Pharmacotherapeutic advances in fibromyalgia: what's new on the horizon?

INTRODUCTION

This review delves into Fibromyalgia Syndrome (FMS), a chronic pain condition demanding thorough understanding for precise diagnosis and treatment. Yet, a definitive pharmacological solution for FMS remains elusive.

AREAS COVERED

In this article, we systematically analyze various pharmacotherapeutic prospects for FMS treatment, organized into sections based on the stage of drug development and approval. We begin with an overview of FDA-approved drugs, discussing their efficacy in FMS treatment. Next, we delve into other medications currently used for FMS but still undergoing further study, including opioids and muscle relaxants. Further, we evaluate the evidence behind medications that are currently under study, such as cannabinoids and naltrexone. Lastly, we explore new drugs that are in phase II trials. Our research involved a thorough search on PUBMED, Google Scholar, and clinicaltrials.gov. We also discuss the action mechanisms of these drugs and their potential use in specific patient groups.

EXPERT OPINION

A focus on symptom-driven, combination therapy is crucial in managing FMS. There is also a need for ongoing research into drugs that target neuroinflammation, immunomodulation, and the endocannabinoid system. Bridging the gap between benchside research and clinical application is challenging, but it holds potential for more targeted and effective treatment strategies.

Effective Doses of Low-Dose Naltrexone for Chronic Pain - An Observational Study

Purpose

Despite the availability of a wide variety of analgesics, many patients with chronic pain often experience suboptimal pain relief in part related to the absence of any medication to address the nociplastic component of common pain syndromes. Low-dose naltrexone has been used for the treatment of chronic pain, typically at 4.5 mg per day, even though it is also noted that effective doses of naltrexone for chronic pain presentations range from 0.1 to 4.5 mg per day. We performed an observational analysis to determine the range of effective naltrexone daily dosing in 41 patients with chronic musculoskeletal pain.

Methods

Charts of 385 patients, 115 males, 270 females, ages 18-92, were reviewed. Two hundred and sixty patients with chronic diffuse, symmetrical pain were prescribed a titrating dose of naltrexone to determine a maximally effective dose established by self-report of 1) reduction of diffuse/generalized and/or severity level of pain and/or 2) positive effects on mood, energy, and mental clarity. Brief Pain Inventory and PROMIS scales were given pre- and post-determining a maximally effective naltrexone dose.

Results

Forty-one patients met all criteria for inclusion, successfully attained a maximally effective dose, and completed a pre- and post-outcome questionnaire. Hormesis was demonstrated during the determination of the maximally effective dosing, which varied over a wide range, with statistically significant improvement in BPI.

Conclusion

The maximally effective dose of low-dose naltrexone for the treatment of chronic pain is idiosyncratic, suggesting the need for 1) dosage titration to establish a maximally effective dose and 2) the possibility of re-introduction of low-dose naltrexone to patients who had failed initial trials on a fixed dose of naltrexone.

Efficacy and Safety of Low Dose Naltrexone for Chronic Pain

Naltrexone is a mu-opioid receptor antagonist increasingly used as an analgesic for chronic pain at low doses. This retrospective, observational cohort study was conducted at an academic medical center to evaluate low-dose naltrexone (LDN) efficacy and describe its use in routine clinical practice. Adults receiving LDN, doses <10 mg for ≥1 month, seen at an outpatient pain clinic from January 1, 2014 to April 1, 2022 were included. The primary outcome was change in the Pain, Enjoyment of Life, and General Activity (PEG) score after LDN. Thirty-one patients were included. Median age was 50 years and 71% were female. Median duration of pain at baseline was 5 years. Mean PEG scores were 7.27 ± 1.39 and 6.62 ± 2.04 at baseline and follow-up, respectively. Mean difference was 0.66 (95% CI [0.10-1.21], p = 0.022). Eighty-seven percent (27) of patients discontinued LDN, 52% (16) for lack of benefit, 23% (7) for loss of benefit, 10% (3) for side effects, and 3% (1) for other reasons. Seven (23%) reported side effects. LDN was associated with a statistically significant reduction in PEG in adult chronic pain patients, however the clinical significance is unclear as over 75% of patients discontinued LDN due to lack of benefit.

