Effectiveness of Tizanidine in Neuropathic Pain: An Open-Label Study

Long-Term Use of Muscle Relaxant Medications for Chronic Pain: A Systematic Review

Importance

Stricter opioid prescribing guidelines have increased prescriptions of skeletal muscle relaxants (SMRs) for chronic pain, but the efficacy of long-term use of SMRs for chronic pain is unknown.

Objective

To systematically review the effectiveness or efficacy of long-term use of SMRs for chronic pain.

Evidence Review

Two reviewers systematically searched Ovid MEDLINE, Embase (Ovid), Web of Science, CINAHL, and Cochrane through December 4, 2023. They included articles published in English, Spanish, or Italian. Only randomized clinical trials (RCTs) and cohort studies with comparator groups evaluating at least 1-month duration of SMRs for chronic pain were included. The reviewers dually reviewed data abstraction, risk-of-bias, and quality. They characterized studies by chronic pain syndrome: low back pain, fibromyalgia, headaches, painful cramps or spasticity, and other syndromes.

Findings

A total of 30 RCTs with 1314 participants and 14 cohort studies with 1168 participants assessed SMRs for chronic pain. Studies were primarily short-term (4-6 weeks). Nine unique SMRs were represented by the studies identified. Eleven studies (25%) examined baclofen, 8 (18%) examined tizanidine, and 7 (16%) examined cyclobenzaprine. Evidence for effectiveness was strongest for SMRs used for trigeminal neuralgia, neck pain, and painful cramps; evidence suggested SMRs for fibromyalgia, low back pain, and other syndromes were not more beneficial than placebo. The most common adverse effects were sedation and dry mouth. RCTs had a low to moderate risk of bias, and the quality of cohort studies was fair to good.

Conclusions and Relevance

In this systematic review of long-term use of SMRs for chronic pain, findings suggest that their long-term use may benefit patients with painful spasms or cramps and neck pain; their long-term use for low back pain, fibromyalgia, and headaches did not appear to be beneficial. Clinicians should be vigilant for adverse effects and consider deprescribing if pain-related goals are not met.

Assessing suicide risk in chronic pain management: a narrative review across drug classes

INTRODUCTION

Chronic pain presents a multifaceted challenge in clinical practice, necessitating a nuanced understanding of pharmacological interventions to optimize treatment outcomes. This review provides an outline of various pharmacological agents commonly used in chronic pain management and highlights their safety considerations, particularly regarding suicide risk.

AREAS COVERED

This review discusses the role of antidepressants, anticonvulsants, GABA receptor agonists, NMDA receptor antagonists, corticosteroids, cannabis and cannabinoids, bisphosphonates, calcitonin, and alpha-2 adrenergic receptor agonists in chronic pain management. It assesses their therapeutic benefits, potential for misuse, and psychiatric adverse effects, including the risk of suicide. Each pharmacological class is evaluated in terms of its efficacy, safety profile, and considerations for clinical practice. We searched peer-reviewed English literature on the topic using the MEDLINE database without time restrictions.

EXPERT OPINION

While pharmacological interventions offer promise in alleviating chronic pain, healthcare providers must carefully weigh their benefits against potential risks, including the risk of exacerbating psychiatric symptoms and increasing suicide risk. Individualized treatment approaches, close monitoring, and multidisciplinary collaboration are essential for optimizing pain management strategies while mitigating adverse effects. Ongoing research efforts are crucial for advancing our understanding of these pharmacological interventions and refining pain management practices.

Chronic pain, a narrative review for the internist in 2024

Chronic pain is a complex and pervasive condition that profoundly affects individuals physically, emotionally, and socially. This narrative review aims to provide internists and healthcare professionals with a comprehensive overview of chronic pain, its various types, pathophysiology, epidemiology, clinical presentation, evaluation tools, and the burden it imposes on patients. We discuss the importance of recognizing chronic pain as a legitimate condition and the need for a compassionate, individualized approach to management. The review highlights the role of both pharmacological and non-pharmacological interventions in treating chronic pain, emphasizing the value of reducing pain, improving function, enhancing quality of life, and minimizing medication dependence. Additionally, we touch upon the promising future of pain treatment, including advancements in technology and personalized medicine. While not a comprehensive systematic review, this article serves as a valuable resource for healthcare providers seeking to understand, manage, and treat chronic pain effectively in their daily practice.

Tizanidine: Advances in Pharmacology & Therapeutics and Drug Formulations

Background

Skeletal muscle relaxants (SMRs) are widely used in treating musculoskeletal conditions. All SMRs, with the exception of baclofen and tizanidine, are on the list of 2023 American Geriatrics Society Beers Criteria® for potentially inappropriate medication use in older adults. In our geriatric practice, off-label use of tizanidine as preemptive analgesia drove us to find recent advances in its pharmacology and therapeutics. An update review of tizanidine was thus presented, aiming to bring the latest knowledge to clinicians and promote further research and practical exploration.

