The neurotoxicity of drugs given intrathecally (spinal)

Association between perioperative neuraxial local anesthetic neurotoxicity and arachnoiditis: a narrative review of published reports

BACKGROUND/IMPORTANCE

Arachnoiditis is a rare but devastating disorder caused by various insults, one of which is purported to be local anesthetic neurotoxicity following neuraxial blockade. However, the relationship between local anesthetics administered into the neuraxis and the development of arachnoiditis has not been clearly elucidated.

OBJECTIVE

We aimed to summarize the existing complex body of literature and characterize both the essential features and strength of any association between neuraxial local anesthetic neurotoxicity and arachnoiditis with a view toward mitigating risk, enhancing prevention, and refining informed consent discussions.

EVIDENCE REVIEW

We reviewed all published reports of arachnoiditis attributed to local anesthetic neurotoxicity following perioperative neuraxial anesthesia. This narrative review was based on a systematic search methodology, which included articles published up until December 2022.

FINDINGS

Thirty-eight articles were included, comprising 130 patients, over one-half of which were published prior to this century and inconsistent with modern practice. Neuraxial techniques included 78 epidurals, 48 spinals, and 5 combined spinal-epidurals, mostly for obstetrics. Reporting of essential procedural data was generally incomplete. Overall, at least 57% of patients experienced complicated needle/catheter insertion, including paresthesia, pain, or multiple attempts, irrespective of technique. The onset of neurological symptoms ranged from immediate to 8 years after neuraxial blockade, while the pathophysiology of arachnoiditis, if described, was heterogeneous.

CONCLUSIONS

The existing literature attributing arachnoiditis to local anesthetic neurotoxicity is largely outdated, incomplete, and/or confounded by other potential causes, and thus insufficient to characterize the features and strength of any association.

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

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

Neurotoxic Effects of Local Anesthetics on Developing Motor Neurons in a Rat Model

Neurotoxic effects of local anesthetics (LAs) on developing motor neurons have not been documented. We investigated the neurotoxic effects of LAs on developing motor neurons in terms of cell viability, cytotoxicity, reactive oxygen species (ROS), and apoptosis. Embryonic spinal cord motor neurons were isolated from Sprague-Dawley rat fetuses and exposed to one of the three LAs-lidocaine, bupivacaine, or ropivacaine-at concentrations of 1, 10, 100, or 1000 µM. The exposure duration was set to 1 or 24 h. The neurotoxic effects of LAs were determined by evaluating the following: cell viability, cytotoxicity, ROS production, and apoptosis. In the 1-h exposure group, the motor neurons exposed to lidocaine and bupivacaine had reduced cell viability and increased cytotoxicity, ROS, and apoptosis in a concentration-dependent manner. Lidocaine showed the highest toxicity, followed by bupivacaine. In the 24-h exposure group, all three LAs showed significant effects (decreased cell viability and increased cytotoxicity, ROS, and apoptosis) on the motor neurons in a concentration-dependent manner. The neurotoxic effects of lidocaine were greater than those of bupivacaine and ropivacaine. Ropivacaine appeared to have the least effect on motor neurons. This study identified the neurotoxic effects of lidocaine and bupivacaine on developing spinal cord motor neurons.

Analysing the blood-stemming effect of Ankaferd Blood Stopper in medulla spinalis surgery

Background/aim

The aim of this study was to investigate the possible toxicity of the Ankaferd Blood Stopper (ABS) on the neural system.

Materials and methods

Thirty Sprague Dawley rats were randomized into ABS (n: 15) and control (n: 15) groups. Following the anaesthetic induction, total laminectomy was performed to the lower thoracic, and upper lumbar areas in both groups and medulla spinalis was exposed. Two myelotomies were performed on the medulla spinalis. One millilitre ABS was applied to the incision site in the ABS group, and one millilitre 0.9% saline solution was applied in the control group. Rats were observed for 15 days regarding general behaviour, neurological signs, mobility, and signs of infection. Sixteen days later, all rats were decapitated under anaesthesia. Medulla spinalis was removed en bloc from all rats and was stained with Heamatoxylin & Eosin and luxol fast blue.

Results

There was no significant difference between the ABS group and the control group regarding oedema, gliosis, the intensity of inflammatory cells, the presence of neuronal degeneration, neuron counts, and myelin degeneration.

Conclusion

No clinical or histopathological evidence for the neurotoxic effect of the ABS was observed in the present study. Our findings might precipitate the use of ABS on human subjects regarding medulla spinalis surgery.

Intrathecal betamethasone for cancer pain: A study of its analgesic efficacy and safety

BACKGROUND

A preliminary study has shown effective cancer pain relief by intrathecal betamethasone (ITB). However, further evidence is needed to support this new approach.

METHODS

Cancer patients with opioid-resistant pain received lumbar intrathecal administration of betamethasone 2 or 3 mg once a week for 28 days. Immediate and short-term analgesia (using a percentage pain reduction scale and a numerical rating scale, NRS) and long-term analgesia (using NRS) were assessed. Patients were classified into two groups according to the most painful site of metastasis: vertebral column and/or surrounding nerve plexus metastases (group A) and other metastases distal from the vertebral column (group B).

RESULTS

A total of 104 patients received ITB. Pain relief was observed not only in the lower half but also in the upper half of the body. The proportion of group A patients who experienced immediate analgesia was 81% (47/58), which was significantly greater than that of group B (P < 0.001). A decrease in NRS scores 1 day after ITB administration was observed in significantly more patients in group A than in group B (P < 0.001). Long-term analgesia was also recorded in a greater proportion of patients in group A than in group B in the 7-day (59%, 38/64 vs 6%, 2/33) and 28-day periods (71%, 40/56 vs 31%, 8/26) (P < 0.001). No adverse effects related to neurotoxicity were recorded.

CONCLUSION

Intrathecal injection of betamethasone produced analgesia for opioid-resistant cancer pain, and may be a potent therapeutic option for intolerable pain from vertebral column and/or surrounding nerve plexus metastases.

Monosialoganglioside protects against bupivacaine-induced neurotoxicity caused by endoplasmic reticulum stress in rats

Background

Local anesthetics in spinal anesthesia have neurotoxic effects, resulting in severe neurological complications. Intrathecal monosialoganglioside (GM1) administration has a therapeutic effect on bupivacaine-induced neurotoxicity. The aim of this study was to determine the underlying mechanisms of bupivacaine-induced neurotoxicity and the potential neuroprotective role of GM1.

