A randomized, controlled trial of a β2-agonist in painful polyneuropathy

Neuropathic pain: Evidence based recommendations

Neuropathic pain continues to be a significant problem that lacks effective solutions for every single patient. In 2015, international guidelines (NeuPSIG) were published, while the French recommendations were updated in 2020. The purpose of this minireview is to provide an update on the process of developing evidence-based recommendations and explore potential changes to the current recommendations. Primary treatments for neuropathic pain include selective serotonin-norepinephrine reuptake inhibitors (SNRIs) such as duloxetine and venlafaxine, gabapentin, tricyclic antidepressants, as well as topical lidocaine and transcutaneous electrical nerve stimulation, which are specifically suggested for focal peripheral neuropathic pain. Pregabalin is a first line treatment according to international guidelines but second-line in the more recent French guidelines, due to lower efficacy seen in more recent studies and misuse risk. Additionally, tramadol, combination therapies, and psychotherapy as adjuncts are proposed second line; high-concentration capsaicin patches, and botulinum toxin A are proposed specifically for focal peripheral neuropathic pain. In cases where primary and secondary treatments prove insufficient, third-line options come into play. These include high-frequency repetitive transcranial magnetic stimulation (rTMS) targeting the motor cortex, spinal cord stimulation, and the use of strong opioids when no alternative is available. To ensure optimal management of neuropathic pain in real-life situations, it is imperative to disseminate these recommendations widely and secure the acceptance of practitioners. By doing so, we can bridge the gap between theory and practice, and enhance the overall care and treatment of individuals suffering from neuropathic pain.

Antidepressants for pain management in adults with chronic pain: a network meta-analysis

BACKGROUND

Chronic pain is common in adults, and often has a detrimental impact upon physical ability, well-being, and quality of life. Previous reviews have shown that certain antidepressants may be effective in reducing pain with some benefit in improving patients' global impression of change for certain chronic pain conditions. However, there has not been a network meta-analysis (NMA) examining all antidepressants across all chronic pain conditions.

OBJECTIVES

To assess the comparative efficacy and safety of antidepressants for adults with chronic pain (except headache).

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, CINAHL, LILACS, AMED and PsycINFO databases, and clinical trials registries, for randomised controlled trials (RCTs) of antidepressants for chronic pain conditions in January 2022.

SELECTION CRITERIA

We included RCTs that examined antidepressants for chronic pain against any comparator. If the comparator was placebo, another medication, another antidepressant, or the same antidepressant at different doses, then we required the study to be double-blind. We included RCTs with active comparators that were unable to be double-blinded (e.g. psychotherapy) but rated them as high risk of bias. We excluded RCTs where the follow-up was less than two weeks and those with fewer than 10 participants in each arm.  DATA COLLECTION AND ANALYSIS: Two review authors separately screened, data extracted, and judged risk of bias. We synthesised the data using Bayesian NMA and pairwise meta-analyses for each outcome and ranked the antidepressants in terms of their effectiveness using the surface under the cumulative ranking curve (SUCRA). We primarily used Confidence in Meta-Analysis (CINeMA) and Risk of Bias due to Missing Evidence in Network meta-analysis (ROB-MEN) to assess the certainty of the evidence. Where it was not possible to use CINeMA and ROB-MEN due to the complexity of the networks, we used GRADE to assess the certainty of the evidence. Our primary outcomes were substantial (50%) pain relief, pain intensity, mood, and adverse events. Our secondary outcomes were moderate pain relief (30%), physical function, sleep, quality of life, Patient Global Impression of Change (PGIC), serious adverse events, and withdrawal.