Methods

Relevant literature up to December 2023 was identified through searches of PubMed, Web of Science, and Embase.

Results

Tizanidine, a centrally acting alpha-2 adrenoceptor agonist with both antispastic and antispasmodic activity, shows efficacy in the common indications for all SMRs. From the perspective of drug safety, tizanidine has lower incidences of adverse events (injury, delirium, encephalopathy, falls, and opioid overdose) compared to baclofen, no association with risk of Alzheimer's disease as with orphenadrine, no risk of serotonin syndrome like metaxalone when comedicated with serotonergic drugs, no significant pharmacokinetic changes in CYP2C19 poor metabolizers unlike diazepam and carisoprodol, and no physically addictive or abuse properties like carisoprodol and diazepam. From the perspective of new and potential therapeutic uses, tizanidine has additional benefits (eg, gastroprotection that can improve patient tolerance to nonsteroidal anti-inflammatory agents, anti-neuropathic pain, a key component of multimodal analgesia strategy to reduce early postoperative pain, and anti-tumor effects). New delivery systems of tizanidine are developing to improve the pharmacokinetics of oral products, including buccal patches, transdermal delivery systems, nasal spray, and in situ rectal gel.

Conclusion

Tizanidine is an SMR with unique features and may be an optimal initial choice for older adults. There would be more scientific studies, wider therapeutic applications, and new drug formulations in the future.

Does adding muscle relaxant make post-operative pain better? a narrative review of the literature from US and European studies

Centrally acting skeletal muscle relaxants (CASMR) are widely prescribed as adjuncts for acute and chronic pain. Given the recent interest in multimodal analgesia and reducing opioid consumption, there has been an increase in its use for perioperative/postoperative pain control. The mechanism of action, pharmacodynamics, and pharmacokinetics of these drugs vary. Their use has been studied in a wide range of operative and non-operative settings. The best evidence for the efficacy of CASMRs is in acute, nonoperative musculoskeletal pain and, in the operative setting, in patients undergoing total knee arthroplasty and abdominal surgery, including inguinal herniorrhaphy and hemorrhoidectomy. The risk of complications and side effects, coupled with the limited evidence of efficacy, should prompt careful consideration of individual patient circumstances when prescribing CASMRs as part of perioperative pain management strategies.

Promising Advances in Pharmacotherapy for Patients with Spinal Cord Injury-A Review of Studies Performed In Vivo with Modern Drugs

Spinal cord injury (SCI) is a pathological neurological condition that leads to significant motor dysfunction. It is a condition that occurs as a result of tragic accidents, violent acts, or as a consequence of chronic diseases or degenerative changes. The current treatments for patients with SCI have moderate efficacy. They improve the quality of life of patients, but they are still doomed to long-term disability. In response to the modern directions of research on possible therapeutic methods that allow for the recovery of patients with SCI, a scientific review publication is needed to summarize the recent developments in this topic. The following review is focused on the available pharmacological treatments for SCIs and the problems that patients face depending on the location of the injury. In the following review, the research team describes problems related to spasticity and neuropathic pain; possible therapeutic pathways are also described for neuroprotection and the improvement of neurotransmission within the injured spinal cord, and the review focuses on issues related to oxidative stress.

A Disproportionality Analysis of Drug-Drug Interactions of Tizanidine and CYP1A2 Inhibitors from the FDA Adverse Event Reporting System (FAERS)

INTRODUCTION

Tizanidine is primarily metabolized via cytochrome P450 (CYP) 1A2 and therefore medications that inhibit the enzyme will affect the clearance of tizanidine, leading to increased plasma concentrations of tizanidine and potentially serious adverse events.

OBJECTIVES

Our aim was to study the occurrence of adverse events reported in the FDA Adverse Event Reporting System (FAERS) involving the combination of tizanidine and drugs that inhibit the metabolic activity of CYP1A2.

METHODS

A disproportionality analysis of FAERS reports from 2004 quarter 1 through 2020 quarter 3 was conducted to calculate the reporting odds ratio (ROR) of reports mentioning tizanidine in a suspect or interacting role or having any role, a CYP1A2 inhibitor, and the following adverse events: hypotension, bradycardia, syncope, shock, cardiorespiratory arrest, and fall or fracture.

RESULTS

A total of 89 reports were identified mentioning tizanidine, at least one CYP1A2 inhibitor, and one of the adverse events of interest. More than half of the reports identified tizanidine as having a suspect or interacting role (n = 59, 66.3%), and the reports more frequently involved women (n = 58, 65.1%). The median age was 56.1 years (standard deviation 17.1). Some of the important safety signals included interactions between tizanidine in a suspect or interacting role and ciprofloxacin (ROR for hypotension 28.1, 95% confidence interval [CI] 19.2-41.2) or fluvoxamine (ROR for hypotension 36.9, 95% CI 13.1-103.4), and also when reported in "any role" with ciprofloxacin (ROR for hypotension 6.3, 95% CI 4.7-8.5), fluvoxamine (ROR for hypotension 11.4, 95% CI 4.5-28.8), and zafirlukast (ROR for falls 16.0, 95% CI 6.1-42.1).

