Interaction between intrathecal neostigmine and epidural clonidine in human volunteers

Comparison of adjuvant pharmaceuticals for caudal block in pediatric lower abdominal and urological surgeries: A network meta-analysis

STUDY OBJECTIVE

Caudal block helps relieve pain after sub-umbilical surgery in pediatric patients; however, the duration for which it exerts its analgesic effect is limited. The addition of certain adjuvant agents to local anesthetics (LAs) that are used to administer caudal block can prolong postoperative analgesia. Therefore, we aimed to compare the efficiencies and side effects of caudal adjuvants in the settings of pediatric lower abdominal and urological surgeries.

DESIGN

A network meta-analysis (NMA).

PATIENTS

One hundred and twelve randomized controlled trials (RCTs) involving 6800 pediatric patients were included in the final analysis.

INTERVENTIONS

Different adjuvant agents, namely clonidine, dexamethasone, dexmedetomidine, fentanyl, ketamine, magnesium, midazolam, morphine, neostigmine, and tramadol.

MEASUREMENTS

The primary outcome was the duration of analgesia. The secondary outcomes included the requirement for additional analgesia, analgesic consumption, and postoperative complications. The effects and rankings were evaluated using NMA and the surface under the cumulative ranking curve scores, respectively.

RESULTS

Neostigmine, dexmedetomidine, and dexamethasone were found to be the three most effective adjuvants that prolong the duration of analgesia for caudal block, and these adjuvants extended this duration by 8.9 h (95% confidence interval [CI], 7.1-10.7), 7.3 h (95% CI, 6.0-8.6), and 5.9 h (95% CI, 4.0-7.7), respectively. Caudal neostigmine was associated with an increase in the incidence of postoperative nausea and vomiting, whereas dexmedetomidine and dexamethasone showed no postoperative complications.

CONCLUSIONS

This NMA provided evidence and suggested that dexmedetomidine and dexamethasone may be the most beneficial adjuvant pharmaceutics adding to LAs for caudal block in children. However, given the off-label status of caudal dexmedetomidine and dexamethasone, further high-quality RCTs are still warranted, especially to determine whether delayed neurological complications will occur.

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.

Clinical Practice: Should we Radically Alter our Sedation of Critical Care Patients, Especially Given the COVID-19 Pandemics?

The high number of patients infected with the SARS-CoV-2 virus requiring care for ARDS puts sedation in the critical care unit (CCU) to the edge. Depth of sedation has evolved over the last 40 years (no-sedation, deep sedation, daily emergence, minimal sedation, etc.). Most guidelines now recommend determining the depth of sedation and minimizing the use of benzodiazepines and opioids. The broader use of alpha-2 adrenergic agonists ('alpha-2 agonists') led to sedation regimens beginning at admission to the CCU that contrast with hypnotics+opioids ("conventional" sedation), with major consequences for cognition, ventilation and circulatory performance. The same doses of alpha-2 agonists used for 'cooperative' sedation (ataraxia, analgognosia) elicit no respiratory depression but modify the autonomic nervous system (cardiac parasympathetic activation, attenuation of excessive cardiac and vasomotor sympathetic activity). Alpha-2 agonists should be selected only in patients who benefit from their effects ('personalized' indications, as opposed to a 'one size fits all' approach). Then, titration to effect is required, especially in the setting of systemic hypotension and/or hypovolemia. Since no general guidelines exist for the use of alpha-2 agonists for CCU sedation, our clinical experience is summarized for the benefit of physicians in clinical situations in which a recommendation might never exist (refractory delirium tremens; unstable, hypovolemic, hypotensive patients, etc.). Because the physiology of alpha-2 receptors and the pharmacology of alpha-2 agonists lead to personalized indications, some details are offered. Since interactions between conventional sedatives and alpha-2 agonists have received little attention, these interactions are addressed. Within the existing guidelines for CCU sedation, this article could facilitate the use of alpha-2 agonists as effective and safe sedation while awaiting large, multicentre trials and more evidence-based medicine.

Adjuvants in pain medicine. Selection of the drug depending on the desired effect – so which drug to choose?

To date, much research has focused on finding the ideal adjuvant for local anesthetics. Each of them can have different effects. In anesthesiology and pain medicine, depending on the purpose, one or another effect may be desirable. For example, in some situations it is desirable to accelerate the onset of action or prolong the duration of the block, in others the desired effect may be a “response to intravascular administration”, it should also be borne in mind that not all adjuvants are allowed for intrathecal administration.

Adjuvants in clinical regional anesthesia practice: A comprehensive review

Adjuvants are medications that work synergistically with local anesthetics to help enhance the duration and quality of analgesia in regional techniques. Regional anesthesia has become more prevalent as evidence continues to show efficacy, enhancement of patient care, increased patient satisfaction, and improved patient safety. Practitioners in the perioperative setting need to not only be familiar with regional techniques but also the medications used for them. Some examples of adjuvant medications for regional techniques include dexamethasone, alpha 2 agonists such as clonidine and dexmedetomidine, midazolam, buprenorphine, NMDA antagonists, including ketamine and magnesium, neostigmine, sodium bicarbonate, epinephrine, and non-steroidal anti-inflammatory drugs. The aim of the present investigation, therefore, is to provide a comprehensive review of the most commonly used non-opioid adjuvants in clinical practice today. Regional adjuvants can improve patient safety, increase patient satisfaction, and enhance clinical efficacy. Future studies and best practice techniques can facilitate standardization of regional anesthesia adjuvant dosing when providing nerve blocks in clinical practice.