Materials and methods

A rat spinal cord neurotoxicity model was established by injecting bupivacaine (5%, 0.12 μL/g) intrathecally. The protective effect of GM1 (30 mg/kg) was evaluated by pretreating the animals with it prior to the bupivacaine regimen. The neurological and locomotor functions were assessed using standard tests. The histomorphological changes, neuron degeneration and apoptosis, and endoplasmic reticulum stress (ERS) relevant markers were analyzed using immunofluorescence, quantitative real-time PCR, and Western blotting.

Results

Bupivacaine resulted in significant neurotoxicity in the form of aberrant neurolocomoter functions and spinal cord histomorphology and neuronal apoptosis. Furthermore, the ERS specific markers were significantly upregulated during bupivacaine-induced neurotoxicity. These neurotoxic effects were ameliorated by GM1.

Conclusion

Pretreatment with GM1 protects against bupivacaine-induced neurotoxicity via the inhibition of the GRP78/PERK/eIF2α/ATF4-mediated ERS.

Determination of ED50 and time to effectiveness for intrathecal hydromorphone in laboring patients using Dixon's up-and-down sequential allocation method

Background

With the increasing occurrence of drug shortages, understanding the pharmacokinetics of alternative intrathecal opioid administration has gained importance. In particular, additional data are needed to comprehensively evaluate the analgesic properties of intrathecal hydromorphone in the laboring patient. In a phase 2 clinical trial, we set out to determine the median effective dose (ED₅₀) and time to effectiveness for this drug in this population.

Methods

Using Dixon’s up-and-down sequential allocation method, twenty women presenting for labor analgesia were prospectively enrolled. A combined spinal-epidural technique was used to deliver the determined dose of intrathecal hydromorphone. Visual analog pain scores were obtained assessing peak pain scores during serial uterine contractions. Effective pain relief was defined as achieving a pain score of less than or equal to 3 out of 10. The dose was deemed to be ineffective if the patient failed to achieve this level of relief after 30 min.

Results

The ED₅₀ of hydromorphone in our population was 10.9 μg (95% confidence interval 5.6–16.2 μg). Amongst patients for whom the dose was effective, the median time to pain relief was 24 min. One patient experienced both nausea and pruritus. No other complications were noted.

Conclusion

Due to the prolonged time to onset, hydromorphone cannot be recommended in favor of substantively better alternatives such as sufentanil and fentanyl.

Trial registration

Clinicaltrials.gov registration number: NCT01598506.

Morphine-alcohol treatment impairs cognitive functions and increases neuro-inflammatory responses in the medial prefrontal cortex of juvenile male rats

In the developed and developing world, opioid consumption in combination with alcohol has become one of the substances abused. In this experiment, we examined the effects of alcohol, morphine, and morphine+alcohol combination on cognitive functions and neuroinflammatory responses in the medial prefrontal cortex (mPFC) of juvenile male rats. Alcohol (1.0 ml of 15% v/v ethanol twice daily, subcutaneously, 7 hours apart), morphine (0.5 ml/kg of 0.4 mg/kg morphine chlorate twice daily, subcutaneously, 7 hours apart), morphine+alcohol co-treatment (0.5 ml/kg of 0.4 mg/kg morphine chlorate+1.0 ml of 15% v/v ethanol twice daily, subcutaneously, 7 hours apart) were administered for 21 days. Treatment with morphine+alcohol significantly impairs cognition functions in the Morris water maze, passive avoidance, and novel object recognition tests, furthermore, the treatment significantly increased the quantitative count of astrocytic cells and also conferred marked neuronal cell death in the mPFC, which were studied by glial fibrillary acidic protein immunochemistry for astrocytes and Cresyl violet for Nissl's substance distribution in neurons respectively. These results suggest that alcohol, morphine, and morphine+alcohol co-treatment may trigger cognitive deficits and neuroinflammatory responses in the brain.

Cytotoxicity of Oxycodone and Morphine in Human Neuroblastoma and Mouse Motoneuronal Cells: A Comparative Approach

Background and Objectives

Oxycodone is the mo st commonly used opioid for the treatment of moderate to severe pain. The peak cerebrospinal fluid concentration after epidural oxycodone was reported to be 300-fold greater (0.025 mM) than when administered intravenously after gynecologic surgery. Additionally, those patients administered epidural oxycodone had lower pain scores, needed less rescue analgesics and had fewer adverse effects compared with intravenous administration. However, oxycodone neurotoxicity requires evaluation before intrathecal implementation for routine clinical use.

Methods

We used two in vitro cell culture models to compare the cytotoxicity of oxycodone with that of morphine, and to study the mechanisms underlying toxicity. Human neuroblastoma cells and mouse motoneuronal cells were treated with increasing concentrations (0.0125–2 mM) of oxycodone or morphine, and were harvested at 24, 48 or 96 h. Cell cultures were evaluated with 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide and resazurin reduction assays.

Results

Both morphine and oxycodone decreased cell viability in a dose-dependent manner at concentrations between 0.5 and 2 mM. Morphine increased the number of apoptotic cells compared with oxycodone when assessed by flow cytometry, and transmission electron microscopy images revealed that exposure to both opioids evoked the appearance of numerous electron-dense, probable autophagic vacuoles in the cytoplasm of the cells.

Conclusions

Based on these results, it seems that the cytotoxicity of oxycodone in motoneuronal cells is similar to or less than that of morphine, and occurs only at concentrations above the peak clinical concentration in the cerebrospinal fluid after epidural administration.

Adjuvant Agents in Regional Anesthesia in the Ambulatory Setting

PURPOSE OF REVIEW

A majority of surgical practice has involved ambulatory centers with the number of outpatient operations in the USA doubling to 26.8 million per year. Local anesthesia delivery provides numerous benefits, including increased satisfaction, earlier discharge, and reduction in unplanned hospital admission. Further, with the epidemic of opioid mediated overdoses, local anesthesia can be a key tool in providing an opportunity to reduce the need for other analgesics postoperatively.

RECENT FINDINGS

Adjuvants such as epinephrine and clonidine enhance local anesthetic clinical utility. Further, dexmedetomidine prolongs regional blockade duration effects. There has also been a significant interest recently in the use of dexamethasone. Studies have demonstrated a significant prolongation in motor and sensory block with perineural dexamethasone. Findings are conflicting as to whether intravenous dexamethasone has similar beneficial effects. However, considering the possible neurotoxicity effects, which perineural dexamethasone may present, it would be prudent not to consider intravenously administered dexamethasone to prolong regional block duration. Many studies have also demonstrated neurotoxicity from intrathecally administered midazolam. Therefore, midazolam as an adjuvant is not recommended. Magnesium prolongs regional block duration but related to paucity of studies as of yet, cannot be recommended. Tramadol yields inconsistent results and ketamine is associated with psychotomimetic adverse effects. Buprenorphine consistently increases regional block duration and reduce opioid requirements by a significant amount. Future studies are warranted to define best practice strategies for these adjuvant agents. The present review focuses on the many roles of local anesthetics in current ambulatory practice.