CONCLUSIONS

Reports involving tizanidine and a CYP1A2 inhibitor have higher odds of reporting hypotension. This study suggests that concurrent use of tizanidine with CYP1A2 inhibitors may lead to serious health consequences associated with low blood pressure such as falls and fractures.

Sex-dependent antiallodynic effect of α2 adrenergic receptor agonist tizanidine in rats with experimental neuropathic pain

The purpose of this study was to investigate the mechanism of antiallodynic effect of tizanidine in neuropathic rats. Spinal nerve ligation reduced withdrawal threshold which was interpreted as tactile allodynia. Increasing doses of tizanidine induced a dose-dependent antiallodynic effect in nerve injured rats. Tizanidine was more effective in female than male neuropathic rats. This drug induced a lower antiallodynic effect in ovariectomized, compared with non-ovariectomized, neuropathic rats, while systemic reconstitution of estradiol (E2) levels in ovariectomized neuropathic females fully restored the antiallodynic effect of tizanidine. Naloxone reduced the antiallodynic effect of tizanidine in male but not in female neuropathic rats. Ovariectomy restored the antagonizing effect of naloxone in the antiallodynic effect of tizanidine, whereas treatment with E2 abolished the effect of naloxone on tizanidine activity. Rauwolscine (α₂ antagonist) and imiloxan (α_2B antagonist) completely abated tizanidine-induced antiallodynic effect in female neuropathic rats. In contrast, BRL-44408 (α_2A antagonist) partially decreased the effect of tizanidine while JP-1302 (α_2C antagonist) was ineffective. Rauwolscine, imiloxan and BRL-44408 decreased withdrawal threshold in naïve female rats. Rauwolscine did not modify withdrawal threshold in naïve male rats. AGN192403 (I₁ antagonist), BU224 (I₂ antagonist), prazosin (α₁ antagonist) and methiothepin (5-HT antagonist) did not modify tizanidine-induced antiallodynia in neuropathic females and males. These data indicate that tizanidine exhibits a sex-dependent antiallodynic effect in neuropathy. Data also suggest that activation of adrenergic α_2B and α_2A and opioid receptors participate in the antiallodynic effect of tizanidine in female and male, respectively, neuropathic rats.

Spinal α2 -adrenoceptors and neuropathic pain modulation; therapeutic target

Neuropathic pain can arise from disease or damage to the nervous system. The most common symptoms of neuropathic pain include spontaneous pain, allodynia, and hyperalgesia. There is still limited knowledge about the factors that initiate and maintain neuropathic pain. However, ample evidence has proved the antinociceptive role of spinal α-adrenoceptors following nerve injury. It is well-documented that noradrenergic descending pathways from supraspinal loci exert an inhibitory influence on the spinal cord nociceptive neurons, mostly through the activation of spinal α₂ -adrenoceptors. This, in turn, suppresses transmission of pain input and the hyperexcitability of spinal dorsal horn neurons. There is considerable evidence demonstrating that spinal application of α₂ -adrenoceptor agonists leads to analgesic effects in animal models of neuropathic pain. Today, despite the recent rapid development of neuroscience and drug discovery, effective drugs with clear basic mechanisms have remained a mystery. Here, we give an overview of the cellular mechanisms through which brainstem adrenergic descending inhibitory processing can alter spinal pain transmission to the higher centres, and how these pathways change in neuropathic pain conditions focusing on the role of spinal α₂ -adrenoceptors in the spinal dorsal horn. We then suggest that α₂ -adrenoceptor agonist may be useful to treat neuropathic pain. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

A Guide to Medications Inducing Salivary Gland Dysfunction, Xerostomia, and Subjective Sialorrhea: A Systematic Review Sponsored by the World Workshop on Oral Medicine VI

BACKGROUND

Medication-induced salivary gland dysfunction (MISGD), xerostomia (sensation of oral dryness), and subjective sialorrhea cause significant morbidity and impair quality of life. However, no evidence-based lists of the medications that cause these disorders exist.

OBJECTIVE

Our objective was to compile a list of medications affecting salivary gland function and inducing xerostomia or subjective sialorrhea.

DATA SOURCES

Electronic databases were searched for relevant articles published until June 2013. Of 3867 screened records, 269 had an acceptable degree of relevance, quality of methodology, and strength of evidence. We found 56 chemical substances with a higher level of evidence and 50 with a moderate level of evidence of causing the above-mentioned disorders. At the first level of the Anatomical Therapeutic Chemical (ATC) classification system, 9 of 14 anatomical groups were represented, mainly the alimentary, cardiovascular, genitourinary, nervous, and respiratory systems. Management strategies include substitution or discontinuation of medications whenever possible, oral or systemic therapy with sialogogues, administration of saliva substitutes, and use of electro-stimulating devices.

