHODS

We conducted a systematic literature search in Medline, Embase, the Cochrane Library databases and trial registries for randomised trials assessing intrathecal clonidine as an adjuvant to local anaesthetics in patients undergoing caesarean delivery. Studies were assessed for quality, and data were extracted on study characteristics, safety and efficacy. Pooled data analysis using random-effects models was performed. Relative risk (RR) or mean difference with 95% confidence intervals (CI) were used to analyse outcomes.

RESULTS

Of 201 reports screened, 12 relevant clinical trials were included. Clonidine prolonged the duration of sensory block by 128.2min (95% CI 81.7 to 174.8) and motor block by 44.7min (95% CI 8.7 to 80.7). Clonidine increased sedation, RR 3.92 (95% CI 1.17 to 13.14), but did not increase the risk of hypotension, pruritus or postoperative nausea and vomiting. Apgar scores at 1 or 5min were not influenced by the addition of intrathecal clonidine.

CONCLUSION

Clonidine is an effective and safe adjuvant to local anaesthetics for spinal anaesthesia for caesarean delivery. This opens the debate as to whether intrathecal clonidine as an "off label" prescription should be reconsidered by medical regulatory authorities.

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

Background and aims

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

Methods

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

Results

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

Conclusions and implications

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

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

Multimodal intrathecal analgesia in refractory cancer pain

Background and aims

Cancer pain treatment has improved over the last decades. The majority of this population can be treated effectively with analgesics following the Guidelines of the original World Health Organisation (WHO). Unfortunately 10–15% of these patients still suffer from severe and refractory cancer pain, especially in the terminal phases of disease and require additional pain management modalities. Therefore, end-stage clinical interventions are particularly needed to minimize the perception of pain. With intrathecal therapy (ITT), drugs are delivered close to their site of action in the central nervous system avoiding first-pass metabolism and blood–brain barrier. It may improve analgesia with a smaller dose and possibly achieve a reduction in systemic or cerebral side effects compared to oral supplied medication alone. Multimodal analgesia enables further dose reduction with improved analgesia and fewer side effects.

Methods

In this retrospective research we investigated the effectiveness and side-effect profile of intrathecal morphine, bupivacaine and clonidine. Patients were followed until death occurred. Pain scores and side effects were recorded before initiating ITT (T0), just after initiating ITT (T1), at hospital discharge (T2), in the ambulant setting (T3) and the last obtained scores before death occurred (T4).

Results

Nine patients were included who suffered from severe and refractory cancer pain, not reacting to conventional pain management or had intolerable side effects. Primary tumour location was pancreatic (4), urothelial (3) and prostate (2). Primary pain was considered neuropathic or mixed neuropathic-nociceptive. The treatment team consisted of an anaesthetist, specialized nurse in coordination with primary physician, treating oncologist and specialized home care.

All patients were free of pain after initiation of the intrathecal therapy. The average follow-up period was 11 weeks in which there was a slight increase in NRS-score. In the last days before death occurred, half the patients were still free of pain. There were no problems during insertion of the catheter, device malfunction or infection. No severe adverse events defined as hypotension requiring inotropes, respiratory depression or neurological deficits were observed. Three patients experienced mild hypotension which gradually decreased after clonidine dose adjustment. Lower extremity weakness occurred in three patients as well. After bupivacaine dose adjustment the weakness disappeared in two patients and in one patient the lower extremity weakness persisted as a result of conus compression by tumour.

Conclusion and implications

Multimodal IT treatment with morphine, bupivacaine and clonidine is effective and safe for treating refractory cancer pain in the terminal phase of disease.

The study offers an important contribution to literature where there is still lack of convincing evidence about the benefits and harms of this type of pain management in patients with otherwise refractory cancer pain.

Activation of the trigeminal α2-adrenoceptor produces sex-specific, estrogen dependent thermal antinociception and antihyperalgesia using an operant pain assay in the rat

