Methadone in post-herpetic neuralgia: A pilot proof-of-concept study

METHA-NeP: effectiveness and safety of methadone for neuropathic pain: a controlled randomized trial

ABSTRACT

In this randomized, double-blind, parallel placebo-controlled clinical trial, we evaluated the efficacy of methadone as an add-on therapy for people with chronic neuropathic pain (NP). Eighty-six patients were randomly assigned to receive methadone or placebo for 8 weeks. The primary outcome was the proportion of participants achieving at least 30% pain relief from baseline using a 100-mm pain Visual Analogue Scale. Secondary outcomes included global impression of change, NP symptoms, sleep quality, quality of life, pain interference in daily activities, and mood. A larger number of responders were found in the methadone (68%), compared to the placebo (33%) arm; risk difference 33.6%; 95% confidence interval 13.0%-54.3%; P = 0.003; number needed to treat = 3.0. Methadone reduced pain intensity ( P < 0.001), burning ( P = 0.023), pressing ( P = 0.005), and paroxysmal dimensions ( P = 0.006) of NP. Methadone also improved sleep ( P < 0.001) and increased the patient's global impression of improvement ( P = 0.002). Methadone did not significantly impact quality of life, pain interference, or mood. Treatment-emergent adverse events occurred in all methadone- and in 73% of placebo-treated patients ( P < 0.001). No serious adverse events or deaths occurred. Discontinuation due to adverse events was reported in 2 participants in the methadone and none in the placebo arm. Methadone use as an add-on to an optimized treatment for NP with first- and/or second-line drugs provided superior analgesia, improved sleep, and enhanced global impression of change, without being associated with significant serious adverse effects that would raise safety concerns.

Two Patients Experience Same-Day Analgesic Effect of Methadone on Trigeminal Neuralgia Secondary to Malignancy: A Case Report

Trigeminal neuralgia (TN) secondary to malignancy leads to significant distress and subsequently impacts a patient's quality of life. Use of methadone as a first-line opioid analgesic in this subset of oncology patients is uncommon and is rarely initiated after traditional first-line therapies have failed. We report two patients with TN secondary to tumor burden who experienced significant analgesia within 24 hours of methadone initiation.

Dissecting neuropathic from poststroke pain: the white matter within

ABSTRACT

Poststroke pain (PSP) is a heterogeneous term encompassing both central neuropathic (ie, central poststroke pain [CPSP]) and nonneuropathic poststroke pain (CNNP) syndromes. Central poststroke pain is classically related to damage in the lateral brainstem, posterior thalamus, and parietoinsular areas, whereas the role of white matter connecting these structures is frequently ignored. In addition, the relationship between stroke topography and CNNP is not completely understood. In this study, we address these issues comparing stroke location in a CPSP group of 35 patients with 2 control groups: 27 patients with CNNP and 27 patients with stroke without pain. Brain MRI images were analyzed by 2 complementary approaches: an exploratory analysis using voxel-wise lesion symptom mapping, to detect significant voxels damaged in CPSP across the whole brain, and a hypothesis-driven, region of interest-based analysis, to replicate previously reported sites involved in CPSP. Odds ratio maps were also calculated to demonstrate the risk for CPSP in each damaged voxel. Our exploratory analysis showed that, besides known thalamic and parietoinsular areas, significant voxels carrying a high risk for CPSP were located in the white matter encompassing thalamoinsular connections (one-tailed threshold Z > 3.96, corrected P value <0.05, odds ratio = 39.7). These results show that the interruption of thalamocortical white matter connections is an important component of CPSP, which is in contrast with findings from nonneuropathic PSP and from strokes without pain. These data can aid in the selection of patients at risk to develop CPSP who could be candidates to pre-emptive or therapeutic interventions.