LIMITATIONS

While xerostomia was a commonly reported outcome, objectively measured salivary flow rate was rarely reported. Moreover, xerostomia was mostly assessed as an adverse effect rather than the primary outcome of medication use. This study may not include some medications that could cause xerostomia when administered in conjunction with others or for which xerostomia as an adverse reaction has not been reported in the literature or was not detected in our search.

CONCLUSIONS

We compiled a comprehensive list of medications with documented effects on salivary gland function or symptoms that may assist practitioners in assessing patients who complain of dry mouth while taking medications. The list may also prove useful in helping practitioners anticipate adverse effects and consider alternative medications.

Pharmacological treatment of neuropathic cancer pain: a comprehensive review of the current literature

Neuropathic cancer pain (NCP), commonly encountered in clinical practice, may be cancer-related, namely resulting from nervous system tumor invasion, surgical nerve damage during tumor removal, radiation-induced nerve damage and chemotherapy-related neuropathy, or may be of benign origin, unrelated to cancer. A neuropathic component is evident in about 1/3 of cancer pain cases. Although from a pathophysiological perspective NCP may differ from chronic neuropathic pain (NP), such as noncancer-related pain, clinical practice, and limited publications have shown that these two pain entities may share some treatment modalities. For example, co-analgesics have been well integrated into cancer pain-management strategies and are often used as First-Line options for the treatment of NCP. These drugs, including antidepressants and anticonvulsants, are recommended by evidence-based guidelines, whereas, others such as lidocaine patch 5%, are supported by randomized, controlled, clinical data and are included in guidelines for restricted conditions treatment. The vast majority of these drugs have already been proven useful in the management of benign NP syndromes. Treatment decisions for patients with NP can be difficult. The intrinsic difficulties in performing randomized controlled trials in cancer pain have traditionally justified the acceptance of drugs already known to be effective in benign NP for the management of malignant NP, despite the lack of relevant high quality data. Interest in NCP mechanisms and pharmacotherapy has increased, resulting in significant mechanism-based treatment advances for the future. In this comprehensive review, we present the latest knowledge regarding NCP pharmacological management.

Pediatric safety of tizanidine: clinical adverse event database and retrospective chart assessment

BACKGROUND

Tizanidine is an imidazoline with central alpha(2)-adrenoceptor agonist activity at both spinal and supraspinal levels, which is indicated as a short-acting drug for the management of spasticity. Despite being used in pediatric populations, there is no adequate information or well controlled studies to document the safety and efficacy of tizanidine in this group.

OBJECTIVE

To evaluate the safety of tizanidine in the pediatric population. We compared spontaneous adverse event reports in the Acorda Therapeutics worldwide clinical adverse event database for children (< or = 16 years; n = 99) and adults (>16 years; n = 1153) who had received tizanidine and for whom at least one adverse event was reported, and performed a retrospective chart review of the safety of tizanidine in children (< or = 16 years; n = 76) at a large US pediatric neurology practice. Causality of adverse events in our worldwide clinical adverse event database were neither assessed nor assigned by the company.

RESULTS

When adverse events from the clinical adverse event database were collapsed into the 25 Medical Dictionary for Regulatory Activities (MedDRA; version 9.0) organ system classes, five classes were more frequent in adults (general disorders and administration site conditions [p = 0.0006], hepatobiliary disorders [p = 0.0031], nervous system disorders [p = 0.0108], skin and subcutaneous disorders [p = 0.0063], and vascular disorders [p = 0.0029]), while one class was more frequent in children (psychiatric disorders [p < 0.0001]). The most common adverse event classes in children were psychiatric disorders (52.5%) followed by nervous system disorders (29.3%), and gastrointestinal disorders (16.2%), whereas the most common adverse event classes in adults were nervous system disorders (42.4%), general disorders and administration site conditions (28.6%), and gastrointestinal disorders (21.3%). Serious adverse events were substantially less frequent in children than adults (19.2% vs 45.9%) in the clinical adverse event database. In the pediatric practice chart review, the incidence of adverse events in the MedDRA psychiatric disorders class was very similar (52.6%) to that for children in the clinical adverse event database, while the next most common classes were gastrointestinal disorders (14.5%), and nervous system disorders (13.2%). There were three deaths in children across the databases, including one from accidental exposure and two from cardiac events; the relationship of cardiac events in relation to tizanidine or other causes was difficult to assess with the limited available information.The major causes of death in adults were related to suicide or overdose. Minor, transient liver transaminase increases were occasionally reported; the effect of tizanidine could not be ruled out.

CONCLUSION

The overall safety of tizanidine in the pediatric group appeared good; however, the adverse event profile differed from that in adults. This difference most likely reflects the off-label use of tizanidine as adjunctive treatment for attention disorders and autism. The frequency and nature of adverse events in adults were consistent with the tizanidine prescribing information as reported for its approved indication, i.e. management of spasticity.