Naltrexone 6 mg once daily versus placebo in women with fibromyalgia: a randomised, double-blind, placebo-controlled trial

BACKGROUND

Low-dose naltrexone is used to treat fibromyalgia despite minimal evidence for its efficacy. This trial aimed to investigate whether 12-week treatment with 6 mg low-dose naltrexone was superior to placebo for reducing pain in women with fibromyalgia.

METHODS

We did a single-centre, randomised, double-blind, placebo-controlled trial in Denmark. We enrolled women aged 18-64 years who were diagnosed with fibromyalgia. Participants were randomly assigned 1:1 to receive low-dose naltrexone (6 mg) or an identical-appearing placebo, using a computerised algorithm with no stratifications applied. Participants, investigators, outcome assessors, and statistical analysts were all masked to treatment allocation. The primary outcome was change in pain intensity on an 11-point numeric rating scale from baseline to week 12, in the intention-to-treat population. Safety was assessed in participants in the intention-to-treat population who received at least one dose of their allocated intervention. This trial was registered with ClincalTrials.gov (NCT04270877) and EudraCT (2019-000702-30).

FINDINGS

We screened 158 participants for eligibility from Jan 6, 2021, to Dec 27, 2022, and 99 patients were randomly assigned to low-dose naltrexone (n=49) or placebo (n=50). The mean age was 50·6 years (SD 8·8), one (1%) of 99 participants was Arctic Asian and 98 (99%) were White. No participants were lost to follow-up. The mean change in pain intensity was -1·3 points (95% CI -1·7 to -0·8) in the low-dose naltrexone group and -0·9 (-1·4 to -0·5) in the placebo group, corresponding to a between-group difference of -0·34 (-0·95 to 0·27; p=0·27, Cohen's d 0·23). Discontinuations due to adverse events were four (8%) of 49 in the low-dose naltrexone group and three (6%) of 50 in the placebo group. 41 (84%) of 49 patients in the low-dose naltrexone group had an adverse event versus 43 (86%) of 50 in the placebo group. One serious adverse event occurred in the placebo group and no deaths occurred.

INTERPRETATION

This study did not show that treatment with low-dose naltrexone was superior to placebo in relieving pain. Our results indicate that low-dose naltrexone might improve memory problems associated with fibromyalgia, and we suggest that future trials investigate this further.

FUNDING

The Danish Rheumatism Association, Odense University Hospital, Danielsen's Foundation, and the Oak Foundation.

[Fibromyalgia as a Rheumatic Pain Syndrome]

Epidemiology and pathophysiology: Fibromyalgia is significantly more common in people with rheumatic diseases than in the general population. Nevertheless, it can occur independent of other diseases. Physical and psychosocial factors are responsible for the genesis for fibromyalgia making it a multifactorial disease. Most importantly, central pain processing seems to be abnormal. The relevance of a small fibre neuropathy is yet to be determined. For the very first time, a study was able to demonstrate that fibromyalgia might be passively transferred from one organism to another in an experimental setting.Diagnosis: Fibromyalgia is a clinical diagnose. Besides generalized pain, sleep disturbances and fatigue are common features. Furthermore, there can be an association with depressive disorders. Determining the Widespread Pain Index (WPI) and the Symptom Severity Score (SSS) can help in diagnosing Fibromyalgia and to determine severity of the disease.Therapy: Cornerstones of the treatment are patient education, physical exercise, physical therapy, and cognitive behavioural therapy. In therapy-resistant cases, a multimodal approach might be considered. Analgesic drugs, particularly opioids, should basically be avoided or only be used for a short period of time. Naltrexone, an opioid antagonist, is a promising treatment candidate. Another possible approach might be the use of TENS. While there are positive observational studies on the therapeutic use of cannabinoids, evidence from controlled trials is still missing.

Low-dose naltrexone for treatment of pain in patients with fibromyalgia: a randomized, double-blind, placebo-controlled, crossover study

Introduction

Fibromyalgia (FM) is a chronic fluctuating, nociplastic pain condition. Naltrexone is a µ-opioid-receptor antagonist; preliminary studies have indicated a pain-relieving effect of low-dose naltrexone (LDN) in patients with FM. The impetus for studying LDN is the assumption of analgesic efficacy and thus reduction of adverse effects seen from conventional pharmacotherapy.