Higher prevalence of several pain disorders in women and sexual dimorphism in G-protein coupled receptor-induced analgesia has been reported. We have previously shown that α2-adrenoceptor-induced antinociception is sex-specific and attenuated by estrogen in the female rat. However, this evidence was obtained using reflexive withdrawal-based nociceptive assays conducted on restrained animals that may not involve cerebral processing. Hence, we evaluated whether activation of the trigeminal α2-adrenoceptor produces sex-specific antinociceptive and antihyperalgesic effects in the orofacial region of the rat using a reward conflict-based operant paradigm in which animals must tolerate nociceptive thermal stimulation to be rewarded. Male and ovariectomized (OVX) Sprague-Dawley rats were implanted intracisternally with a PE10 cannula for drug injections. A group of OVX rats (OVX+E) was administered subcutaneously with estradiol 48h before the test. Effect of clonidine, an α2-adrenoceptor agonist, was determined on the operant pain assay using a fully automated Orofacial Pain Assessment Device. Number of spout licks, thermode contacts, and amount of reward intake were automatically recorded by the ANY-maze software. Using acute pain modeling, clonidine produced a dose-dependent increase in all three parameters in male and OVX groups, however, it was ineffective in the OVX+E group. Similarly, using inflammatory pain modeling, clonidine significantly increased these parameters in carrageenan-treated male and OVX groups but not in the OVX+E group. Thus, α2-adrenoceptor activation produces sex-specific antinociception and antihyperalgesia and estrogen attenuates these effects in female rats using an operant pain assay. These findings may help the discovery of effective analgesics for each sex.

Canadian recommendations for the management of breakthrough cancer pain

Breakthrough cancer pain (btcp) represents an important element in the spectrum of cancer pain management. Because most btcp episodes peak in intensity within a few minutes, speed of medication onset is crucial for proper control. In Canada, several current provincial guidelines for the management of cancer pain include a brief discussion about the treatment of btcp; however, there are no uniform national recommendations for the management of btcp. That lack, accompanied by unequal access to pain medication across the country, contributes to both regional and provincial variability in the management of btcp. Currently, immediate-release oral opioids are the treatment of choice for btcp. This approach might not always offer optimal speed for onset of action and duration to match the rapid nature of an episode of btcp. Novel transmucosal fentanyl formulations might be more appropriate for some types of btcp, but limited access to such drugs hinders their use. In addition, the recognition of btcp and its proper assessment, which are crucial steps toward appropriate treatment selection, remain challenging for many health care professionals. To facilitate appropriate management of btcp, a group of prominent Canadian specialists in palliative care, oncology, and anesthesiology convened to develop a set of recommendations and suggestions to assist Canadian health care providers in the treatment of btcp and the alleviation of the suffering and discomfort experienced by adult cancer patients.

Pain Modulation and Autonomic Function: The Effect of Clonidine

OBJECTIVE

The α2-agonist clonidine is an analgesic agent, whose yet uncertain action may involve either increase in pain modulation efficiency, change in autonomic function, and/or decrease in anxiety level. The present study aimed to examine the effect of oral clonidine on pain perception in healthy subjects in order to reveal its mode of action.

DESIGN

Randomized, double-blind, placebo-controlled study.

SUBJECTS

Forty healthy subjects.

METHODS

Subjects received either 0.15 mg oral clonidine or placebo. We measured pain parameters of heat pain thresholds, tonic heat stimulus, mechanical temporal summation, offset analgesia (OA) and conditioned pain modulation (CPM); autonomic parameters of deep breathing ratio and heart rate variability indices obtained before, during, and after tonic heat stimulus; and psychological parameters of anxiety and pain catastrophizing.

RESULTS

Clonidine decreased systolic blood pressure (P = 0.022) and heart rate (P = 0.004) and increased rMSSD (P = 0.020), though no effect was observed on pain perception, pain modulation, and psychological parameters. Autonomic changes were correlated with pain modulation capacity; for OA, the separate slope model was significant (P = 0.008); in the clonidine group, more efficient OA was associated with lower heart rate (r = 0.633, P = 0.005), unlike in the placebo group.

CONCLUSIONS

The change in autonomic function that was related to the increase in pain modulation capacity, and the lack of change in anxiety, suggest a combined modulatory-autonomic mode of analgesic action for clonidine.

The Relationships Between Parasympathetic Function and Pain Perception: The Role of Anxiety

BACKGROUND

Previous studies have identified relationships between autonomic function and pain perception. Anxiety was found to influence both autonomic and pain responses. We examined the effect of anxiety level on parasympathetic function and pain perception as well as on the relationships between these 2 systems.

METHODS

Thirty healthy females were divided into high- and low-anxiety groups according to their trait anxiety levels. Parasympathetic function was obtained using heart rate variability, deep breathing, and Valsalva ratios. Pain perception parameters of heat pain thresholds, pain rating of supra-thresholds stimulus, mechanical temporal summation, and conditioned pain modulation response were examined.