Use of Intrathecal Neostigmine as an Adjunct to Other Spinal Medications in Perioperative and Peripartum Analgesia: A Meta-analysis

Intrathecal neostigmine has been used as an adjunct to intrathecal local anaesthetic or opioid to prolong regional analgesia and improve haemodynamic stability, with variable results. This meta-analysis aims to evaluate the effectiveness and side-effects of intrathecal neostigmine in the perioperative and peripartum settings. The literature search was based on Cochrane Controlled Trials Register, EMBASE and MEDLINE (from 1966 to 14 November 2003) databases. Volunteer and animal studies were excluded. We identified 26 studies and 19 were considered suitable for detailed data extraction. Intrathecal neostigmine increased the incidence of nausea and vomiting (OR 5.0, 95% CI: 3.4 to 7.3; P<0.00001), bradycardia requiring intravenous atropine (OR 2.7, 95% CI: 1.4 to 5.4; P=0.005), and anxiety, agitation, or restlessness (OR 10.3, 95% CI: 3.7 to 28.9; P=0.00001). It improved the overall 24 hour VAS score (–1.4 VAS pain score, 95% CI: -1.7 to -1.2, P<0.00001), delayed the time of first request for rescue analgesia (168 min, 95% CI: 125 to 211; P<0.00001), and reduced the total number of rescue injections of nonsteroidal anti-inflammatory drug within the first 24 hours (-0.8, 95% CI: -1.1 to -0.4; P=0.00001). It did not affect the duration of motor blockade (3.5 min, 95% CI: -1.5 to 8.6; P=0.17) or the total amount of ephedrine required (-0.4 mg, 95% CI: -1.5 to 0.7; P=0.5). Adding intrathecal neostigmine to other spinal medications improves perioperative and peripartum analgesia marginally when compared with placebo. It is associated with significant side-effects and the disadvantages outweigh the minor improvement in analgesia achieved.

Hypothesis: Fever control, a niche for alpha-2 agonists in the setting of septic shock and severe acute respiratory distress syndrome?

During severe septic shock and/or severe acute respiratory distress syndrome (ARDS) patients present with a limited cardio-ventilatory reserve (low cardiac output and blood pressure, low mixed venous saturation, increased lactate, low PaO2/FiO2 ratio, etc.), especially when elderly patients or co-morbidities are considered. Rescue therapies (low dose steroids, adding vasopressin to noradrenaline, proning, almitrine, NO, extracorporeal membrane oxygenation, etc.) are complex. Fever, above 38.5-39.5°C, increases both the ventilatory (high respiratory drive: large tidal volume, high respiratory rate) and the metabolic (increased O2 consumption) demands, further limiting the cardio-ventilatory reserve. Some data (case reports, uncontrolled trial, small randomized prospective trials) suggest that control of elevated body temperature ("fever control") leading to normothermia (35.5-37°C) will lower both the ventilatory and metabolic demands: fever control should simplify critical care management when limited cardio-ventilatory reserve is at stake. Usually fever control is generated by a combination of general anesthesia ("analgo-sedation", light total intravenous anesthesia), antipyretics and cooling. However general anesthesia suppresses spontaneous ventilation, making the management more complex. At variance, alpha-2 agonists (clonidine, dexmedetomidine) administered immediately following tracheal intubation and controlled mandatory ventilation, with prior optimization of volemia and atrio-ventricular conduction, will reduce metabolic demand and facilitate normothermia. Furthermore, after a rigorous control of systemic acidosis, alpha-2 agonists will allow for accelerated emergence without delirium, early spontaneous ventilation, improved cardiac output and micro-circulation, lowered vasopressor requirements and inflammation. Rigorous prospective randomized trials are needed in subsets of patients with a high fever and spiraling toward refractory septic shock and/or presenting with severe ARDS.

A Comparison of Intrathecal Dexmedetomidine and Neostigmine as Adjuvant to Ropivacaine for Lower Limb Surgeries: A Double-blind Randomized Controlled Study

Objective:

The primary objective of this study was to compare the analgesic effects of intrathecal ropivacaine with or without neostigmine or dexmedetomidine in lower limb surgeries. Secondary objectives were to study the characteristics of block, duration of analgesia, postoperative analgesic requirement, and associated side effects.

Materials and Methods:

Seventy-five patients posted for elective orthopedic lower limb surgeries under spinal anesthesia were randomly divided into three equal groups to receive intrathecal ropivacaine 0.5% alone (Group R), with adjuvant 5 μg dexmedetomidine (Group R + D) or 50 μg neostigmine (Group R + N). Time to achieve T10 sensory block, time to 2-segment regression, duration of regression to L4, maximum modified Bromage score and duration of analgesia were noted. The incidences of adverse events such as nausea, vomiting, hypotension, bradycardia, desaturation, shivering, and itching were also noted. Statistical analysis was performed using two sample t-test for normally distributed variables and Pearson's Chi-squared test for categorical data. The level of significance was set as P < 0.05.

Results:

Quality of motor and sensory blockage was significantly better in both Group R + D and Group R + N than Group R. Mean time to achieve T10 sensory block was lowest, time taken in regression of block by 2-segments and duration of regression to L4 was longest in Group R + D and was significant when compared to other groups. Adverse effects such as nausea and vomiting were highest in Group R + N and was statistically significant as compared to other groups.

Conclusions:

Dexmedetomidine is a better intrathecal adjuvant emerged as compared to neostigmine due to faster onset of anesthesia, better intra- and post-operative analgesia and prolonged duration of motor and sensory blockade without significant increase in adverse effects.

Short Term Analgesic Effects of 5% Dextrose Epidural Injections for Chronic Low Back Pain: A Randomized Controlled Trial

Background

Hypertonic dextrose injection (prolotherapy) is reported to reduce pain including non-surgical chronic low back pain (CLBP), and subcutaneous injection of 5% dextrose is reported to reduce neurogenic pain, hyperalgesia and allodynia. The mechanism in both cases is unclear, though a direct effect of dextrose on neurogenic pain has been proposed. This study assessed the short-term analgesic effects of epidural 5% dextrose injection compared with saline for non-surgical CLBP.

Methods

Randomized double-blind (injector, participant) controlled trial. Adults with moderate-to-severe non-surgical low back pain with radiation to gluteal or leg areas for at least 6 months received a single epidurogram-confirmed epidural injection of 10 mL of 5% dextrose or 0.9% saline using a published vertical caudal injection technique. The primary outcome was change in a numerical rating scale (NRS, 0 - 10 points) pain score between baseline and 15 minutes; and 2, 4, and 48 hours and 2 weeks post-injection. The secondary outcome was percentage of participants achieving 50% or more pain improvement at 4 hours.