Update on tizanidine for muscle spasticity and emerging indications

BACKGROUND

Tizanidine hydrochloride, an alpha(2)-adrenergic receptor agonist, is a widely used medication for the treatment of muscle spasticity. Clinical studies have supported its use in the management of spasticity caused by multiple sclerosis (MS), acquired brain injury or spinal cord injury. It has also been shown to be clinically effective in the management of pain syndromes, such as: myofascial pain, lower back pain and trigeminal neuralgia. This review summarizes the recent findings on the clinical application of tizanidine.

OBJECTIVE

Our objective was to review and summarize the medical literature regarding the evidence for the usefulness of tizanidine in the management of spasticity and in pain syndromes such as myofascial pain.

METHODS

We reviewed the current medical and pharmacology literature through various internet literature searches. This information was then synthesized and presented in paragraph and table form.

RESULTS/CONCLUSION

Tizanidine hydrochloride is a very useful medication in patients suffering from spasticity caused by MS, acquired brain injury or spinal cord injury. It can also be helpful in patients suffering from chronic neck and/or lower back pain who have a myofascial component to their pain. Doses should be started at low dose and gradually titrated to effect.

[Treatment of neuropathic pain in HIV-infected patients]

Neuropathic pain of various etiologies is a frequent symptom in HIV-infected patients that is underdiagnosed and inadequately treated. It requires a multidisciplinary pain approach based on psychosocial factors, diet and exercise, etiologic treatment whenever possible, symptomatic medical treatment, and sometimes, interventional techniques. Medical treatment should be individualized and introduced gradually, with a mind to potential drug interactions. Neuropathic pain responds poorly to conventional analgesics, such as nonsteroidal antiinflammatory drugs and opiates; tricyclic antidepressants and anticonvulsants are the drugs of choice. Before establishing an analgesic treatment, possible drug interactions should be ruled out, mainly those occurring with antiretroviral agents.

Adjuvant analgesics

Adjuvant analgesics represent a diverse group of drugs that were originally developed for a primary indication other than pain. Many of these medications are currently used to enhance analgesia under specific circumstances. The proper use of adjuvant drugs is one of the keys to success in effective pain management. Since adjuvant analgesics are typically administered to patients who take multiple medications, decisions regarding administration and dosage must be made with a clear understanding of the stage of the disease and the goals of care. The article discusses major classes of adjuvant analgesics, with the focus on the mechanism of action, clinical application, and risks and benefits associated with each particular class of adjuvants.

Nonoperative management of osteoporotic vertebral compression fractures

As the population ages, vertebral compression fractures are an increasing source of pain and dysfunction. The immobilisation that often occurs with fractures can lead to multiple medical complications and their management can be complex as care may require multiple treatment modalities. Each individual responds to pain differently and a treatment plan must be tailored to the individual's pain, functional limitations and goals. The likely first choice for managing stable osteoporotic vertebral compression fractures is conservative management. Treatment options usually involve a combination of medications, bracing and physical therapy. If radicular pain is a component of the pain syndrome, epidural steroid injections may be beneficial. In addition, some patients may benefit from vertebral augmentation. This paper reviews current recommendations for managing vertebral compression fractures. Treatment options including vertebral augmentation are reviewed, including indications and complications.

Evaluation of a muscle relaxant on sequelae of third molar surgery: a pilot study

OBJECTIVE

The aim of this preliminary study was to evaluate the influence of the muscle relaxant tizanidine following third molar surgery on the main variables trismus and pain as well as on swelling.

STUDY DESIGN

Fifty healthy patients participated in this prospective clinical study. The test group received tizanidine (4 mg in the evenings for the first 2 postoperative days) in addition to antibiotic and antiinflammatory medications. Postoperatively, 1 independent investigator performed clinical examinations. Appropriate statistical analysis was used to evaluate data.

RESULTS

There was no statistically significant difference in facial pain and swelling between the two groups. Statistically significant improvement was detected when the groups were compared for mouth opening ability at days one and three.

CONCLUSION

The results of this trial indicate that the influence of tizanidine on trismus, pain, and swelling does not justify prescription of the additional medication.

Conservative Care for Patients with Osteoporotic Vertebral Compression Fractures

As the aging population grows, vertebral compression fractures are becoming an important source of pain and dysfunction. Management can be complex, because care may require multiple treatment modalities and the treatment plan must be tailored to the individual's pain, functional limitations, and goals. Treatment options usually involve a combination of medications, bracing, and physical therapy. This article reviews current recommendations for managing vertebral compression fractures. Indications, complications, and treatment options, including vertebral augmentation, are discussed.