RESULTS

The low-anxiety and high-anxiety groups exhibited no significant differences in the parasympathetic function and pain perception parameters. Assessment of the associations revealed that in the high-anxiety group, higher mean ratings of the tonic heat pain stimulus were significantly correlated with higher rMSSD (r² = 0.358, P = 0.019), but this was not found for the low-anxiety group (P = 0.282). In addition, in the high-anxiety group, efficient conditioned pain modulation response was correlated with higher deep breathing ratio (r² = 0.363, P = 0.023); however, in the low-anxiety group, the correlation did not reach significance (P = 0.109).

CONCLUSIONS

This study demonstrates the role of anxiety level on the relationships between parasympathetic function and pain perception. We suggest that a situation of high anxiety leads to higher norepinephrine levels that can influence both parasympathetic function and pain perception, thus explaining the significant relationships found between these 2 systems only in subjects with high anxiety.

Clonidine, an alpha-2 adrenoceptor agonist relieves mechanical allodynia in oxaliplatin-induced neuropathic mice; potentiation by spinal p38 MAPK inhibition without motor dysfunction and hypotension

Cancer chemotherapy with platinum-based antineoplastic agents including oxaliplatin frequently results in a debilitating and painful peripheral neuropathy. We evaluated the antinociceptive effects of the alpha-2 adrenoceptor agonist, clonidine on oxaliplatin-induced neuropathic pain. Specifically, we determined if (i) the intraperitoneal (i.p.) injection of clonidine reduces mechanical allodynia in mice with an oxaliplatin-induced neuropathy and (ii) concurrent inhibition of p38 mitogen-activated protein kinase (MAPK) activity by the p38 MAPK inhibitor SB203580 enhances clonidine's antiallodynic effect. Clonidine (0.01-0.1 mg kg(-1), i.p.), with or without SB203580(1-10 nmol, intrathecal) was administered two weeks after oxaliplatin injection(10 mg kg(-1), i.p.) to mice. Mechanical withdrawal threshold, motor coordination and blood pressure were measured. Postmortem expression of p38 MAPK and ERK as well as their phosphorylated forms(p-p38 and p-ERK) were quantified 30 min or 4 hr after drug injection in the spinal cord dorsal horn of treated and control mice. Clonidine dose-dependently reduced oxaliplatin-induced mechanical allodynia and spinal p-p38 MAPK expression, but not p-ERK. At 0.1 mg kg(-1), clonidine also impaired motor coordination and decreased blood pressure. A 10 nmol dose of SB203580 alone significantly reduced mechanical allodynia and p-p38 MAPK expression, while a subeffective dose(3 nmol) potentiated the antiallodynic effect of 0.03 mg kg(-1) clonidine and reduced the increased p-p38 MAPK. Coadministration of SB203580 and 0.03 mg kg(-1) clonidine decreased allodynia similar to that of 0.10 mg kg(-1) clonidine, but without significant motor or vascular effects. These findings demonstrate that clonidine treatment reduces oxaliplatin-induced mechanical allodynia. The concurrent administration of SB203580 reduces the dosage requirements for clonidine, thereby alleviating allodynia without producing undesirable motor or cardiovascular effects.

Interventional options for the management of refractory cancer pain--what is the evidence?

PURPOSE

Pain is the most common symptom in cancer patients. Standard pain treatment according to the WHO three-step analgesic ladder provides effective pain management in approximately 70-90% of cancer patients. Refractory pain is defined as not responding to "standard" treatments. Interventional analgesic techniques can be used in an attempt to control refractory pain in patients in whom conventional analgesic strategies fail to provide effective pain relief or are intolerable due to severe adverse effects. This systematic review aims to provide the latest evidence on interventional refractory pain management in cancer patients.

METHODS

Systematic literature search in Cochrane, EMBASE and PubMed including reviews and randomised controlled trials (RCTs) and non-randomised controlled trials in the absence of reviews.

RESULTS

Neuraxial analgesia may play a role in refractory cancer pain management. Paravertebral blocks decrease the incidence of persistent post-surgical pain after breast cancer. Coeliac plexus blocks improve pain scores in refractory pancreatic cancer pain for up to 4 weeks after the intervention with fewer burdensome side effects as compared to opioids. Cordotomy has mainly been studied in mesothelioma, and the case series suggest possible benefit for pain at the expense of a relatively high risk of side effects.

CONCLUSIONS

Overall, very few RCTs have been conducted on interventional pain techniques. In reality, it is very difficult to undertake large controlled trials for a number of reasons. Therefore, today's best evidence for practice may be from large case series of comparable patients with careful response and toxicity evaluation and follow-up.