Results and Conclusions

No baseline differences existed between groups; 35 participants (54 ± 10.7 years old; 11 female) with moderate-to-severe CLBP (6.7 ± 1.3 points) for 10.6 ± 10.5 years. Dextrose participants reported greater NRS pain score change at 15 minutes (4.4 ± 1.7 vs 2.4 ± 2.8 points; P = 0.015), 2 hours (4.6 ± 1.9 vs 1.8 ± 2.8 points; P = 0.001), 4 hours (4.6 ± 2.0 vs 1.4 ± 2.3 points; P < 0.001), and 48 hours (3.0 ± 2.3 vs 1.0 ± 2.1 points; P = 0.012), but not at 2 weeks (2.1 ± 2.9 vs 1.2 ± 2.4 points; P = 0.217). Eighty four percent (16/19) of dextrose recipients and 19% (3/16) of saline recipients reported ≥ 50% pain reduction at 4 hours (P < 0.001). These findings suggest a neurogenic effect of 5% dextrose on pain at the dorsal root level; waning pain control at 2 weeks suggests the need to assess the effect of serial dextrose epidural injections in a long-term study with robust outcome assessment.

Central Antinociceptive and Mechanism of Action of Pereskia bleo Kunth Leaves Crude Extract, Fractions, and Isolated Compounds

Pereskia bleo (Kunth) DC. (Cactaceae) is a plant commonly used in popular medicine in Malaysia. In this work, we evaluate the antinociceptive effect of P. bleo leaf extracts and isolated compounds in central antinociceptive model. Ethanol extract (E), hexane (H), ethyl acetate (EA), or butanol (B) fractions (30, 50, or 100 mg/kg, p.o.), sitosterol (from hexane) and vitexin (from ethyl acetate), were administered to mice. Antinociceptive effect was evaluated in the hot plate and capsaicin- or glutamate-induced licking models. Morphine (1 mg/kg, p.o.) was used as reference drug. Naloxone (1 mg/kg, i.p.), atropine (1 mg/kg, i.p.), and L-nitro arginine methyl ester (L-NAME, 3 mg/kg, i.p.) were administered 30 min earlier (100 mg/kg, p.o.) in order to evaluate the mechanism of the antinociceptive action. Higher dose of B developed an effect significantly superior to morphine-treated group. Naloxone prevented the antinociceptive effect of all fractions. L-NAME demonstrated effect against E, EA, and B. In all fractions, sitosterol and vitexin reduced the licking time after capsaicin injection. Glutamate-induced licking response was blocked by H, EA, and B. Our results indicate that Pereskia bleo fractions, sitosterol and vitexin, possessed a central antinociceptive effect. Part of this effect is mediated by opioid receptors and nitrergic pathway.

A systematic review of the effects of adding neostigmine to local anesthetics for neuraxial administration in obstetric anesthesia and analgesia

BACKGROUND

Drugs used in obstetric patients must accomplish two goals: efficacy and safety for both mother and fetus. Neostigmine has been co-administered epidurally and intrathecally with local anesthetics and other adjuncts in the obstetric setting. The aim of this meta-analysis was to assess the efficacy and incidence of adverse events related to the use of neostigmine in obstetric anesthesia.

METHODS

A meta-analysis of randomized-controlled human trials was conducted using the data sources Google Scholar and PubMed (updated 1 November 2014). Inclusion criteria were: random allocation to treatment; comparison of neostigmine or neostigmine with local anesthetics and/or other adjuvants versus placebo or placebo with local anesthetics and/or other adjuvants; and approval by an ethics committee.

RESULTS

The use of neostigmine as an adjuvant in neuraxial anesthesia is associated with a reduction in the dose of local anesthetic during labor analgesia and postoperative analgesia following cesarean section: mean reduction of local anesthetic (ropivacaine or bupivacaine) vs. control -4.08 (95% CI -6.7 to -1.5) mg/h (P=0.002). The risk of nausea was increased vs. control with intrathecal neostigmine (OR 8.99 [95% CI 4.74 to 17.05], P <0.001) but not with epidural neostigmine (OR 0.97 [95% CI 0.46 to 2.05], P=0.94). Use of neuraxial neostigmine was associated with a decrease in the risk of pruritus but there was no increase in the incidence of hypotension, dizziness or sedation and no effect on the incidence of abnormal fetal heart rate patterns or Apgar scores.

CONCLUSIONS

Neuraxial administration of neostigmine significantly reduces local anesthetic consumption without serious adverse side effects to the mother or fetus. However, neostigmine is only recommended for epidural administration as intrathecal use significantly increases the incidence of maternal nausea and vomiting.

Pharmacology of novel treatments for COPD: are fixed dose combination LABA/LAMA synergistic?

Bronchodilators are mainstay for the symptomatic treatment of chronic obstructive pulmonary disease (COPD) and the introduction of long-acting bronchodilators has led to an improvement in the maintenance treatment of this disease. Various clinical trials have evaluated the effects of fixed dose long-acting β2-agonists (LABA)/long-acting anti-muscarinics (LAMA) combinations and documented greater improvements in spirometry but such improvements do not always translate to greater improvements in symptom scores or reduction in the rates of exacerbation compared with a single component drug. An analysis of whether this significantly greater change in spirometry with combination therapy is additive or synergistic was undertaken and is the subject of this review. Bronchodilators are not disease modifiers and whilst glucocorticosteroids have been shown to reduce rates of exacerbation in moderate to severe COPD, the increase risk of pneumonia and bone fractures is a motivation enough to warrant developing novel anti-inflammatory and disease-modifying drugs and with the expectation of positive outcomes.