Local Anesthetic-Induced Neurotoxicity

This review summarizes current knowledge concerning incidence, risk factors, and mechanisms of perioperative nerve injury, with focus on local anesthetic-induced neurotoxicity. Perioperative nerve injury is a complex phenomenon and can be caused by a number of clinical factors. Anesthetic risk factors for perioperative nerve injury include regional block technique, patient risk factors, and local anesthetic-induced neurotoxicity. Surgery can lead to nerve damage by use of tourniquets or by direct mechanical stress on nerves, such as traction, transection, compression, contusion, ischemia, and stretching. Current literature suggests that the majority of perioperative nerve injuries are unrelated to regional anesthesia. Besides the blockade of sodium channels which is responsible for the anesthetic effect, systemic local anesthetics can have a positive influence on the inflammatory response and the hemostatic system in the perioperative period. However, next to these beneficial effects, local anesthetics exhibit time and dose-dependent toxicity to a variety of tissues, including nerves. There is equivocal experimental evidence that the toxicity varies among local anesthetics. Even though the precise order of events during local anesthetic-induced neurotoxicity is not clear, possible cellular mechanisms have been identified. These include the intrinsic caspase-pathway, PI3K-pathway, and MAPK-pathways. Further research will need to determine whether these pathways are non-specifically activated by local anesthetics, or whether there is a single common precipitating factor.

A randomized controlled study between fentanyl and Butorphanol with low dose intrathecal bupivacaine to facilitate early postoperative ambulation in urological procedures

Introduction:

Opioids are widely used in conjunction with local anesthetics as they permit the use of lower dose of local anesthetics while providing adequate anesthesia and analgesia. It both provides adequate anesthesia as well as lower drug toxicity neuraxial administration of opioids in conjunction with local anesthetics improves the quality of intraoperative analgesia and prolongs the duration of postoperative analgesia. Bupivacaine is the most commonly used drug for subarachnoid block due to its lesser side effects. The present study was conducted to decrease the overall dose of local anesthetics with opioid combination for urological procedure with respect to quality of anesthesia and recovery with patient's satisfaction.

Materials and Methods:

The study population was randomly allocated by computer generated table into two groups; Group A: 5 mg 0.5% bupivacaine + 25 mcg and Group B: 5 mg 0.5% bupivacaine + 25 mg butorphanol.

Results:

Highest level of sensory block was T9 and T8 with the fentanyl group and butorphanol group, respectively. The onset of sensory block was early in fentanyl group than butorphanol group. Duration of both sensory and motor block was significantly higher in butorphanol group. There was no incidence of itching in both groups. There were two patients in fentanyl group and one in butorphanol with hypotension for which injection mephentermine was given. Two patients in fentanyl group complained of nausea and vomiting, for which injection ondansetron was given. One patient complained of pain in fentanyl group for which injection propofol with injection fentanyl was supplemented.

Conclusion:

Low-dose bupivacaine with butorphanol group was devoid of any side effects in the present study but low dose bupivacaine in addition with fentanyl is superior in terms of early postoperative recovery resulting in early discharge and better outcome in comparison to bupivacaine and butorphanol group, which is beneficial in elderly patients with comorbidity.

Comparison of efficacy and safety of ropivacaine with bupivacaine for intrathecal anesthesia for lower abdominal and lower limb surgeries

Background:

A prospective randomized clinical study was conducted to study the efficacy and safety of ropivacaine with bupivacaine intrathecally for lower abdominal and lower limb surgeries.

Material and Methods:

70 patients aged between 18 to 65 years were randomized into two groups, n = 35 in each group. Group A received 3 ml of (0.5%) isobaric bupivacaine (15 mg) and Group B 3 ml of (0.75%) isobaric ropivacaine (22.5 mg). Spinal anesthesia procedure was standardized. Haemodynamic parameters, onset and duration of sensory and motor blockade, level achieved, regression and side effects were compared between the two groups.

Results:

Onset and regression of sensory blockade in ropivacaine group was faster with a P < 0.001 which was statistically significant. Onset of motor blockade was rapid in both the groups but duration of motor blockade was significantly shorter in ropivacaine group. Excellent analgesia, with no side effects and stable haemodynamics was noted in ropivacaine group.

Conclusion:

Hence ropivacaine was safe and equally effective as bupivacaine for lower abdominal and lower limb surgeries with early motor recovery, providing early ambulation.

Efficacy of spinal additives neostigmine and magnesium sulfate on characteristics of subarachnoid block, hemodynamic stability and postoperative pain relief: A randomized clinical trial

Background:

Intrathecal neostigmine and magnesium sulfate (MgSO₄) produce substantial antinociception, potentiate analgesia of bupivacaine without neurotoxicity.

Aims:

The aim was to investigate the effect of neostigmine and MgSO₄ on characteristics of spinal anesthesia (SA), hemodynamic stability and postoperative analgesia when added to 0.5% hyperbaric bupivacaine for SA.

Subjects and Methods:

In this prospective, randomized, double-blind study 75 American Society of Anesthesiologist status I and II adult females posted for major gynecological surgery were assigned to one of the three groups (n = 25). Group N received Neostigmine 25 μg, Group M received MgSO₄ 50 mg, Group C received 0.5 ml saline as an adjuvant to 17.5 mg hyperbaric bupivacaine. Onset, duration of block, heart rate, mean arterial pressure, postoperative analgesia, analgesic requirement, and adverse effects were recorded. Data expressed as mean (standard deviation) or number (%). P <0.05 were statistically significant.

Results:

The three groups were comparable in characteristics of SA. The mean duration of analgesia was significantly longer in Group N (5.1 h) followed by Group M (4.2 h) and Group C (3.8 h) (P = 0.0134). Analgesic requirement was significantly less in Group N followed by Group M and Group C (P = 0.00232). The pain score was significantly less in Group M (P < 0.05). The incidence of hypotension and vasopressor requirement was lowest (48%) in Group N than in Group M (64%) and Group C 84% (P = 0.0276). The incidence of bradycardia and atropine requirement was the lowest in Group M (P = 0.0354). Sedation was observed in 56% patients in Group M compared to 20% in Group N and 8% in Group C (P = 0.0004).

Conclusion:

Intrathecal Neostigmine and MgSo₄ does not affect characteristics of SA. Postoperative analgesia of neostigmine was better than MgSO₄. Neostigmine provides some protection against hypotension of SA whereas MgSO₄ protects against bradycardia.