Neuropathic pain in soft tissue complaints

Many soft tissue complaints are associated with the development of neuropathic pain. This pain is produced by pathophysiological processes that are different to the processes involved in the generation of the inflammatory or nociceptive pain more commonly encountered in soft tissue disorders. One of the consequences of this is that neuropathic pain can often be less responsive to standard analgesic therapies. The use of alternative analgesic strategies may be necessary if we are to treat neuropathic pain successfully. This chapter aims to outline some of the clinical features associated with neuropathic pain, the aetiological factors leading to its development and the evidence base (or lack) behind current treatment strategies. It will try to provide a rational approach to the management of neuropathic pain in patients with soft tissue disorders, particularly focusing on pharmacological management. Neuropathic pain is the focus of much current research activity, particularly pharmacological research, and this chapter will attempt to identify gaps in our clinical knowledge and highlight opportunities for further research.

Management of painful neuropathies

Inadequately assessed and poorly managed pain contributes both to high general medical cost and to increasing numbers of societal problems. A large determining factor of inadequate pain care is the lack of understanding about the complex nature of pain and of a rational approach to its assessment and treatment. The less than adequate assessment of neuropathic pain and its relatively poor response to typical analgesic medications are major determinants to the undertreatment of pain. Other than the important management concept of treating the underlying cause, current approaches to the treatment of pain in general, and neuropathic pain in particular, have shifted away from treatment of individual syndromes toward the identification and management of common symptoms and the mechanisms upon which such symptoms are presumed to be based. This article summarizes the features of neuropathic pain that commonly appear in most peripheral neuropathies, regardless of the mechanism of injury, and provides an approach for the selection of treatment.

Adjuvant analgesics

Chronic pain, whether arising from viscera, bone, or any other tissue or structure, is, more often than commonly thought, the result of a mixture of pain mechanisms, and therefore there is no simple formula available to manage chronic complex pain states. Box 1 summarizes a pharmacological algorithm for difficult-to-treat chronic pain, which merely introduces the medication aspect of the treatment. In effect, any comprehensive algorithm should call for an interdisciplinary approach that would include rehabilitation, as well as psychosocial, and when indicated, interventional techniques. Box 1 Analgesic algorithm for difficult-to-treat pain syndromes. Pharmacological Interventions. Moderate to severe pain/functional impairment; pain with a score of >4 on the brief pain inventory. 1. Gabapentinoid (gabapentin, pregabalin)+/-Opioid/opioid rotation or 2. Antidepressant (TCA, duloxetine, venlafaxine)+/-Opioid/opioid rotation or 3. Gabapentinoid+antidepressant+Opioid/opioid rotation; in addition, may consider trials of one or more of the following adjuvants when clinically appropriate: Topical therapies for cutaneous allodynia/hyperalgesia. Anti-inflammatory drugs (corticosteroids for acute inflammatory neuropathic pain)IV bisphosphonates for cancer bone pain or CRPS/RSDNon-gabapentinoid AEDs such as carbamazepine or oxcarbazepine or lamotrigine+/-baclofen for intermittent lancinating pain due to cranial neuralgiasNMDA antagonists Mexiletine On a compassionate basis, according to the patient's clinical condition and pain mechanism, the physician may want to consider an empirical trial of one or more of the emergent topical, oral or parenteral/intrathecal therapies as discussed in the text. If SMP, consider topical clonidine and sympatholytic interventions; if clinically feasible, trials of topical therapies, eg, lidocaine 5% patch, may be considered for a variety of pain states and features.The major rationale for introducing adjuvants is to better balance efficacy and adverse effects. The following scenarios should prompt the use of adjuvants in clinical practice: The toxic limit of a primary analgesic has been reached. The therapeutic benefit of a primary analgesic has plateaued, eg, treatment has reached its true efficacy limit or pharmachodynamic tolerance has developed. The primary analgesic is contraindicated, eg, substance abuse, aberrant behavior, organ failure, allergy, and so forth. Subjective and qualitative symptoms demand broader coverage. Patients often convey that different medications will impart distinct analgesic benefits. Presence of disabling nonpainful complaints and need to manage symptoms such as insomnia, depression, anxiety, and fatigue that all cause worsening of the patient's quality of life and function. Physicians have also been drawn to the adjuvants secondary to new realities of clinical practice. Moreover, aversion to addiction and diversion remains a potent force that shapes prescribing profiles.