The evolution of spinal/epidural neostigmine in clinical application: Thoughts after two decades

Since the first clinical application of analgesia following spinal anticholinesterase by 1940's, several clinical double-blind studies have been conducted to date, where intrathecal doses of neostigmine in humans ranged from 750 to 1 μg, due to side-effects. Conversely, epidural neostigmine has been evaluated in proportionally higher doses and represents an alternative, but still deserves more investigation concerning both acute and chronic pain, as it seems devoid of important side-effects.

The effects of dexmedetomidine added to spinal levobupivacaine for transurethral endoscopic surgery

BACKGROUND

Intrathecal α2 agonists prolong the duration of action of local anesthetics and reduce the required dose. Dexmedetomidine is an α2 receptor agonist and its α2/α1 selectivity is 8 times higher than that of clonidine.

AIMS

In this study, we aimed to investigate the effect of adding dexmedetomidine to intrathecal levobupivacaine on the onset time and duration of motor and sensory blocks.

STUDY DESIGN

Randomized controlled study.

METHODS

Patients were randomly assigned into two groups. Group L (n= 30) patients received 3 mL (15 mg) of 0.5% levobupivacaine +0.3 mL normal saline and Group LD (n= 30) patients received 3 mL (15 mg) of 0.5% levobupivacaine + 0.3 mL (3 μg) dexmedetomidine. Sensory block onset time, block reaching time to T10 dermatome, the most elevated dermatome level, two dermatome regression time, sensory block complete regression time as well as motor block onset time, reaching Bromage 3 and regressing to Bromage 0 were recorded.

RESULTS

Sensory and motor block onset times were shorter in Group LD than in Group L (p<0.001). The regression of the sensory block to S1 dermatome and Bromage 0 were longer in Group LD than Group L (p<0.001). The two dermatome regression time was longer in Group LD than Group L (p< 0.001). There were no statistically significant differences between groups in blood pressure and heart rate. There was no statistically significant difference between groups when adverse effects were compared.

CONCLUSION

We conclude that intrathecal dexmedetomidine addition to levobupivacaine for spinal anaesthesia shortens sensory and motor block onset time and prolongs block duration without any significant adverse effects.

[Dexmedetomidine and clonidine: a review of their pharmacodynamy to define their role for sedation in intensive care patients]

Alpha-2 adrenergic agonists ("alpha-2 agonists") present multiple pharmacodynamic effects: rousable sedation, decreased incidence of delirium in the setting of critical care, preservation of respiratory drive, decreased whole body oxygen consumption, decreased systemic and pulmonary arterial impedance, improved left ventricular systolic and diastolic function, preserved vascular reactivity to exogenous catecholamines, preserved vasomotor baroreflex with lowered set point, preserved kidney function, decreased protein catabolism. These pharmacodynamic effects explain the interest for these drugs in the critical care setting. However, their exact role for sedation in critically ill-patients remains open for further studies. Given the few double-blind randomized multicentric trials available, the present non exhaustive analysis of the literature aims at presenting the utilization of alpha-2 agonists as potential first-line sedative agents, in the critical care setting. Suggestions regarding the use of alpha-2 agonists as sedatives are detailed.

Pharmacological mechanisms involved in the antinociceptive effects of dexmedetomidine in mice

Dexmedetomidine (DEX) is a α₂ -adrenoceptor (α₂ -AR) agonist used as an anesthetic adjuvant and as sedative in critical care settings. Typically, α₂ -AR agonists release nitric oxide (NO) and subsequently activate NO-GMPc pathway and have been implicated with antinociception. In this study, we investigate the pharmacological mechanisms involved in the antinociceptive effects of DEX, using an acetic acid-induced writhing assay in mice. Saline or DEX (1, 2, 5, or 10 μg/kg) was intravenously injected 5 min before ip administration of acetic acid and the resulting abdominal constrictions were then counted for 10 min. To investigate the possible mechanisms related to antinociceptive effect of DEX (10 μg/kg), the animals were also pretreated with one of the following drugs: 7-nitroindazole (7-NI; 30 mg/kg ip); 1H-[1,2,4] oxadiazole [4,3-a] quinoxaline-1-one (ODQ; 2.5 mg/kg, ip); yohimbine (YOH; 1 mg/kg, ip); atropine (ATRO; 2 mg/kg, ip); glibenclamide (GLIB; 1 mg/kg, i.p.) and naloxone (NAL; 0.2 mg/kg, ip). A rotarod and open-field performance test were performed with DEX at 10 μg/kg dose. DEX demonstrated its potent antinociceptive effect in a dose-dependent manner. The pretreatment with 7-NI, ODQ, GLIB, ATRO, and YOH significantly reduced the antinociceptive affects of DEX. However, NAL showed no effecting DEX-induced antinociception. The rotarod and open-field tests confirmed there is no detectable sedation or even significant motor impairment with DEX at 10 μg/kg dose. Our results suggest that the α₂ -AR and NO-GMPc pathways play important roles in the systemic antinociceptive effect of DEX in a murine model of inflammatory pain. Furthermore, the antinociceptive effect exerted by DEX appears to be dependent on KATP channels, independent of opioid receptor activity.

Muscarinic pain pharmacology: realizing the promise of novel analgesics by overcoming old challenges

The antinociceptive and analgesic effects of muscarinic receptor ligands in human and nonhuman species have been evident for more than half a century. In this review, we describe the current understanding of the roles of different muscarinic subtypes in pain modulation and their mechanism of action along the pain signaling pathway, including peripheral nociception, spinal cord pain processing, and supraspinal analgesia. Extensive preclinical and clinical validation of these mechanisms points to the development of selective muscarinic agonists as one of the most exciting and promising avenues toward novel pain medications.