Objectives

First, to examine if LDN is associated with analgesic efficacy compared with control in the treatment of patients with FM. Second, to ascertain the analgesic efficacy of LDN in an experimental pain model in patients with FM evaluating the competence of the descending inhibitory pathways compared with controls. Third, to examine the pharmacokinetics of LDN.

Methods

The study used a randomized, double-blind, placebo-controlled, crossover design and had a 3-phase setup. The first phase included baseline assessment and a treatment period (days -3 to 21), the second phase a washout period (days 22-32), and the third phase a baseline assessment followed by a treatment period (days 33-56). Treatment was with either LDN 4.5 mg or an inactive placebo given orally once daily. The primary outcomes were Fibromyalgia Impact Questionnaire revised (FIQR) scores and summed pain intensity ratings (SPIR).

Results

Fifty-eight patients with FM were randomized. The median difference (IQR) for FIQR scores between LDN and placebo treatment was -1.65 (18.55; effect size = 0.15; P = 0.3). The median difference for SPIR scores was -0.33 (6.33; effect size = 0.13; P = 0.4).

Conclusion

Outcome data did not indicate any clinically relevant analgesic efficacy of the LDN treatment in patients with FM.

Opiate Antagonists for Chronic Pain: A Review on the Benefits of Low-Dose Naltrexone in Arthritis versus Non-Arthritic Diseases

Chronic pain conditions create major financial and emotional burdens that can be devastating for individuals and society. One primary source of pain is arthritis, a common inflammatory disease of the joints that causes persistent pain in affected people. The main objective of pharmacological treatments for either rheumatoid arthritis (RA) or osteoarthritis (OA) is to reduce pain. Non-steroidal anti-inflammatory drugs, opioids, and opioid antagonists have each been considered in the management of chronic pain in arthritis patients. Naltrexone is an oral-activated opioid antagonist with biphasic dose-dependent pharmacodynamic effects. The molecule acts as a competitive inhibitor of opioid receptors at high doses. However, naltrexone at low doses has been shown to have hormetic effects and provides relief for chronic pain conditions such as fibromyalgia, multiple sclerosis (MS), and inflammatory bowel disorders. Current knowledge of naltrexone suggests that low-dose treatments may be effective in the treatment of pain perception in chronic inflammatory conditions observed in patients with either RA or OA. In this review, we evaluated the therapeutic benefits of low-dose naltrexone (LDN) on arthritis-related pain conditions.

The Safety and Efficacy of Low-Dose Naltrexone in Patients with Fibromyalgia: A Systematic Review

Fibromyalgia (FM) is a chronic pain sensitivity syndrome characterized by diffuse musculoskeletal pain and many other systemic manifestations. Low-dose naltrexone (LDN) has been increasingly used as an off-label treatment option in FM. However, current evidence on the safety and efficacy of LDN in patients with FM is not well known. To systematically assess the current evidence on the safety and efficacy of LDN use in the treatment of FM. A comprehensive bibliographic search was conducted on EBM Reviews - Cochrane Central Register of Controlled Trials, EBM Reviews - Cochrane Database of Systematic, Embase, Ovid MEDLINE(R) and Epub Ahead of Print, In-Process, In-Data-Review & Other Non-Indexed Citations, Daily and Versions and Scopus databases in September 2022. Inclusion criteria were articles that were published in English, focusing on clinical trials involving LDN for the treatment of FM. Two reviewers independently screened and extracted the data. A qualitative analysis was used due to the high methodological heterogeneity between studies. The electronic search produced 805 articles. After applying the inclusion criteria, 9 articles (one RCT, two case reports, two case series, and four pilot trials) were selected for evaluation. LDN intervention protocols, study designs, and follow-up periods were different among the included studies. Overall, LDN was found to be effective in the symptomatic management of FM, and of the 78% of included studies that evaluated for safety, no severe adverse events were reported. Proving the efficacy and safety of low-dose naltrexone is a future possibility based on current study data, but the level of scientific evidence is limited. Future well-designed trials with large sample sizes are required.

Study protocol for a randomised, double-blinded, placebo-controlled phase III trial examining the add-on efficacy, cost-utility and neurobiological effects of low-dose naltrexone (LDN) in patients with fibromyalgia (INNOVA study)

INTRODUCTION

There is evidence that low-dose naltrexone (LDN; <5.0 mg/day) reduces pain and improves the quality of life of people with fibromyalgia syndrome (FMS). However, no randomised controlled trials with long-term follow-ups have been carried out. The INNOVA study will evaluate the add-on efficacy, safety, cost-utility and neurobiological effects of LDN for reducing pain in patients with FMS, with a 1-year follow-up.