Impaired Pain-evoked Analgesia after Nerve Injury in Rats Reflects Altered Glutamate Regulation in the Locus Coeruleus

Background:

Patients with neuropathic pain show reduced endogenous analgesia induced by a conditioned noxious stimulus. Here, the authors tested whether peripheral nerve injury impairs descending noradrenergic inhibition from the locus coeruleus (LC) after L5–L6 spinal nerve ligation (SNL) in rats.

Methods:

A subdermal injection of capsaicin was used to examine noxious stimulation–induced analgesia (NSIA), evoked LC glutamate and spinal noradrenaline release, and evoked LC neuronal activity in normal and SNL rats. The authors also examined the role of presynaptic metabotropic glutamate receptors or the astroglial glutamate transporter-1 (GLT-1).

Results:

SNL increased basal extracellular glutamate concentration in the LC (170.1%; 95% CI, 44.7 to 295.5; n = 15) and basal spinal cord noradrenaline release (252.1%; 95% CI, 113.6 to 391.3; n = 15), which was associated with an increased tonic LC neuronal activity and a down-regulation of GLT-1 in the LC. SNL reduced NSIA (−77.6%; 95% CI, −116.4 to −38.8; n = 14) and capsaicin evoked release of glutamate in the LC (−36.2%; 95% CI, −49.3 to −23.2; n = 8) and noradrenaline in the spinal cord (−38.8%; 95% CI, −45.1 to −32.5; n = 8). Capsaicin-evoked LC neuronal activation was masked in SNL rats. Removing autoinhibition of glutamatergic terminals by metabotropic glutamate receptor blockade or increasing GLT-1 expression by histone deacetylase inhibition restored NSIA in SNL rats. SNL-induced impairment of NSIA was mimicked in normal rats by knockdown of GLT-1 in the LC.

Conclusions:

These results suggest that increased extracellular glutamate in the LC consequent to down-regulation of GLT-1 contributes to LC dysfunction and impaired pain-evoked endogenous analgesia after nerve injury.

The evidence of neuraxial administration of analgesics for cancer-related pain: a systematic review

BACKGROUND

The present systematic review analysed the existing evidence of analgesic efficacy and side effects of opioids without and with adjuvant analgesics delivered by neuraxial route (epidural and subarachnoid) in adult patients with cancer.

METHODS

Search strategy was elaborated with words related to cancer, pain, neuraxial route, analgesic and side effects. The search was performed in PubMed, EMBASE, and Cochrane for the period until February 2014. Studies were analysed according to methods, results, quality of evidence, and strength of recommendation.

RESULTS

The number of abstracts retrieved was 2147, and 84 articles were selected for full reading. The final selection comprised nine articles regarding randomised controlled trials (RCTs) divided in four groups: neuraxial combinations of opioid and adjuvant analgesic compared with neuraxial administration of opioid alone (n = 4); single neuraxial drug in bolus compared with continuous administration (n = 2); single neuraxial drug compared with neuraxial placebo (n = 1); and neuraxial opioid combined with or without adjuvant analgesic compared with other comprehensive medical management than neuraxial analgesics (n = 2). The RCTs presented clinical and methodological diversity that precluded a meta-analysis. They also presented several limitations, which reduced study internal validity. However, they demonstrated better pain control for all interventions analysed. Side effects were described, but there were few significant differences in favour of the tested interventions.

CONCLUSION

Heterogeneous characteristics and several methodological limitations of the studies resulted in evidence of low quality and a weak recommendation for neuraxial administration of opioids with or without adjuvant analgesics in adult patients with cancer.

Intrathecal clonidine and adenosine: effects on pain and sensory processing in patients with chronic regional pain syndrome

Chronic pain may be accompanied by hyperalgesia and allodynia, and analgesic interventions may reduce these hypersensitivity phenomena. Preclinical data suggest that intrathecal clonidine and adenosine reduce hypersensitivity, but only clonidine reduces pain; therefore, we tested the effects of these interventions in patients with chronic pain. Twenty-two subjects with pain and hyperalgesia in a lower extremity from complex regional pain syndrome were recruited in a double-blind crossover study to receive intrathecal clonidine, 100 μg, or adenosine, 2 mg. Primary outcome measure was proportion with ≥30% reduction in pain 2 hours after injection, and secondary measures were pain report, areas of hypersensitivity, and temporal summation to heat stimuli. Treatments did not differ in the primary outcome measure (10 met success criterion after clonidine administration and 5 after adenosine administration), although they did differ in pain scores over time, with clonidine having a 3-fold greater effect (P = 0.014). Both drugs similarly reduced areas of hyperalgesia and allodynia by approximately 30% and also inhibited temporal summation. The percentage change in pain report did not correlate with the percentage change in areas of hyperalgesia (P = 0.09, r = 0.08) or allodynia (P = 0.24, r = 0.24) after drug treatment. Both intrathecal clonidine and adenosine acutely inhibit experimentally induced and clinical hypersensitivity in patients with chronic regional pain syndrome. Although these drugs do not differ in analgesia by the primary outcome measure, their difference in effect on pain scores over time and lack of correlation between effect on pain and hypersensitivity suggest that analgesia does not parallel antihyperalgesia with these treatments.