Evaluation of the clinical and analgesic effects of subarachnoid ketamine-lidocaine administration in goats undergoing mastectomy

Twenty adult female goats affected with chronic mastitis were subjected to mastectomy or hemimastectomy under subarachnoid regional analgesia using a ketamine-lidocaine combination. Ketamine at 1.5 mg/kg and lidocaine hydrochloride at 1.25 mg/kg were administered intrathecally at the lumbosacral intervertebral space. Goats were then subjected to a 120-minute observation period for systemic or neurotoxic symptoms such as agitation, restlessness, hind limb paralysis, or seizures. In addition, analgesia of the caudal abdominal region and signs of systemic sedation were scored on a scale of 0–3. Heart rate, respiratory rate, and rectal temperature were also recorded prior to (baseline values) and at 5, 15, 30, 60, 90, and 120 minutes after administration. Mastectomy or hemimastectomy operation was carried out after full assurance of the analgesic effect on the udder and caudal abdominal region. Time of onset of surgical analgesia (score 3) was achieved at 15 minutes and lasted for 60 minutes. Maximal sedation score was recorded at 15 minutes and lasted for 60 minutes, then decreased thereafter, with the lowest sedation score recorded at 120 minutes. There was a significant (P<0.05) rise in heart rate at some point between 5–90 minutes, while the respiratory rate and rectal temperature did not change significantly from baseline values. Postoperatively, animals did not show any signs of pain or discomfort. Follow-up on the operated goats showed that all wounds were fully healed without any significant complications. In goats, intrathecal administration of ketamine-lidocaine combination resulted in a safe and effective analgesia of the caudal abdominal and udder region sufficient to perform mastectomy or hemimastectomy.

Effects of intravenous and intrathecal dexmedetomidine in spinal anesthesia: a meta-analysis

PURPOSE

To assess the effects of dexmedetomidine on the duration of sensory and motor block, postoperative analgesia, hypotension, bradycardia, and side effects in patients undergoing spinal anesthesia.

METHODS

Two researchers searched MEDLINE, EMBASE, and the Cochrane controlled trial register independently for randomized controlled trials comparing dexmedetomidine with a placebo without any language restrictions.

RESULTS

A total of 412 patients from eight trials were included in this study. The results revealed that dexmedetomidine was statistically significant in prolonging the duration of sensory block (mean difference, MD = 73.55; 95% CI, [55.69, 91.40] P < 0.00001, I(2)  = 89%) and motor block (MD = 59.11; 95% CI, [29.58, 88.65] P < 0.00001, I(2)  = 91%) and the time to first request for postoperative analgesia (MD = 245.77, 95% CI, [143.53, 348.00] P < 0.00001, I(2)  = 98%). The occurrence of hypotension (OR = 0.60, 95% CI, [0.3-1.23], P = 0.40, I(2)  = 3%) and side effects (OR = 0.9, 95% CI, [0.36-2.22], P = 0.88, I(2)  = 0%) was not significantly different between dexmedetomidine and placebo. However, dexmedetomidine was associated with more frequent bradycardia requiring atropine (OR = 7.55; 95% CI, [2.76-20.63], P = 0.63, I(2)  = 0%).

CONCLUSIONS

This meta-analysis has shown that dexmedetomidine prolonged the duration of spinal anesthesia and improved postoperative analgesia and did not increase the incidence of hypotension and adverse events, but needs more atropine to reverse bradycardia.

Stereological study of the effects of morphine consumption and abstinence on the number of the neurons and oligodendrocytes in medial prefrontal cortex of rats

Quantitative studies to date on the effects of opioid consumption and abstinence on the nervous system using modern stereological methods have not received enough attention. In addition, they have yielded controversial results. The present study was conducted to investigate the effects of morphine, with or without abstinence, on the neurons and oligodendrocytes of the medial prefrontal cortex (MPFC) in rats using quantitative stereological methods. The male rats were divided into four groups: the first (saline [SAL]) and second (morphine [MOR]) groups were treated with saline and an escalating dose of morphine (5-20 mg/kg) for 30 days, respectively; the third (SAL+abstinence [ABS]) and fourth (MOR+ABS) groups were treated in the same manner as the previous groups plus they had a 30-day abstinence period. The results showed that the volume of the MPFC and its subdivisions decreased by approximately 15% in the MOR group compared with that in the SAL group (P<0.05). In addition, the volume decreased by approximately 24% in the MOR+ABS group compared with that in the SAL+ABS group (P<0.05). The number of neurons in the MOR and MOR+ABS groups decreased by approximately 44% and 35%, respectively, compared with that in their corresponding control groups. Moreover, the number of the oligodendrocytes in the MOR and MOR+ABS groups decreased by approximately 41% and 37%, respectively. No significant difference was noted in the number of cells in the MOR and MOR+ABS groups. In conclusion, morphine consumption leads to a permanent reduction in the number of neurons and oligodendrocytes, and no additional neuron and oligodendrocyte loss occurs after abstinence.

Evaluation of antinociceptive and neurotoxic effects of intrathecal dexmedetomidine in rats

OBJECTIVE

Dexmedetomidine has been reported to produce analgesia after intrathecal administration. In the present study the α2-adrenoceptor agonist dexmedetomidine was evaluated for its potential spinal neurotoxic effects.

MATERIAL AND METHODS

Three days after intrathecal cannulation, rats were administered either dexmedetomidine (3 μg/30 μL, i.t.) or saline (30 μL, i.t.). Antinociceptive, sedative and motor effects of intrathecal administrations of dexmedetomidine or saline were evaluated during 90 min. The tail-flick and hot plate tests were used to assess the thermal nociceptive threshold. Seven days after drug administration, animals were sacrified and spinal cords were evaluated for histopathological changes by light microscopy.

RESULTS

Dexmedetomidine administered intrathecally produced antinociception. Antinociception was accompanied by immediate sedation and loss of placing-stepping reflexes that lasted over 40 min in all dexmedetomidine administered rats. In all rats, microscopic examination revealed mild gliosis and minimal infiltration of inflamatory r cells in posterior white matter. Mild (total score 4-6) histopathologic lesions were seen in four animals in dexmedetomidine adminisered rats, but there was no statistically significant difference when compared with the saline administered rats.

CONCLUSION

We observed that intrathecal injections of dexmedetomidine at the dose of 3 μg/30 μL produce antinociception but did not cause any histopathological sign of injury in the spinal cord.

Intrathecal midazolam as supplementary analgesia for chronic lumbar pain--15 years' experience

BACKGROUND

The antinociceptive effect of intrathecal midazolam is based on its affecting spinal gamma-amino butyric acid receptors.