METHODS AND ANALYSIS

A single-site, prospective, randomised, double-blinded, placebo-controlled, parallel design phase III trial will be performed. Eligibility criteria include being adult, having a diagnosis of FMS and experiencing pain of 4 or higher on a 10-point numerical rating scale. Participants will be randomised to a LDN intervention group (4.5 mg/day) or to a placebo control group. Clinical assessments will be performed at baseline (T0), 3 months (T1), 6 months (T2) and 12 months (T3). The primary endpoint will be pain intensity. A sample size of 60 patients per study arm (120 in total), as calculated prior to recruitment for sufficient power, will be monitored between January 2022 and August 2024. Assessment will also include daily ecological momentary evaluations of FMS-related symptoms (eg, pain intensity, fatigue and sleep disturbance), and side effects via ecological momentary assessment through the Pain Monitor app during the first 3 months. Costs and quality-adjusted life years will be also calculated. Half of the participants in each arm will be scanned with MRI at T0 and T1 for changes in brain metabolites related to neuroinflammation and central sensitisation. Inflammatory biomarkers in serum will also be measured.

ETHICS AND DISSEMINATION

This study has been approved by the Ethics Committee of the Fundació Sant Joan de Déu. The results will be actively disseminated through peer-reviewed journals, conference presentations, social media and community engagement activities.

TRIAL REGISTRATION NUMBER

NCT04739995.

Low-dose naltrexone for the treatment of fibromyalgia: protocol for a double-blind, randomized, placebo-controlled trial

BACKGROUND

Low-dose naltrexone (LDN) is used widely as an off-label treatment for pain despite limited evidence for its effectiveness. A few small trials with a high risk of bias have investigated the effect of LDN on pain associated with fibromyalgia in women, but larger and more methodologically robust studies are needed. The primary aim of this randomized controlled trial is to investigate if 12 weeks of LDN treatment is superior to placebo in reducing the average pain intensity during the last 7 days in women with fibromyalgia.

METHODS

A single-center, permuted block randomized, double-blind, placebo-controlled, parallel-group trial will be performed in Denmark. Randomization comprises 100 women aged 18-64 years diagnosed with fibromyalgia who will be treated with either LDN or placebo for 12 weeks including a 4-week titration phase. The primary outcome is change in average pain intensity (during the last 7 days) from baseline to 12 weeks. Secondary outcomes are other fibromyalgia-related symptoms, i.e., tenderness, fatigue, sleep disturbance, stiffness, memory problems, depression, anxiety and measures of global assessment, physical function, impact of fibromyalgia, pain distribution, and health-related quality of life. Intention-to-treat analysis will be performed, and the number of responders with a more than 15%, 30%, and 50% improvement of pain after 12 weeks will be calculated for the LDN and placebo groups. Exploratory outcomes include measures of pain sensitivity, muscle performance, and biomarkers.

DISCUSSION

This study will contribute with high-level evidence on the efficacy of low-dose naltrexone for the treatment of pain in women with fibromyalgia. Secondary outcomes include both disease-specific and generic components investigating whether LDN influences other symptoms than pain. Explorative outcomes are included to provide greater insight into the mechanism of action of LDN and possibly a better understanding of the underlying pathology in fibromyalgia.

TRIAL REGISTRATION

EudraCT 2019-000702-30. Registered on 12 July 2019. ClinicalTrials.gov NCT04270877. Registered on 17 February 2020.

Fibromyalgia in Older Individuals

Fibromyalgia (FM) is a condition of chronic widespread pain (CWP) that can occur throughout the life cycle and is likely underrecognized in older patients. FM is associated with considerable suffering and reduction in quality of life and may occur as a unique condition, but in older patients is most likely to be associated with another medical illness. Understood mechanistically to be a sensitization of the nervous system, recently identified as nociplastic pain, FM is accepted as a valid medical illness that requires a positive diagnosis and directed treatments. The cornerstone of treatments for FM are nonpharmacologic interventions, with the understanding that medications provide only modest benefit for most patients, and with particular concern about adverse effects in older patients. If FM is not recognized, treatments may be misdirected to the other medical condition, with failure to address FM symptoms, leading to overall poor outcome. In contrast, new complaints in older patients should not immediately be attributed to FM, and physicians should be vigilant to ensure that onset of a new illness is not ignored. As FM is most often a lifelong condition, patients should be encouraged to identify their own personal strategies that can attenuate symptoms, especially when symptoms flare. Continued life participation should be the outcome goal.