Therapeutic Management of Chronic Neuropathic Pain: An Examination of Pharmacologic Treatment

Neuropathic pain is defined as pain caused by a lesion in the nervous system and is common in clinical practice. Diagnosis can be difficult. Recommendations for first-line pharmacologic treatments are based on positive results from multiple, randomized, controlled trials, and recommendations for second-line pharmacologic treatments are based on the positive result of a single, randomized, controlled trial or inconsistent results of multiple, randomized, controlled trials. The results of published trials and clinical experience provide the foundation for specific recommendations for first-line treatments, which include gabapentin, 5% lidocaine patch, opioid analgesics, tramadol hydrochloride, and tricyclic antidepressants (TCAs). Gabapentin (up to 3,600 mg/day) significantly reduced pain compared with placebo; improvements in sleep, mood, and quality of life were also demonstrated. Adverse effects of gabapentin include somnolence and dizziness, and, less commonly, gastrointestinal symptoms and mild peripheral edema. Thus, monitoring and dosage adjustment are required, without discontinuation of the drug. Gabapentin combined with morphine achieved better analgesia at lower doses of each drug than each drug alone, with only mild adverse effects. The first medication that proved effective for neuropathic pain in placebo-controlled trials was TCAs. Treatment decisions for patients with neuropathic pain can be difficult. Interest in the mechanisms and treatment of chronic neuropathic pain has increased during the past years, resulting in significant treatment advances in the future. In this article all recent knowledge on therapeutic management of chronic neuropathic pain is presented.

Muscle Relaxants and Antispasticity Agents

Muscle relaxants make up a heterogeneous group of agents and can have a clinically significant role in the treatment of chronic muscle pain. These medications are not without possible serious side effects; hence, care should be taken in deciding on their appropriateness and ongoing monitoring performed, if prescribed.

Using Pain Quality Assessment Measures for Selecting Analgesic Agents

Although those in the field of pain management have long recognized the multidimensional character of pain, global pain intensity remains the most frequently assessed domain measured in clinical trials of pain treatments. However, a number of specific pain qualities have been shown to be associated with neuropathic versus nociceptive pain and, as such, can be used for diagnostic purposes. In addition, preliminary evidence suggests that pain quality measures may be helpful for measuring outcomes in clinical trials. A number of such measures are currently available, each with its strengths and weaknesses. These measures are reviewed, and potential future uses of these tools are discussed.

Peripheral neuropathy pain: mechanisms and treatment

Pain is a disabling symptom for many patients with peripheral neuropathy. The mechanisms responsible for neuropathic pain are not fully understood. Theories include ectopic discharges of damaged fibers and dorsal root ganglia, sensitization of nociceptors, central sensitization of dorsal horn neurons, loss of inhibitory neurons, and sprouting of afferent fibers after nerve injury into new regions of the nervous system. Several drugs have been effective in controlled clinical trials, but not all patients respond or tolerate the available agents.

Treatment of painful peripheral neuropathy

Treatment of neuropathic pain is the primary focus of management for many patients with painful peripheral neuropathies. Antidepressants and anticonvulsants are the two medication classes most widely studied and represent first-line agents in the management of neuropathic pain. The number of pharmacologic agents and interventional procedures that have shown effectiveness in the treatment of neuropathic pain continues to expand. Pain management should begin with a concerted effort to identify the etiology of the neuropathy, because directed therapy can help alleviate the symptoms. When initiating pharmacotherapy for neuropathic pain, one must individualize treatment and choose an agent that is likely to be tolerated, because adverse events are common for many of these agents. Neuropathic pain management remains challenging because of heterogeneous responses between individuals and the fact that pain relief is rarely complete. However, monotherapy with a well-chosen agent or rational polypharmacy that combines medications with different mechanisms of action will benefit a majority of patients with neuropathic pain.

Electrophysiologic characterization of the antinociceptive actions of S18616, a novel and potent alpha2-adrenoceptor agonist, after acute and persistent pain states

alpha (2)-Adrenoceptor (AR) agonists are active in behavioral models of persistent pain involving tissue and nerve damage. We evaluated the spinal effect of a novel, potent, and selective alpha (2)-AR agonist, [7,8](2-chlorobenzo)-2-amino-1-aza-3-oxa[4,5]spirodeca-1,7-diene (S18616), on the responses of dorsal horn neurons in halothane-anesthetized rats. Intrathecal administration of S18616 (0.1 to 3.0 microg) dose-dependently suppressed C- and A delta-fiber evoked responses but not the A beta-fiber evoked response. Drug effects were reversed by the alpha (2)-AR antagonists, atipamezole and idazoxan (100 microg). In rats with unilateral spinal nerve (L5-L6) ligation performed 2 weeks before study, S18616 (0.1 to 3.0 microg) dose-dependently suppressed the C- and A delta-fiber evoked responses and blocked "wind-up" in these neurons. The potency was comparable between nerve-injured and sham-operated rats, and S18616 was equally effective against responses to thermal and high-intensity mechanical stimuli. Interestingly, the effectiveness of S18616 on the low-intensity mechanical evoked response was significantly enhanced after nerve injury. Finally, S18616 (0.3 and 3.0 microg) reduced the neuronal responses produced by intraplantar injection of formalin. In conclusion, S18616 dose-dependently and potently inhibits the responses of dorsal horn neurons to peripheral stimulation in normal, inflamed, and neuropathic rats. These data support the use of spinal S18616 and other alpha (2)-AR agonists in the management of clinical pain.