Topical clonidine for neuropathic pain

BACKGROUND

Clonidine is a presynaptic alpha-2-adrenergic receptor agonist used for many years to treat hypertension and other conditions, including chronic pain. Adverse events associated with systemic use of the drug have limited its application. Topical use of drugs is currently gaining interest, as it may limit adverse events without loss of analgesic efficacy. Topical clonidine (TC) formulations have been investigated recently in clinical trials.

OBJECTIVES

The objectives of this review were to assess the analgesic efficacy of TC for chronic neuropathic pain in adults and to assess the frequency of adverse events associated with clinical use of TC for chronic neuropathic pain.

SEARCH METHODS

We searched the Cochrane Register of Studies (CRS) Online (Cochrane Central Register of Controlled Trials (CENTRAL)), MEDLINE and EMBASE databases, reference lists of retrieved papers and trial registries, and we contacted experts in the field. We performed the most recent search on 17 September 2014.

SELECTION CRITERIA

We included randomised, double-blind studies of at least two weeks' duration comparing TC versus placebo or other active treatment in patients with chronic neuropathic pain.

DATA COLLECTION AND ANALYSIS

Two review authors extracted data from the studies and assessed bias. We planned three tiers of evidence analysis. The first tier was designed to analyse data meeting current best standards, by which studies reported the outcome of at least 50% pain intensity reduction over baseline (or its equivalent) without use of the last observation carried forward or other imputation method for dropouts, reported an intention-to-treat (ITT) analysis, lasted eight weeks or longer, had a parallel-group design and included at least 200 participants (preferably at least 400) in the comparison. The second tier was designed to use data from at least 200 participants but in cases in which one of the above conditions was not met. The third tier of evidence was assumed in other situations.

MAIN RESULTS

We included two studies in the review, with a total of 344 participants. Studies lasted 8 weeks and 12 weeks and compared TC versus placebo. 0.1%. TC was applied in gel form to the painful area two to three times daily.Studies included in this review were subject to potential bias and were classified as of moderate or low quality. One drug manufacturer supported both studies.We found no top-tier evidence for TC in neuropathic pain. Second-tier evidence indicated slight improvement after the drug was used in study participants with painful diabetic neuropathy (PDN). A greater number of participants in the TC group had at least 30% reduction in pain compared with placebo (risk ratio (RR) 1.35, 95% confidence interval (CI) 1.03 to 1.77; number needed to treat for an additional beneficial outcome (NNTB) 8.33, 95% CI 4.3 to 50). Third-tier evidence indicated that TC was no better than placebo for achieving at least 50% reduction in pain intensity and on the Patient Global Impression of Change Scale. The two included studies could be subject to significant bias. We found no studies that reported other neuropathic pain conditions.The rate of adverse events did not differ between groups, with the exception of a higher incidence of mild skin reactions in the placebo group, which should have no clinical significance.

AUTHORS' CONCLUSIONS

Limited evidence from a small number of studies of moderate to low quality suggests that TC may provide some benefit in peripheral diabetic neuropathy. The drug may be useful in situations for which no better treatment options are available because of lack of efficacy, contraindications or adverse events. Additional trials are needed to assess TC in other neuropathic pain conditions and to determine how patients who have a chance to respond to the drug should be selected for treatment.

Effects of centrally acting analgesics on spinal segmental reflexes and wind-up

BACKGROUND

The spinal cord is a prime site of action for analgesia. Here we characterize the effects of established analgesics on segmental spinal reflexes. The aim of the study was to look for the pattern of action or signature of analgesic effects on these reflexes.