Pharmacological treatment of pain among persons with opioid addiction: A systematic review and meta-analysis with implications for drug development

The clinical features and neurobiology of pain and opioid use disorder (OUD) are inextricably linked. Despite emerging evidence supporting the negative impact of ongoing pain in the treatment of OUD, the pharmacological management of pain in the presence of OUD has received limited attention. We sought to systematically review the studies investigating pharmacotherapies for pain among persons with OUD. Eligible studies had participants with OUD and outcomes including evoked or spontaneous pain. We searched Scopus, Cochrane Database of Systematic Reviews, Medline, and Embase. Out of 1,097 studies that met the search criteria, 12 studies provided data relevant to the research question-five laboratory studies and seven clinical trials. Random effects pooled estimates suggested no significant difference between groups at baseline but a response favoring the active treatment group over placebo, with nonsignificant heterogeneity between studies. Findings from these studies provide preliminary evidence for analgesic and antihyperalgesic effects of gabapentin, GABA agonists, and NMDA antagonists among persons with OUD. To establish the tradeoffs between the analgesic effects and abuse liability of these compounds, further well-controlled clinical trials are required among persons with OUD. This review also underscores the need for methodological enhancement in drug development for pain in OUD. Future research should address the clinical and neurobiological overlap between pain- and addiction-related phenomena. Transdisciplinary approaches may identify biomarkers of these shared phenomena and their neural substrates. The development of novel therapeutics for pain in OUD may be accelerated by such integration of pain and addiction research.

Preclinical and clinical studies into the bioactivity of low-dose naltrexone (LDN) for oncotherapy

Naltrexone (NTX) is a nonspecific opioid antagonist that exerts pharmacological effects on the opioid axis by blocking opioid receptors distributed in cytoplastic and nuclear regions. NTX has been used in opioid use disorder (OUD), immune-associated diseases, alcoholism, obesity, and chronic pain for decades. However, low-dose naltrexone (LDN) also exhibits remarkable inhibition of DNA synthesis, viability, and other functions in numerous cancers and is involved in immune remodeling against tumor invasion and chemical toxicity. The potential anticancer activity of LDN is a focus of basic research. Herein, we summarize the associated studies on LDN oncotherapy to highlight the potential mechanisms and prospective clinical applications.

The Effects of Low Dose Naltrexone on Opioid Induced Hyperalgesia and Fibromyalgia

Objectives: While opioids temporarily alleviate pain, the overshoot of balancing pain drivers may increase pain, leading to opioid induced hyperalgesia (OIH). Our goal was to find out what chronic opioid treatment does to pain tolerance as measured by the cold pressor test (CPT), an objective measure of pain tolerance, and to find an alternative effective treatment for chronic pain and FM. Materials and Methods: The setting was an academic addiction medicine service that has an embedded pain service. Patients had routine clinical care starting with an evaluation that included assessment of medical and psychiatric conditions. Participants were 55 patients with OIH and 21 patients with fibromyalgia; all had at least two CPTs. Treatment included a single dose of buprenorphine for detoxification. In this open-label case series, patients were treated with low dose naltrexone (LDN), a pure opioid receptor antagonist that, we hypothesize, treats OIH and FM by restoring endogenous opioid tone. Results: Comparing initial and last CPT times, those with OIH more than quadrupled their pain tolerance, and those with FM doubled theirs. This improved pain tolerance for OIH and FM was statistically significant (p < 0.0001 and p = 0.003, respectively) and had a large effect size (r = 0.82 and r = 0.63, respectively). Discussion: Results suggest that patients on chronic opioid therapy should have pain tolerance measured by CPT with detoxification and LDN provided to correct opioid induced hyperalgesia if found. FM may also be treated with LDN. The main limitation of the findings was lack of a randomized control group treated with placebo.