Painful Peripheral Neuropathy

Treatment of neuropathic pain is the primary focus of management for many patients with painful peripheral neuropathies. Neuropathic pain is a common feature of many peripheral neuropathies including those associated with diabetes, uremia, HIV infection, and alcohol abuse. Pain is also present in the majority of patients with idiopathic sensory and sensorimotor polyneuropathies. A growing number of pharmacologic agents are available for the treatment of neuropathic pain. The medications that have undergone the most rigorous study are the tricyclic antidepressants and anticonvulsants. These two families of medications are widely used and represent first-line agents in the management of neuropathic pain. Pain management should begin with a concerted effort to identify the etiology of the neuropathy, as directed therapy may help alleviate the symptoms. When initiating pharmacotherapy for neuropathic pain, one must individualize treatment and choose an agent that is likely to be tolerated, as adverse events are not uncommon for some of the medications. Treatment of neuropathic pain remains challenging, with considerable variability in an individual's response to the various agents and even to different drugs in the same class. However, monotherapy with a well-chosen agent or rational polypharmacy that combines medications with different mechanisms of action will benefit a majority of patients with neuropathic pain.

Descending control of pain

Upon receipt in the dorsal horn (DH) of the spinal cord, nociceptive (pain-signalling) information from the viscera, skin and other organs is subject to extensive processing by a diversity of mechanisms, certain of which enhance, and certain of which inhibit, its transfer to higher centres. In this regard, a network of descending pathways projecting from cerebral structures to the DH plays a complex and crucial role. Specific centrifugal pathways either suppress (descending inhibition) or potentiate (descending facilitation) passage of nociceptive messages to the brain. Engagement of descending inhibition by the opioid analgesic, morphine, fulfils an important role in its pain-relieving properties, while induction of analgesia by the adrenergic agonist, clonidine, reflects actions at alpha(2)-adrenoceptors (alpha(2)-ARs) in the DH normally recruited by descending pathways. However, opioids and adrenergic agents exploit but a tiny fraction of the vast panoply of mechanisms now known to be involved in the induction and/or expression of descending controls. For example, no drug interfering with descending facilitation is currently available for clinical use. The present review focuses on: (1) the organisation of descending pathways and their pathophysiological significance; (2) the role of individual transmitters and specific receptor types in the modulation and expression of mechanisms of descending inhibition and facilitation and (3) the advantages and limitations of established and innovative analgesic strategies which act by manipulation of descending controls. Knowledge of descending pathways has increased exponentially in recent years, so this is an opportune moment to survey their operation and therapeutic relevance to the improved management of pain.

Systemic tizanidine hydrochloride (Zanaflex) relieves thermal hyperalgesia in rats with an experimental mononeuropathy

We sought to determine whether tizanidine, an alpha2-agonist, relieved thermal hyperalgesia in rats with surgically induced neuropathic pain. We used a Sprague-Dawley rat model in which a chronic constriction of the sciatic nerve caused the rats to develop postural changes, mechanical allodynia, and thermal hyperalgesia. Thermal hyperalgesia was verified through paw withdrawal latency (PWL). PWL was tested before surgery, after surgery, and after injections with tizanidine (0.5, 1.0, or 2.0 mg/kg) or normal saline. Ambulatory and total movements were evaluated by placing the rats in activity cages. Thermal hyperalgesia was induced in all rats after surgery. Tizanidine, but not saline, caused a significant improvement in PWL (P < 0.05), with complete reversal of thermal hyperalgesia at all doses on postoperative Day 6. Rats who received tizanidine 2 mg/kg maintained complete reversal of thermal hyperalgesia through postoperative Day 9. Some sedation was observed with tizanidine 2 mg/kg, but not with smaller doses. We conclude that tizanidine effectively reversed thermal hyperalgesia in a rat model.

IMPLICATIONS

This study was conducted to determine whether tizanidine could attenuate the thermal hyperalgesia that occurs in rats with surgically induced chronic constriction of the sciatic nerve. Tizanidine was effective in reducing sensitivity to heat, as measured by paw withdrawal latency, and did not cause sedation at smaller doses.

Alpha2 receptors and agonists in pain management

Alpha(2) agonists have been in clinical use for decades, primarily in the treatment of hypertension. In recent years, alpha(2) agonists have found wider application, particularly in the fields of anesthesia and pain management. It has been noted that these agents can enhance analgesia provided by traditional analgesics, such as opiates, and may result in opiate-sparing effects. This has important implications for the management of acute postoperative pain and chronic pain states, including disorders involving spasticity or myofascial pain, neuropathic pain, and chronic daily headaches. The clinical utility of these agents is ever expanding, as they are gaining broader use in neuraxial analgesia, and new applications are continuously under investigation. The alpha(2) agonists that are currently employed in anesthesia and pain management include clonidine, tizanidine, and dexmedetomidine. Moxonidine and radolmidine, which are not currently in clinical use in humans, may offer favorable side-effect profiles when compared with traditional alpha(2) agonists, and may thereby allow for more widespread pain management applications.