OBJECTIVE

To evaluate pain relief in patients with chronic low back pain and failed back surgery syndrome after a single-shot intrathecal administration of midazolam.

DESIGN

A prospective, open-label study.

OUTCOME MEASURES

The analgesic effect was determined using a patient questionnaire during subsequent visits to the pain therapy service. We classified at least a 50% pain reduction with improved quality of life and improved functional condition as a positive outcome.

RESULTS

Between 1995 and 2010, we performed 500 administrations: 227 administrations in 57 male patients and 273 administrations in 69 female patients. We performed 81 administrations for chronic low back pain and 419 administrations for failed back surgery syndrome. The average age of our patients was 50 years (range 28 to 86). The dose administered ranged from 2 to 5 mg of midazolam. The analgesic effect lasted 9.7 weeks on average, ranging from 1 week to 3 years; the most common reported duration was between 4 and 12 weeks (3 months). In 65% of patients, we achieved pain relief lasting 4 weeks or longer; in 13%, the administration provided no analgesic effect at all. The incidence of side effects (drowsiness, nausea, headache, or transient worsening of complaints) was rather low.

CONCLUSION

Intrathecal midazolam is a useful supplement to standard analgesic therapy with opioids, non-opioids, or spinal steroids.

Evaluation of the neurological safety of epidurally-administered pregabalin in rats

Background

The primary site of action of pregabalin, i.e. the α-2-δ subunit of the voltage-dependent calcium channel, is located at the dorsal root ganglion and dorsal horn of the spinal cord. Therefore, the epidural administration of pregabalin could have advantages over oral administration. However, the possibility of its neurotoxicity should be excluded before any attempt at epidural administration. We evaluated the neuronal safety of epidurally-administered pregabalin by observing the sensory/motor changes and examining the histopathology of spinal cord in rats.

Methods

Sixty rats of 180-230 g were divided into three groups; 3 mg of pregabalin dissolved in 0.3 ml saline (group P, n = 20), 0.3 ml 40% alcohol (group A, n = 20), or 0.3 ml normal saline (group N, n = 20) was administered epidurally to the rats in each group. Pinch-toe test, motor function evaluation, and histopathologic examination of vacuolation, chromatolysis, meningeal inflammation, and neuritis were performed at the 1st, 3rd, 7th, and 21st day after each epidural administration.

Results

All rats enrolled in group P, like those in group N, showed neither sensory/motor dysfunction nor any histopathological abnormality over the 3-week observation period. In contrast, in group A, 80% of the rats showed abnormal response to the pinch-toe test and all rats showed decreased motor function during the entire evaluation period. In addition, all histopathologic findings of neurotoxicity were observed exclusively in group A.

Conclusions

The epidurally administered pregabalin (about 15 mg/kg) did not cause any neurotoxic evidence, in terms of both sensory/motor function evaluation and histopathological examination in rats.

The Safety of EXPAREL ® (Bupivacaine Liposome Injectable Suspension) Administered by Peripheral Nerve Block in Rabbits and Dogs

A sustained-release DepoFoam injection formulation of bupivacaine (EXPAREL, 15 mg/mL) is currently being investigated for postsurgical analgesia via peripheral nerve block (PNB). Single-dose toxicology studies of EXPAREL (9, 18, and 30 mg/kg), bupivacaine solution (Bsol, 9 mg/kg), and saline injected around the brachial plexus nerve bundle were performed in rabbits and dogs. The endpoints included clinical pathology, pharmacokinetics, and histopathology evaluation on Day 3 and Day 15 (2/sex/group/period). EXPAREL resulted in a nearly 4-fold lower C_max versus Bsol at the same dose. EXPAREL was well tolerated at doses up to 30 mg/kg. The only EXPAREL-related effect seen was minimal to mild granulomatous inflammation of adipose tissue around nerve roots (8 of 24 rabbits and 7 of 24 dogs) in the brachial plexus sites. The results indicate that EXPAREL was well tolerated in these models and did not produce nerve damage after PNB in rabbits and dogs.

Activation of TRPA1 by membrane permeable local anesthetics

Background

Low concentrations of local anesthetics (LAs) suppress cellular excitability by inhibiting voltage-gated Na⁺ channels. In contrast, LAs at high concentrations can be excitatory and neurotoxic. We recently demonstrated that LA-evoked activation of sensory neurons is mediated by the capsaicin receptor TRPV1, and, to a lesser extent by the irritant receptor TRPA1. LA-induced activation and sensitization of TRPV1 involves a domain that is similar, but not identical to the vanilloid-binding domain. Additionally, activation of TRPV1 by LAs involves PLC and PI(4,5)P₂-signalling. In the present study we aimed to characterize essential structural determinants for LA-evoked activation of TRPA1.

Results

Recombinant rodent and human TRPA1 were expressed in HEK293t cells and investigated by means of whole-cell patch clamp recordings. The LA lidocaine activates TRPA1 in a concentration-dependent manner. The membrane impermeable lidocaine-derivative QX-314 is inactive when applied extracellularly. Lidocaine-activated TRPA1-currents are blocked by the TRPA1-antagonist HC-030031. Lidocaine is also an inhibitor of TRPA1, an effect that is more obvious in rodent than in human TRPA1. This species-specific difference is linked to the pore region (transmembrane domain 5 and 6) as described for activation of TRPA1 by menthol. Unlike menthol-sensitivity however, lidocaine-sensitivity is not similarly determined by serine- and threonine-residues within TM5. Instead, intracellular cysteine residues known to be covalently bound by reactive TRPA1-agonists seem to mediate activation of TRPA1 by LAs.

Conclusions

The structural determinants involved in activation of TRPA1 by LAs are disparate from those involved in activation by menthol or those involved in activation of TRPV1 by LAs.

[Regional anesthesia and neurological diseases]

Modern anesthesia is handling an increasing number of patients with neurological diseases who require narcosis. Regional anesthesia techniques offer qualities which might be advantageous for this group particularly for childbirth. The number of pregnant women with neurological diseases has increased significantly in the recent years due to improved diagnostics and therapy. A more careful approach to regional anesthesia in patients with neurological diseases is necessary as the drugs themselves possess neurotoxic effects and the procedure might worsen the underlying neurological diseases. Additionally, performing regional anesthesia might be more complicated and the resulting blockade might be different from the expected neuronal block. Published data concerning regional anesthesia in this patient group are limited and mainly restricted to case reports. In this review general considerations regarding regional anesthesia, techniques, drugs and methods in these patient groups will be discussed. In the second part the practical approach to regional anesthesia for some of the most important neurological diseases is highlighted.