Methadone for Pain Management: A Pharmacotherapeutic Review

Methadone is increasingly being used for its analgesic properties. Despite the increasing popularity, many healthcare providers are not familiar with methadone's complex pharmacology and best practices surrounding its use. The purpose of this narrative review article is to discuss the pharmacology of methadone, the evidence surrounding methadone's use in acute pain management and both chronic cancer and non-cancer pain settings, as well as highlight pertinent safety, monitoring, and opioid rotation considerations. Methadone has a unique mechanism of action when compared with all other opioids and for this reason methadone has come to hold a niche role in the management of opioid-induced hyperalgesia and central sensitization. Understanding of the mechanisms of variability in methadone disposition and drug interactions has evolved over the years, with the latest evidence revealing that CYP 2B6 is the major determinant of methadone elimination and plays a key role in methadone-related drug interactions. From an acute pain perspective, most studies evaluating the use of intraoperative intravenous methadone have reported lower pain scores and post-operative opioid requirements. Oral methadone is predominantly used as a second-line opioid treatment for select chronic pain conditions. As a result, several oral morphine to oral methadone conversion ratios have been proposed, as have methods in which to rotate to methadone. From an efficacy standpoint, limited literature exists regarding the effectiveness of methadone in the chronic pain setting with most of the available efficacy data pertaining to methadone's use in the treatment of cancer pain. Many of the prospective studies that exist feature low participant numbers. Few clinical trials investigating the role of methadone as an analgesic treatment are currently underway. The complicated pharmacokinetic properties of methadone and risks of harm associated with this drug highlight how critically important it is that healthcare providers understand these features before prescribing/dispensing methadone. Particular caution is required when converting patients from other opioids to methadone and for this reason only experienced healthcare providers should undertake such a task. Further randomized trials with larger sample sizes are needed to better define the effective and safe use of methadone for pain management.

A single-institution, randomized, pilot study evaluating the efficacy of gabapentin and methadone for patients undergoing chemoradiation for head and neck squamous cell cancer

BACKGROUND

The objective of the current study was to compare the safety and efficacy between 2 analgesic regimens for patients with head and neck cancer (HNC) undergoing definitive chemoradiation (CRT).

METHODS

The current study was a prospective, single-institution, 2-arm, randomized pilot study. Patients with American Joint Committee on Cancer seventh edition stage II to stage IV squamous cell carcinoma of the head and neck who were undergoing CRT were randomized to either arm 1, which entailed high-dose gabapentin (2700 mg daily) with the institutional standard of care (hydrocodone and/or acetaminophen progressing to fentanyl as needed), or arm 2, which comprised low-dose gabapentin (900 mg daily) with methadone. The primary endpoints were safety and toxicity. Secondary endpoints were pain, opioid requirement, and quality of life (QOL). Differences between the treatment arms at multiple time points were compared using a generalized linear mixed regression model with Sidak correction.

RESULTS

A total of 60 patients (31 in arm 1 and 29 in arm 2) were enrolled from April 2015 to August 2017. There was no difference between the treatment arms with regard to adverse events or serious adverse events. Pain was not found to be different between the treatment arms. More patients in arm 1 did not require an opioid during treatment (42% vs 7%; P = .002). Patients in arm 2 experienced significantly better QOL outcomes across multiple domains, including overall health (P = .05), physical functioning (P = .04), role functioning (P = .01), and social functioning (P = .01).

CONCLUSIONS

High-dose prophylactic gabapentin increased the percentage of patients who required no opioid during treatment. Methadone may improve QOL compared with a regimen of short-acting opioids and fentanyl. However, pain was found to significantly worsen throughout treatment regardless of treatment arm, necessitating further studies to identify a more optimal regimen.

A Systematic Review of NMDA Receptor Antagonists for Treatment of Neuropathic Pain in Clinical Practice

OBJECTIVE

To investigate the efficacy of N-methyl-D-aspartate receptor (NMDAR) antagonists for neuropathic pain (NeuP) and review literature to determine if specific pharmacologic agents provide adequate NeuP relief.