The synergistic interaction between rilmenidine and paracetamol in the writhing test in mice

The aim of the study was to ascertain antinociceptive effects of rilmenidine, a second-generation imidazoline-alpha-2-adrenoreceptor agonist, and to see whether rilmenidine was able to increase the analgesic effects of paracetamol in the writhing test in mice. An acetic acid (0.7%) solution was injected into the peritoneal cavity and the number of writhes was counted. The influence on locomotor performance was tested using the rotarod test. Rilmenidine, paracetamol, and rilmenidine-paracetamol fixed-ratio combinations produced dose-dependent antinociceptive effects. ED(50) values were estimated for the individual drugs and an isobologram was constructed. The derived theoretical additive ED(50) value for the rilmenidine-paracetamol combination was 109.23 +/- 35.05 mg/kg. This value was significantly greater than the observed ED(50) value which was 56.35 +/- 20.86 mg/kg, indicating a synergistic interaction. Rilmenidine did not impair motor coordination, as measured by the rotarod test, at antinociceptive and higher doses.

Postoperative analgesia induced by intrathecal neostigmine or bethanechol in rats

1. Cholinergic agonists and acetylcholinesterase inhibitors, such as neostigmine, produce a muscarinic receptor-mediated antinociception in several animal species that depends on activation of spinal cholinergic neurons. However, neostigmine causes antinociception in sheep only in the early, and not late, postoperative period. 2. In the present study, a model of postoperative pain was used to determine the antinociceptive effects of bethanechol (a muscarinic agonist) and neostigmine administered intrathecally 2, 24 or 48 h after a plantar incision in a rat hind paw. Changes in the threshold to punctate mechanical stimuli were evaluated using an automated electronic von Frey apparatus. 3. Mechanical hyperalgesia was obtained following plantar incision, the effect being stronger during the immediate (2 h) than the late post-surgical period. Bethanechol (15-90 microg/5 microL) or neostigmine (1-3 microg/5 microL) reduced incision-induced mechanical hyperalgesia, the effects of both drugs being more intense during the immediate (2 h) than the late post-surgical period. 4. The ED(50) for bethanechol injected at 2, 24 and 48 h was 5.6, 51.9 and 82.5 microg/5 microL, respectively. The corresponding ED(50) for neostigmine was 1.62, 3.02 and 3.8 microg/5 microL, respectively. 5. The decline in the antinociceptive potency of neostigmine with postoperative time is interpreted as resulting from a reduction in pain-induced activation of acetylcholine-releasing descending pathways. However, the similar behaviour of bethanechol in the same model points to an additional mechanism involving intrinsic changes in spinal muscarinic receptors.

Targeting the cholinergic system as a therapeutic strategy for the treatment of pain

Acetylcholine mediates its effects through both the nicotinic acetylcholine receptors (ligand-gated ion channels) and the G protein-coupled muscarinic receptors. It plays pivotal roles in a diverse array of physiological processes and its activity is controlled through enzymatic degradation by acetylcholinesterase. The effects of receptor agonists and enzyme inhibitors, collectively termed cholinomimetics, in antinociception/analgesia are well established. These compounds successfully inhibit pain signaling in both humans and animals and are efficacious in a number of different preclinical and clinical pain models, suggesting a broad therapeutic potential. In this review we examine and discuss the evidence for the therapeutic exploitation of the cholinergic system as an approach to treat pain.

Use of neostigmine in the management of acute postoperative pain and labour pain: a review

Neostigmine is a parasympathomimetic agent that has been recently investigated for use as an adjunct analgesic agent in the perioperative and peripartum period. A number of studies have investigated the intrathecal, epidural, caudal and intra-articular routes of administration of this agent, as well as the addition of neostigmine to local anaesthetics used for brachial plexus block and intravenous regional anaesthesia. While the intrathecal administration of neostigmine produced useful analgesic effects in the postoperative period in some studies, the high incidence of adverse events, mainly nausea and vomiting, limit the clinical usefulness of this route of administration. Several studies investigated the postoperative analgesic effects of epidural neostigmine using a number of different regimens. Overall, this route of administration appeared to improve postoperative analgesia in most studies without increasing the incidence of adverse events, and merits further research. Neuraxial administration of neostigmine appears to be safe in the obstetric population, with no reported adverse effects in the mother or fetus. While intrathecal administration is limited by a high incidence of nausea and vomiting in this patient population, the epidural route appears more promising and requires further investigation. The addition of neostigmine to caudal local anaesthetics was associated with improved postoperative analgesia in a number of studies. A dose of 2 microg/kg proved to be effective in several studies but was associated with an increased incidence of vomiting in some studies. Intra-articular administration of neostigmine 500microg produced a useful analgesic effect in the postoperative period in several studies and was not associated with an increase in the incidence of adverse effects. Studies investigating the efficacy of adding neostigmine to the local anaesthetics used for brachial plexus block and intravenous regional anaesthesia reported conflicting results. Further studies are required to determine the place of the administration of neostigmine by these routes.

The Effect of a Lidocaine Test Dose on Analgesia and Mobility After an Epidural Combination of Neostigmine and Sufentanil in Early Labor

We previously demonstrated the effectiveness of epidural sufentanil and the cholinesterase inhibitor, neostigmine, to initiate selective labor analgesia. Because the traditional lidocaine plus epinephrine test dose (TD) may alter the effect of subsequent epidural drugs, we undertook this investigation to evaluate the impact of a lidocaine TD on analgesia from a combination of epidural neostigmine plus sufentanil administered in early labor. Eighty healthy parturients were randomly allocated to two groups to receive a 3 mL-TD, either lidocaine 2%-epinephrine (1:200,000) or saline-epinephrine (1:200,000), followed 3 min later by epidural neostigmine 500 microg plus sufentanil 10 microg. Pain scores were recorded for 30 min after injection, as was the time elapsed from initial bolus until request for supplemental analgesia. Thirty minutes after injection, adequacy of motor function was evaluated by the parturient's ability to sit, stand up, bend her knees, and walk. Lidocaine TD hastened the onset (5 min vs 15 min) and increased duration (122 +/- 53 min vs 98 +/- 54 min; P = 0.02) of analgesia from epidural neostigmine plus sufentanil bolus. In contrast, the TD did not significantly impair the ability to sit, stand up, or bend the knees. The ability to ambulate, however, was reduced (57% vs 82%; P = 0.04). In conclusion, a traditional lidocaine TD significantly enhances the analgesic effect from the epidural neostigmine plus sufentanil combination, but affects ambulation in early labor.