Complications and pitfalls of lumbar interlaminar and transforaminal epidural injections

Lumbar interlaminar and transforaminal epidural injections are used in the treatment of lumbar radicular pain and other lumbar spinal pain syndromes. Complications from these procedures arise from needle placement and the administration of medication. Potential risks include infection, hematoma, intravascular injection of medication, direct nerve trauma, subdural injection of medication, air embolism, disc entry, urinary retention, radiation exposure, and hypersensitivity reactions. The objective of this article is to review the complications of lumbar interlaminar and transforaminal epidural injections and discuss the potential pitfalls related to these procedures. We performed a comprehensive literature review through a Medline search for relevant case reports, clinical trials, and review articles. Complications from lumbar epidural injections are extremely rare. Most if not all complications can be avoided by careful technique with accurate needle placement, sterile precautions, and a thorough understanding of the relevant anatomy and contrast patterns on fluoroscopic imaging.

The vanilloid receptor TRPV1 is activated and sensitized by local anesthetics in rodent sensory neurons

Local anesthetics (LAs) block the generation and propagation of action potentials by interacting with specific sites of voltage-gated Na(+) channels. LAs can also excite sensory neurons and be neurotoxic through mechanisms that are as yet undefined. Nonspecific cation channels of the transient receptor potential (TRP) channel family that are predominantly expressed by nociceptive sensory neurons render these neurons sensitive to a variety of insults. Here we demonstrated that the LA lidocaine activated TRP channel family receptors TRPV1 and, to a lesser extent, TRPA1 in rodent dorsal root ganglion sensory neurons as well as in HEK293t cells expressing TRPV1 or TRPA1. Lidocaine also induced a TRPV1-dependent release of calcitonin gene-related peptide (CGRP) from isolated skin and peripheral nerve. Lidocaine sensitivity of TRPV1 required segments of the putative vanilloid-binding domain within and adjacent to transmembrane domain 3, was diminished under phosphatidylinositol 4,5-bisphosphate depletion, and was abrogated by a point mutation at residue R701 in the proximal C-terminal TRP domain. These data identify TRPV1 and TRPA1 as putative key elements of LA-induced nociceptor excitation. This effect is sufficient to release CGRP, a key component of neurogenic inflammation, and warrants investigation into the role of TRPV1 and TRPA1 in LA-induced neurotoxicity.

Management of chronic back and leg pain by intrathecal drug delivery

Intrathecal delivery of analgesic drugs by implantable pump systems has been recognized as a treatment option for patients with chronic pain of benign or malignant origin that is resistant to oral or parenteral medication. Patients with chronic back and leg pain (CBLP), a benign but severely disabling condition of the lumbar spine with multifactorial genesis, have been demonstrated in a number of retrospective and in some prospective clinical studies to benefit from intrathecal delivery of opioid and/or non-opioid substances, either as single drugs or in combinations. In addition, intrathecal therapy for CBLP has been proven safe and less expensive that conventional medical therapy. This chapter summarizes the clinical and experimental evidence and the personal experience of the authors with long-term intrathecal infusion therapy for CBLP. It discusses important clinical issues such as drug selection, drug combinations, and side effects and complications of intrathecal infusion. It is concluded that further clinical research is needed in order to provide stronger evidence for the usefulness of a number of drugs currently used for intrathecal therapy on a mostly empirical basis.

Bupivacaine induces transient neurological symptoms after subarachnoid block

Bupivacaine is a long-acting amide local anesthetic that was introduced to clinical practice in the early 1980s. Since then it has been extensively used for both peripheral blocks as well as neuraxial blockade in concentrations varying from 0.125% to 0.75%. Despite the relatively narrow safety margin, bupivacaine has become the most frequently used local anesthetic in obstetric anesthesia. It is 95% metabolized in the liver and 5% excreted unchanged in urine. Bupivacaine cardiotoxicity is related to the total dose rather than to the concentration of bupivacaine administered. It produces a dose-dependent delay in the transmission of impulses through the cardiac conduction system by blocking sodium channels. Transient neurologic symptoms (TNS) defined as bilateral symmetrical pain in the lower back and buttocks with radiation to both lower extremities after 5% lidocaine spinal anesthetic was first described by Schneider in 1993. Several studies have failed to show TNS after spinal anesthesia using bupivacaine 0.5% or 0.75%. In the literature there is only 1 case report of TNS after spinal anesthesia using bupivacaine and morphine. The following report describes a case of TNS following spinal anesthesia with bupivacaine 0.75%.

Intrathecal betamethasone pain relief in cancer patients with vertebral metastasis: a pilot study

BACKGROUND

We have reported previously the usefulness of intrathecal betamethasone for pain relief in cancer patients who suffer from intractable pain caused by vertebral metastasis. The mechanism by which betamethasone relieves pain may be related to alterations in cerebrospinal fluid (CSF) concentrations of pro-inflammatory cytokines and prostanoids.

METHODS

Thirteen cancer patients with intractable pain caused by vertebral metastasis received 2-3 mg betamethasone in the lumbar subarachnoid space. CSF concentrations of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-6, IL-8 and prostaglandin E(2) (PGE(2)) were measured with an enzyme-linked immunosorbent assay (ELISA) and a chemiluminescence enzyme immunoassay. Pain was measured using a numerical pain score (range, 0-10; 0, no pain; 10, worst pain imaginable).

RESULTS

Intrathecal betamethasone was associated with a significant decrease in the pain score in six patients. In these cases, the pain score decreased from 6.7 +/- 0.5 (mean +/- standard error of the mean) to 3.3 +/- 0.3 (P < 0.05), and the CSF concentrations of IL-8 and PGE(2) decreased significantly compared with pre-treatment levels (IL-8, 183.3 +/- 21.2 to 116.5 +/- 10.6 pg/ml; PGE(2), 43.8 +/- 10.3 to 14.7 +/- 3.0 pg/ml). There were no significant changes in the CSF concentrations of cytokines and PGE(2) in the remaining seven patients.

CONCLUSION

Pain relief with intrathecal betamethasone is related to decreases in the CSF concentration of IL-8 and PGE(2).