METHODS

We used a spinal cord in vitro preparation of neonate mice to record ventral root responses to dorsal root stimulation. Pregabalin, clonidine, morphine and duloxetine and an experimental sigma-1 receptor antagonist (S1RA) were applied to the preparation in a cumulative concentration protocol. Drug effects on the wind-up produced by repetitive stimulation of C-fibres and on responses to single A- and C-fibre intensity stimuli were analysed.

RESULTS

All compounds produced a concentration-dependent inhibition of total spikes elicited by repetitive stimulation. Concentrations producing ∼50% reduction in this parameter were (in μM) clonidine (0.01), morphine (0.1), pregabalin (1), duloxetine (10) and S1RA (30). At these concentrations clonidine, pregabalin and S1RA had significant effects on the wind-up index and little depressant effects on responses to single stimuli. Morphine and duloxetine did not depress wind-up index and showed large effects on responses to single stimuli. None of the compounds had strong effects on the amplitude of the non-nociceptive monosynaptic reflex.

CONCLUSIONS

morphine and duloxetine had general depressant effects on spinal reflexes, whereas the effects of clonidine, pregabalin and S1RA appeared to be restricted to signals originated by strong repetitive activation of C-fibres. Results are discussed in the context of reported behavioural effects of the compounds studied.

Audit of intrathecal drug delivery for patients with difficult-to-control cancer pain shows a sustained reduction in pain severity scores over a 6-month period

BACKGROUND

Intrathecal drug delivery is known to be effective in alleviating cancer pain in patients for whom the conventional World Health Organization approach has proved insufficient. A multidisciplinary interventional cancer pain service was established in the West of Scotland in 2008 with the aim of providing a safe and effective intrathecal drug delivery service for patients with difficult-to-control cancer pain.

AIM

The aim of the intrathecal drug delivery service is to improve pain scores as evaluated by pain scores before and after insertion of an intrathecal drug delivery device.

DESIGN

Pain is monitored before and after intrathecal drug delivery implantation using the Brief Pain Inventory. Following implantation, pumps are refilled fortnightly and repeat Brief Pain Inventory assessments are undertaken. This prospective case series analyses change in Brief Pain Inventory domains for patients who had an intrathecal drug delivery implanted using a paired sample t-test.

RESULTS

Data are presented from 2008-2013 for 22 patients receiving an intrathecal drug delivery system who experienced an immediate improvement in their pain that was both clinically and statistically significant. One week after insertion, the average pain score on the Brief Pain Inventory fell from 6.8 (pre-intrathecal drug delivery) to 3.0 (post-intrathecal drug delivery). Improvement in pain scores was sustained over a 6-month period.

CONCLUSION

Evaluation of results of this case series shows that with the appropriate use of intrathecal drug delivery systems, patients with difficult-to-control cancer pain can benefit from effective pain relief for many months.

Evidence-based Clinical Practice Guidelines for Interventional Pain Management in Cancer Pain

Intractable cancer pain not amenable to standard oral or parenteral analgesics is a horrifying truth in 10-15% of patients. Interventional pain management techniques are an indispensable arsenal in pain physician's armamentarium for severe, intractable pain and can be broadly classified into neuroablative and neuromodulation techniques. An array of neurolytic techniques (chemical, thermal, or surgical) can be employed for ablation of individual nerve fibers, plexuses, or intrathecalneurolysis in patients with resistant pain and short life-expectancy. Neuraxial administration of drugs and spinal cord stimulation to modulate or alter the pain perception constitutes the most frequently employed neuromodulation techniques. Lately, there is a rising call for early introduction of interventional techniques in carefully selected patients simultaneously or even before starting strong opioids. After decades of empirical use, it is the need of the hour to head towards professionalism and standardization in order to secure credibility of specialization and those practicing it. Even though the interventional management has found a definite place in cancer pain, there is a dearth of evidence-based practice guidelines for interventional therapies in cancer pain. This may be because of paucity of good quality randomized controlled trials (RCTs) evaluating their safety and efficacy in cancer pain. Laying standardized guidelines based on existing and emerging evidence will act as a foundation step towards strengthening, credentialing, and dissemination of the specialty of interventional cancer pain management. This will also ensure an improved decision-making and quality of life (QoL) of the suffering patients.

Glial cell line-derived neurotrophic factor-mediated enhancement of noradrenergic descending inhibition in the locus coeruleus exerts prolonged analgesia in neuropathic pain

BACKGROUND AND PURPOSE

The locus coeruleus (LC) is the principal nucleus containing the noradrenergic neurons and is a major endogenous source of pain modulation in the brain. Glial cell line-derived neurotrophic factor (GDNF), a well-established neurotrophic factor for noradrenergic neurons, is a major pain modulator in the spinal cord and primary sensory neurons. However, it is unknown whether GDNF is involved in pain modulation in the LC.