MAIN RESULTS

This review and NMA included 176 studies with a total of 28,664 participants. The majority of studies were placebo-controlled (83), and parallel-armed (141). The most common pain conditions examined were fibromyalgia (59 studies); neuropathic pain (49 studies) and musculoskeletal pain (40 studies). The average length of RCTs was 10 weeks. Seven studies provided no useable data and were omitted from the NMA. The majority of studies measured short-term outcomes only and excluded people with low mood and other mental health conditions. Across efficacy outcomes, duloxetine was consistently the highest-ranked antidepressant with moderate- to high-certainty evidence. In duloxetine studies, standard dose was equally efficacious as high dose for the majority of outcomes. Milnacipran was often ranked as the next most efficacious antidepressant, although the certainty of evidence was lower than that of duloxetine. There was insufficient evidence to draw robust conclusions for the efficacy and safety of any other antidepressant for chronic pain.  Primary efficacy outcomes Duloxetine standard dose (60 mg) showed a small to moderate effect for substantial pain relief (odds ratio (OR) 1.91, 95% confidence interval (CI) 1.69 to 2.17; 16 studies, 4490 participants; moderate-certainty evidence) and continuous pain intensity (standardised mean difference (SMD) -0.31, 95% CI -0.39 to -0.24; 18 studies, 4959 participants; moderate-certainty evidence). For pain intensity, milnacipran standard dose (100 mg) also showed a small effect (SMD -0.22, 95% CI -0.39 to 0.06; 4 studies, 1866 participants; moderate-certainty evidence). Mirtazapine (30 mg) had a moderate effect on mood (SMD -0.5, 95% CI -0.78 to -0.22; 1 study, 406 participants; low-certainty evidence), while duloxetine showed a small effect (SMD -0.16, 95% CI -0.22 to -0.1; 26 studies, 7952 participants; moderate-certainty evidence); however it is important to note that most studies excluded participants with mental health conditions, and so average anxiety and depression scores tended to be in the 'normal' or 'subclinical' ranges at baseline already. Secondary efficacy outcomes Across all secondary efficacy outcomes (moderate pain relief, physical function, sleep, quality of life, and PGIC), duloxetine and milnacipran were the highest-ranked antidepressants with moderate-certainty evidence, although effects were small. For both duloxetine and milnacipran, standard doses were as efficacious as high doses. Safety There was very low-certainty evidence for all safety outcomes (adverse events, serious adverse events, and withdrawal) across all antidepressants. We cannot draw any reliable conclusions from the NMAs for these outcomes.

AUTHORS' CONCLUSIONS

Our review and NMAs show that despite studies investigating 25 different antidepressants, the only antidepressant we are certain about for the treatment of chronic pain is duloxetine. Duloxetine was moderately efficacious across all outcomes at standard dose. There is also promising evidence for milnacipran, although further high-quality research is needed to be confident in these conclusions. Evidence for all other antidepressants was low certainty. As RCTs excluded people with low mood, we were unable to establish the effects of antidepressants for people with chronic pain and depression. There is currently no reliable evidence for the long-term efficacy of any antidepressant, and no reliable evidence for the safety of antidepressants for chronic pain at any time point.

Impact of variability in baseline pain on the placebo response in randomized, placebo-controlled, crossover trials in peripheral neuropathic pain

ABSTRACT

Large placebo responses often negatively affect randomized controlled trials within the pain area. Understanding different possible factors that influence the placebo response is therefore important. In this retrospective analysis, we hypothesized that a large variability in baseline pain score would predict a greater placebo response and analyzed the impact of the coefficient of variation, SD, and difference between the highest and lowest numeric rating scale (NRS) score at baseline on the placebo response. A total of 160 observations on placebo response from 3 controlled clinical trials with a crossover design were included in this study. In general, the placebo response was low with a mean reduction in pain intensity of 0.5 points (range -5 to 7) measured on a 0 to 10 point NRS, and only 15% were placebo responders as defined by more than 30% reduction in NRS pain score from baseline to the end of the placebo treatment period. We found no significant impact of baseline pain coefficient of variation, SD, or the difference between lowest and highest baseline pain score on the placebo response. Placebo response in one trial did not predict placebo response in another trial. A large placebo response was not associated with a large treatment response. In conclusion, in this retrospective data analysis, there was no impact of baseline pain variability on the placebo response in controlled clinical trials with a crossover design in patients with peripheral neuropathic pain.

French guidelines for neuropathic pain: An update and commentary

Neuropathic pain remains a significant unmet need. French recommendations were updated in 2020. The goal of this minireview is to provide an update on these published guidelines. Despite newer relevant studies, our proposed algorithm remains relevant. First-line treatments include serotonin-noradrenaline reuptake inhibitors (duloxetine and venlafaxine), gabapentin and tricyclic antidepressants, topical lidocaine and transcutaneous electrical nerve stimulation being specifically proposed for focal peripheral neuropathic pain. Second-line treatments include pregabalin (such position being confirmed by newer studies), tramadol, combinations and psychotherapy as add on, high-concentration capsaicin patches and botulinum toxin A being proposed specifically for focal peripheral neuropathic pain. Third-line treatments include high-frequency repetitive transcranial magnetic stimulation of the motor cortex, spinal cord stimulation and strong opioids (in the lack of alternative). Disseminating these recommendations and ensuring that they are well accepted by French practitioners will be necessary to optimize neuropathic pain management in real life.