[A case of a second cancer of metachronous multiple primary non-small cell lung cancer successfully treated with TS-1 and CDDP chemotherapy]

The patient was a 66-year-old man who had undergone right upper lobectomy and ND 2a systematic lymph node dissection for lung cancer (M/D adenocarcinoma, p-stage IB) in March of 1999 . On November 2003, postoperative routine chest computed tomography(CT) demonstrated a mass in left S6, and pathological diagnosis revealed P/D squamous cell carcinoma (cT1N2M0, stage IIIA) by CT-guided needle biopsy and mediastinoscopy. At first, we tried two courses of a combination chemotherapy consisting of carboplatin (CBDCA) and paclitaxel every 3 weeks. After 2 courses, the regimen was stopped because of grade 3 arthritis. Then, two courses of CBDCA and gemcitabine were performed. The evaluation of the response was SD by the guidelines of Response Evaluation Criteria in Solid Tumor Groups. Next, gefitinib was orally administered for 6 months but the tumor and mediastinal lymph nodes were growing. In January 2005, oral administration of TS-1 (60 mg/1, 2 courses, 75 mg/3-6 courses) was begun twice a day for 21 consecutive days while cisplatin (60 mg/m(2)) was administered intravenously on day 8. The response was PR (the tumor decreased by 46%), no serious adverse effect was observed, and the patient maintained good quality of life throughout the chemotherapy. This case suggests that TS-1+CDDP chemotherapy may be an effective treatment in patients with advanced lung cancer even after many protocols of chemotherapy.

Combination pharmacotherapy for neuropathic pain: current evidence and future directions

Current drugs reduce neuropathic pain and improve mood and quality of life. However, as single agents they are limited by incomplete efficacy and dose-limiting adverse effects. Recent experimental and clinical data support the potential of combination pharmacotherapy for neuropathic pain. Therapeutic benefits may include greater efficacy, lower doses and fewer adverse effects. Due to potential adverse, as well as beneficial, drug interactions, safety and efficacy of specific combinations must be empirically evaluated. Techniques such as isobolographic analysis, response-surface modeling and other model-free tests have been used in order to characterize analgesic interactions as antagonistic, additive or synergistic. Whether synergistic or not, a clinically useful combination could simply have additive or even subadditive analgesia, provided that there is less additivity for side effects. Despite widespread clinical use, there are surprisingly few published observations on combination therapy for neuropathic pain. This review discusses future directions and proposes research strategies aimed at bridging current knowledge gaps, including safety, compliance and cost-effectiveness; discovering optimal drug combinations and dose ratios; comparing concurrent with sequential combination therapy; and combining more than two drugs. Continued close integration of basic and clinical sciences is crucial in further harnessing the potential of combination pharmacotherapy in neuropathic pain.

The effects of chemical or surgical deafferentation on [3H]-acetylcholine release from rat spinal cord

Cholinergic modulation of nociceptive transmission through both nicotinic and muscarinic receptors in the spinal cord represents an important mechanism in pain signaling. However, what neuronal elements release acetylcholine and how release might change in response to deafferentation are unclear. The present studies demonstrated Ca++- and K+-dependent release of [3H]-acetylcholine from slices of regional areas of rat spinal cord. That [3H]-acetylcholine was synthesized from [3H]-choline was demonstrated by the lack of [3H]-acetylcholine release following incubation with either the choline uptake inhibitor hemicholinium or the choline acetyltransferase inhibitor bromoacetylcholine. Rats treated neonatally with capsaicin or with spinal nerve ligation as adults showed a significantly decreased K+-stimulated release of [3H]-acetylcholine from dorsal horn but not ventral horn lumbar spinal cord slices. In rats subjected to dorsal rhizotomy, while basal release from lumbar dorsal spinal cord slices was reduced, K+-stimulated [3H]-acetylcholine release, while decreased, was not significantly different compared with controls. The data presented here show that there are regional differences in the release of acetylcholine from spinal cord and that this release can be modulated by chemical or surgical deafferentation. These results also indicate that the source of acetylcholine in the dorsal cord originates mainly from resident somata and their collaterals, interneurons and/or descending terminals, with only very minor contributions coming from primary afferents. The present data help to further elucidate the role of acetylcholine in spinal signaling, particularly with respect to the effects of nerve injury and nociceptive neurotransmission.

Antinociceptive effects of bethanechol or dimethylphenylpiperazinium in models of phasic or incisional pain in rats

The mechanism by which muscarinic or nicotinic agonists produce antinociception has been the subject of several studies. In the present investigation, we used intrathecal administration of drugs to rats to show that muscarinic or nicotinic agonists such as bethanechol (BCh) and dimethylphenylpiperazinium (DM), respectively, dose-dependently increased the tail flick latency and reduced the pain produced by a surgical incision performed on the plantar aspect of a hind paw. The effects of BCh in both tests were inhibited by the previous intrathecal administration of atropine, but not mecamylamine (muscarinic and nicotinic antagonists, respectively). Mecamylamine significantly reduced the effects of DM in both tests. Atropine significantly reduced the effect of DM in the tail flick test and inhibited the effect of DM against the incisional pain. Intrathecal hemicholinium-3 (HC-3), a reversible inhibitor of choline transporter, did not change the effect of BCh in the tail flick test but produced a non-significant reduction of the effect of BCh against incisional pain. In contrast, HC-3 produced a non-significant reduction of the effect of DM in the tail flick test but fully inhibited the effect of DM against incisional pain. Therefore, the BCh-induced antinociception depends on a direct activation of muscarinic receptors, whereas DM-induced antinociception results in drug interaction with nicotinic receptors to activate the further release of acetylcholine from intrinsic spinal cholinergic terminals. The acetylcholine released by DM in turn induces antinociception via activation of muscarinic receptors.