EXPERIMENTAL APPROACH

Rats with chronic constriction injury (CCI) of the left sciatic nerve were used as a model of neuropathic pain. GDNF was injected into the left LC of rats with CCI for 3 consecutive days and changes in mechanical allodynia and thermal hyperalgesia were assessed. The α2 -adrenoceptor antagonist yohimbine was injected intrathecally to assess the involvement of descending inhibition in GDNF-mediated analgesia. The MEK inhibitor U0126 was used to investigate whether the ERK signalling pathway plays a role in the analgesic effects of GDNF.

KEY RESULTS

Both mechanical allodynia and thermal hyperalgesia were attenuated 24 h after the first GDNF injection. GDNF increased the noradrenaline content in the dorsal spinal cord. The analgesic effects continued for at least 3 days after the last injection. Yohimbine abolished these effects of GDNF. The analgesic effects of GDNF were partly, but significantly, inhibited by prior injection of U0126 into the LC.

CONCLUSIONS AND IMPLICATIONS

GDNF injection into the LC exerts prolonged analgesic effects on neuropathic pain in rats by enhancing descending noradrenergic inhibition.

Clonidine Reduces Nociceptive Responses in Mouse Orofacial Formalin Model: Potentiation by Sigma-1 Receptor Antagonist BD1047 without Impaired Motor Coordination

Although the administration of clonidine, an alpha-2 adrenoceptor agonist, significantly attenuates nociception and hyperalgesia in several pain models, clinical trials of clonidine are limited by its side effects such as drowsiness, hypotension and sedation. Recently, we determined that the sigma-1 receptor antagonist BD1047 dose-dependently reduced nociceptive responses in a mouse orofacial formalin model. Here we examined whether intraperitoneal injection of clonidine suppressed the nociceptive responses in the orofacial formalin test, and whether co-administration with BD1047 enhances lower-dose clonidine-induced anti-nociceptive effects without the disruption of motor coordination and blood pressure. Formalin (5%, 10 µL) was subcutaneously injected into the right upper lip, and the rubbing responses with the ipsilateral fore- or hind-paw were counted for 45 min. Clonidine (10, 30 or 100 µg/kg) was intraperitoneally administered 30 min before formalin injection. Clonidine alone dose-dependently reduced nociceptive responses in both the first and second phases. Co-localization for alpha-2A adrenoceptors and sigma-1 receptors was determined in trigeminal ganglion cells. Interestingly, the sub-effective dose of BD1047 (3 mg/kg) significantly potentiated the anti-nociceptive effect of lower-dose clonidine (10 or 30 µg/kg) in the second phase. In particular, the middle dose of clonidine (30 µg/kg) in combination with BD1047 produced an anti-nociceptive effect similar to that of the high-dose clonidine, but without a significant motor dysfunction or hypotension. In contrast, mice treated with the high dose of clonidine developed severe impairment in motor coordination and blood pressure. These data suggest that a combination of low-dose clonidine with BD1047 may be a novel and safe therapeutic strategy for orofacial pain management.

Morphine and clonidine combination therapy improves therapeutic window in mice: synergy in antinociceptive but not in sedative or cardiovascular effects

Opioids are used to manage all types of pain including acute, cancer, chronic neuropathic and inflammatory pain. Unfortunately, opioid-related adverse effects such as respiratory depression, tolerance, physical dependence and addiction have led to an underutilization of these compounds for adequate pain relief. One strategy to improve the therapeutic utility of opioids is to co-administer them with other analgesic agents such as agonists acting at α₂-adrenergic receptors (α₂ARs). Analgesics acting at α₂ARs and opioid receptors (ORs) frequently synergize when co-administered in vivo. Multimodal analgesic techniques offer advantages over single drug treatments as synergistic combination therapies produce analgesia at lower doses, thus reducing undesired side effects. This inference presumes, however, that the synergistic interaction is limited to the analgesic effects. In order to test this hypothesis, we examined the effects of α₂AR/OR combination therapy in acute antinociception and in the often-undesired side effects of sedation and cardiovascular depression in awake unrestrained mice. Morphine, clonidine or their combination was administered by spinal or systemic injection in awake mice. Antinociception was determined using the warm water tail flick assay (52.5°C). Sedation/motor impairment was evaluated using the accelerating rotarod assay and cardiovascular function was monitored by pulse oximetry. Data were converted to percent maximum possible effect and isobolographic analysis was performed to determine if an interaction was subadditive, additive or synergistic. Synergistic interactions between morphine and clonidine were observed in the antinociceptive but not in the sedative/motor or cardiovascular effects. As a result, the therapeutic window was improved ∼200-fold and antinociception was achieved at non-sedating doses with little to no cardiovascular depression. In addition, combination therapy resulted in greater maximum analgesic efficacy over either drug alone. These data support the utility of combination adrenergic/opioid therapy in pain management for antinociceptive efficacy with reduced side-effect liability.