METHODS

Literature was reviewed on PubMed using a variety of key words for 8 NMDAR antagonists. These key words include: "Ketamine and Neuropathy," "Ketamine and Neuropathic Pain," "Methadone and Neuropathy," "Methadone and Neuropathic Pain," "Memantine and Neuropathic pain," "Memantine and Neuropathy," "Amantadine and Neuropathic Pain," "Amantadine and Neuropathy," "Dextromethorphan and Neuropathic Pain," "Dextromethorphan and Neuropathy," "Carbamazepine and Neuropathic Pain," "Carbamazepine and Neuropathy," "Valproic Acid and Neuropathy," "Valproic Acid and Neuropathic Pain," "Phenytoin and Neuropathy," and "Phenytoin and Neuropathic Pain." With the results, the papers were reviewed using the PRISMA (Preferred Reporting in Systematic and Meta-Analyses) guideline.

RESULTS

A total of 58 randomized controlled trials were reviewed among 8 pharmacologic agents, which are organized by date and alphabetical order. Of the trials for ketamine, 15 showed some benefit for analgesia. Methadone had 3 positive trials, while amantadine and memantine each only had 2 trials showing NeuP analgesic properties. Dextromethorphan and valproic acid both had 4 randomized controlled trials that showed some NeuP treatment benefit while carbamazepine had over 8 trials showing efficacy. Finally, phenytoin only had 1 trial that showed clinical response in treatment.

CONCLUSIONS

There are a variety of NMDAR antagonist agents that should be considered for treatment of NeuP. Nevertheless, continued and further investigation of the 8 pharmacologic agents is needed to continue to evaluate their efficacy for treatment of NeuP.

Methadone for neuropathic pain in adults

BACKGROUND

This review replaces an earlier review, "Methadone for chronic non-cancer pain in adults". This review serves to update the original and includes only studies of neuropathic pain. Methadone belongs to a class of analgesics known as opioids, that are considered the cornerstone of therapy for moderate-to-severe postsurgical pain and pain due to life-threatening illnesses; however, their use in neuropathic pain is controversial. Methadone has many characteristics that differentiate it from other opioids, which suggests that it may have a different efficacy and safety profile.

OBJECTIVES

To assess the analgesic efficacy and adverse events of methadone for chronic neuropathic pain in adults.

SEARCH METHODS

We searched the following databases: CENTRAL (CRSO), MEDLINE (Ovid), and Embase (Ovid), and two clinical trial registries. We also searched the reference lists of retrieved articles. The date of the most recent search was 30 November 2016.

SELECTION CRITERIA

We included randomised, double-blind studies of two weeks' duration or longer, comparing methadone (in any dose, administered by any route, and in any formulation) with placebo or another active treatment in chronic neuropathic pain.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Two review authors independently considered trials for inclusion in the review, assessed risk of bias, and extracted data. There were insufficient data to perform pooled analyses. We assessed the overall quality of the evidence for each outcome using GRADE and created a 'Summary of findings' table.

MAIN RESULTS

We included three studies, involving 105 participants. All were cross-over studies, one involving 19 participants with diverse neuropathic pain syndromes, the other two involving 86 participants with postherpetic neuralgia. Study phases ranged from 20 days to approximately eight weeks. All administered methadone orally, in doses ranging from 10 mg to 80 mg daily. Comparators were primarily placebo, but one study also included morphine and tricyclic antidepressants.The included studies had several limitations related to risk of bias, particularly incomplete reporting, selective outcome reporting, and small sample sizes.There were very limited data for our primary outcomes of participants with at least 30% or at least 50% pain relief. Two studies reported that 11/29 participants receiving methadone achieved 30% pain relief versus 7/29 participants receiving placebo. Only one study presented data in a manner that allowed us to calculate the number of participants with at least 50% pain relief. None of the 19 participants achieved a 50% reduction in pain intensity, either when receiving methadone or when receiving placebo. No study provided data for our other primary outcomes of Patient Global Impression of Change scale (PGIC) much or very much improved (equivalent to at least 30% pain relief) and PGIC very much improved (equivalent to at least 50% pain relief).For secondary efficacy outcomes, one study reported maximum and mean pain intensity and pain relief, and reported statistically significant improvements versus placebo for all outcomes with 20 mg daily doses of methadone, but not with 10 mg daily doses. The second study reported differences in pain reduction between methadone (n = 26) and morphine (n = 38) and found morphine to be statistically superior. The third study reported the number of responders (variously defined) for several pain and functional outcomes and found methadone to be statistically superior to placebo for the outcomes of categorical pain intensity and evoked pain. In the two studies that reported data, 0/29 participants withdrew due to lack of efficacy, whereas 4/29 participants withdrew due to adverse events while taking methadone versus 3/29 while taking placebo.One study reported incidences for several individual adverse events, but found a statistically significant increased incidence for methadone over placebo for only one event, dizziness. The other studies did not report data in a manner that enabled us to analyze adverse events. There were no serious adverse events or deaths reported.We assessed the quality of the evidence as very low for all efficacy and safety outcomes using GRADE, primarily because of the heterogeneity of study designs and populations, short durations, cross-over methodology, and few participants and events.