Intrathecal Clonidine for Postoperative Analgesia in Elderly Patients: The Influence of Baricity on Hemodynamic and Analgesic Effects

Intrathecal (IT) clonidine is an effective analgesic, but it also produces hemodynamic depression and sedation which are likely to be related to IT clonidine's cephalad spread within the cerebrospinal fluid. We hypothesized that IT clonidine's side effects could be reduced without compromising the duration and quality of analgesia by injecting clonidine IT in a hyperbaric solution and elevating the patient's trunk. We prospectively randomized 30 elderly patients to receive IT 150 microg of either isobaric (ISO) or hyperbaric (HYPER) clonidine for postoperative analgesia after surgical repair of traumatic hip fracture. Hemodynamics, IV fluid administration, visual analog pain scores, sedation scores, and clonidine cerebrospinal fluid levels were recorded at fixed intervals. Patients in the ISO group required significantly more crystalloid fluid administration (median, 2500 mL; range, 1500-3000 mL) than those in the HYPER group (median, 1500; range, 500-3000 mL) to maintain adequate arterial blood pressure (P < 0.01). Also, the decrease in heart rate was significantly more pronounced in the ISO than in the HYPER group (P < 0.01). The duration of analgesia was significantly larger in the ISO (median, 400 min; range, 115-400 min) than in the HYPER (median, 265 min; range, 205-400 min) group (P < 0.05). Sedation scores did not differ between groups. We conclude that increasing the baricity of IT clonidine solution in the conditions of our experiment reduces hemodynamic side effects but also analgesia from IT administered clonidine.

The efficacy of intra-articular ketamine for postoperative analgesia in outpatient arthroscopic surgery

PURPOSE

The purpose of this study was to compare the postoperative analgesic effects of intra-articularly administered ketamine, neostigmine, and bupivacaine after outpatient arthroscopic surgery.

TYPE OF STUDY

Prospective, randomized, double-blind, clinical study.

METHODS

In this study, 60 patients undergoing arthroscopic surgery other than ligament reconstruction were evaluated for postoperative pain. Ketamine, neostigmine, and bupivacaine were administered intra-articularly. The period of effective analgesia, recorded in minutes, was measured between time 0 and first usage of patient-controlled anesthesia (PCA) by the patients. The visual analog scale (VAS) was used to describe the pain level of the patient.

RESULTS

VAS values were lower for the 3 medication groups compared with the placebo at rest and 90 degrees knee flexion. Intra-articular administration of 0.5 mg/kg ketamine provided longer duration of analgesia as defined by the first PCA use time (P <.05). The total amount of pethidine and analgesia time were longer for the 3 medication groups.

CONCLUSIONS

Our basic finding was reduction in postoperative pain and consumption of adequate analgesic drugs with intra-articular ketamine, bupivacaine, or neostigmine use. We have not seen any psychomimetic side effects, particularly as seen with higher doses or systemic use. This study may conclude that intra-articular administration of ketamine provides long-lasting and effective analgesia, similar to neostigmine but less effective than bupivacaine after knee arthroscopy without any adverse effects. LEVEL OF EVEIDENCE: Level I.

The effect of intrathecal medetomidine on small bowel transit in the rat

BACKGROUND AND OBJECTIVE

Gastrointestinal motility is influenced by abdominal trauma, laparotomy and particularly by intestinal ischaemia. The reflex inhibition of gastrointestinal motility is mediated mainly by the sympathetic nervous system. There are reports on the effects of systemically applied alpha2-adrenoceptor agonists on gastric emptying and recovery of bowel motility, but the effect of spinally applied alpha2-adrenoceptor agonists on intestinal motility has not been studied. The aim of this study was to investigate the effects of intrathecal medetomidine on gastrointestinal transit in rats after transient intestinal ischaemia.

METHODS

Forty rats were randomly assigned to four groups of 10 each. Intrathecal catheter insertion and laparotomy were performed on each rat. Saline (10 microL) was injected intrathecally in Groups A and B. Medetomidine (10 microg in 10 microL) was injected intrathecally in Groups C and D. Intestinal ischaemia was induced in Groups B and D. Gastrointestinal transit was determined by measuring the length that a standardized marker meal of activated charcoal had travelled. Intrathecal medetomidine was compared to intrathecal saline in their effect on intestinal motility after 30 min period of bowel ischaemia.

RESULTS

Laparotomy and intestinal ischaemia slowed gastrointestinal transit. Intrathecal medetomidine accelerated transit in both ischaemia and non-ischaemia groups.

CONCLUSION

Intrathecal medetomidine markedly accelerated small intestinal transit and may also hasten the recovery from post-ischaemic paralytic ileus.

Management strategies for the treatment of neuropathic pain in the elderly

Pain caused by dysfunction or damage to the peripheral or central nervous system is typified by the symptoms described by patients with painful diabetic neuropathy, post-herpetic neuralgia and central poststroke pain. All these conditions are more common in the elderly. Neuropathic pain has long been recognised as one of the more difficult types of pain to treat; however, with the current emphasis on providing a multidisciplinary assessment and approach to management, more patients will be offered relief of their symptoms and an improved quality of life. Despite the use of combination drug therapy, adequate pain relief in the elderly is difficult to achieve without adverse effects. In an attempt to minimise these it is important to include non-drug treatment options in the management plan. Lifestyle changes and environmental modification, together with encouragement to adopt an appropriate exercise programme and an emphasis on maintaining mobility and independence should always be considered. Interventional therapy ranging from simple nerve blocks to intrathecal drug delivery can be of value. Drug treatment remains the mainstay of therapy. Tricyclic antidepressants such as amitriptyline, while having significant adverse effects in the elderly, have a number needed to treat (NNT) of 3.5 for 50% pain relief in diabetic neuropathy and 2.1 for 50% pain relief in postherpetic neuralgia. The newer antiepileptic drugs, such as gabapentin, appear to have a better adverse effect profile and provide similar efficacy with the NNT for treating painful diabetic neuropathy being 3.7 and 3.2 for treating pain in postherpetic neuralgia. As our understanding of the complexities of the pain processes increases, we are becoming more able to appropriately combine treatments to achieve not only improved pain relief but also improved function.