Activation of mesocorticolimbic reward circuits for assessment of relief of ongoing pain: a potential biomarker of efficacy

Preclinical assessment of pain has increasingly explored operant methods that may allow behavioral assessment of ongoing pain. In animals with incisional injury, peripheral nerve block produces conditioned place preference (CPP) and activates the mesolimbic dopaminergic reward pathway. We hypothesized that activation of this circuit could serve as a neurochemical output measure of relief of ongoing pain. Medications commonly used clinically, including gabapentin and nonsteroidal anti-inflammatory drugs (NSAIDs), were evaluated in models of post-surgical (1 day after incision) or neuropathic (14 days after spinal nerve ligation [SNL]) pain to determine whether the clinical efficacy profile of these drugs in these pain conditions was reflected by extracellular dopamine (DA) release in the nucleus accumbens (NAc) shell. Microdialysis was performed in awake rats. Basal DA levels were not significantly different between experimental groups, and no significant treatment effects were seen in sham-operated animals. Consistent with clinical observation, spinal clonidine produced CPP and produced a dose-related increase in net NAc DA release in SNL rats. Gabapentin, commonly used to treat neuropathic pain, produced increased NAc DA in rats with SNL but not in animals with incisional, injury. In contrast, ketorolac or naproxen produced increased NAc DA in animals with incisional but not neuropathic pain. Increased extracellular NAc DA release was consistent with CPP and was observed selectively with treatments commonly used clinically for post-surgical or neuropathic pain. Evaluation of NAc DA efflux in animal pain models may represent an objective neurochemical assay that may serve as a biomarker of efficacy for novel pain-relieving mechanisms.

Descending pain modulation and chronification of pain

PURPOSE OF REVIEW

Chronic pain is an important public health problem that negatively impacts quality of life of affected individuals and exacts an enormous socio-economic cost. Currently available therapeutics provide inadequate management of pain in many patients. Acute pain states generally resolve in most patients. However, for reasons that are poorly understood, in some individuals, acute pain can transform to a chronic state. Our understanding of the risk factors that underlie the development of chronic pain is limited. Recent studies have suggested an important contribution of dysfunction in descending pain modulatory circuits to pain 'chronification'. Human studies provide insights into possible endogenous and exogenous factors that may promote the conversion of pain into a chronic condition.

RECENT FINDINGS

Descending pain modulatory systems have been studied and characterized in animal models. Human brain imaging techniques, deep brain stimulation and the mechanisms of action of drugs that are effective in the treatment of pain confirm the clinical relevance of top-down pain modulatory circuits. Growing evidence supports the concept that chronic pain is associated with a dysregulation in descending pain modulation. Disruption of the balance of descending modulatory circuits to favour facilitation may promote and maintain chronic pain. Recent findings suggest that diminished descending inhibition is likely to be an important element in determining whether pain may become chronic. This view is consistent with the clinical success of drugs that enhance spinal noradrenergic activity, such as serotonin/norepinephrine reuptake inhibitors (SNRIs), in the treatment of chronic pain states. Consistent with this concept, a robust descending inhibitory system may be normally engaged to protect against the development of chronic pain. Imaging studies show that higher cortical and subcortical centres that govern emotional, motivational and cognitive processes communicate directly with descending pain modulatory circuits providing a mechanistic basis to explain how exogenous factors can influence the expression of chronic pain in a susceptible individual.

SUMMARY

Preclinical studies coupled with clinical pharmacologic and neuroimaging investigations have advanced our understanding of brain circuits that modulate pain. Descending pain facilitatory and inhibitory circuits arising ultimately in the brainstem provide mechanisms that can be engaged to promote or protect against pain 'chronification'. These systems interact with higher centres, thus providing a means through which exogenous factors can influence the risk of pain chronification. A greater understanding of the role of descending pain modulation can lead to novel therapeutic directions aimed at normalizing aberrant processes that can lead to chronic pain.