Neuraxial drug administration: a review of treatment options for anaesthesia and analgesia

Neuraxial drug administration describes techniques that deliver drugs in close proximity to the spinal cord, i.e. intrathecally into the CSF or epidurally into the fatty tissues surrounding the dura, by injection or infusion. This approach was initially developed in the form of spinal anaesthesia over 100 years ago. Since then, neuraxial drug administration has evolved and now includes a wide range of techniques to administer a large number of different drugs to provide anaesthesia, but also analgesia and treatment of spasticity in a variety of acute and chronic settings. This review concentrates on the pharmacological agents used and the clinical basis behind currently utilised approaches to neuraxial drug administration. With regard to local anaesthetics, the main focus is on the development of the enantiomer-specific compounds ropivacaine and levobupivacaine, which provide similar efficacy to bupivacaine with a reduced risk of severe cardiotoxicity. Opioids are the other group of drugs widely used neuraxially, in particular to provide analgesia alone or more commonly in combination with other agents. The physicochemical properties of the various opioids explain the main differences in efficacy and safety between these drugs when used intrathecally, of which morphine, fentanyl and sufentanil are most commonly used. Another group of drugs including clonidine, dexmedetomidine and epinephrine (adrenaline) provide neuraxial analgesia via alpha-adrenergic receptors and are used mainly as adjuvants to local anaesthetics and opioids. Furthermore, intrathecal baclofen is in routine clinical use to treat spasticity in a number of neurological conditions. Beside these established approaches, a wide range of other drugs have been assessed for neuraxial administration to provide analgesia; however, most are in various early stages of investigation and are not used routinely. These drugs include neostigmine, ketamine, midazolam and adenosine, and the conotoxin ziconotide. The latter is possibly the most unusual compound here; it has recently gained registration for intrathecal use in specific chronic pain conditions.

Clinical evaluation of clonidine added to lidocaine solution for subarachnoid analgesia in sheep

Clonidine (CL) is a alpha2-adrenergic agonist that produces analgesia in animals and humans by a non-opiate alpha2-adrenergic action in the spinal cord dorsal horn. The objective of this prospective randomized study was to investigate the clinical effects of CL/lidocaine (LD) combination administered by the subarachnoid route in sheep. Each sheep received each of three treatments, at no shorter than weekly intervals. Treatments consisted of 0.003 mg/kg CL, 1.2 mg/kg LD and a combination of CL (0.003 mg/kg) and LD (1.2 mg/kg) (CLLD). Subarachnoid injections were given in all animals between the last lumbar and first sacral vertebra. Heart rate (HR), arterial pressures, respiratory rate, rectal temperature, analgesia, sedation, and motor blockade were determined before drug administration (basal) and 5, 10, 15 and 30 min after drug administration, and at 30-min intervals until loss of analgesia occurred. The duration of analgesia after subarachnoid CLLD administration was 187 +/- 24 min (mean +/- SD), i.e. more than twice of that obtained with CL (99 +/- 19 min) or LD (55 +/- 4.4 min) alone. In all sheep, CL, administered either alone or with LD, induced moderate sedation. After subarachnoid administration of three treatments, all sheep had ataxia and subsequent sternal recumbency. The CL treatment causes decreases in blood pressure (diastolic arterial pressure and mean arterial pressure) and HR. Data suggest that the CLLD combination could be used subarachnoidally in sheep requiring prolonged surgery.

Intrathecal clonidine in the treatment of intractable pain: a phase I/II study

OBJECTIVE

Epidural clonidine has been proven effective in relieving intractable cancer pain, especially neuropathic. This phase I/II study was performed to investigate if intrathecal clonidine is well tolerated and effective for long-term treatment of intractable chronic pain.

DESIGN

Thirty-one patients, previously implanted with programmable pumps and unable to obtain adequate pain relief with opioids and adjuvant oral medications, were enrolled. Clonidine monotherapy was initiated at 1 mcg/hr and escalated to a maximum of 40 mcg/hr (960 mcg/day). Efficacy measurements included Verbal Digital Pain Ratings, and side effects were determined by physical exam and patient reports.

RESULTS

Patients achieving 50% or greater reduction in pain intensity scores in the dose-titration phase continued for long-term follow-up. Twenty-two patients (71%) entered long-term follow-up with intrathecal clonidine; nine patients (29%) did not obtain adequate pain control in the dose-titration phase. Thirteen patients were considered long-term successes with a mean follow-up of 16.7 months (range = 6.3 to 44 months). Nine patients failed to achieve adequate pain relief due to side effects or lack of efficacy. Fifty-nine percent of the patients successful in the dose-titration stage (42% of all patients considered) were considered long-term successes. Patients in the long-term phase maintained adequate pain control with minimal dose escalation.

CONCLUSIONS

This study demonstrates the tolerability and effectiveness of intrathecal clonidine in the treatment of chronic pain. The physician using clonidine for long-term intrathecal infusion should be cognizant of the risk that severe rebound systemic hypertension can occur with abrupt cessation of the intrathecal infusion of clonidine.

Efficacy of Intrathecal Bupivacaine: How Important Is the Flow Rate?

We present two cases of cancer patients with intractable mechanical and visceral pain that was unrelieved with either comprehensive medical management or intrathecal morphine who received intrathecal bupivacaine. While the continuous administration of a seemingly significant daily dose neither relieved pain nor caused measurable clinical changes, the addition of small, presumably negligible bolus doses on top of the continuous infusion resulted in spectacular pain control, clear thermoanalgesic suspended block, and in one of the patients, significant hypotension. To the best of our knowledge, such an observation has neither been reported before nor can we provide a satisfactory explanation for it. However, we believe it may have significant implications for the treatment of some patients, in particular, cancer patients with mechanical pain that cannot be adequately relieved with morphine whatever the route of administration.

A comparison of the neurotoxic effects on the spinal cord of tetracaine, lidocaine, bupivacaine, and ropivacaine administered intrathecally in rabbits

We have reported that increased glutamate concentrations in microdialysate of the cerebrospinal fluid (CSF) may be clue phenomena to elucidate mechanisms of neurotoxicity of intrathecal tetracaine. However, little is known about whether this is true for other local anesthetics. In this study, we compared the effects of local anesthetics on glutamate concentrations in CSF microdialysate and neurologic and histopathologic outcome. Rabbits were assigned into 5 groups (n = 6 in each) and intrathecally received 0.3 mL of NaCl solution (control), 2% tetracaine, 10% lidocaine, 2% bupivacaine, or 2% ropivacaine. Neurologic and histopathologic assessments were performed 1 wk after the administration. Intrathecal local anesthetics significantly increased glutamate concentrations with no significant differences among the four local anesthetics. The sensory and motor functions in the lidocaine group were significantly worse than in the other groups. Characteristic histopathologic changes were vacuolation in the dorsal funiculus and chromatolytic damage of motor neurons. The extent of vacuolation of the dorsal funiculus was in the order of lidocaine = tetracaine > bupivacaine > ropivacaine. Although the differences among the local anesthetics cannot be explained by glutamate concentrations, the results suggest that the margin of safety may be smallest with lidocaine.

IMPLICATIONS

Large concentrations of local anesthetics administered intrathecally increased glutamate concentrations in the cerebrospinal fluid. The margin of safety may be smallest with lidocaine.