[Neostigmine added to bupivacaine in axillary plexus block: which benefit?]

INTRODUCTION

Recent study showed that neostigmine (500 microg) by intra-articular produces postoperative analgesia without adverse effect. The author's goal was to determine whether 500 microg of neostigmine added to bupivacaine in axillary plexus block could prolonged postoperative analgesia without increasing the incidence of side effects.

METHODS

Ninety patients scheduled for orthopedic or plastic surgery with axillary plexus block were randomly assigned to one of 3 groups : group 1 (TGr n = 30) received saline solution (1 ml) in the axillary plexus, group 2 (NAGr n = 30) received 500 microg (1 ml) neostigmine in the axillary plexus and group 3.500 microg neostigmine subcutaneously (NSGr n = 30). We evaluated visual analog pain scores (VAS), the consumption of the ketoprofene, nausea and vomiting incidence during the first 24 h. ANOVA, Kruskall Wallis and Fisher tests were used for statistical analysis. A p value of <0.05 was considered significant.

RESULTS

The VAS score was lower in NAGr (21 +/- 18) vs NSGr (31 +/- 14) and control group TGr (45 +/- 2) (p < 0.05). The consumption of the ketoprofene is 127 +/- 65 mg in NAGr vs 150 +/- 53 mg in NSGr and 200 +/- 50 mg in group TGr (p = 0.02). Incidence of nausea and vomiting was 3.5% in NAGr vs 6.8% in NSGr and 0% for TGr.

CONCLUSION

Neostigmine combined to a mixture of lidocaine and bupivacaine prolongs postoperative analgesia after axillary plexus block.

Intrathecal clonidine reduces hypersensitivity after nerve injury by a mechanism involving spinal m4 muscarinic receptors

alpha2-Adrenergic agonists reduce mechanical and thermal hypersensitivity in animals with nerve injury and effectively treat neuropathic pain in humans. Previous studies indicate a reliance of alpha2-adrenergic agonists in this setting on spinal cholinergic activation and stimulation of muscarinic receptors. The subtype(s) of muscarinic receptors in the spinal cord that produces antinociception in normal animals is controversial, and those involved in reducing hypersensitivity and interacting with alpha2-adrenergic systems after nerve injury are unstudied. To examine this, the left L5 and L6 spinal nerves were tightly ligated in rats, resulting in reduction in withdrawal threshold to punctate mechanical stimuli. Intrathecal clonidine, 15 micro g, returned the withdrawal threshold to normal. Using highly specific m1 and m4 antagonists, we observed no reduction in the effect of clonidine by the m1 antagonist, but inhibition of clonidine's effect by the m4 antagonist. Western analysis revealed no difference in quantitative expression of m1 and m4 receptor protein in the dorsal spinal cord of spinal nerve-injured animals compared with sham-operated controls, suggesting this interaction with m4 receptors does not reflect an increase in receptor expression.

IMPLICATIONS

Neuraxial clonidine is an effective adjunct in the treatment of neuropathic pain and increases acetylcholine concentrations in cerebrospinal fluid in humans. These data in animals suggest that spinal m4 type muscarinic receptors are important to the effect of clonidine in treating hypersensitivity to touch after nerve injury.

Epidural and intrathecal analgesia for cancer pain

The three-step analgesic ladder approach developed by the World Health Organization works well in treating the vast majority (70-90%) of patients suffering from pain related to cancer. In those patients who do not get pain relief by this three-step approach, intraspinal agents can be a fourth step in managing pain of malignant origin. Although morphine is the only opioid approved by the US Food and Drug Administration for intraspinal use, many different opioid analgesics are used intraspinally, including hydromorphone, fentanyl, sufentanil, meperidine and methadone in the treatment of cancer pain. Many non-opioid agents have also been used intraspinally either alone or in combination with opioids in the treatment of intractable cancer pain. This chapter summarizes the clinical use of these agents with some practical points.

From pain research to pain treatment: the role of human experimental pain models

There is no objective measure of a complete pain perception; we can, however, measure different aspects of nociceptive processing and pain perception. Earlier, experimental pain models often only involved induction of cutaneous pain using a single stimulus modality. Recently new experimental models have been developed eliciting various modalities of deep and visceral pain which more closely resemble clinical pain conditions. It is imperative to use multi-modal and multi-structure pain induction and assessment techniques, because a simple model cannot describe the very complex and multi-factorial aspects of clinical pain. Furthermore, it is important to assess pain under normal and pathophysiological conditions. The importance of peripheral and central hyperexcitability for acute and chronic pain has been demonstrated in animals and, to some extent, in humans. However, in spite of our immense knowledge, we still do not know how to prevent and treat this hyperexcitability efficiently. Our understanding of nociceptive mechanisms involved in acute and chronic pain and the effects of anaesthetic drugs or combinations of drugs on these mechanisms in humans may also be expanded using human experimental models. This mechanism-based approach may help us to develop and test therapeutic regimes in patients with acute and chronic pain.

From pain research to pain treatment: role of human pain models

There is no objective measure of pain; we can however measure different aspects of the pain perception. Earlier experimental pain models often only involved induction of cutaneous pain. Recently new experimental models have been developed eliciting deep muscle and visceral pain that may more closely resemble the clinical pain condition. It is imperative to use multi-modal and multi-structure pain induction and assessment techniques, as a simple model cannot describe the very complex and multi-factorial aspects of clinical pain. The importance of peripheral and central hyperexcitability for acute and chronic pain has been demonstrated in animals and to some extent in humans. But in spite of our immense knowledge we still do not know how to prevent and treat this hyperexcitability. Our understanding of nociceptive mechanisms involved in acute and chronic pain and the effects of anaesthetic drugs or combinations of drugs on these mechanisms in humans may also be expanded with experimental human models. This knowledge can then help us to develop and test therapeutic regimes in patients with acute and chronic pain.