AUTHORS' CONCLUSIONS

The three studies provide very limited, very low quality evidence of the efficacy and safety of methadone for chronic neuropathic pain, and there were too few data for pooled analysis of efficacy or harm, or to have confidence in the results of the individual studies. No conclusions can be made regarding differences in efficacy or safety between methadone and placebo, other opioids, or other treatments.

Management of Pain Associated with Selected Conditions in Dermatology

Dermatologists face a wide range of pain control challenges in daily practice, from the transient pain of dermatologic surgery to the persistent pain that plagues some chronic dermatologic conditions. Although the pathophysiology of pain is well described and the profound impact of dermatological pain on patients' quality of life is well appreciated, there is an identified need for clear therapeutic plans for providing symptomatic pain relief of common painful dermatoses. In this paper, we will review and clearly outline approaches to pain management of a number of common painful dermatoses such as herpes zoster and post-herpetic neuralgia, ulcers, oral dermatoses, dysesthesias, and many others.

Treatment of Neuropathic Pain

OPINION STATEMENT

Neuropathic pain is notoriously variable in its severity and impact on patients, as well as in its response to treatment. Certain therapies for neuropathic pain have better evidence for their use; however, it is apparent that although some therapies provide relief for only a minority of patients, the relief may be significant. Without a trial of therapy, there is no way to know if that relief is achievable. Our treatment experiences have shown that occasionally unexpected benefit is obtained through a thorough investigation of all options, even in the setting of failure of those with the most compelling evidence or indication. Chronic neuropathic pain is generally best treated with regularly dosed medications, balancing efficacy and tolerability. Evidence supports first-line trials of anticonvulsants, tricyclic antidepressants, and serotonin-norepinephrine reuptake inhibitors, alone or in certain combinations. While opioid medications, particularly methadone, can be effective in treating neuropathic pain, they are best used only in refractory cases and by experienced clinicians, due to concerns for both short- and long-term safety. Some therapies have a long history of successful use for certain syndromes (e.g., carbamazepine for trigeminal neuralgia pain), but these should not be considered to the exclusion of other more recent, less-supported therapies (e.g., botulinum toxin A for the same), particularly in refractory cases. We find the principles of palliative care highly applicable in the treatment of chronic neuropathic pain, including managing expectations, mutually agreed-upon meaningful outcomes, and a carefully cultivated therapeutic relationship.

Allodynia and hyperalgesia in neuropathic pain: clinical manifestations and mechanisms

Allodynia (pain due to a stimulus that does not usually provoke pain) and hyperalgesia (increased pain from a stimulus that usually provokes pain) are prominent symptoms in patients with neuropathic pain. Both are seen in various peripheral neuropathies and central pain disorders, and affect 15-50% of patients with neuropathic pain. Allodynia and hyperalgesia are classified according to the sensory modality (touch, pressure, pinprick, cold, and heat) that is used to elicit the sensation. Peripheral sensitisation and maladaptive central changes contribute to the generation and maintenance of these reactions, with separate mechanisms in different subtypes of allodynia and hyperalgesia. Pain intensity and relief are important measures in clinical pain studies, but might be insufficient to capture the complexity of the pain experience. Better understanding of allodynia and hyperalgesia might provide clues to the underlying pathophysiology of neuropathic pain and, as such, they represent new or additional endpoints in pain trials.