Critical care and perioperative management in traumatic spinal cord injury

Traumatic spinal cord injury is frequently associated with brain injury and with alterations in respiratory and cardiovascular function that require critical care management. Complications include respiratory failure, atelectasis, pneumonia, neurogenic shock, autonomic dysreflexia, venous thromboembolism, and sepsis. While complications may be managed with supportive care, the goal of ameliorating neurologic outcome has proved elusive. Methylprednisolone, when instituted <8 hours after traumatic spinal cord injury, was associated in two clinical trials with statistically significant improvements in motor scores at 6 months and 1 year; however, critical reappraisal of these data raises questions about their validity and clinical relevance. Until more evidence of clinically effective therapies is available, acute management must be driven by pathophysiologic principles, with emphasis on interventions that attenuate secondary neurologic injury; these include the rational use of immobilization, cautious airway management, and promotion of cord perfusion and oxygenation with the appropriate level of hemodynamic and respiratory support. Clinical trials of pharmacologic neuroprotection have yielded disappointing results, but the ongoing elucidation of spinal cord repair and regenerative mechanisms suggests new therapeutic prospects.

Benefit and risks of local anesthetics in infants and children

Regional anesthesia has become a routine part of the practice of anesthesiology in infants and children. Local anesthetic toxicity is extremely rare in infants and children; however, seizures, dysrhythmias, cardiovascular collapse, and transient neuropathic symptoms have been reported. Infants and children may be at increased risk from local anesthetics compared with adults. Larger volumes of local anesthetics are used for epidural anesthesia in infants and children than in adults. Metabolism and elimination of local anesthetics can be delayed in neonates, who also have decreased plasma concentrations of alpha(1)-acid glycoprotein, leading to increased concentrations of unbound bupivacaine. Most regional anesthetic procedures in infants and children are performed with the patient heavily sedated or anesthetized; because of this, and because a test dose is not a particularly sensitive marker of intravenous injection in the anesthetized patient, detection of intravascular local anesthetic injection is extremely difficult. The same local anesthetics used in adult anesthetic practice are also used in infants and children. Because of its extremely short duration of action, chloroprocaine has been used primarily for continuous epidural techniques in infants and children. The use of tetracaine has generally been limited to spinal and topical anesthesia. Lidocaine (lignocaine) has been used extensively in infants and children for topical, regional, plexus, epidural and spinal anesthesia. The association between prilocaine and methemoglobinemia has generally restricted prilocaine use in infants and children to the eutectic mixture of local anesthetics (EMLA). Because of its greater degree of motor block compared with other long-acting local anesthetics, etidocaine has generally been limited to plexus blocks in infants and children. Mepivacaine has been used for both plexus and epidural anesthesia in infants and children. Because postoperative analgesia is often the primary justification for regional anesthesia in infants and children, bupivacaine, a long-acting local anesthetic, is the most commonly reported local anesthetic for pediatric regional anesthesia. Given the lower toxic threshold of bupivacaine compared with other local anesthetics, the risk-benefit ratio of bupivacaine may be greater than that of other local anesthetics. Two new enantiomerically pure local anesthetics, ropivacaine and levobupivacaine, offer clinical profiles comparable to that of bupivacaine but without its lower toxic threshold. The extreme rarity of major toxicity from local anesthetics suggests that widespread replacement of bupivacaine with ropivacaine or levobupivacaine is probably not necessary. However, there are clinical situations, including prolonged local anesthetic infusions, use in neonates, impaired hepatic metabolic function, and anesthetic techniques requiring a large mass of local anesthetic, where replacement of bupivacaine with ropivacaine, levobupivacaine or (for continuous techniques) chloroprocaine appears prudent.

Pharmaceutics for the anaesthetist

Pharmaceutics is that branch of science concerned with the manufacture and formulation of pharmaceutical products, and is a subject almost exclusively in the domain of pharmacists and those concerned with pharmaceutical manufacture. However, there are some aspects of pharmaceutics that are of particular importance to the anaesthetist, such as the pharmacology of the various preservatives, antimicrobials and other additives found in anaesthetic products, and an understanding of basic processes such as emulsification and lyophylisation. This review aims to survey those areas.

Intrathecal methylprednisolone for intractable postherpetic neuralgia

BACKGROUND

There is no effective treatment for intractable postherpetic neuralgia. Because there is evidence that postherpetic neuralgia has an inflammatory component, we assessed treatment with intrathecally administered methylprednisolone to reduce pain in patients with this disorder.

METHODS

We enrolled 277 patients who had had intractable postherpetic neuralgia for at least one year, 270 of whom were followed for two years. The patients were randomly assigned to receive intrathecal methylprednisolone and lidocaine (3 ml of 3 percent lidocaine with 60 mg of methylprednisolone acetate, 89 patients), lidocaine alone (3 ml of 3 percent lidocaine, 91 patients), or no treatment (90 patients) once per week for up to four weeks. Each weekly dose was injected into the lumbar intrathecal space. Pain was evaluated before randomization, at the end of the treatment period, and then four weeks, one year, and two years later. Samples of cerebrospinal fluid were obtained for measurement of interleukin-8 before and at the end of the treatment period.

RESULTS

There was minimal change in the degree of pain in the lidocaine-only and control groups during and after the treatment period. In the methylprednisolone-lidocaine group, the intensity and area of pain decreased, and the use of the nonsteroidal antiinflammatory drug diclofenac declined by more than 70 percent four weeks after the end of treatment. No complications related to intrathecal methylprednisolone were observed. Before treatment, the concentrations of interleukin-8 in the cerebrospinal fluid were inversely related to the duration of neuralgia in all the patients (r=-0.49, P<0.001). In the patients who received methylprednisolone, interleukin-8 concentrations decreased by 50 percent, and this decrease correlated with the duration of neuralgia and with the extent of global pain relief (P<0.001 for both comparisons).

CONCLUSIONS

The results of this trial indicate that the intrathecal administration of methylprednisolone is an effective treatment for postherpetic neuralgia.

Potential for patient harm from intrathecal administration of preserved solutions

Intrathecal drug administration is an important component of the management of malignancy and symptom control. This route of administration reduces systemic adverse effects, but can increase the risk of local adverse effects such as arachnoiditis. It is accepted practice that any spinal injection should not contain any preservatives (such as benzyl alcohol and parabens-containing compounds). The intrathecal administration of solutions preserved with benzyl alcohol has been shown in case studies to increase the risk of adverse neurological events. Available data do not support the safety of intrathecal injection of products preserved with parabens; rather, they demonstrate a need for further investigation. Steps should be taken to ensure that preservative-free products are used. Staff involved with the preparation and administration of intrathecal preparations need to be educated about the risks associated with preservatives in this setting.